International Conference on Rain Water Cistern Systems
"Rainwater Catchment for Future Generations"
Keelung, Taiwan, R.O.C. - August 1991
4: Hydrological Data and Analysis
A Coupled Model Of Overland
Flow, Soil Water Variation And Groundwater Regime In North-China Semi-Arid Plain
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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