and
INTERNATIONAL
GEOGRAPHICAL UNION
Conference
on
ENVIRONMENTAL
CHANGE AND WATER SUSTAINABILITY
Zaragoza,
2-6 July, 2001
SOCIEDAD
ESPAÑOLA DE GEOMORFOLOGÍA
"WARMICE"
PROJECT (European Commission)
INSTITUTO
AGRONÓMICO MEDITERRÁNEO DE ZARAGOZA
WATER RESOURCES AND ENVIRONMENTAL
CHANGE IN SPAIN. A KEY ISSUE FOR SUSTAINABLE "INTEGRATED" CATCHMENT MANAGEMENT.
Francesc
Gallart and Pilar Llorens
Institute
of Earth Sciences "Jaume Almera" (CSIC), Barcelona, Spain
"Integrated
catchment management" is easier said than done. Sometimes it is merely
an offer-demand study that considers that the catchment is just a system
of reservoirs, pipes and taps. Hydrology became just an appendix of applied
statistics, evolving into a more sophisticated but scientifically empty
information technology. An example of the need for integrative approaches
may be taken from Spain.
There
are many evidences of water resources diminution in different parts of
Spain for the last 70 years, representing in average about 0.4% per year.
This diminution has been claimed to be the result of the increasing irrigation
and climate variability. Indeed, the observed reduction in discharge may
be partly explained by the increment of the irrigation surface in downstream
areas, but the assessment of the water balance for the Ebro catchment shows
that there is still a significant decrease of rainfall-runoff relationship
after consideration of the increase of water abstractions. Furthermore,
most of the headwater areas show decreasing trends that can not be explained
only considering climate variability.
The
findings of experimental hydrology obtained along the 20 century demonstrated
that changes in land cover determine different water consumption in the
catchments, and therefore changes in water resources. Water resource assessment
in Spain can not be made without taking into account the relevant increase
of forest cover occurred in headwater areas during the last 50 years, as
a result of land abandonment as well as environmental and agricultural
policies. Conversely, land management can not be made without considering
the hydrological implications of land cover change.
The
above example illustrates that the interdependence of water and land must
be taken into account for true ëIntegrated catchment managementí.
Non-irrigated rural areas (forests, rangelands and dry-farming areas) have
also water requirements, directly taken from precipitation, that must also
considered in the catchment water budget.
ASSESSING
THE EFFECT OF CLIMATE OSCILLATIONS AND LAND-USE CHANGES ON THE AVAILABILITY
OF WATER RESOURCES IN MOUNTAIN MEDITERRANEAN AREAS
Santiago
Beguería, Juan Ignacio López-Moreno, Adrián Lorente,
Manuel Seeger & José M. García-Ruiz
Instituto
Pirenaico de Ecología, CSIC, Zaragoza, Spain
In
Mediterranean areas, mountains have an extreme importance from a hydrological
point of view, since they behave as humidity islands. This is the reason
why most of the discharge of the Mediterranean rivers comes from the headwaters,
sometimes located at more than 2000 m a.s.l. This allowed in the past the
development and progressive enlargement of irrigated areas. In the Ebro
Depression, for example, irrigation of semi-arid areas has been, since
the roman times, the solution for introducing a diversity of crops and
for ensuring a much higher productivity, both in the main river (the Ebro
River) and in its tributaries. During the 20th century a dramatic increase
of irrigated areas has occurred, far away from the fluvial channels, by
means of large reservoirs and a complex network of waterways. This evolution,
together with the urban growth and the process of industrialization, obligate
to carefully manage the water resources and to know -and even forecast-
their temporal oscillations.
A
recent evaluation of water resources in the Central Spanish Pyrenees has
demonstrated that there are frequent, positive and negative oscillations
around the average. The last negative oscillation started at the beginning
of the 60's, and though it has not been the deepest of the 20th century,
it has no precedent due to its length. A regional analysis of precipitation
and discharge anomalies shows that there is a close parallelism between
both variables. Nevertheless, since 1965 the decrease in discharge is faster
than the decrease in precipitation. This could be explained by the evolution
of temperature, which shows a positive trend since the 70's, but there
is evidence that its role is relatively limited. The evolution of land
uses and plant cover could help to interpret the increasing separationbetween
the curve of precipitation and that of discharge. During the 20th century,
most of the hillslope cultivated fields have been abandoned and recolonised
by dense communities of shrubs; likewise, many old grazed areas and abandoned
fields have been afforested with pines. In the water balance, interception
and direct water consumption have increased very much, in such a manner
that less water is available to become surface or groundwater runoff. Floods
have also reduced their frequency and intensity, thus affecting the management
patterns of reservoirs.
SEDIMENTATION
IN RESERVOIRS: A CHALLENGE FOR WATER SUSTAINABILITY
Blas
L. Valero-Garcés
Instituto
Pirenaico de Ecología, CSIC, Zaragoza, Spain
The
importance of reservoirs is likely to increase over time as population,
economic activity, and irrigation demands grow. More than 39000 dams higher
than 15 m were reported in the world in 1996, although the number of smaller
impoundments is several times higher. Agricultural communities and industrial,
developed urban areasare heavily
dependent on reservoir water supply.In
most regions, reservoirs are the single most important component of the
regulated water supply system. Most of these structures have been designed
totrap sediments continuously with
an average usable life of about 100 years.
Sedimentation
in reservoirs has large consequences for the rivers, the impoundments,
and the associated hydraulic structures, but the single most important
is the loss of waterstorage capacity.
The loss of water storage capacity caused by sediment accumulation makes
reservoirskeynon-sustainable
components of the water supply systems. The estimated annual lost water
storage capacity worldwide is about 1 %, however there is a great range
of siltation rates. The geographical, geological, geomorphological , and
ecological characteristics of the watershed are significant factors for
erosion and sediment sources. The climate and the rivers hydrological regime
greatly affect sediment deliver. Human activities and changes in land uses
are also significant controls on reservoir siltation. Finally, reservoir
management practices can mitigate or increase siltation.
The
traditional management of reservoirs does not consider the sustainable
use of these structures. Large water flows and measures to mitigate watershed
erosion are used to span the usable life of a reservoir. Due to the high
cost of elimination of sediments, siltation has to be considered as a non-reversible
process. A new philosophy for sustainable management of reservoirs has
to focus on controlling the sediment accumulation. Water sustainability
requires that the traditional concept of limited (< 100 years) reservoir
usable life be replaced with a longer -termperspective
on sustainable use. A balance between water quantity and quality available
to human communities and preservation of biodiversity should be achieved,
to protect the environment and conserve resources.
The
21th century will witness the loss of over half of present reservoir capacity
in many regions. Siltation of reservoir is not a problem to be solved by
future generations, but an urgent need for sustainable development. Spain
has the largest number of reservoirs in the EU, but siltation during the
last decades is becoming a major concern for the limited waterresources.
Due to the geographical and climaticdiversity of Spain, the average sediment
yieldis very variable, although
is higher in the southern Spanish basins and lower in the Pyrenees. Detailed
sedimentological studies of reservoirs and watershed provide high resolution
depositional histories to define erosion, transport and sedimentation processes
in drainage basins. The influence of antropogenic, climatic and other greographic
factors on sediment transport and delivery can be evaluated within this
integrated framework.
(1) Departament
de Medi Ambient i Ciències del Sòl, Universitat de Lleida
(2) Departamento
de Fundamentos de Economía e Historia Económica, Universidad
de Alcalá de Henares
(3) Department
of Landscape Architecture, University of California, Berkeley
We
comprehensively assessed 20th century hydrological alterations
from reservoirs ranging from 2 to 1,500 hm3
in capacity in the Ebro River basin by analysing thirty-eight flow records
for twenty rivers. Most rivers show substantial reductions in flood magnitude
as a consequence of dam operation, with greater hydrologic change associated
with higher Impounded Runoff index (IR), defined as the ratio between reservoir
capacity and annual runoff. Post -dam peak flows were reduced from pre-dam
flood peaks, on average, by 33% for the 2-year flood, 28% for the 10-year
flood, and 23% for the 50-year floods. Reservoir effects were greater in
the eastern, drier portion of the basin, where same IR produces twice the
flood reduction as in the west.Post-dam
flows show reductions in mean daily flows, reflecting net abstractions
from the river, mostly for irrigation, and reductions in flow variability,
reflecting reservoir regulation. Most series reveal severe flow reductions
(40%) in flows equalled or exceeded 50% of the time (Q50).Low
flows (Q95) are the most affected, being reduced, on average,
to half. Flow Standard Deviation index indicates reduction of flow variability
from 12% to 90% in some flow records.A
correlation coefficient [1 ? rx,y ? -1] measuring the relation
between post and pre-dam monthly flows is used to assess alterations on
river regime. Mean rx,y is 0.67, suggesting a general moderate
effect of reservoirs. Values range from -0.84 (Ebro River downstream Ebro
dam) to 0.95 for less dammed rivers. Results show a threshold IR around
50%, suggesting an acceleration of dams’ effects on river regime once the
dam is able to capture half of annual runoff. Downstream reaches of the
Ebro River had a significant reduction in the mean annual runoff (-30%)
between 1960 and 1992. Impounded runoff was already 2 km3 in
1960 and 4,3 km3 in 1975, 15% and 32% of annual runoff respectively.
Reduction in annual runoff had probably already started before the sixties
but unusually wet years at the beginning of the decade masked immediate
effects of dams on water yield. Several other rivers also show significant
reductions (20% to 70%) on annual runoff after dams got in operation.
Results
of this study suggest that construction of additional irrigation impoundments,
as proposed in the New Spanish Hydrological Plan, will likely have substantial
effects on river geomorphology and ecology, because they will further reduce
flows, diminish sediment transport, alter river-bed structure and degrade
water quality.
S.
Beguería (1), J.M. García-Ruiz (1), J. Arnáez (2),
A. Lorente (1), M. Seeger (1) & C. Martí-Bono (1)
(1)
Instituto Pirenaico de Ecología, CSIC, Campus de Aula Dei, Apartado
202, 50080-Zaragoza, Spain.
(2)
Department of Geography, University of La Rioja, 26004-Logroño,
Spain.
The
Arnás experimental catchment is located in the Upper Aragón
River Basin. It has an area of 250 ha and is occupied by old cultivated
fields, already abandoned 40 years ago. At present, the old fields are
subject to a process of plant colonisation, mainly with dense shrubs. The
catchment has been monitored since 1996 in order to obtain continuous information
on precipitation, temperature, discharge and sediment transport (solutes,
suspended sediment and bedload). This paper studies the relationships between
floods and suspended sediment transport. Main rainstorms and floods occur
in autumn and spring, though some short, intense rainstorms are possible
in summer. The results obtained show that suspended sediment transport
is related not only to the intensity of precipitation and peak flow, but
also to the state of soil humidity.
Fluid
Mechanics, C.P.S., University of Zaragoza, Zaragoza, Spain
In
mountain torrents, intense and localised storms may cause flash floods
with important sediment transport. In steep torrents, the sediment discharge
may increase so that the solid concentration often exceeds figures of 40-50
%. This is the case of the debris flows that transport downstream huge
volumes of sediments that are then deposited on the alluvial fans, often
highly populated. These wide areas are periodically exposed to catastrophic
events. To reduce the debris flow hazard, it is common to couple structural
and non structural protections such as zoning of the risk prone areas and
emergency plans. Protection plans require the description of scenarios
that can be defined only by means of simulations with mathematical models.
Debris flow is modelled using the equations governing the dynamics of a
liquid-solid mixture. These equations have a structure similar to those
of the monophasic water flow, differing from them by the presence of some
terms characteristic of the bifasic nature of the mixture, such as granular
bed erosion velocity, sediment concentration, bed shear stress, etc.The
set of equations includes two mass conservation equations (one for the
mixture and another for the solid phase) and a single momentum balance
equation of the flow. The friction term is simulated according to Takahashi
(1991). The system is completed with equations to estimate the erosion/deposition
rate derived from the Egashira and Ashida (1987) or Takahashi (1991) relationships.
An upwind explicit finite volume numerical model based on first order Roe's
scheme for unsteady debris flow is presented. The advection equation of
the coarse solid fraction is solved in cascade at each time step after
the momentum balance equation of the mixture has been integrated. The model
will be applied to simulate different test conditions in channels with
simple geometry and some comparison with laboratory experiments are presented.
A one-dimensional scheme is proposed whilst a two-dimensional scheme for
the more complex wave propagation on alluvial fans will be developed in
future work.
Department
of Geography, National University of Ireland, Maynooth (NUIM), Maynooth,Co.
Kildare, Ireland
Predictions
are made of changes in effective runoff at a high spatial resolution for
the island of Ireland under different climate change scenarios.Although
previous studies have examined the response of selected Irish catchments
to various climate change scenarios this is the first time that the whole
area of the island has been considered.GCM
model output from HadCM3 for 2 x CO2 is downscaled and further refined
using recent research on Irish climate change to develop reference scenarios.This
is complemented by an alternative approach based on circulation / precipitation
yield relationships.These temperature
and rainfall scenarios are incorporated into a spatial grid (10 x 10 km)
of Irish climatology derived for current conditions.The
spatially resolved climate scenario data is used to drive a hydrological
model, HYSIM, applied to the spatial grid.
The
gridded baseline climatology is used to validate the effective runoff predicted
by HYSIM.Individual grid cells are
parameterised using soil survey and CORINE land use data together with
information on major aquifers provided by the Geological Survey of Ireland.The
flexible data requirements of HYSIM allow some representation of the diverse
hydrological conditions found within Ireland.For
example, approximately 40% of Ireland is underlain by limestones, many
of which are karstified.These karst
aquifers are an important water resource and respond very rapidly to precipitation.There
are also extensive areas of lakes and wetlands.The
land area is divided into broad hydrological zones to provide some representation
of this variability.Results from
the simulations under future climatic scenarios are discussed.
M.P.
Errea (1), A. Cerdá (1), T. Lasanta (1) & L. Ortigosa (2)
(1)
Instituto Pirenaico de Ecología (CSIC), Zaragoza.
(2)
Dpt. of Geography, Universidad de La Rioja, Logroño, Spain.
The
European mountainous areas, such as the Pyrenees, have suffered important
land use changes since the XIX century. There, the land abandonment developed
a landscape characterised by a mosaic of different land-uses. These changes
affect the vegetation recovery process and then the runoff and sediment
production. Although, soil moisture plays an important role in the hydrological
cycle, very little is know about his behaviour in a changing environment
such as the Pyrenees. Soil
moisture influences the runoff and infiltration processes and then the
sediment detachment. Moreover, soil moisture also determines the vegetation
recovery and soil development after abandonment.
This
paper aims to study the influence of land-use and season on the soil moisture.
Measurements were carried out weekly during 1997 and 1998 by means of the
Time Domain Reflectrometry method.
The
selected land-uses were Cereal (fertilised and with artiga management),
Fallow, Grassland (fertilised and with artiga management), Burnt(two
plots under different post-fire recovery conditions), and the Control plot
which is a dense Scrubland.
The
result shows that land-use is a key factor in the seasonal and spatial
variability of soil moisture. Plant cover was found to favours greater
soil moisture content such as was found on the Scrubland plot. The ploughed
plots showed the lowest soil moisture content. Differences between the
fallow and the Cereal plots were negligible. Seasonally, the greatest differences
amongst land-uses were found during the summer, the hottest and the driest
season at the study area. These conditions determined that the ploughed
soils reached extremely low soil moisture values.
VARIABILITY
AND NON?LINEAR PREDICTION OF STREAM FLOWS INTO THE EL PEÑOL HYDROELECTRIC
PROJECT, COLOMBIA.
C.D.
Hoyos (1), O. Mesa (1), G. Poveda (1), P. Waylen (2).
1.
Posgrado en Recursos Hidráulicos, Universidad Nacional de Colombia,
Medellín, Colombia.
2.
Department of Geography, University of Florida, USA, 32611-7315.
There
is ample evidence of hydrologic variability at annual and interannual time
scales over the northern regions of tropical South America.Hydroelectric
power provides a cheap regional energy source, yielding over seventy percent
of Colombiaís national energy annually. The El PeÒol scheme
on the Nare River is the countryís largest providing roughly 14%
of national production.The region
isparticularly susceptible to droughts
during warm phases of ENSO, however stream flow inputs are also subject
to a variety of regional and local factors other than ENSO, which may makes
forecasting difficult.The identification
of a model which permits the reliable incorporation ofreadily
available ocean-atmosphere variables, and those which available from standard
forecasts, to a potentially non-linear prediction of monthly stream flowsis
crucial to the optimal operation of the reservoir. The MARS (Multiple Adaptive
Regression Splines) model is calibrated to provide forecasts of monthly
stream flows over the period 1956-1986.The
applicability of the forecast technique is discussed by reference to comparisons
between observed and forecasted flows in a separate model validation series
(1987-1992).Reliability of the stream
flowforecasting methodology is investigated
over “forecast horizons” ranging from 3 to 12 months, and the potential
economic value of incorporating the methodology into the operation of the
national power generating system is illustrated.
Paloma
Ibarra, Juan Martínez and Teresa Echeverría
Department
of Geography and Territory Planning, Faculty of Philosophy and Arts, University
of Zaragoza, 50.009- Zaragoza (Spain)
Water
behaviour in forest soils, an oak-wood (Quercus pyrenaica) and a pine-wood
(Pinus sylvestris) located on the northern side of the Moncayo Massif (Sistema
IbÈrico, Zaragoza, Spain) is analysed in this study. After a description
of the area being studied, the northern side of the Moncayo, and specially
of the test areas in the selected forests, an introduction of methodological
character is carried out, in which the process to obtain different experimental
data and the characterisation of soils are developed.
The
results are expressed graphically, demonstrating the different behaviour
of water in the soils of the two forests subject to study. Soil moisture
values correspond to the different depths (duft, 0-5, 5-10 and 10-15 cm)
and at different times during the year, and is related to climatic parameters
such as rainfall and temperature, linked phenologically to the presence
of canopy and soil cover, pointing out the texture and quantity of organic
matter in each of the defined depths.
A
clear seasonal behaviour of soil moisture in relation with climatic and
phenological reasons is observed in both forests; however, the differences
in soil moisture, always in favour of the pine-wood in the superior subhorizons
(duft, 0-5 and 5-10 cm), are nullified in the inferior depth (10-15 cm),
in which the soil moisture of oak-wood is generally higher, in relation
with the soil texture and the morphology on which the soils of both forests
are developed.
Department
of Geography, University of Haifa, Israel
In
the last century, human activities have altered rivers and swamps by drainage,
water abstraction, regulation and many other activities.
In
Israel 95% of natural streams and rivers had been regulated to a large
extent. The major project was the drainage of the Hula lake and swamps
in the 1950s. The Hula basin is an elongated U shaped tectonic valley covering
an area of 110 km2 in the northern part of Israel. Its general outline
is determined by tectonic features of the Dead Sea transform. The Jordan
river drains the Hula valley and then trough a narrow basaltic canyon flows
into Lake Kinneret. The annual rainfall ranges from 400 mm in the south
to 650 mm in the north.
After
the drainage, the annual mean maximum peak discharges have increased from
57 m3/s to 90 m3/s. The Flood Routing Index has been doubled and floods
are transmitted in a much shorter time. Most of the riverís annual
suspended sediment transport were deposited before the drainage into lake
Hula, which acted as a silting depositional intermediate dam, but after
the drainage there is a direct and rapid transmission of sediment directly
to the lake. A new delta at the Jordan river outlet was formed in 1969,
increasing the length of the river channel by about 1000 m.
Man-made
control of the river has created a delicate new equilibrium in the Jordan
river-lake Kinneret system, the major change being expressed in a more
rapid transmission of water and sediments by the new system and a completely
new morphological transfer system.
DAMMED
LAKE: A NEED TO RETURN LIMNOSYSTEM TO THE NATURAL STATE
Kestutis
Kilkus
Vilnius
University, Lithuania
Lithuania
is rich in waters if all surface water resources are considered (about
7000 m?/capita per year), but problems sometimes are caused by uneven distribution
of precipitation and runoff in space and time, especially, in case of always-possible
several year-long sequences of dry years. That is why about 1000 reservoirs
with total area of 268 km? were constructed in Lithuania since 1970. The
reservoirs are/ or were used for power generation, fishery, irrigation,
sanitation and other purposes. Because it was much cheaper to get the same
storage capacity damming the outlet of natural lake as the river valley,
the first option was very popular in the engineering too.
Subject:
Lake Zuvintas. Shallow
(mean depth is 1.2 m) eutrophicated lake located in the middle reaches
of the Dovine River (the tributaryof
the Susupe River). Catchment area and water surface area are 345 and 9.3
km?, accordingly. The ratio of the amount of precipitation on the surface
of the lake to the total amount of inflow is 1:10 and the renewal rate
of the water stored in the lake is about 5 times per year. It is nature
reserve since 1938; a large number of rare and endangered species are under
protection.
Environmental
aims of the damming: (1) to increase the efficiency of water supply system
based on the storage capacities (14 x 106 m?) of dammed lakes (Lake Dusia
and Lake Simnas) locating upstream the Lake Zuvintas and, consequently,
to increase the low runoff of heavy polluted Sesupe River near the Marijampole
town; (2) to minimize the Lake Zuvintas level fluctuations during the nesting
period of waterfowl, i.e. in spring.
Ecological
consequences. Short-term fluctuations in the Lake Zuvintas level (seasonal
amplitude) decreased from 0.83 to 0.44 m, in average, and the maximum discharge
of the outlet also decreased, accordingly. Flood reduction caused that
more detritus was deposited in the lake and the mats of reeds compacted.
The diversity of biotops as well as waterfowl species decreased. Further,
the effect of accumulation of the weak fulvic-humic acids derived from
the plants and peats was evident; the acidification of water inside the
reed mats went on especially fast. The yield of submerged macrophytes,
e.g. Chara, decreased, and the same was reaction of population of swans
due to the food shortage. The accumulation of organics contributed to the
severe reduction in oxygen and fish mortality in winterkill conditions
increased in frequency.
Since
environmental protection aim has a priority in Lake Zuvintas management,
the decision to reconstruct the natural hydrological regime of the unique
ìLake of Swansî as well as two lakes located upstream has
been made, and the second option would be doing nothing with lake water
resources. The estimated costs of reconstruction of ìcheapî
reservoirs are about 150 000 USD. Is it cheap, really?
Kestutis
Kilkus
Vilnius
University, Lithuania
Different
approaches to the estimation of the overgrowth of river channel by aquatic
vegetation are possible. Hydrologists are very interested in this greatly
because macrophytes have an effect upon hydraulic conductivity of river
channel as well as processes of river-bed deformation. The overgrowth of
channel should also be taken into account in some runoff calculation procedures.
The
impact of macrophytes on water quality could be described by simplified
chain of factors/ or processes: biogenic backwater ( water current velocity
( water ventilation ( nitrification / denitrification ratio ( accumulation
of nutrients in the biomass of macrophytes. Almost all links of the chain
are closely connected with the runoff so we can expect for the fluctuations
in hydro-ecological conditions might be pre-determined by runoff fluctuations.
The
main approach to the study of the river channel overgrowth is, of course,
biometric one, but opportunities to use such approach are limited because
of high costs and insufficiency of information. Hydrometric approach we
used in our research is indirect one but it is valuable enough as necessary
systematic data are collected already, so the researcher has a good start
for his work at the beginning. In this case, the effect of channelís
overgrowth should be estimated as biogenic backwater (H), i.e. the deviation
of discharge measured in summer from the stage-discharge graph corresponding
to the free channel conditions.
More
objective information about long-term fluctuations of (H should be gained
from the relationship between the elements (water stage-discharge) oflake-outlet
hydraulic system. Such modification of the stage-discharge graph was applied
for 8 Lithuanian streams flowing from lakes and having systematic hydrometrical
data as well as episodically made measurements.
The
calculated (H values show that distinct seasonal cycle in the overgrowing
of outlet channel exists. In all investigated lake-river systems biogenic
backwater is especially significant at the end of summer and/ or in the
early autumn and later on it gradually decreases. On the other hand, the
backwater at the beginning of winter is more significant than at the start
of summer, because the remains of macrophytes in channels are washed away
by spring flood. The thickness of dammed water layer in lakes amounts on
average from 5 to 27 cm in June-October and it takes up to 70-80% of storage
capacity of the lake. Consequently, the minimum discharge of the out-flowing
river is reduced in summer. Long-term fluctuations of (H have been observed
too, and it seems that they should be pre-determined by synergetic impact
of fluctuations of heat, nutrients and, especially, runoff.
EFFECTS
OF IRRIGATION ON WATER SALINIZATION IN SEMI-ARID ENVIRONMENTS: A CASE STUDY
IN THE CENTRAL EBRO DEPRESSION, SPAIN
T.
Lasanta (1), W. Mosch (2), M.C. Pérez-Rontomé (1), M. Maestro
(1) & J. Machín (3)
(1)
Instituto Pirenaico de Ecología, CSIC, Campus de Aula Dei, Apartado
202, 50080-Zaragoza, Spain.
(2)
Centro de Edafología y Biología Aplicada del Segura, CSIC,
Apartado 4195, Murcia, Spain.
(3)
Estación Experimental de Aula Dei, CSIC, Campus de Aula Dei, Apartado
202, 50080-Zaragoza, Spain.
The
irrigated areas are one of the most important sediment sources in semi-arid
environments, causing a loss of water quality as a consequence of high
discharges as return flow. In this paper the temporal and spatial variability
of the sedfiment exported from an irrigated area is studied. The area selected
is located in the middle Ebro Depression, where irrigated areas rest upon
gypsipherous soils. In the study area, 67 % of the territory is cultivated
qith rice, lucerne, sunflower and corn, and the rest corresponds to bare
badlands.
Every
15 days during 16 months the inflow and outflow discharge was measured
in a small irrigated catchment (650 ha) and water samples were taken for
laboratory analysis purposes. Furthermore, other 12 points within the study
area were controlled in order to estimate the supply of materials according
to land uses.
The
results obtained show an increase of sediment concentration at the outlet
of the catchment, with high values of solute outputs as sulfates, sodium,
chlorides, calcium and carbonates. During the irrigation season, salt concentration
is slightly lower than during the non-irrigated season, though total sediment
losses are much higher due to higher discharges.
Li
Lijuan & Zheng Hongxing
Institute
of Geographic Sciences and Natural Resources Research, Chinese Academy
of Sciences, Beijing, 100101, China
In
the history of water utilization and development, our attention was mainly
paid on the benefit we can get from rivers while the environmental and
ecological function of the river system used to be neglected. Thus the
activities of water utilization and development were accompanied by more
and more serious environmental and ecological problems. In order to reduce
the environmental and ecological problems induced by water resources development
and utilization, this paper has proposed a concept of environmental and
ecological water requirement. It is defined as the minimum water amount
to be required or consumed by the natural water body to conserve its environmental
and ecological functions. Based on the definition, the methods on calculating
the amount of environmental and ecological water requirement are determined.
In the case study on Haihe-luanhe river system, the water requirement is
divided into three parts, i.e. the basic water requirement of rivers, water
requirement for sediment transfer and water consumption by evaporation
of the lakes. The methods of calculating the different parts of water requirement
were shown in expressions. In a case study on Hai-Luanhe Basins, the hydrological
records before 1960, which may represent the natural condition of the river
systems, were used for calculating. The results of the calculation have
shown that the environmental and ecological water requirement in the Basins
is about 124 (108m3, including 57 (108m3 for basic in-stream flow, 63 (108m3
for sediment transfer and 4 (108m3 for net evaporation loss of lakes. Thus
it was estimated that the total amount of environmental and ecological
water requirement accounts 54% of the amount of runoff (228(108m3). However,
there are still some aspects of environmental and ecological requirement
that are not under our consideration. It should be realized that the amount
of environmental and ecological water requirement must be more than that
we have calculated. According to the results, we considered that the rational
utilization rate of the runoff in the Basins must be no more than 40%.
Since the current utilization rate of the Basins, which is as high as 80%,
has been far beyond the limitation, the problems of environment and ecology
are quite serious. It is urgent to control and adjust water development
and utilization to eliminate those problems existed and to avoid the potential
ecological or environmental crisis.
Institute
of Earth Sciences "Jaume Almera", CSIC, Solé i Sabarís, s/n
08028-Barcelona, Spain
The
main environmental change occurring in the Mediterranean mountainous areas
is afforestation of old agricultural lands. Land cover change have a direct
influence on catchment water balance, as this has been largely demonstrated
in experimental catchments around the world. The effect of land cover on
water balance is due principallyto
the differences in water losses to the atmosphere between different vegetation
types.
This
work analyses the effect of land use change on surface hydrology and water
resources using the SIMBAL water balance model. This daily time step model
is a simple tool, able to cope with the particular evapo-transpirative
dynamics of different land covers. The model has been successfully validated
both with discharge and using catchment soil water reserve in the small
Can Vila research catchment in the pre-Pyrenees.
The
SIMBAL model has been used to explore an extended set of plausible land
use scenarios in the study area. Theland
use scenarios correspond to multiple combinations of 3 land covers: pastures,
pine and oak forest. Results show a reduction of runoff, when changing
from a scenario where pastures are the dominant cover to another where
trees are dominant. The scenario where pine forest is the dominant cover
produce the highest flow reduction.
J.I.
López-Moreno, S. Beguería & J.M. García-Ruiz
Instituto
Pirenaico de Ecología, CSIC, Campus de Aula Dei, Apartado 202, 50080-Zaragoza,
Spain
Reservoirs
represent strong changes in the river regimes downstream the dam. Particularly,
floods are partially retained by the reservoirs, in order to increase the
reservoir storage and reduce the impact of the peak flow. The Yesa reservoir
drains an area of 2,181 km2 in the Upper Aragón River Basin, and
is mainly devoted to supply water to the new irrigated areas of Bardenas,
in the Central Ebro Depression. It was constructed in 1959. Since 1914
there is a gaugins station at Yesa, immediately downstream the actual location
of the dam. Thus, it is possible to compare the behaviour of the river
before and after the construction of the reservoir.
The
Yesa reservoir is mainly infilled during the high flows of autumn and spring,
when most of the floods occur. The greatest volume stored is reached at
the end of May, and then it is quickly reduced. The behaviour of the reservoir
against any flood will depend on the season of the year and the intensity
of the flood. A statistical analysis of the floods suggests that the Yesa
reservoir clearly reduces the intensity of high and medium-frequency floods,
but increases the peak flow of the low-frequency floods.
Estación
Experimental de Aula Dei, CSIC, Apartado 202, 50080-Zaragoza, Spain
Degradation
of water quality ofsurface waters
in the Ebro river basin constitutes an important environmental concern
because of the increasing salinity trends observed in this region. A significant
contribution to the salt load transported by the rivers is supplied by
non-point sources from irrigation return flows.
The
Bardenas I irrigated area occupies 28000 has inthe
semiarid central part of the Ebro valley. Return flows from this area have
been monitored during the last decade. Since 1990, a total of 16 sampling
points on return irrigation canals and another 6 sites along the Arba river,
the natural drainage system ofthis
area, have been sampled on a weekly/fortnightlybasis.A
high spatial variability in salinity levels has been found in the area,
thus electrical conductivity varies from 0.3 to 10 dSm-1 depending on the
irrigation period and on the soil types drained. The electrical conductivity
in the Arba river increases from 0.3 to 4.7 dSm-1 from the inlet to the
outlet of the Bardenas area.Therefore,
the salt load supplied from the irrigation return flows amounts more than
50% of the total load transported by the Arba river. This river presents
the highest salinity levels in the Ebro basin. Poor water quality due to
the high salinity determines restricted use for several purposes, that
according to Ayers & Wescott (1976) is classified between moderate
and severe.In order to reduce this
environmental impact, it is necessary to establish good management practices
involving design of more water efficient uses to avoid further water quality
deterioration.
Dpto.
de Geografía, Universidad de Extremadura, Cáceres, Spain,
Rainfall
interception by holm oaks (Quercus rotundifolia) was studied in the dehesas,
a landuse system widespread in the southwestern part of the Iberian Peninsula,
which consists of pastureland with openly spaced tree cover. Measurements
of throughflow and stemflow were carried out in the Guadalperalón
study catchment, located in Extremadura, and data of three hydrological
years (1995-1998) are available on an event basis. The effect of tree pruning
on interception was also investigated. In dehesas holm oaks are usually
pruned in intervals of approximately 10 years in order to obtain firewood
and to increase acorn production. Four trees were selected for monitoring,
two non-pruned and two pruned individuals. Meteorological data (rainfall,
temperature, solar radiation, air humidity and wind velocity) was registered
in intervals of 5 minutes. Throughfall was measured with a total number
of 163 raingauges distributed in a regular grid below the tree canopies,
allowing an analysis of its spatial distribution.
On
average 26.7% of the annual rainfall is intercepted. The pruned trees intercept
clearly less rainfall than the unpruned ones, with 23.6% and 29.9%, respectively.
Stemflow is of little importance, representing less than 1% of the annual
precipitation. The spatial variation of throughfall is high and is mainly
related with morphological characteristics of the tree canopy, though the
effect of wind could also be demonstrated. On an event basis, throughfall
is mainly controlled by the amount of precipitation and to a minor degree
by rainfall intensity, temperature and air humidity. Although individual
holm oaks intercept a considerable amount of rainfall, the importance on
the water balance of the catchment is small due to the low tree density.
With a canopy cover of 8%, the water loss due to interception constitutes
only 4% of the annual precipitation.
(1)
GKSS Research Center Geesthacht, Institut for Atmospheric Physics
Max-Planck-Str. 1,
D-21502 Geesthacht
(2)
German Aerospace Center DLR, D-51147 Cologne
In
July 1997 two episodes of heavy rainfall in the upper catchment of the
Odra river caused severe flooding in the Czech Republic, Poland and some
areas in Germany. Hundreds of cities and villages were inundated, more
than 100 casualties occured and vast areas of land were flooded for weeks.
The disaster management demanded the development of an integrated flood
forecasting system.
ODRAFLOOD
is a combination of model components covering a wide range of spatial scales
including a rainfall-runoff model for the whole Odra catchment, simulation
models forfloodplain inundation
and embankment breaches as well as reservoir management and the flooding
of urban areas. In its present state ODRAFLOOD is driven by observed or
forecasted precipitation data. At a later stage the model chain is planned
to be nested in a weather forecast system. This was already succesfully
performed for the upper Odra catchment where the flood originated.
The
model components were tested separately. Examples will be shown for the
grid-pint based rainfall-runoff model covering the whole Odra catchment,
for a 2-dimensional model for embankment breaches, based on the Navier-Stokes-equations,
and a high-resolution dynamical-statistical model to simulate the inundation
of urban areas.
H.-T.
Mengelkamp, J. Sutmüller, T. Zhao
GKSS
Research Center Geesthacht, Institut for Atmospheric Physics, Max-Planck-Str.
1, D-21502 Geesthacht
The
generation of surface runoff, subsurface runoff and baseflow is described
in the atmospheric land-surface model SEWAB (Surface Energy and Water Balance)
by scale dependend concepts which require tuning of appropriate parameters
using observed rainfall and streamflow. Alternatively, the concept of the
topographic index is implemented. Here, digital high resolution terrain
data are used to estimate the subgrid scale runoff generation. The only
tuning parameter is the vertical profile of the saturation hydraulic conductivity.
Both
concepts are used to simulate discharge from the upper Odra catchment from
April to August 1997. SEWAB is forced with observations. The time series
of both simulations differ only slightly and agree well with the observed
data.
SEWAB
is implemented in the non-hydrostatic atmospheric mesoscale model GESIMA
(Geesthacht Simulation Model of the Atmosphere) which is coupled to a horizontal
routing scheme. Nudged into the Deutschlandmodell of the German Weather
Service the model chain is used to simulate discharge from the upper Odra
catchment during the flooding event in 1997, which was the largest flood
desaster in this region for decades. We will discuss simulated and observed
streamflow data.
O.
Mesa, G. Poveda, J. I. Vélez, O. J. Barco, L. A. Cuartas, R. Mantilla,
C. D. Hoyos, J. F. Mejía, B. A. Botero & M. I. Montoya
Postgrado
en Recursos Hidráulicos, Universidad Nacional de Colombia, A. 1027
Medellín, Colombia
We
have developed a 5-arcmin digital atlas of monthly and long-term average
rainfall, evapotranspiration and runoff for Colombia, including maps of
input variables such as temperature, humidity, radiation, etc. The maps
capture the spatial variability of the geophysical fields resulting from
major geographic, topographic and climatic controls. The spatial scale
of such maps has been defined as a function of the quantity and distribution
of the observations and of the dependence structure of the field itself.
Colombia has a great variety of hydro-climatic regions, due to its tropical
location, the influence of the Andes mountains ranges and sea-land interactions.
Construction of the rainfall map was based on the available rain gages
observations, satellite estimates, re-analysis global maps and previous
studies. For interpolation purposes we used Kriging with drift. Evaporation
was estimated using diverse methods. Runoff was estimated using the long-term
water budget equation. The existing streamflow records at a wide range
of basin sizes where then used for checking and evaluation of the methods,
obtaining an average mean square error of 15%.Maps
are digital, interactive and part of a more comprehensive and complex information
systems (GIS) and data base to access and consult many hydrometeorological
variables throughout Colombia. Estimation of diverse hydrological and climatological
fields can be largely improved by including trans-boundary data, in particular
for the tropical Americas. Undergoing work includes maps of extreme values
and hydrological anomalies associated with El NiÒo-Southern Oscillation
(ENSO) and sediment yield. Water resource management and planning and multiple
applications in hydropower, agriculture, human health, sustainable development,
ecology and other environmental and socio-economic tasks benefit from the
maps.
N.C.
Mountain and J.A.A. Jones
Institute
of Geography and Earth Sciences, University of Wales, Aberystwyth, UK
The
research reported here uses a methodology that has been developed to generate
riverflow scenarios for future climate change from GCMs. The method involves
simulation of daily flows to assess the degree of change in flow frequencies,
lengths of low flow periods and seasonal distributions in catchments in
mid-Wales under two climate change scenarios derived from the Hadley Centre
HadCM2 GCM. The method consists of: (1) establishing statistical relationships
between interval-scale airflow indices (vorticity, the strength of the
geostrophic wind, and its zonal and meridional directional components)
and recorded precipitation and potential evapotranspiration (PET) for the
period of instrumental record within each catchment, (2) using the derived
transitional probabilities and correlations as input to a daily Stochastic
Weather Generator, and (3) inputting this synthesised daily weather sequence
into a physically-based hydrological simulation model (HYSIM). Split-sample
tests indicate good agreement between predicted and recorded daily flow
frequencies, with a Nash-Sutcliffe efficiency criterion of 0.7 for daily
flows and 0.9 for monthly totals. The results suggest that there will be
increased frequency of low flow days during the summer and a slight increase
in the length of individual low flow spells.
Jordi
Nadal (1) & Joan Saldaña (2)
(1)
Geography Department, Universitat Autonoma de Barcelona, 08193 Bellaterra
(Spain)
(2)
IMA, Universitat de Girona, 17071 Girona (Spain)
The
research project ìManagement and analysis of land uses, landscape
and sustainable development in natural protected areasî studies the
evolution of landscapes after farm abandonment. One way to understand this
evolution is studying the information that we can obtained from the water
cycle.
The
first hypotesis of this work is that the vegetable cover of catchments
has a decisive role in the hydrological behaviour. This behaviour can be
evaluated through the study of hydrographs or through water analysis. We
have worked in seven catchments with different land uses: Bare rokc, Natural
forest, Transition forest, Scrubland, Abandoned agricultural fields and
Active agricultural fields.
These
catchments are located in the National Park of Sant Llorenç in the
Catalan Prelitoral Range (41?40íN, 2?W), with a Mediterranean climate
modified by altitude (from 300m to 1100m).
Methodology
used has been the description of study areas, the calculation of land uses
and water analysis of 10 diferent parameters after rain episodes. From
the results obtained it is possible to deduce the followings:
Behaviour
of catchments follows two different paths: natural covers and humanized
covers. Scrubland offers a soil protection similar to that of forest. Abandoned
lands have a similar behaviour than as active lands. This for a long period
of time (more than fifty years).
Manfred
Ostrowski (1) & Hubert Lohr (2)
(1)
Darmstadt University of Technology, Engineering Hydrology and Water Resources
Management. (2) Mll-WIS Consulting Engineers, Darmstadt, Germany
From
early civilisation reservoirs have been considered the most efficient technical
measures to balance the unequal temporal and spatial distribution of runoff.
For the largest part design and operation were looked at and evaluated
merely from an economical point of view.
However,
besides manifold benefits, such as flood control, low flow augmentation,
water supply for industry or irrigation, hydropower generation etc., reservoirs
can also have negative effects e.g. in the area of environmental disturbances
or safety of downstream dwellers. Also, many existing reservoirs are still
operated under the assumptions initially made during their design phase.
In
1994 the Federal State of North-Rhine-Westphalia, Germany took the initiative
to develop a generic simulation and optimisation modelling system as part
of a decision support tool to enable interested reservoir owners and operators
to reassess their operation rules under changing objectives and boundary
conditions such as system extension.
The
discussion on benefits and costs, both tangible and intangible is less
of technical than of political nature. However it seems compulsory to provide
a sound objective technological base for this discussion to avoid misuse
and misunderstanding of subjective arguments.
During
the last 15 years so called decision support systems are under development
to serve this purpose. Despite obvious successes it is still difficult
to combine objective information and modelling parts of DSS with the evaluation
and decision making parts, respectively.
This
model base of the decision support tool TALSIM has recently been completed.
It has been applied to several small systems during the development and
testing phase. At present the tool is applied to one of the most complicated
systems in Germany, the Eifel-Rur reservoir system.
This
paper will provide: I) A problem description; ii) An overview of DSS for
reservoir operation ; iii)A discussion of strengths and limitations of
such systems; iv) A demonstration of some case studies.
THE
IMPACT OF LONG TERM LAND USE CHANGES ON THE OCCURENCE OF EXTREME FLOODS
- THE MODAU CASE STUDY
Manfred
Ostrowski (1), Steffen Heusch (1) & Marcus Lempert (2)
(1)
Darmstadt University of Technology, Engineering Hydrology and Water Resources
Management
(2)
Kisters Consulting Engineers, Aachen, Germany
The
Modau River is a small direct tributary of River Rhine with a catchment
area of about 200 km2, located in the Federal State of Hesse, Germany.
During the last centuries the river has been heavily modified by industrial
and other anthropogenic impacts, like agricultural use and ongoing urbanisation.
It can be expected that besides water quality deterioration the flood regime
of the river has significantly changed. This is the hypothesis of a model
based study of the Modau river basin being part of the European 4th Framework
Project FRAMEWORK.
Based
on multi-temporal air photographs starting from 1935 important changes
of land use were digitised at 10 year intervals and stored in a GIS. In
addition important changes of hydraulic characteristics such as river training
and flood retention facilities were also detected and documented.
A
physically oriented deterministic model (WBMTUD) was applied to the Modau
River basin to describe and analyse its flood regime for changing historical
and synthetic land use scenarios. Based on simultaneous rainfall and runoff
observations optimum model parameters were estimated, both for continuous
long term and single event short term mode. Statistical analysis and deterministic
modelling were used to test the hypothesis. However, results could not
confirm the hypothesis, rather a variety of less expected results will
be presented.
Giovanni
Pardini, Maria Gispert, Gemma Dunjo, & Luis Laporta
Soil
Science Unit, University of Girona, 17003 Girona, Spain
Rural
abandonment of hillside soils may have beneficial or detrimental effects
on soil properties and water availability depending on post-abandonment
land management and soil resilience. When agro-forestry practices fail,
early-diffused dense shrub-dominated ecosystems are affected by wildfire
recurrence, which may severely affect the composition of vegetation, and
both soil and water quality. Likewise, damaging effects on soil properties
may be expected when partial abandonment occurs and soil is continuously
exploited without any amendment. Increase in structure deterioration and
crusting may produce higher overland flow, resulting in accelerated erosion
and nutrient depletion and the concentration of soluble compounds in runoff
water may increase as well. The Serra de Rodes cathment (Girona Province,
NE Spain) is a typical Mediterranean environment where Lithic Xerorthents
are predominant and soil properties vary with the varying canopy covers.
In this area, the rural abandonment took place at the beginning of the
last century and landscape has been modelled according to the periodical
passage of fire. The objective of this research was to determine soil and
water quality indicators during a period of six months before and six months
after the wildfire occurred the 7th august 2000, in a sequence of partially
abandoned fields, abandoned fields at different age of abandonment, and
a pine forested area. Accordingly, partially abandoned fields, (PAF), recently
(5 years) abandoned fields (RA5), fields at middle (25 years) abandonment
(MA25), late (50 years) abandoned fields (LA50) and a fifty years old pine
forested area (PA50) were sampled at 0-10 cm depth at random after any
rainfall event during the period of observation. Samples were analysed
for Texture, Moisture content (M) and Water Holding Capacity (WHC), Bulk
Density (BD), Mechanic Impedance (MI), pH, Soil Organic Matter (SOM), Total
nitrogen (TN), Cation Exchange Capacity (CEC), exchangeable cations (Ca,
Mg, Na, K). After any rainfall event sediments and runoff water were collected
from erosion tanks and analysed for organic carbon and nitrogen (the eroded
soil) and for dissolved organic carbon (DOC), dissolved organic nitrogen
(DON), electrical conductivity (EC), pH, and soluble (Ca, Mg, Na, and K)
cations, (the runoff water). Results show that before the wildfire the
age of abandonment enhances water holding capacity and nutrient reserve
due to the accumulation of organic litter and the enrichment of humus compounds
in organic horizon, although nutrient depletion by runoff water was also
higher in more vegetated soils. The highest sediment yield was found in
the partially abandoned fields (PAF) whilst the recent abandonment (RA5)
was comparatively the less eroded environment due to the presence of grass
at the soil surface. Moreover, the best structure of this environment and
the reduced surface litter (rye-grass provides iso-humic enrichment in
the organic horizon) also lowered the removal of dissolved nutrients like
DOC and DON. After the wildfire a steep increase in runoff and sediment
yield was observed and the content of organic carbon and nitrogen either
in the eroded soil or in the runoff water increased to a large extent.
Also, a drastic modification of selected soil properties was recorded during
the period of observations after the fire.
R.
Pelosini (1), D. Gandini (1), G. Paesano (1), R. Cremonini (1), G. P. Balsamo
(1), C. Cassardo (2), M. W. Qian (2)
(1)
Regional Meteorological Service of Piedmont, Turin, Italy
(2)
Department of General Physics, University, Turin, Italy
The
disastrous flood occurred in the whole Piedmont (in North-Western Italy)
during 13th-16th of October 2000 was associated with heavy rainfall over
the North-Western Alpine chain in successive episodes spanning the whole
period. The most intense rainfall (where values larger than 600 mm have
been reported) occurred over the mountainous region. The event started
when Southern strong and moist flows established over the North-Western
Italy. The atmosphere was strongly barocline during day 13th, and caused
a strong convergence in the lower layers on the western Po Valley. At the
same time, the high temperature of the Mediterranean Sea caused an high
rate of moisture enrichment of the air mass moving towards Piedmont. The
precipitations intensified starting from day 13th over the Northern sector
of Piedmont. During day 14th, the baric situation changed slowly causing
an eastern rotation of the air flow; the areas affected by the strongest
precipitations were the Western basins. During this day, apparently convection
played an important role, and the high temperatures forced the snow-rain
threshold at very high levels. During day 15th, the arrival of a cold front
from West produced a destabilization of the atmosphere, causing some thunderstorm
activity. The maxima rainfalls were observed in the North-Western areas,
but high rainfall rates were observed also in the flat areas. Finally,
during the last day of the event (16th), an intensification of the Southern
flows caused again strong precipitations in the Northern mountain areas?.
This
event was one of the more intense events of the last 200 years in the Piedmont
area. The majority of the basins suffered strong flood episodes; most of
the mountainous portion of the basins and also part of the city of Turin
were seriously damaged by the strong rainfall. During the presentation,
we will describe the meteorological conditions that caused the event and
the main hydrological consequences on the Piedmont basins.
M.W.
Qian (1), C. Cassardo (1), A. Longhetto (1), R. Pelosini (2), D. Gandini
(2), G. Paesano (2)
(1)
Department of General Physics, University, Turin, Italy
(2)
Regional Meteorological Service of Piedmont, Turin, Italy
We
simulated the flood event described in the previous presentation by using
the mesoscale model RAMS (Regional Atmospheric Modeling System), driven
by the ECMWF analyses and coupled with the surface scheme LSPM (Land Surface
Process Model), in order to evaluate the hydrologic budget during the flood.
We focused our attention on the entire Piedmont area. During the simulation,
we were particularly interested in observing the components of the hydrologic
budget (runoff, drainage and the variation of the soil moisture content)
and the contribution of the evaporation and of the latent heat flux during
the flood episode. As the RAMS/LSPM is a regional model, it is also possible
to check some parameters at a regional scale and over a tridimensional
grid. During this presentation,
we want to show the more interesting characteristics emerging from this
study.
M.W.
Qian (2,4), N. Loglisci (1), C. Cassardo (1), A. Longhetto (1,4) &
C. Giraud (3)
(1)
Department of General Physics, University of Turin, Italy
(2)
Inst. of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,
China
(3)
Institute of Cosmo-Geophysics, National Research Council (CNR), Turin,
Italy
(4)
ICSC-World Laboratory-Lausanne-Switzerland
The
aim of this work is an improvement of the parameterisation of the soil
moisture in the scheme of the Land Surface Process Model (LSPM) for applications
over desert areas. In fact, in very dry conditions, the water vapour flux
plays an important role in the evaporation processes and influences the
underground profiles of humidity and temperature. The improved version
of soil moisture parameterisation in the LSPM scheme has been checked by
using the data taken from the database of the field experiment HAPEX-Sahel
(Hydrology-Atmosphere Pilot EXperiment in the Sahel, 1990-1992). Model
simulations refer to three different stations located in Niger (Fallow,
Millet and Tiger sites) where input data for LSPM and observations were
simultaneously available. The results of simulations, taking into account
the water vapour flux in the soil model LSPM, seem to compare better with
the observed behaviour of soil moisture and turbulent heat fluxes than
those overlooking the water vapour flux, confirming the great importance
of the water vapour in such dry conditions.
E.
Reis (1), C. Ramos(1), A. Ramos Pereira(1), T.M. Azevedo(2), E. Nunes(2)
D. Pereira (3), C. Aires (3), C.F. Andrade (2), M.C. Freitas (2) &
N. Pimentel (2)
(1)
Centro de Estudos Geográficos, FLUL, 1600-214 Lisboa, Portugal.
(2)
Centro de Geologia, FCUL, Campo Grande, 1749-016 Lisboa, Portugal
(3)
Dep. Ciéncias da Terra, Universidade do Minho, Campus de Gualtar,
Braga, Portugal.
With
the scope to accomplish the comparative study of the Tagus, Douro and Sado
riversí floods, in the ambit of the Praxis XXI project ìAn
interdisciplinary approach to flood risk evaluation ñ hydrology,
geomorphology and sedimentology of the Douro, Tagus and Sado Basins (IDAFRE)î,
a parallel broach of the heavy metal analyses, in the respective floodplains
was effectued.
The
geomorphological characteristics of the three drainage basins are quite
different. The Lower Tagus runs, after leaving the high quartzitic crests
of Portas do Rod„o, in an extensive floodplain about 6 km wide, in cenozoic
sediments, the Douro is strongly encased in high granitic banks and the
Sado is an intermediate situation, runing in a not very large alluvial
plain, in paleozoic and cenozoic formations. Due to these different situations,
their behaviour in hydrological terms is also different.
The
samples for the heavy metal evaluation were taken using manual drilling
but in distinct positions relatively to the present channel: for the Tagus,
two drillings were done, one right in the channel (3.7 m deep) and the
other approximately 3.0 km away from it (7.4 m deep); for the Douro, the
samples were taken in a good outcrop, in a meander at an altitude of 123
m and reaching a depth of 10 m; for the Sado, a manual coring in the present
channel was complemented by sampling in 3 m high banks, to a total thickness
of 8 m.
For
all the samples, sedimentological, geochemical and radiochronological analyses
were carried out, being detected very important variations in the heavy
metal concentrations and in the percentage < 4µm fraction, related
with the geological and geomorphological characteristics of the correspondent
basins.
The
results presented also show the different hydrodynamics of the three rivers
as well as the human influence over the last 5000 years BP, namely concerning
the mining activities.
C.
Ramos (1), E. Reis (1), A. Ramos Pereira (1), T. M. Azevedo (2), E. Nunes
(2), C. Andrade (2) & C. Freitas (2)
(1)
Centro de Estudos Geográficos, FLUL, 1600-214 Lisboa, Portugal.
(2)
Centro de Geologia, FCUL, Campo Grande, 1749-016 Lisboa, Portugal.
This
work has been undertaken in the ambit of the Praxis XXI Project titled
ìAn interdisciplinary approach to flood risk evaluation ñ
hydrology, geomorphology and sedimentology of the Douro, Tagus and Sado
Basins (IDAFRE)î. The purpose of this project is to improve the knowledge
of the behaviour of the studied rivers far back to times where there was
no reading registration, trying to improve in this manner the estimates
for large return periods, like high magnitude floods, as well as to fill
an important gap in the Portuguese research in what concerns Earth Sciences.
To
undergo this study two sampling sites (Quinta da Boavista and Fonte Bela)
in an approximately 6 km width alluvial plain, both on the right margin
of the Tagus River and distancing about 16 km from one another, were chosen
due to their geographical position and different morphological characteristics.
Quinta
da Boavista, north of SantarÈm, is located on the Tagusí
fluvial channel, at an altitude of about 9 m. The sediments studied were
collected by manual coring and reached a depth of 3.70 m below the water
level. The sampling at Fonte Bela, south of SantarÈm, was carried
out on the alluvial plain, roughly 3 km away from the present fluvial channel.
This sampling reached a total depth of 7.40 m in a drainage trench, of
which 2.50 m were sampled subaerially and the remaining in depth.
All
the samples, from both sites, underwent sedimentological, geochemical and
radiochronological analyses.
The
results achieved show accentuated variations in the clay and heavy metal
contents, which are in part imputed to lateral migrations of the fluvial
channel and to anthropic contaminations from the present to times before
the foundation of the Portuguese nationality. Besides these results, the
radiochronological datings have allowed determine sedimentation rates for
this region.
These
studies are being developed in the ambit of the PRAXIS/C/CTE/14271/1998
Project financed by the Foundation for Science and Technology (FCT).
RUNOFF
GENERATION ON ABANDONED FIELDS IN THE CENTRAL EBRO BASIN - RESULTS FROM
EXPERIMENTS
Institut
für Physische Geographie, Johann Wolfgang Goethe-Universität
Frankfurt am Main, Senckenberganlage 36, D-60325 Frankfurt a. M., Germany.
In
the semi-arid Central Ebro Basin experimental rainfall simulations with
a small mobile jet rainfall simulator according to Calvo et al. (1988),
Lasanta et al. (1994), Lasanta et al. (2000) were carried
out on abandoned fields near María de Huerva to investigate the
conditions of runoff generation and local erodibility on abandoned fields.
On the silty soils, susceptible to soil sealing and crusting, very divergent
rates of runoff and erosion caused by water are found. On the crusted 5-year
old fallow land runoff coefficients range between 20 and 95%, erosion rates
range between 9 and 70 gm-2 in the experiments. The means are 63% and 27
gm-2. Soil surface sealing leads to a decrease of infiltration rates and
a consequent increase of runoff compared with freshly tilled agricultural
fields. On the 65-year old fallow land, values range from 0 to 76% and
0 to 78 gm-2 depending on other parameters such as slope and the activity
of the edaphon, the means are 28% and 16 gm-2. A remarkable fact is that
material delivery does not significantly decrease with increasing vegetation
cover. Only with a vegetation cover of over 60% there is an evident decrease
of material output.
The
runoff rates show the same order of magnitude in comparison with the recorded
rates, which Lasanta et al. (2000) presented recently for abandoned
fields near Peñaflor, but the erosion rates in María de Huerva
are significantly lower.
CALVO,
A., GISBERT, J. M., PALAU, E. & ROMERO, M. (1988): Un simulador de
lluvia portátil de fácil construcción. - In: SALA,
M. & GALLART, F. [eds.]: Métodos y Técnicas para la Medición
en el Campo de Procesos Geomorfológicos. Sociedad
Española de Geomorfología, Monografía No. 1; Barcelona,
p. 6-15.
LASANTA,
T., GARCÍA-RUIZ, J. M., PÉREZ-RONTOMÉ, C. & SANCHO-MARCÉN,
C. (2000): Runoff and sediment yield in a semi-arid environment.The
effect of land management after farmland abandonment. - Catena, 38: 265-278.
LASANTA,
T., PÉREZ RONTOMÉ, M. C. & GARCÍA-RUIZ, J. M.
(1994): Efectos hidromorfológicos de diferentes alternativas de
retirada de tierras en ambientes semiáridos de la Depresión
del Ebro. - In: GARCÍA-RUIZ, J. M. & LASANTA, T. [eds.]: Efectos
Geomorfológicos del Abandono de Tierras; Zaragoza, p. 69-82.
TRENDS
IN THE EXTENT OF HYDROLOGIC DROUGHT IN NORTH CAROLINA.
Department
of Geography, University of North Carolina, Chapel Hill, NC 27599, USA
North
Carolina has few inflowing rivers, so that the amount of fresh water naturally
available to the state is largely constrained by the balance between the
atmospheric processes of precipitation and evaporation. Drought provides
a lower bound for water availability, and changes in the extent, intensity
and duration of drought largely control the input side of water sustainability
studies. However, statewide trends in drought have not been adequately
addressed.
In
the context of water sustainability, it is not clear what drought metric
is appropriate. This preliminary investigation uses the records of the
Palmer Hydrologic Drought Index, P, as the pertinent variable.This
allows the development of a simple measure
SI
= SPi,i = 1?8(representing
the 8 climate divisions in the state).
This
can be calculated for all months from 1900 onwards, both unweighted and
withweighting by area and by population.
Linear regression techniques, and a threshold crossing time-series model
are used to suggest possible trends. However, no unambiguous trend appears
at the moment.
It
is not clear that PHDI, which incorporates a specific, largely undefined,
response timescale, is the correct variable to use. Studies of agricultural
drought in North Carolina suggest that the Standardized Precipitation Index
is better for that shorter term phenomenon, and may, with a suitably chosen
time-scale, be appropriate here. Further, a simple mass balance approach,
using areally integrated precipitation and evaporation directly, must be
tested.
INCREASED FLOODING INDUCED BY TOURISTIC URBAN LAND USES
Grupo
de Investigación Ambiental Mediterránea, Universidad de Barcelona,
Spain.
The
occurrence of high intensity storm rainfall in the western Mediterranean
results in severe and often catastrophic flooding.In
the Catalan coastal catchments alone, located at the northeast of the Iberian
peninsula, 296 zones have been estimated to be at risk from flooding (Berga,
1987). The change in catchment response to rainfall induced by urbanization
is one of the most dramatic of man's impact on the hydrological cycle (Packman,
1979; Sala & Inbar, 1992). The basic effect of the increment of urban
impervious areas on the rainfall-runoff processes is to increase storm
runoff, thus increasing flood potential. Major trends of land use changes
in the Mediterranean coastal streams show a marked progressive increment
of the urbanized areas, basically related to touristic development of the
coast. This study presents the characteristics of intense storm rainfall
and flash flooding, which occur in the Ridaura catchment, located at the
northeast Spanish coast. The maximum daily rainfall values associated with
significant runoff events is in the order of 200 mm over a 24 hours period
and a recurrence interval of 7 to 10 years. The discharges resulting from
the rainfall events are approximately 200 m3/sec to 250 m3/sec and produce
flooding in the downstream summer resort of Platja d'Aro.
THE
WATER BALANCE OF DIFFERENT SOILS ON ABANDONED FIELDS ALONG A TRANSECT FROM
THE CENTRAL EBRO BASIN TO THE PYRENEES
Institut
für Physische Geographie, Johann Wolfgang Goethe-Universität
Frankfurt am Main, Senckenberganlage 36, D-60325 Frankfurt a. M., Germany,
The
water storage capacity of five typical soils on abandoned fields in five
test areas along a transect from the Central Ebro Basin to the High Pyrenees
(Leptic Haplogypsid, Haplic Calcixerept, Lithic Xerortent, Oxyaquic Vertic
Haplustalf, Humic Dystrocryept) are related to climatic factors as precipitation
and evapotranspiration. The annual precipitation increases from 300 mm
in the Central Ebro Depression to 1800 mm in the subalpine area, the potential
evapotranspiration decreases from 1000 mm to 600 mm. Thus there is a remarkable
gradient of the climatic water balance. However in the High Pyrenees, months
with a negative climatic water balance are frequent. For a period of 6
years the potential soil water balance was calculated on the base of soil
physics and climatic data on a daily time step and compared with field
data. The results show a very low content of plant available water within
5 months in the basin up to 2 weeks in the mountainous region, due to the
long dry periods and the high content of fine pores because of high clay
content of the soils. The limitation of plant available water is the main
reason for a slow vegetation succession on abandoned fields. Due to the
low vegetation cover runoff generation and soil erosion increase and the
water deficit becomes higher.
Olga
E. Scarpati (1, 2), Liliana Spescha (1, 3), MarÌa J. Fioriti (4)
& Alberto D. Capriolo (1)
(1)
National Council of Scientific and Technical Research, Argentina.
(2)
Geography Department, Humanities and Education Sciences Faculty, La Plata
National University, Argentina.
(3)
Faculty of Agronomy, Buenos Aires University, Argentina.
(4)
Water Resources Subsecretary, Serrano 669 (1414) Buenos Aires, Argentina
To
forecast interannual and seasonal variability of the hydrological processes
is very important when planification of water resources is involved.
The
hydrological cycle and the climate system are intimately linked and the
knowledge of the atmospheric general circulation disturbances allows to
the mentioned forecast.
It
is increasingly clear that hydrological variability can be interpreted
in terms of large-scale climatic anomalies-such as those associated with
El Niño/Southern Oscillation (ENSO) and that there are strong relationships
between hydrological anomalies in different parts of the world.
Geographical
and societal characteristics of Patagonian region also contribute to its
vulnerability to changes in water availability. Important characteristics
are large demand relative to supply, extensive development in floodplains,
vulnerable groundwater supplies, water-quality problems, dependence on
rain fed agriculture, and extensive dependence on hydroelectricity.
Regions
where water is already short during part or all of the year are vulnerable
to the disruption of supply caused by such climatic variability as prolonged
or intense droughts.
This
paper proposes a methodology for forecasting extreme discharges of some
rivers located at patagonian basins. The period with the biggest drainage
was selected and the accumulated anomalies of the river discharges were
used as hydrological variable.
The
predictor considered was the sea surface temperature (SST) in the Pacific
Ocean as a function of El Niño 3 (90?W-180?W; 5?N-5?S) on the Tropical
Pacific Ocean and the results were evaluated with a simple linear regression
model.
(1)
Instituto Pirenaico de Ecología, CSIC, Campus de Aula Dei, Apartado
202, 50080-Zaragoza, Spain.
(2)
Department of Geography, University of La Rioja, 26004-Logroño,
Spain.
For
the modelling and prediction of stormflow peaks of a small catchment the
processes leading to runoff have to be understood broadly. Due to the actual
lack of knowledge for understanding the runoff generation processes after
the summer droughts, it was expected to gain additional information by
investigating the runoff peaks in relation to the rainfall events. For
this, the hydrographs of two catchments in the Central Pyrenees (Arnás,
Borau Valley, unforested, and San Salvador, Aísa Valley, forested)
have been studied in detail and compared with the structure of the rainfall
causing the runoff. Previous investigations showed that, on the one hand,
the response of the deforested catchment was very fast to precipitations
of any volume and intensity in the cold (and humid) season. On the other
hand, there was no significant relationship found between antecedent rainfall
or rainfall intensity and the runoff in the warm (and dry) season.
The
present study shows that even a dry catchment -
evidenced by no or very low runoff before and after the stormflow event -
can generate a high stormflow peak with a runoff coefficient exceeding
0.5. There was observed, too, that the stormflow hydrograph reflects the
structure of the rainfall event, showing an increase and a decrease of
the runoff with a lag of about 2 h to the variations of the rainfall intensity.
Previous rainfall events, with similar intensities lead to no runoff. These
first results indicate, first, that stormflows after the dry period is
mainly caused by superficial runoff generation. Second, the runoff may
be caused by exceeding a threshold rainfall intensity in function to the
antecedent water surplus. The forested catchment shows very much lover
variations of the runoff following rainfall. This can be explained by a
higher water retention capacities of the soils under forest, the higher
infiltration capacities and the attenuation of the rainfall intensity due
to the vegetation cover.
M.
Seeger (1), J.B. Ries(2)
(1)
instituto Pirenaico de Ecología, CSIC, Campus de Aula Dei, Zaragoza,
Spain.
(2)
Institut für Physische Geographie, Johann Wolfgang Goethe-Universität
Frankfurt am Main, Senckenberganlage 36, D-60325 Frankfurt a. M., Germany,
The
present paper is based on the results of rainfall simulations done by the
project EPRODESERT an presented here by Ries & Neeb. Using the soil
hydraulic characteristics measured in laboratory and the runoff data obtained
by mobile plot rainfall simulator a physically based model ñ HILLFLOW-1†D
ñ was applied to understand and quantify the infiltration processes
on abandoned fields of different ages in the Central Ebro Basin. The experimental
data were used to calibrate the model. Further, different rainfall intensities
and soil moisture conditions were modelled to understand runoff generation.
The
results of the investigations indicate that especially the infiltration
properties of the soil crust are determinant factors for runoff generation.
It could be observed, too, that the hydraulic conductivity of the crust
decreases with age within the first 5 years after abandonment. Different
soil moistures, predominantly lower than pF 4.2, have low influence on
the runoff generation by rainfall. In all cases, the increase of soil water
content is limited to the soil crust. Modelling different rainfall intensities
there can be stated, that with intensities of more than 20 mm h-1 the beginning
of the runoff is within the first 10†min of the rainfall, and the runoff-coefficients
are higher than 0.4.
The
modelling of rainfall simulations on more than 60 years old fallow land
confirm the field observations: the infiltration characteristics, and consequently
the runoff generation, depends on very low variations of the macroporosity
of the soils. This has a very high variability in time and especially in
space. The higher superficial infiltration rates do not lead, depending
on the structure of the macropores and on the rainfall intensity or quantity,
to higher soil water contents. Infiltrating water into the macropores does
not infiltrate into the soil matrix and can lead as consequence of a rapid
subsuperficial stormflow to piping processes.
A.K.Sinha,
Anup Sharma & Nazmul Hoda
Environmental
Geologylab, Department of Geology,
University of Rajasthan, India.
Persuant
to growing environmental awareness and concern for depleting water resources
at global, regional and local levelthe
need and demand forimproved environmental
technologies like rainwater /rainfall-runoff water harvestingis
re-emerging all over the globe. The age old traditions and structuresfor
rainwater harvesting in some of the water scarce regions of Asia have fallen
into disuse and are attracting renew attention
In
western India, as the deleterious effects of ground water depletion and
pollution and its consequences are surfacing out a variety of responses
are being forged to mitigate or even reverse these. One such response gaining
popularity isreturn to the old
wisdom of Rainwater Harvesting. Despite large number of dams and reservoir
in India 1150Km3 of its rainwater precipitation still run off to the seas
annually in the form of rejected recharge. If a fraction of this can be
stored underground in an appropriate reservoir / storage system groundwater
could be enhance significantly and may provide great succor to semiarid
and arid regions of India which are highly water scarce region and where
water table is sinking comparatively at much faster rate (10-40cm/year).
The
paper deals withan effort to create
additional storage for rainfall runofffor
which a study was carried out by Remote Sensing methodto
locate sites to increase residence time of rainfall runoff so thatadditional
quantity of the ground water may become available. The various locales
have been identified and delineated for Rainfall runoff harvestingwhichifproperly
applied, would not onlyenhance the
water availability but would also help toward the ecological regeneration
in the region where considerable ecological degeneration has taken place
during last few years due to increasing scarcity of water and prevailing
drought condition.
K.
U. Sirinanda
Department
of Geography, Faculty of Arts &Social
Sciences
University
of Brunei Darussalam, Bandar Seri Begawan,BE1410,
Brunei Darussalam
Brunei
Darussalam (hereinafter, Brunei) has aland
area of about 5765sq km and about47,000
sq km of territorial waters. The total population is about 350,000 with
an average density of about 60 persons per sq km. The per capita GDP is
about US$ 20,000, owing mainly to the small population and the presence
ofhydrocarbon resources as the mainstay
of the economy. It has a tropical-equatorial-monsoonal climate with uniformly
high temperatures and copious rainfall throughout the year although a seasonality
is evident in the intra-annual rainfall pattern. The atmospheric environment
is generally hazard-free, occasional flash floods, relative dry conditions
in certain years due to abnormal negative deviations in the rainfall, occasional
strong winds, and infrequent haze phenomena notwithstanding.
Space-averaged
annual rainfall is about 3000 mm,distribution
being uneven ranging from about 2000 in the coastal areas to over 5000
in the highlands. There is no dry season as such although relatively less
rainy conditions can prevailfrom
January to April. With a very high drainage density it is natural that
Brunei should depend on rivers as sources ofpiped
water supply.Over 95 per cent ofhouseholds
inurbanized areashave
piped water supplies while the figure may be about 65 in the more rural
areas.Due to the particularstructure
of the Brunei economy, over 90 per cent of the water supply isfor
domestic requirementsand only a
relatively small amount is being used foragricultural
andcommercial purposes. There is
no significant industrial activity at present. However,with
the total population estimated to double by the year2015and
the plans for economic diversification through the development ofindustries,
the above pattern ofdemand for water
is likely to change.
Per
capita daily water consumption for domestic purposes is estimated to be
about 400 litres which is considered to beon
the high side.The main thrust ofpublic
water supply strategies has been towards making water availableas
needed.Water charges are so nominalthatwater
use efficiency israther low. However,
in time to come, measures may have to be in place to address the question
of managing the demand side of theequation.
The
paper will examine the water supply sustainability with reference to the
climate and hydrology of the countryas
well as the socio-economic factors.
SEDIMENT AND
WATER QUALITY IN THE RÍO GUADIAMAR FOLLOWING THE AZNALCÓLLAR
TAILINGS DAM FAILURE: IMPLICATIONS FOR RIVER RECOVERY AND MANAGEMENT
1
Institute of Geography and Earth Sciences, University of Wales, Aberystwyth,
Ceredigion, Wales SY23 3DB, UK
2
School of Earth Sciences, Birkbeck College, University of London, Malet
Street, London WC1E 7HX, UK
3
School of Geography, University of Leeds, Leeds LS2 9JT, UK
On
25 April 1998 the AznalcÛllar tailings dam failure discharged an
estimated 6 million m3 of acid water and fine-milled pyrite ore into the
Guadiamar River.Subsequent clean-up
operations removed in excess of 90% of the contaminated material but, in
turn, produced considerable geomorphological instability in the system,
exposing channel banks and floodplain sediments to erosion and residual
contaminants to remobilisation.
This
paper aims to examine the geochemical and physical controls on the distribution
of contaminants between sediments and waters and their delivery downstream
under these disequilibrium conditions.Emphasis
is given to the relative contribution of variable flow stages in the Guadiamar.The
river has a typically Mediterranean regime, dominated by low flows with
occasional high magnitude flood events.
Heavy
metal (Cd, Cu, Pb and Zn) and arsenic levels are presented for sediment-associated
and solute loads at low and high flows, and for freshly deposited overbank
material.Results indicate the relative
importance of sediment-associated contaminant delivery at peak flows due
to the buffering capacity of the calcareous lithologies in the catchment.There
is a variable pattern of contaminant dispersal away from the spill source,
with isolated ëhotspotsí of elevated contamination throughout
the Guadiamar system superimposed on declining concentrations during the
three years following the spill event.
Radiometrically-dated
floodplain sediment cores have been used to establish pre-spill contaminant
conditions, providing context for current contamination and future risks
to the wetlands of Doñana National Park.
Institute
of Environmental Geoscience Russ. Acad. Sci.,Russia, 101000, Moscow,
Economically,
the organizational and functional tasks of ground-water monitoring should
be solved along with solving serious financial and technical problems,
which are always very acute. The development of monitoring network and
observation program appears to be the most expensive part of this work.
Taking into account the complexity of monitoring problems, the large territory
of observation, the limited possibilities of the local monitoring-governing
bodies, as well as the occasional location of the existing observation
systems, the importance of developing adequate scientific and practical
approaches to the optimization of the entire system of ground-water monitoring
becomes evident.
The
optimization of ground-water monitoring implies working out a system of
scientifically valid measures aimed at selecting an adequate combination
of programs (frequency of measurements, the observation duration, the density
of observation network, the spatial position of observation posts, etc.)
that would provide the best proportion between the reliability of the information
obtained and the monitoring expenditures.
Upon
planning the ground-water monitoring, the following optimization principles
should be followed:
It
should provide database for solving as many problems of ground-water monitoring
as possible;
The
monitoring data obtained should be related to the possible methods of solving
the scientific and practical problems set;
The
optimization of ground-water monitoring can be achieved only by the step-by-step
consideration of both genetic regularities of the ground-water regime formation
as well as the geostatical and probabilistic analysis of the variability
of the ground-water components and parameters in time and space;
The
proportion between the required accuracy (reliability) of the information
and the expenditures on its obtaining serves as the optimization criterion.
As
proceeds from this discussion, the ground-water monitoring appears to be
a multistep and complex procedure to be carried out in the following subsequent
stages:
(1)
Hydrogeological zoning according to the conditions of ground-water regime
formation; (2) Ecological and hydrogeological zoning aimed at solving environmental
problems; (3) Application of optimization procedures based on the solution
of minimax problems (within the selected areas).
I.J.
van der Walt & Ben Nell
(2)
Geography & Environmental Studies, School of Environmental Sciences,
Potchefstroom Univ. for Christian Higher Education, Potchefstroom 2520,
South Africa
(2)
Potchefstroom City Council, Potchefstroom, 2520, South Africa
The
city of Potchefstroom is situated at the lower end of the Mooi River catchment.
Since 1842 the Mooi River has been the sole water supply of Potchefstroom,
which currently has about 210 000 inhabitants.
The
Mooi River is fed mainly by dolomitic eyes and springs.During
the Mokolian age (1300 Ma), the dolomitic layers underlying the catchment
were separated into various compartments by the intrusion of a swarm of
syenite dykes.Since the 1940ís,
large-scale gold mining commenced to work the ore, which occur in the Witwatersrand
sedimentary layer underlying the dolomites.To
reduce the danger of flooding, many of these dolomitic compartments were
de-watered by the gold mines, sometimes resulting in catastrophic environmental
impacts.Furthermore, slimes dams
were constructed with little regard to the underlying strata resulting
in the release of large volumes of polluted water into the underlying aquifer.
The
indiscriminate mining practices, as well as the rapid development of informal
and formal settlements, various diamond mining enterprises as well as agriculture
in the central and upper reaches of the catchment, resulted in a steady
increase in salt loads in the water of the Mooi River, as well as the deposition
of high concentrations of trace metals, especially uranium, which is associated
with the gold bearing ore.Recently,
it was announced that some mines in the Mooi River Catchment have reached
the end of their productive lives, and that projects to re-water the dolomitic
compartments were underway.
This
paper explores the possible environmental impacts associated with re-watering
the dolomitic compartments, and indicates how a lack of integrated catchment
planning and management are currently exacerbating the already manifested
environmental impacts.Finally, an
integrated approach to the rehabilitation and restoration of the catchment
to a sustainable water resource is suggested.
P.
Waylen (1) & M.E. Quesada (2)
(1)
Department of Geography, University of Florida, USA, 32611-7315.
(2)
Departamento de Ciencias Sociales, Univ. de Costa Rica sede Occidentale,
San José.
Although
only small in spatial extent, Costa Rica exhibits a tremendous variability
in both its precipitation regimes and the nature and degree of their interannual
variability.Located between two
major oceans and separating the continents of North and South America its
precipitation climatology is dominated by a series of global and regional
scale ìcentres of actionî, whose influences are exaggerated
by the topographic effects associated with the major northwest-southeast
trending cordillera. Signals of opposing associations to ENSO have previously
been detected on either side of the cordillera, however there appear to
be extended periods during the historic records when this signal becomes
effaced.This partially explains
why this region was not initially identified as possessing a particularly
strong association to ENSO.The modulation
of the rainfall response appears to be the result of the interaction between
the dominant frequencies associated with ENSO in the Equatorial Pacific
(2-7 years) and lower frequency variability in the tropical North Atlantic
(decadal). Seasonal rainfall records at over one hundred stations in Costa
Rica for the period 1950-1999 are statistically compared according to the
state (above/below average) of sea surface temperature anomalies in both
the tropical North Atlantic (5-20?N, 30-60?W) and NiÒo3.4 (5?N-5?S,
120-170?W).The greatest and most
spatially distinct response to ENSO occurs when the tropical North Atlantic
has anomalously low temperatures, while a warmer than normal Atlantic appears
to greatly diminish both the magnitude of response and the signalís
spatial distinction on either side of the cordillera.Some
stations report average seasonal rainfall departures during periods of
a warm Pacific and cool Atlantic compared to those of cold Pacific and
warm Atlantic, to be as large as+/-
2.25 standard deviations of the undifferentiated time series.
THE ROLE OF SEDIMENT IN SUSTAINABILITY. THE CASE OF ESTUARINE BARRAGES
School
of Engineering, University of Durham, South Road, Durham, DH1 3LE, UK
Sediment
inputs to two estuarine barrages in the north-east of England are being
monitored using a combination of continuous turbidity measurements and
event-based automated sampling.A
fingerprinting study of sediment sources is also underway.The
aim of the study is both to quantify the inputs of sediment to the system
and to understand the dynamics of sediment supply.Ultimately
it is hoped that such knowledge will allow better management of the catchments
and/or the barrages to minimise sedimentation problems.
The
Wansbeck barrage, at 26 years old, is the oldest tidal barrage in the UK.It
is a partial exclusion barrage allowing 30% of tides to input saline water
to the impounded water body.It
has extreme sediment and water quality problems.In
contrast, the Tees barrage at 5 years old is one of Britainís newest.It
is a total exclusion barrage with no intrusion of seawater.The
catchment areas of these two barrages are quite different in size, geology,
soils and land use and are influenced by differing climatic influences.These
differences are reflected in the dynamics of sediment transport seen in
the two rivers.
At
the runoff event scale, sediment supply limitations and the consequences
of individual supply events are evident for the Wansbeck. There is also
some evidence to suggest exhaustion in sediment supply between storms in
the Wansbeck, suggesting that the Wansbeck has a predominantly supply-limited
suspended sediment transport regime. In contrast, the Tees initially exhibited
the smoothed, lagged sedigraphs characteristic of the routing effects that
occur in larger catchments.Over
the first winter-spring-summer of monitoring on the Tees it appeared that
sediment transport in the Tees was predominantly energy-limited.Sediment
sources appeared to be dominantly in the upper reaches of the catchment.However,
in the autumn of 2000 three major flood events happened within the space
of one week.The sediment dynamics
of the river were completely different after this week, due to the mobilisation
of large amounts of sediment from river banks lower down the catchment.This
change has persisted ever since.It
thus became clear that the sediment supply in the Tees had also been supply
limited before the flood events.Subsequent
sediment dynamics are much more complex and difficult to predict.
At
monthly and annual time scales the sediment yield per unit area was similar
for the two catchments, in spite of the higher total flow volume of the
Tees, until the storms of autumn 2000.Following
these events, the cumulative sediment yield for the Tees far exceeds that
for the Wansbeck.Such episodes of
frequent high flows are one of the probable consequences of climate change
and thus raise questions as to the adequacy of current sediment yield estimation
techniques.
As
a means of identifying the sources of sediments supplied to the barrages
a sediment fingerprinting exercise is also underway.Here
samples from potential sediment sources throughout the catchment (fields,
river banks, mass movements, moorland) are analysed for their chemical
signature.Statistical analysis
is then used to characterise these sediment sources according to various
groupings of interest: sub-catchments, geological types, land uses, soil
types.At the same time, flood flows
in the rivers are sampled for suspended sediment load.This
is carried out at a number of sites around the catchment in an attempt
to isolate different classes of sediment sources.Sediment
collected from flood events undergoes the same analysis for chemical signature,
and a mixing model is used to ascertain the most likely sources of the
sediment moved in different flood events.It
is intended that this part of the project will help to explain variations
in sediment dynamics at our monitoring sites.The
results may also assist in the planning of possible sediment control measures
in the catchments.
F
Winde
University
of Jena, Department for Geography, Löbdergraben 32, D-07743 Jena,
Germany
Potchefstroom
University for CHE, Dep. for Geography and Environmental Studies, Potchefstroom,
Republic of South Africa
Tailings
deposits from gold- and uranium mining often containing high amounts of
radioactive and chemotoxical heavy metals. By seepage and waterborne transport
dissolved uranium and other contaminants migrating into the groundwater,
finally entering adjacent fluvial systems. The subsequent transport in
rivers is one of the most efficient pathways of distributing contaminants
throughout the biosphere. In a comparative study of mining areas in Germany
(Wismut area in East-Thuringia) and South Africa (goldmines on the Witwatersrandformation)
mechanisms of non-point river contamination and the fluvial transport of
uranium were investigated. As part of the investigation, the hydraulic
interaction between the surface water and ground water (as diffuse source
of river contamination), as well as the hydrochemical environment within
the river and its sediments were tracked in real-time with computerised
data logger in situ-measurements.
In
this paper results to the hydrogeochemical behaviour of uranium at the
Koekemoerspruit (South Africa) are presented.
Despite
a negative annual water balance, the waterborne transportation of dissolved
uranium and other heavy metals leaching from gold tailings (slimes dams)
constitutes a major source of diffuse river contamination in South Africa.
Due to the vast volume of deposited tailings in the densely populated gold
mining areas, a better understanding of transportation mechanisms and the
immobilisation of pollutants is needed in order to develop adequate water
management strategies in South Africa. The worldwide decline in uranium
production resulted in increased concentrations of uranium being deposited
onto the slimes dams, thereby considerably worsening the problem.
In
the Koekemoerspruit - which constitutes a typical mining affected river
in the Klerksdorp Goldfield - the solute transport of dissolved uranium
along the aqueous pathway was investigated. Ratios between dissolved and
solid phases of uranium for various water-sediment-systems along the aqueous
pathway were calculated.Contrary
to expectations, a significantly higher rate of uranium binding on sediments
in the running water system than on the highly sorptive sediments of the
associated ground water system underlying the floodplain, was found. Geochemical
correlation suggests that in flowing waters immobilisation is caused mainly
by precipitation of carbonates and insoluble iron/manganese-compounds,
rather than by adsorption processes. Co-precipitation of uranium and other
dissolved metals results in them binding onto sediments. The formation
of hydrous iron- and manganese-oxides and -hydroxides in particular, take
place within sediments in the river channel.At
the ground water-surface water interface in the river channel, mixing between
reducing ground water and oxidising river water causes redox-initiated
precipitation. Thus, bottom sediments act as a geochemical barrier as well
as a sink for dissolved uranium being transported from the slimes dam to
the river. The binding of uranium in neutral charged uranyl-sulfate-complexes
simultaneously prevents the cation from stronger adsorption on floodplain
sediments. However, the evaporation of ascending ground water results in
superficial salt crusts on the floodplain sediments, containing very high
concentrations of uranium. Due to re-solution by rainwater, such salt crusts
easily turn from sinks into sources of uranium causing peaks of solute
concentration in rivers.
F
Winde (1) & I.J. van der Walt (2)
(1)
University of Jena, Department for Geography, Löbdergraben 32, D-07743
Jena, Germany.
(2)
Potchefstroom University for CHE, Department for Geography and Environmental
Studies, 2520 Potchefstroom, Republic of South Africa.
A
computerised datalogger with 16 probes measuring with 10 minute intervals
i.a. the water level in the stream, ground water levels, precipitation,
temperature, pH and redox potential of the river water as well as the ground
water, was installed in the Lerchenbach (a tributary to the Weisse Elster
in the Wismut area of East-Thurungia, Germany), as well as in the Koekemoerspruit
(a tributary of the Vaal River in the NorthWest Province, South Africa)
to track the fluvial transport mechanism of pollution, especially uranium.
Recent
sources of river contamination with uranium in South Africa are mainly
connected to gold mining activities. Possible mechanisms of contamination
are the transfer of uranium bearing slimes particles into adjacent river
channels (e.g. by wind and water erosion of tailing dams, stability failures
of slimes dams, spills etc.) as well as the input of dissolved uranium
into the hydrological cycle. With respect to the latter one can distinguish
between contaminated mine effluent directly discharged into rivers (point
sources) and pollution resulting from seepage from slimes dams migrating
via aquifers into the receiving watercourses (diffuse sources).
In
both regions uranium and other heavy metals are contaminating the ground
water of the associated floodplains as a result of seepage from slimes
dams. This contaminated ground water is the main source of diffuse pollution
of the river channels. The extent of river contamination therefore depends
on the concentration of dissolved uranium in the groundwater and the hydraulic
conductivity of the sediments. To track river-groundwater interactions,
the water levels in the river (gauging weir) and the groundwater levels
were measured by piezometric probes. In both sites significant hydraulic
interactions between the river and the ground water were found.
Despite
a permanent steep hydraulic gradient from the water-saturated tailing deposits
to the receiving water course in general, under certain conditions the
overwhelming exfiltration, which constitutes the baseflow in the river,
can turn into infiltration. In case of the Koekemoerspruit, where the water
level in the river is mainly controlled by a pumping scheme from the goldmines,
this infiltration / exfiltration cycle occurs daily. Because the pumping
of ground water into the river is not constant (mainly due to cheaper electricity
during off-peak times), pronounced water level changes occur in the river
on a daily and a weekly basis, allowing for contaminated ground water to
seep into the river channel only at night time, making it highly unlikely
that elevated levels of uranium in the river water will be picked up by
normal monitoring practices.
Time
series data of EC from the Lerchenbach show that during flood events, the
highly contaminated porewater from the bottom sediments is completely replaced
within a few hours by cleaner surface water infiltrating into the sediments.
The reverse process, however, takes up to two weeks. Besides the input
of polluted porewater into the running water column, the sudden change
of the chemical composition of the porewater during flood conditions (to
an oxidising environment) may affect the immobilisation and re-mobilisation
of dissolved uranium in the sediment, resulting in individual pulses of
contamination moving downstream.
F
Winde
University
of Jena, Department for Geography, Löbdergraben 32, D-07743 Jena,
Germany
Potchefstroom
University for CHE, Geography and Environmental Studies, 2520 Potchefstroom,
Republic of South Africa
In
this paper, results from data-logger measurements of river chemistry in
the Koekemoerspruit (South Africa) and the Lerchenbach (Germany) are presented.
The
hazardous potential of tailing deposits mainly depends on the ease with
which their toxic constituents are able to migrate in the dissolved phase
along the aqueous pathway into the receiving environment. In the case of
uranium and other heavy metals, the mobility is strongly influenced by
their speciation. It not only determines whether a metal will be in the
dissolved or solid phase, but also to what extent a dissolved element can
bind to or is released from adsorbents in a water-sediment system. Speciation
in its turn, depends on the concentration of the metal in the solution,
its ionic composition as well as ñ to a great extent - on the pH
and the redox potential (Eh). To investigate this relationship, sensors
measuring pH, Eh, water-temperature (t) and electric conductivity (EC)
were placed in the river, providing data with ten-minute intervals over
a period of 24 months (Lerchenbach) and 18 months (Koekemoerspruit) respectively.
A
statistical time series analyses of the pH of the running water revealed
pronounced diurnal cycles with maximal daily changes from 0.7 to 2 units
in the Koekemoerspruit and the Lerchenbach respectively. Simultaneously,
the EC and the redox potential of the river water fluctuate daily as well,
with Eh showing an inverse correlation with pH. Interactions and dependencies
between the parameters, as well as possible causes of the cyclic behaviour
are discussed.
Besides
being responsible for changes in metal speciation, these fluctuations in
the river chemistry are also likely to affect the precipitation of hydrous
iron and manganese oxides and hydroxides, which is an important immobilisation
process for dissolved uranium in rivers. This is partly due to the exceedence
of certain thresholds during the diurnal cycle and partly due to the acceleration/inhibition
of the precipitation rate itself.For
example, the formation of manganese oxides only occurs when the pH is greater
than 8.5, while the rate of Fe(OH)3-precipitation is amplified by a factor
of 100 if the pH increases by half a unit. The precipitation of carbonates
is controlled by similar interactions. The impact of Eh-fluctuations seems
not to be as important for uranium mobility since the range of change is
significantly smaller than for pH.
Beside
diurnal fluctuations during dry weather conditions, it seems that weather
conditions, especially precipitation, also result in changes in the river
chemistry (e.g. acid rain related decreases of pH in the river). The possibility
of weather induced remobilization of uranium and other heavy metals from
sediments, resulting in short duration peaks of pollution, is also discussed.
School
of Geography and Geology, McMaster Univ, Hamilton, Ontario, Canada L8S
4K1
Annual
floods in western Canada are usually generated by winter rainfall or spring
snowmelt events.Previous studies
have found strong correlations between the December to February precipitation
for most parts of western Canada and the Southern Oscillation Index (SOI),
suggesting that the annual floods may be affected by ENSO events.This
study explores such relationships by extracting the annual floods from
140 western rivers with at least 25 years of record, for correlation with
the average SOI for October to March. One-third of the rivers show positive
correlation with the Oct-Mar SOI, suggesting that these rivers have lower
than average annual floods during the El Niño years, but the reverse
for the La Niña years.The
overall spatial pattern of correlation indicates patches with high r2
confined
within a triangular area with the base extending from interior southern
British Columbia to southern Saskatchewan, and the apex at the triple-boundary
of British Columbia, Yukon and Northwest Territories.Within
this broadly defined area, the coastal belt, the Peace River basin and
the foothills of the Rockies show low r2 values. There appears
to be a correspondence between the major rain shadows and the clusters
of low r2 .
The
general pattern of correlation between annual floods in western Canada
and SOI may be accounted for by the teleconnection between winter precipitation
anomaly and southern oscillation. During El Niño years, a southward
shift of the subtropical branch and a northward shift of the polar branch
of the jet stream leave the southern part of western Canada and the Pacific
Northwest of United States with lower than normal precipitation, hence
generating lesser peak flows.The
precipitation contrasts between El Niño and La Niña years
may be amplified on the windward slopes while the effects are dampened
in the rain shadow areas.
As
winter and spring floods are both hazards and opportunities to recharge
the reservoirs, an understanding of the linkages between annual floods
and SOI will allow such hydrologic events to be related to the atmospheric
phenomena.