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.
After the infiltration wetting front from a river bed of an ephemeral stream in flood reaches the shallow water table, the rate of recharge, which is also that of infiltration, is affected by the development of a groundwater mound. The effect is practically immediate if the water content behind the wetting front is close to saturation. An approximate analytical solution is developed in that case, which predicts the time dependence of the recharge rate. Comparison with experimental results in the laboratory shows that the solution is excellent in spite of the assumptions necessary in the derivations. As long as the ratio of river width over depth to water table exceeds 2 and as long as the ratio of initial saturated thickness over depth to the water table exceeds 2.5, the analytical solution is essentially exact. Under most field conditions these ratios are largely exceeded. Consequently, the predictive equation for the time dependence of the recharge is both quite simple to use and adequately accurate for field applications.
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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