Groundwater recharge in arid regions is intermittent and usually occurs as a result of flood flow transmission losses in dry wadi channels. Hydrograph characteristics play a dominant role in determining the amount of channel abstraction in relation to the width of the wetted perimeter and the time of inundation, and the subsequent groundwater recharge. Large variations in the magnitude of channel losses result mainly from the diversity in inflow volumes. The magnitude of groundwater recharge in relation to bed transmission losses is dependent on flood volume and duration, soil moisture content and physical soil profile characteristics. Runoff volume and duration are the dominant factors influencing the cumulative infiltrated volume and recharge to shallow water tables. Taking into consideration the influence of various hydrological and channel characteristics, several regression equations are suggested to estimate the transmission losses from a wadi bed and the groundwater recharge. Le recharge des nappes par l'infiltration des lits des ouadis dans les régions aridesRésumé L'alimentation des nappes phréatiques dans les régions arides est intermittent et résulte, en principe, des pertes de transmission des eaux des crues dans les lits desséchés des ouadis. Les caractéristiques hydrographiques telle que la largeur du périmètre humidifie et la durée de submersion jouent un rôle principal dans la détermination du volume d'eau qui alimente la nappe phréatique. Les variations importantes dans l'importance des pertes en eau des crues résultent en grande partie, des variations de débit à l'amont. L'amplititude du renouvellement de la nappe phréatique par rapport aux pertes de transmission des lits dépende du volume de la crue et de la durée pendant laquelle le sol reste humide ainsi que des caractères physiques du profil du sol. Le volume et la durée des crues sont les facteurs les plus importants qui influencent le volume cumule d'infiltration et la montée du niveau d'eau de la nappe phréatique peu profonde. Etant donné l'influence des différents caractéristiques de régime hydrologique et du lit du ouadi, on propose plusieurs équations du régressions pour évaluer la perte de transmission de l'eau dans le lit du ouadi et la recharge de la nappe souterraine.
Using regionally downscaled and adjusted outputs of three global climate models (GCMs), meteorological drought analysis was accomplished across Ankara, the capital city of Turkey. To this end, standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI) were projected under (representative concentration pathway) RCP4.5 and RCP8.5 greenhouse gas scenarios. In general, our results show that Ankara experienced six severe and two extreme drought events during the reference period, 1971-2000. However, the projections indicate fewer drought events for the near future period of 2016-2040, with no potential extreme drought events. While the RCP4.5 scenario showed that dry spells will be dominant in the second half of the near future period, the RCP8.5 scenario projected that dry spells will be evenly distributed during the entire near future period.
Snowmelt runoff in the mountainous eastern part of Turkey is of great importance as it constitutes 60-70% in volume of the total yearly runoff during spring and early summer months. Therefore, determining the amount and timing of snowmelt runoff especially in the Euphrates basin, where large dams are located, is an important task in order to use the water resources of the country in an optimal manner.The HBV model, being one of the well-known conceptual hydrological models used more than 45 countries over the world, is applied for the first time in Turkey to a small basin of 242 km 2 on the headwaters of Euphrates river for 2002-2004 water years. The input data are provided from the automatic snow-meteorological stations installed at various locations and altitudes in upper Euphrates basin operating in real-time. Since ground-based observations can only represent a small part of the region of interest, spatially and temporally distributed snow cover data are acquired through the use of Moderate Resolution Imaging Spectroradiometer (MODIS) optical satellite. In the first part of the study, an automatic model parameter estimation method, Shuffled Complex Evolution, University of Arizona (SCE-UA), is utilized to calibrate the HBV model parameters with a multi-variable criteria using runoff as well as snow-covered area (SCA) to ensure the internal validity of the model. Results show that calibrations against SCA in addition to discharge simulate discharge nearly as well as calibrations against discharge only, but further suggest that longer time periods and more study catchments should be included to achieve more comprehensible conclusions. In the second part of the study, the calibrated HBV model is applied to forecast runoff with a 1-day lead time using gridded input data from Mesoscale Model 5 (MM5) for the 2004 snowmelt period. Promising results indicate the possible operational use of runoff forecasting driven by numerical weather prediction data for flood mitigation, reservoir operation and dam safety.
Estimation of groundwater recharge to an uncon®ned aquifer is studied using analytical and numerical techniques and results are compared with ®eld observations. There is an acute need for such estimation in water balance studies in arid climates, and the case study in this paper is for such a region. The wetting front movement in the unsaturated zone depends on antecedent soil moisture, the ponded water depth and its duration, and on the position of the water table and the hydraulic properties of the unsaturated zone. A hydraulic connection between the recharge basin and the aquifer is not immediately established because the wetting front is unsaturated.A numerical model is applied to estimate recharge in an arid-zone wadi, and its validity is tested by comparing it with an analytical solution of the equations. The calculated recharge values matched the piezometric levels observed at a well site at the edge of the wadi channel. The total recharge depths found by integration in the time domain provided a good estimate of the transmitted volume of water per unit length of wadi channel. The ®ndings were con®rmed by runo volume measurements at gauging stations located in the basin.
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