Predictions in Ungauged Basins: Promise and Progress (Proceedings of symposium S7 held during the Seventh IAHS Scientific Assembly at Foz do Iguaçu, Brazil, April 2005). IAHS Publ. 303, 2006, 400-413.

 

Numerical modelling of water transfer among precipitation, surface water, soil moisture and groundwater

 

Xi Chen1, Zhicai Zhang1 & Yongqin David Chen2

1       State Key Lab. of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China

2       Department of Geography and Resource Management, The Chinese University of Hong Kong, Hong Kong, China

xichen@hhu.edu.cn

 

Abstract In the course of the hydrological cycle, when precipitation reaches the ground surface, water may become surface runoff or infiltrate into soil and then possibly further percolate into the groundwater aquifer. A part of the water is returned to the atmosphere through evaporation and transpiration. Soil moisture dynamics driven by climate fluctuations play a key role in the simulation of water transfers between the ground surface, unsaturated zone and aquifer. In this study, a representation of one canopy layer and four soil layers is used for a coupled soil-vegetation modelling scheme. A non-zero hydraulic diffusivity between the deepest soil layer modelled and groundwater table is used to couple the numerical equations of soil moisture and groundwater dynamics. Simulation of runoff generation is based on the mechanism of both infiltration excess overland flow and saturation overland flow nested in a numerical model of soil moisture dynamics. Thus, a comprehensive hydrolog­ical model integrating canopy, soil zone and aquifer has been developed. The model was applied to simulate water transfers between precipitation, surface water, soil moisture and groundwater for assessing water resources in the plain region of the Huaihe River basin in east China. The newly developed model is capable of calculating hydrological components of surface runoff, evapotranspiration from soil and aquifer, and groundwater recharge from precipitation and discharge into rivers. Regional parameterization was carried out by using two approaches. One is to determine the majority of parameters representing specific physical values on the basis of characterization of soil properties in the unsaturated zone and aquifer, and vegetation. The other is to calibrate the remaining few parameters on the basis of comparison between measured and simulated streamflow and groundwater table. The integrated modelling system was successfully used in the Linhuanji catchment of the Huaihe plain region. Study results show that: (a) on the average 14.2% of precipitation becomes surface runoff and baseflow during a 10-year period from 1986 to 1995 and this figure fluctuates between only 3.0% in dry years of 1986, 1988, 1993 and 1994 to 24.0% in the wet year of 1991; (b) groundwater directly deriving from precipitation recharge is about 15.0% of the precipitation amount, and (c) about half of the groundwater recharge flows into rivers and losses through evaporation.

 

Key words  coupled soil–vegetation modelling; groundwater dynamics; Huaihe River, China; numerical modelling; soil moisture