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5th International Conference on Rain Water Cistern Systems
"Rainwater Catchment for Future Generations"
Keelung, Taiwan, R.O.C. - August 1991

Section 4: Hydrological Data and Analysis

Page 219

A Coupled Model Of Overland Flow, Soil Water Variation And Groundwater Regime In North-China Semi-Arid Plain

Huan-yen Loo and Dei-sun Lu
Shanghai Tongji University, China


Rain water, soil water and groundwater are interconnected as an intrinsic system. Differential equations of water movement for individual unit of the system have been solved separately but linked together by regarding their common interfaces, namely the surface- water/soil-water and the soil-water/ground-water, as internal boundary conditions. The soil water variation is a controlling factor in transmitting rain water into groundwater, an one dimensional equation for soil water variation is then solved first using finite analysis method with a prescribed initial soil water content above a variable groundwater level during either precipitation or evaporation. If the precipitation intensity is higher than the soil infiltration rate, a depth-averaged two dimensional solution for the overland flow is approximated by a power series method to see if both the duration and the depth of ponding water are suitable for crop growth, or otherwise a three dimensional groundwater regime due to adjusting the pumping scheme for the agricultural and/or the municipal use is calculated by boundary element method in order to make an optimal management of the water circulation. Such a computational process is repeated until minimizing the water-logging, preventing the soil salinity and balancing the water resource are reached to an expected situation.

For the North-China semi-arid plain, model studies show that the optimal groundwater depth for an excess.rain season is about 3.5 m at the up-plain, but 5.0 m at the down-plain area, especially, near the shore line, the groundwater level must further be lowered owing to both the slow infiltration rate of the fine soil and the existence of saline water unable for plant growth.

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