Average Monthly Discharge Research Articles

The Influences of Climate Change on the Runoff of Gharehsoo River Watershed

The purpose of this study is to survey the impact of climate change on the runoff of Gharehsoo River in northwest of Iran. In this research the outputs of monthly precipitation and temperature data of PRECIS model, which is a regional climate model with 50 × 50 km resolution on the basis of B2 scenario, have been utilized for base (1961-1990) and future (2071-2100) periods. The output results of PRECIS model show that the average temperature of watershed increased up to 2°C - 5°C. In addition, future precipitation is more than the base precipitation on January, February, March, September and December. The observed data of 1996-2002 used for calibration of HSPF model and the data of 2003-2004 were used for HSPF validation. The present monthly patterns for precipitation and temperature were estimated using the geostatistical techniques and the future monthly patterns were retrieved by the combination of future monthly PRECIS data and monthly patterns of precipitation and temperature. Then, the base and future precipitation and temperature patterns were introduced to validate HSPF model for the simulation of monthly runoff in the base and future periods. The results show that in the future, the discharge of Gharehsoo River watershed decreases in all of the months. In addition, the peak discharge in the future period happens one month earlier, in April, because of increase of temperature and earlier beginning of snow melting season. Finally the sensitivity analysis was performed on the monthly runoff. The results showed that monthly discharge increases 0.3% - 35.6% and decreases 0.3% - 32.6% due to 20% increase and decrease of precipitation, respectively. In addition, 1°C and 2°C increase of temperature lead to 0% - 8% and 0.1% - 15% decrease of average monthly discharge, respectively.

Hydrological Process Modelling using RBNN - A Neural Network Computing Technique

Severe erosion in the watersheds under Damodar Valley Corporations (DVC), Hazaribagh, Jharkhand, India has been taking place for a long time. Several soil and water conservation measures are being adopted by the Soil Conservation Department in Damodar Valley. For effective planning of soil conservation programmes, hydrologic models have been used, but with several limitations. In the present study, Nagwa watershed under DVC was selected for simulating monthly surface runoff and sediment yield using radial basis neural network (RBNN) model, which requires lesser data. Different sets of input data were employed and it was observed that only average monthly rainfall was sufficient to estimate surface runoff, while average monthly rainfall and average monthly discharge were needed for estimating sediment yield. The RBNN model was trained for the years 1991-2000 and validated for the period 2001-2007. Results indicate that coefficient of determination, R2, Nash-Sutcliffe simulation efficiency, NSE and root mean square error, RMSE (m3.s-1) values for RBNN model were 0.93, 0.92 and 1.25 during training, and 0.73, 0.73 and 0.77 during validation period, respectively. The model performed quite well for simulation of sediment yield with R2, NSE and RMSE values of 0.92, 0.92 and 1822 during training period; and 0.80, 0.70 and 2288 during validation period, respectively. It could be stated that RBNN model based on simple inputs couldbe a powerful tool for simulation of monthly surface runoff and sediment yield.

The geomorphology and sedimentology of the Tista megafan, Darjeeling Himalaya: Implications for megafan building processes

This paper reports a study of the Tista megafan in the foothills of Darjeeling Himalaya. Spread over parts of India and Bangladesh, the megafan is bounded by the Mahananda River to its west and the Tista River to the east. The Atrai and Karatoya Rivers flow through its axial part. The megafan covers an area of ~ 18,000 km 2. Near its apex the surface slope is ~ 0.19°, that declines to 0.01° near the toe. The east–west transverse profile of the megafan is broadly upward convex, with gently sloping (~ 0.01°) flanks. Maximum width and the length of the megafan are about 145 km and 166 km respectively. The highest point near the megafan apex is ~ 150 m above the Brahmaputra alluvial plain. The Tista River flanking the megafan has an average annual discharge of 609 m 3/s with highest average monthly discharge exceeding 2000 m 3/s during monsoon. Most of the other channels currently traversing the megafan are plains-fed, and compared to Tista and Mahananda Rivers these channels have lesser discharge, higher sinuosity, and decreased widths. A radiating network of abandoned channel belts can be identified in satellite images of the megafan. Each of these major paleochannels is associated with numerous crevasse channels in the distal part of the megafan, forming an intricate network of radial drainage on the megafan surface. Three distinct depositional lobes can be recognised on the Tista megafan. Each of the lobes is identified by a set of ancient and modern radial drainage systems. The lobe boundaries are marked by discordance in drainage network of adjacent lobes. The relative ages of the lobes, as tentatively determined from the drainage discordances, indicate that the megafan first built up the eastern lobe (lobe 1), then shifted to the west to form lobe 2, and finally switched again eastward giving rise to the smallest lobe located close to the mountain front (lobe 3). Although broadly upward convex in cross profiles, subtle reflections of multiple lobes are apparent in some of the cross profiles. Study of the old maps published between 1794 and 1945 reveals that some of the present-day plains-fed rivers, like the Tangon, the Atrai and the Karatoya, were directly connected to the Himalayan catchment basins prior to the late eighteenth century. Archaeological excavations along the banks of these rivers appear to support this paleodrainage configuration. Eight facies and five facies associations were recognised in the uppermost megafan sediments. Facies associations suggest deposition from high-energy sandy streams in the proximal area and deposition from mixed load, sinuous streams and flanking marsh or lake in the distal part of the lobes. Paleocurrent data are consistent with a southwestward spreading paleochannel pattern recognised within the studied part of the megafan. Multiple lobes typify megafans ocurring in different parts of the globe. The existence of the mutiple accretionary lobes in Tista megafan, its radial drainage pattern, its concave-upward longitudinal and convex-upward transverse profile shape make it morphologically comparable with other high-gradient alluvial fans observed in nature and those produced in the laboratory. These morphological features denote the similarities between the small, high-gradient alluvial fans and large, low-gradient megafans, and that in turn may be indicative of the commoness in certain controlling factors between these two depositional systems.

Changes in sediment transport in the Kuye River in the Loess Plateau in China

In this paper, the changes in sediment transport over 51 years from 1955 to 2006 in the Kuye River in the Loess Plateau in China are assessed. Key factors affecting sediment yield and sediment transport, such as precipitation depth, discharge, and human activities are studied. To investigate the changes in sediment yield in this watershed, a trend analysis on sediment concentration, precipitation depth, and discharge is conducted. Precipitation depths at 2 Climate Stations (CSs), as well as discharge and sediment transport at 3 Gauging Stations (GSs) are used to assess the features of sediment transport in the Kuye River. The runoff modulus (defined as the annual average discharge per unit area, L/(s .km 2)) and the sediment transport modulus (defined as the annual suspended sediment transport per unit area, t/(yr km 2)) are introduced in this study to assess the changes in runoff and sediment yield for this watershed. The results show that the highest average monthly discharge during the study period in the Kuye River is 66.23 m 3/s in August with an average monthly sediment concentration of 88.9 kg/m 3. However, the highest average monthly sediment concentration during the study period in the Kuye River is 125.34 kg/m 3 and occurs in July, which has an average discharge of 42.6 m 3/s that is much less than the average monthly discharge in August. It is found that both the runoff modulus and sediment transport modulus at Wenjiachuan GS on the Kuye River has a clear downward trend. During the summer season from July to August, the sediment transport modulus at Wenjiachuan GS is much higher than those at Toudaoguai and Longmen GSs on the Yellow River. The easily erodible loess in the Kuye River watershed and the sparse vegetation are responsible for the extremely high sediment yield from the Kuye River watershed. The analyses of the grain size distribution of suspended load in the Kuye River are presented. The average monthly median grain size of suspended load in the Kuye River is largest in February and then decreases until June. In July, the average monthly median grain size of suspended load approaches another peak and decreases until September. Then, the median grain size of suspended load starts to increase until February of the following year. However, the average monthly median grain size of suspended load in the Yellow River at Toudaoguai and Longmen GSs is the smallest between early summer and late fall. The median grain size in the Yellow River starts to increase in November and approaches the largest size in January.

Predicting climate change impacts on water resources in the tropical Andes: Effects of GCM uncertainty

There is a strong demand from policy makers for predictions about the potential impacts of climate change on water resources. Integrated environmental models, combining climatic and hydrologic models, are often used for this purpose. This paper examines the impact of uncertainties related to GCMs in hydrological impact studies in the tropical Andes. A conceptual hydrological model is calibrated on data from four mesoscale, mountainous catchments in south Ecuador. The model inputs are then perturbed with anomalies projected by 20 GCMs available from the IPCC Data Distribution Centre. The results show that on average, the average monthly discharge is not expected to change dramatically. However, the simulated discharges driven by different global climate model forcing data can diverge widely, with prediction ranges often surpassing current discharge.

Discharge variability for an artesian spring of the Edwards Aquifer: Comal Springs (1933–2007)

AbstractDaily discharge volumes of Comal Springs, the largest artesian spring of the Edwards Aquifer (EA) in Central Texas, were utilized to characterize the flow of Comal Springs for the period of record spanning 1933–2007. The influence of water extraction (pumping) on discharge characteristics during the record was examined and found to be statistically significant for both volume and variability of spring discharge (p < 0.01). Pumping explains approximately a quarter of the variation in annual discharge (r2 = 0.25) and nearly a third of the daily variability (r2 = 0.32) within the Comal Springs discharge record.Statistically significant teleconnections to flow are demonstrated within the discharge record of Comal Springs. The El Niño‐Southern Oscillation (ENSO, as measured by the Southern Oscillation Index) and the Pacific Decadal Oscillation (PDO) are shown to exhibit statistically significant correlations with annual mean flow from Comal Springs. PDO modulation of ENSO results in mean flow anomalies of 21.9% between extreme quintile years. The Atlantic Multi‐decadal Oscillation (AMO) appears to exert influence based on the magnitude of the index value, irrespective of its positive or negative condition (p < 0.01), with the highest quintile (based on magnitude) years correlating with strong positive flow anomalies. A composite index was developed which combines the AMO, PDO and SOI. The extreme quintile years of this index demonstrate a 32.4% divergence in flow (p < 0.01) while demonstrating a stronger skill at capturing negative flow anomalies than positive anomalies.Precipitation data, at 4‐km spatial resolution, were utilized to examine the temporal and spatial correlation of water input to the EA with rates of average monthly discharge from Comal Springs. The spatial dependence of the correlation between precipitation and Comal Springs discharge indicates significant seasonal variability. Overall, the correlation between precipitation and discharge is significant for spring, summer and fall seasons and not significant for winter. Copyright © 2009 Royal Meteorological Society

Computation and prediction of the flood runoff of the Eastern Caucasus rivers

Analysis of observational data of the average monthly discharges, air temperatures, and precipitation totals collected at about 100 hydrological and meteorological stations before 2005 revealed that precipitation fallen on the Eastern Caucasus river basins in winter and spring plays the principal role in formation of floods that are observed in the period from April to June. The precipitation and runoff variability over the territory and altitudinal zones was studied and generalized. The hydrograph decomposition and the rivers classification according to their sources of feeding in the flooding period were performed. Analysis of correlation between the flood flow and winter and spring precipitation allowed obtaining reliable multiple regression equations that are suitable for computation and forecasting of the flood flow.

Forecasting analysis of runoff for reservoir regulation of dams and weirs in terms of hydro power plant operation

In order to meet the needs of Hydropower Plant (HPP) production new algorithms and software were developed for daily, seasonal, annual and long-term control of the runoff for the design of dam and weirs. This control is carried out for monitored periods from 20 to 50 years. The control depends on economic considerations, namely that the accepted probability of required water power is 90%, i.e. concerning the runoff and in this way for the useful volume of water dams. The research is accomplished by a design with the observations. First the hydrometric stations are selected at the available analogy with the building project and then the correlative connection is found assessed by general and true correlative coefficients. The transferring to the project of the observations for the average annual and average monthly water discharges is made with the coefficient of the analogy. The theoretical probability curves are chosen with a minimum dispersion. By the last curves the average monthly distributions are settled with probability from 2% to 90% by statistical method.During the investigated period of the regulation the volumes of discharge, overflow and shortage are calculated as and the determination for the accepted volume of the reservoir if the normative probability of the need is executed. As well the power output of the HPP and its participation in the coverage of the charge diagram on the peak load, under peak load, daily and nightly part are determined in separate observed or forecasting periods. The upper problems about the design and the operation of HPP, water output, reservoir volume and coverage of the charge diagram are solved by iterations. Practical examples are given for the runoff and for the time forecasting system.

Is the Water Temperature of the Danube River at Bratislava, Slovakia, Rising?

Abstract This paper aims to reveal the annual regime, time series, and long-term water temperature trends of the Danube River at Bratislava, Slovakia, between the years 1926 and 2005. First, the main factors affecting the river’s water temperature were identified. Using multiple regression techniques, an empirical relationship is derived between monthly water temperatures and monthly atmospheric temperatures at Vienna (Hohe Warte), Austria, monthly discharge of the Danube, and some other factors as well. In the second part of the study, the long-term trends in the annual time series of water temperature were identified. The following series were evaluated: 1) The average annual water temperature (To) (determined as an arithmetic average of daily temperatures in the Danube at Bratislava), 2) the weighted annual average temperature values (Toυ) (determined from the daily temperatures weighted by the daily discharge rates at Bratislava), and 3) the average heat load (Zt) at the Bratislava station. In the long run, the To series is rising; however, the trend of the weighted long-term average temperature values, Toυ, is near zero. This result indicates that the average heat load of the Danube water did not change during the selected period of 80 yr. What did change is the interannual distribution of the average monthly discharge. Over the past 25 yr, an elevated runoff of “cold” water (increase of the December–April runoff) and a lower runoff of “warm” water (decrease of the river runoff during the summer months of June–August) were observed.

Aquifer response to regional climate variability in a part of Kashmir Himalaya in India

Forty major perennial springs, under different lithological controls, in a part of Kashmir Himalaya in India were studied to understand the response of spring discharges to regional climate variability. The average monthly spring discharge is high in Triassic Limestone-controlled springs (karst springs) and low in alluvium- and Karewa-controlled springs. In general, the measured monthly spring discharges show an inverse relation with the monthly precipitation data. However, a direct correlation exists between the spring discharges and the degree of snow/ice melt. The results suggest that the creation of a low and continuous (but stable) recharge from the Triassic Limestone and Panjal Trap aquifers, due to blockage of groundwater flow between strata with contrasting hydraulic conductivity, attenuates the discharge and gives rise to small fluctuations in the alluvium- and Karewa-controlled springs. The average monthly discharge of the karst and alluvial springs showed an overall decreasing trend for two and a half decades, with the lowest discharge recorded in 2001. The study revealed that the regional/global warming and below-normal precipitation in the period of snow accumulation (PSA) has triggered the receding of glaciers and attenuation of spring discharges.

Fluvial process and morphology of the Brahmaputra River in Assam, India

The Brahmaputra River finds its origin in the Chema Yundung glacier of Tibet and flows through India and Bangladesh. The slope of the river decreases suddenly in front of the Himalayas and results in the deposition of sediment and a braided channel pattern. It flows through Assam, India, along a valley comprising its own Recent alluvium. In Assam the basin receives 300 cm mean annual rainfall, 66–85% of which occurs in the monsoon period from June through September. Mean annual discharge at Pandu for 1955–1990 is 16,682.24 m 3 s − 1. Average monthly discharge is highest in July (19%) and lowest in February (2%). Most hydrographs exhibit multiple flood peaks occurring at different times from June to September. The mean annual suspended sediment load is 402 million tons and average monthly sediment discharge is highest in June (19.05%) and lowest in January (1.02%). The bed load at Pandu was found to be 5–15% of the total load of the river. Three kinds of major geomorphic units are found in the basin. The river bed of the Brahmaputra shows four topographic levels, with increasing height and vegetation. The single first order primary channels of this braided river split into two or more smaller second order channels separated by bars and islands. The second order channels are of three kinds. The maximum length and width of the bars in the area under study are 18.43 km and 6.17 km, respectively. The Brahmaputra channel is characterised by mid-channel bars, side bars, tributary mouth bars and unit bars. The geometry of meandering tributary rivers shows that the relationship between meander wavelength and bend radius is most linear. The Brahmaputra had been undergoing overall aggradation by about 16 cm during 1971 to 1979. The channel of the Brahmaputra River has been migrating because of channel widening and avulsion. The meandering tributaries change because of neck cut-off and progressive shifting at the meander bends. The braiding index of the Brahmaputra has been increasing from 6.11 in 1912–1928 to 8.33 in 1996. During the twentieth century, the total amount of bank area lost from erosion was 868 km 2. Maximum rate of shift of the north bank to south resulting in erosion was 227.5 m/year and maximum rate of shift of the south bank to north resulting in accretion was 331.56 m/year. Shear failure of upper bank and liquefaction of clayey-silt materials are two main causes of bank erosion.

Análise estatística das características de vazão do córrego Capetinga

Em 1996 foram instalados, num dos córregos da Fazenda Experimental da Universidade de Brasília, um linígrafo e três pluviógrafos, iniciando-se, assim, a medição de algumas variáveis hidrometeorológicos referentes à bacia do córrego Capetinga. Conhecendo-se as médias mensais da vazão e as médias específicas, traçaram-se as respectivas curvas de permanência das vazões médias mensais desse córrego. Dessas curvas, extraíram-se os valores da vazão associada à permanência de 95% (Q95) e da vazão específica associada à permanência de 95% (q95). Não houve discrepância entre os valores de q95 e a razão entre Q95 e a área da bacia. Através da distribuição de valores extremos do tipo 1 ou de Gumbel, determinaram-se os períodos de retorno das vazões máximas instantâneas anuais e das mínimas anuais, com duração de sete dias. Calcularam-se, também, os eventos esperados dos máximos anuais e dos mínimos com a mencionada duração, para os períodos de retorno de 5, 10, 20, 50 e 100 anos. Verificou-se que a distribuição de Gumbel, no caso dos máximos, adaptou-se muito bem tanto na descrição dos eventos simulados quanto na descrição dos eventos observados, ao passo que no caso dos mínimos não houve discrepância, seja nos eventos simulados ou nos observados.

Self-tuning predictors with application to river flow prediction

The paper presents developments of recursive self-adaptive prediction algorithms, called ‘self-tuning predictors’, using some common estimation techniques, and their application to prediction of flow discharge of the river Tigris at Baghdad, Iraq. Four kinds of predictors, viz the least-square predictor, the minimum-variance predictor, a predictor using stochastic approximation, and a two-stage predictor, have been developed. Using available data for the River Tigris, prediction results have been obtained for the average daily discharge, the average monthly discharge and the average yearly discharge. In each type of prediction a number of models have been tried. The various prediction results are presented in graphical and in tabular forms for comparison.

Effect of Discharge on the Chlorophyll a Distribution in the Tidally-Influenced Potomac River

In the tidal Potomac River, high river discharges during the spring are associated with high chlorophylla concentrations in the following in the following summer, assuming that summertime light and temperature conditions are favorable. Spring floods deliver large loads of particulate N and P to the tidal river. This particulate N and P could be mineralized by bacteria to inorganic N and P and released to the water column where it is available for phytoplankton use during summertime. However, during the study period relatively low concentrations of chlorophylla (less than 50 μg l−1 occurred in the tidal river if average monthly discharge during July or August exceeded 200 m3s−1. Discharge and other conditions combined to produce conditions favorable for nuisance levels of chlorophylla (greater than 100 μg l−1 approximately one year out of four. Chlorophylla maxima occurred in the Potomac River transition zone and estuary during late winter (dinoflagellates) and spring (diatoms). Typical seasonal peak concentrations were achieved at discharges as high as 970 m3 s−1, but sustained discharges greater than 1,100 m3 s−1 retarded development. Optimum growth conditions occurred following runoff events of 10 to 15 d duration which produced transit times to the transition zone of 7 to 10 d. Wet years with numerous moderate-sized runoff events, such as 1980, tend to produce greater biomass in the transition zone and estuary than do dry years such as 1981.

Flow discharge prediction of river Tigris using Self tuning predictors

The paper presents development of recursive self-adaptive prediction algorithms called the self-tuning predictors using some common estimation techniques and their application to prediction of flow discharge of river Tigris at Baghdad, Iraq. Four kinds of predictors, namely, the least square predictor, the minimum variance predictor, predictor using stochastic approximation and a two stage predictor have been developed. Using available data for the river Tigris, prediction results have been obtained for average daily discharge, average monthly discharge and average yearly discharge. In each type of prediction, a number of models have been tried. The various prediction results are presented graphically and in tabular forms for comparison.

L' hydrologie nord-alpine et la sécheresse de 1976

The 1976 Spring drought and heat had hydrological consequences in the Northern Alps which are interesting to be studied because of their variety. The deficiency of the pluviométrie totals from december 1975 to june 1976 (the lowest ever recorded) caused the lowest wafer levels ever observed in may average monthly discharge and june for pluvial supplied streams = 0,20). 1976 monthly discharge As the snow cover was thinner than usual because of less important snow falls, the deficiency of the discharge for the snow supplied streams was rather high (0,50 to 0,60 of the usual monthly discharge). The peak value of the monthly average flows occurred in may and not in june due to the early heavy heat. This one and this exceptional daily insolation from may 1st to june 24th (50 % days had more than 11 hours of sun) caused surplus discharges in may (1,20 to 1,68 of the normal value) for high altitude streams (having more than 20 % of glacier area in the river-bassin) .

Systems approach in water resources planning

A description is given of the application of the systems approach to the planning of a large catchment basin in central Italy. The aim of the planning was to ensure the optimal satisfaction of water requirements for drinking water, industrial and irrigation purposes, as well as to provide flood control and protect the quality of the water in the river and its tributaries from pollutants.A hydrological study was carried out, using existing discharge data recorded at some gauging stations, and pluviometric data, in order to assess the succession of the average monthly discharges in a large number of sections and for a contemporaneous period of about 50 years. A second hydrological study was made to identify the frequency distribution of the floods and the mechanism by which they were formed and propagated.All sites which previous studies had indicated as potentially suitable for flood protection works were examined, together with others that were selected directly. A feasibility study was made for each of these, the results being used to estimate the law of costs for the works in function of the available storage capacity. With regard to water consumption the requirements of drinking water were calculated, since this was considered a constraint of the system. The requirements for irrigation and industrial use were also calculated, together with the benefits accruing.An analysis was made of the damage caused by floods in the recent past together with an extrapolation of the estimate of this damage in the future.In addition, an assessment has been made of the effects on the dispersal of the flood water and the costs of local protection works such as embankments and diversion channels.As regards pollution, the potential quantity of pollutants produced upstream of each control section has been estimated, as well as the cost of their total or partial elimination. The standards for the maximum permissible pollution in the sections were also fixed.Using the above inputs an optimization process in mixed linear programming was carried out, using the hydrological flows of a year considered significant. This made it possible to identify the optimal degree of satisfaction of water requirements, the optimal degree of flood control for the various places in danger, the degree of purification needed to satisfy the standards, bearing in mind the dilution resulting from the regulation of the discharges. A selection has been made of the works required for the achievement of the above aims at minimum cost.The basin scheme corresponding to the indications provided by the optimization process has been submitted to a simulation which utilized all the available hydrological data, i. e. for a period of about 50 years.In a successive phase the irrigation of a vast district (that the optimization process had not accepted) was considered as a constraint and the related social costs were evaluated.

ÉCHANTILLONNAGE AU HASARD DES DÉBITS MOYENS MENSUELS

SUMMARY After a short look onto the methodology of the random sampling and its fields of application, the problem of the random sampling of the average monthly discharges is examined in detail. Difficulties arose from chronological sequence having periodic seasonal variations are turned over by considering two components: annual yield and its distribution during the year. While yield is given as the yearly mean discharge, the distribution may be considered through the annual sequence of the monthly coefficients. The yearly mean discharge is operated by the usual methods of the statistic of the variates: distribution law, estimation of the coefficients of the law. As for the distribution along the year, a “storage” or “set” of aleatory functions is constituted, from what the “shape” to be used for the yearly mean discharge, is drawn at random. Then, the correlations which may exist between certain shape indexes and the yearly mean discharge, are examined. If there exist such correlations, taking them into ...

Ras-el-Ain: The great karst spring of Mesopotamia: An hydrogeological study

With an average annual discharge of 1,219 million cubic metres, or 38.666 cubic metres per second, Ras-el-Ain is amongst the largest of the great karst springs of the world. Ras-el-Ain lies almost midway between the Tigris and Euphrates Rivers, just south of the Syrian-Turkish frontier, in a region of open rolling plains. The waters issue from some thirteen springs and combine to form the effective head of the Khabour River, tributary of the Euphrates. Around Ras-el-Ain, precipitation is some 280 mm, decreasing to the south, but increasing in other directions. The springs issue above a local anticlinal saddle in a general synclinal structure of Tertiary formations, terminating on the north in the east-west Mardin swell and on the south in the anticline of the Djebel Aabd-el-Azaziz range. The aquifers feeding the spring are the Eocene limestones, with subsidiary supplies from the Miocene evaporites and limestones. The major infiltration area is located over basalt and Eocene limestone outcrops in the north and is estimated to extend over some 8,100 square kilometres; there is minor infiltration in the south. Recharge appears to be a direct function of surface runoff. Two east-west faults are invoked to account for the separation of the springs into a northern and southern group, whose waters are also somewhat different in chemical composition. Karst dissolution of the buried aquifers has resulted in the formation of collapse structures at surface which are occupied by small lakes and ponds, fed by the artesian springs. Discharge gaugings from December 1942 to November 1959, indicate that the average monthly discharge varies from a minimum of 36.000 cubic metres per second in June to a maximum of 41.894 in November. The coefficient of exhaustion has been calculated as 0.000483 and the stored reserves as about 7,420 million cubic metres. The study concludes with the possibilities of geotechnical development allowing still more efficient use of the water for irrigation, by reducing winter and increasing summer discharge from the springs. The danger of additional collapsing is noted.