ИСТИНА

Constantly growing water demand provides increasing scarcity of water resources. The lack of water resources is especially significant for the small river basins where the water demand is higher than the low-water flow. Cyclic groundwater pumping is used to alleviate deficiencies in streamflow discharge during dry seasons. Groundwater-surface water interaction is at the core of such use. Estimation of streamflow depletion is first-priority to evaluate the effectiveness of application of seasonal compensation pumping. It may be examined by analytical equations or numerical models. The problem of stream depletion has been extensively studied by many researchers (C.V.Theis, R.E.Glover, C.G.Balmer, M.S.Hantush, C.T.Jenkins, B.Hunt, J.Bredehoeft, R.B.Wallace, V.A.Zlotnik, E.L.Minkin, F.M.Bochever and other researchers) These solutions are limited in their applicability by their conceptual model of the river, aquifer, and pumping well. Regression dependencies between unit stream depletion and capacitance were obtained by authors for the estimation of stream reduction created by cyclic pumping. The numerical simulation approach is widespread applied to stream–aquifer investigations. Numerical modeling of cyclical compensation pumping has special features: the periodic solution, the seasonal changes through the boundaries and the importance even small drawdown of stream level. When seasonality is a modeling feature, traditional approach leads to mistaken values of streamflow depletion. Set of numerical models showed that miscalculation in some cases exceeds 70 percent and more. Simulation of cyclic pumping requires three-step procedure. The first step is usual construction steady-state model. Then steady oscillatory model is constructed in which heads and flows through boundaries vary through the seasons but repeat from year to year (from cycle to cycle). Steady oscillatory solutions are used as initial conditions for transient pumping model. The stream flow depletion is estimated by difference between the transient solution and steady oscillatory solution. The purpose of these investigations was to determine number of cycles required to reach steady oscillatory solution. Estimation of streamflow depletion created by cyclic pumping is complex and not straight-forward problem. Analytical equations, regression dependencies or numerical simulation has their assumptions and limitations.