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Combined estimation of specific yield and natural recharge in a semi-arid groundwater basin with irrigated agriculture

Soil erosion is a severe problem hindering sustainable agriculture on the Loess Plateau of China. Plot experiments were conducted under the natural rainfall condition during 1995–1997 at Wangdongguo and Aobao catchments in this region to evaluate the effects of various land use, cropping systems, land slopes and rainfall on runoff and sediment losses, as well as the differences in catchment responses. The experiments included various surface conditions ranging from bare soil to vegetated surfaces (maize, wheat residue, Robinia pseudoacacia L., Amorpha fruticosa L., Stipa capillata L., buckwheat and Astragarus adsurgens L.). The measurements were carried out on hill slopes with different gradients (i.e. 0 ° to 36 °). These plots varied from 20 to 60 m in length. Results indicated that runoff and erosion in this region occurred mainly during summer storms. Summer runoff and sediment losses under cropping and other vegetation were significantly less than those from ploughed bare soil (i.e. without crop/plant or crop residue). There were fewer runoff and sediment losses with increasing canopy cover. Land slope had a major effect on runoff and sediment losses and this effect was markedly larger in the tillage plots than that in the natural grass and forest plots, although this effect was very small when the maximum rainfall intensity was larger than 58·8 mm/h or smaller than 2·4 mm/h. Sediment losses per unit area rose with increasing slope length for the same land slope and same land use. The effect of slope length on sediment losses was stronger on a bare soil plot than on a crop/plant plot. The runoff volume and sediment losses were both closely related to rainfall volume and maximum intensity, while runoff coefficient was mainly controlled by maximum rainfall intensity. Hortonian overland flow is the dominant runoff process in the region. The differences in runoff volume, runoff coefficient and sediment losses between the catchments are mainly controlled by the maximum rainfall intensity and infiltration characteristics. The Aobao catchment yielded much larger runoff volume, runoff coefficient and sediment than the Wangdongguo catchment. Copyright © 2001 John Wiley & Sons, Ltd.

Runoff and sediment loss responses to rainfall and land use in two agricultural catchments on the Loess Plateau of China

Hydrochemical identification and salinity problem of ground-water in Wadi Yalamlam basin, Western Saudi Arabia

Characterisation and modelling of conduit restricted karst aquifers – Example of the Auja spring, Jordan Valley

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Use of chloride mass balance and tritium data for estimation of groundwater recharge and renewal rate in an unconfined aquifer from North Africa: a case study from Tunisia

Quantification of the rate of natural ground water recharge is a pre-requisite for efficient ground water resource management. It is particularly important in regions with large demands for ground water supplies, where such resources are the key to economic development. However, the rate of aquifer recharge is one of the most difficult factors to measure in the evaluation of ground water resources. Estimation of recharge, by whatever method, are normally subject to large uncertainties and errors. In this paper, various methods of estimating natural ground water recharge are outlined and critically reviewed with regard to their limitations and associated uncertainties.

Estimation of natural ground water recharge

The purpose of this study is to estimate the ground water recharge due to rainfall by studying one-dimensional vertical flow of water in the unsaturated zone. A model has been formulated for finite difference solution of the non-linear Richards equation applicable to transient, one-dimensional water flow through the unsaturated porous medium. Implicit scheme with implicit linearization (prediction-correction) has been used for discretization. The ground water has been estimated using appropriate initial and boundary conditions for storm and interstrom periods.

Estimation of ground water recharge due to rainfall by modelling of soil moisture movement

The theory for transient isothermal flow of water into nonswelling unsaturated soil has been developed to a large extent in terms of solutions of the non-linear Richards equation. In the field, the description of infiltration is highly complicated since the initial and boundary conditions are usually not constant while the soil characteristics may vary with time and space. In this study, a model has been formulated for finite difference solution of the nonlinear Richards equation applicable to transient, one-dimensional water flow through the unsaturated porous medium. The simulated soil moisture profiles for explicit, Crank-Nicolson and implicit schemes have been compared with the quasi-analytical solution of Philip.

C. P. Kumar M.Ish

Papers

Estimation of natural ground water recharge

Estimation of ground water recharge due to rainfall by modelling of soil moisture movement

A numerical simulation model for one-dimensional infiltration