Groundwater And Surface Water Interactions In Hailiutu River, Ordos Plateau

Identification and quantification of groundwater and surface-water interactions have beenmore important in the field of hydrology. This paper examines the flow regime shifts, changes inthe climatic variables such as precipitation, evaporation, temperature, and crop area in the semi-arid Hailiutu catchment in the middle section of the Yellow River by performing severalstatistical analyses. The Pettitt test, cumulative sum charts (CUSUM), regime shift index (RSI)method, and harmonic analysis were carried out on annual, monthly, and daily discharges.Characteristics of the flow regime were analyzed in the five periods:1957-1967,1968-1985,1986-1991,1992-2000, and2001-2007. From1957to1967, the flow regime reflects quasinatural conditions of the high variability and larger amplitude of6months periodic fluctuations.The river peak flow was reduced by the construction of two reservoirs in the period1968-1985.In the period of1986-1991, the river discharge further decreased due to the combined influenceof river diversions and increase of groundwater extractions for irrigation. In the fourth period of1992-2000, the river discharge reached lowest flow and variation in corresponding to a largeincrease in crop area. The flow regime recovered, but not yet to natural status in the fifth periodof2001-2007. Climatic factors are found not likely responsible for the changes in the flowregime, but the changes in the flow regime are corresponding well to historical land use policychanges.Multiple field measurements were taken in the semi-arid Bulang sub-catchment, part ofthe Hailiutu River basin, to identify and quantify groundwater and surface-water interactions. Aset of instruments such as divers in monitoring wells, temperature sensors at different depths inriverbed, raingage, river stage recorder in front of one weir were installed. The hydraulicsmethod and temperature method were employed for indentifying the interactions betweengroundwater and surfacewater. Hydrochemial and isotopic method was used for quantifying theinteractions during rainfall event. Measurements of groundwater levels at several monitoringwells and stream stages in the bulanghe river for a one-year investigation period indicatecontinuous groundwater discharge to the river. Temperature measurements of stream water,streambed deposits at different depths, and groundwater confirm the upward flow ofgroundwater to the stream during all seasons. Results of a tracer-based hydrograph separationexercise reveal that, even during heavy rainfall events, groundwater contributes much more tothe increased stream discharge than direct surface runoff. The groundwater discharge occupied74.8%of total discharge while the runoff took25.2%, respectively. The baseflow index is0.965,which means almost96.5%of the river water came from the groundwater discharge. Spatially-distributed groundwater seepage along the stream was estimated using mass balance equationswith electrical conductivity measurements during a constant salt injection experiment. Calculatedgroundwater seepage rates showed surprisingly large spatial variations for a relativelyhomogeneous sandy aquifer. The estimated average groundwater seepage is10.84m3/m/d. Thecombined method for estimating groundwater seepage has comparably less uncertainty and cost,which is suitable for the gaining reach in semi aird region.