Abstract:
In the Huaihe River Basin (HRB), the total plain area was 180,000 km2, accounted for 67% of the whole HRB roughly. There were 0.2*109 population and 17*106 ha tillage area in the Plain. Due to the transitional climate from the subtropical climate in the south to the semi-humid temperate monsoon climate in the north, the floods and the droughts happened frequently in HRB. Therefore, it is necessary to research the water cycle in the Plain, to understand the formation of the floods and the drought, and to find some solutions to deal with the natural problems.
The research focused on the water transformation processes between precipitation (P), surface water (SW), soil moisture (SM), and groundwater (GW), and included following 5 topics: (1) the rainfall ¨C runoff relation, (2) soil moisture vertical distributions, (3) infiltration from SW to soil moisture and GW, (4) evaporation of GW, and (5) GW dynamic numerical model. A conceptual hydrological model, the Xin¡¯anjiang Model was selected to analyze the P-R relation. A numerical GW model, Processing MODFLOW for Windows (PMWIN) was selected to simulating groundwater flow system. A sub-basin of HRB, the Xifei River Basin (XRB) was selected as a test basin. XRB was a plain area, located in the north of the Middle Huaihe River Basin, with an area of 1340km2. Almost all of the sub-basin was tillage. The XRB hydrological data was used to calibrate the model. The data included daily P, daily open water E, daily Discharge at the outlet station, GW head data with a time interval of 5 days, irrigation data, and hydrogeological data. All the data were collected and investigated by Anhui Hydrological Bureau and The Huaihe River Commission. After simulating the P ¨C R relation and the groundwater flow system, the water budget components of XRB can be quantified, so the water transformation between SW, GW and groundwater evaporation were calculated.
The physical mechanism of groundwater infiltration and evaporation were discussed. This focused on the unsaturated zone partial differential flow equation, namely, Richards¡¯s equation. The numerical solutions of the equation, which based on a Model for Unsaturated flow for above a Shallow groundwater Table (MUST) were present. The MUST was calibrated by evaporation and infiltration experimental data of the unsaturated soil zones, which were contained in lysimeters. The experiments were implemented by two hydrological experimental stations, namely, Wudaogou near Bengbu of Anhui, and Hanwang near Xuzhou of Jiangsu. The experimental data included soil moisture content, moisture potential, specific yield, hydraulic conductivity, soil evaporation and infiltration in different depth and different water soil types. The routine meteorological and hydrological data were observed also. After calibrating, the numerical model was combined with PMWIN to estimate groundwater infiltration and evaporation in XRB.
Finally, base on the water budget analysis, an integrated water resources development scenario, conjunctive use of surface water and groundwater was recommended present. The scenario can ensure water resources and groundwater-dependent ecosystem sustainability.