Water level response characteristics and runoff threshold estimation of karst depressions in a valley region, western Hubei Province
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摘要: 以湖北省兴山县黄粮镇刘家坝和龙湾两处岩溶洼地作为研究对象,利用其降雨、水文和土壤水等监测数据,探讨灌入式补给条件下洼地汇流的水位响应特征和产流特点,并基于降雨量和洼地内明渠流量的关系,采用数学拟合方程,估算两处洼地的降雨产流阈值,进而分析了影响产流阈值的因素。结果表明:降雨强度增大,产流阈值减小;土壤前期含水率越大,越有利于坡面产流;落水洞和岩溶泉水位与降雨有较好的同步响应关系,水位变化曲线随雨强大小分别表现出“陡升陡降”和“缓升缓降”的特点;刘家坝和龙湾洼地的产流阈值分别为7.4 mm和10.6 mm。Abstract: Liujiaba and Longwan, Huangliang town, Xingshan county, Hubei Province are two karst depressions in valley region with elevations of 886 m and 997 m, and catchment areas 20.9 km2 and 1.83 km2, respectively. After rainfalls, these karst depressions runoff and transform the surface water into groundwater through the sinkholes which connect to the open channels at the bottom of the depressions, and finally discharge to the Bailong spring. To study such a hydrogeological process, rainfall stations, hydrological monitoring stations and soil-water monitoring equipment were installed in these depressions and a hydrological monitoring station constructed in the Bailong Spring. Rainfall stations record air temperature and rainfall, hydrological stations monitor water level and water temperature in the sinkholes, and soil-water monitoring equipment record the soil moisture content and electrical conductivity. Different methods were used to analyze these observational data, so as to reveal characteristics of water level response and runoff yield and their influencing factors under the condition of concentrated recharge. The results show that, (1) the water level responses in the sinkholes and karst springs have better synchronous relationships with the rainfall, expressing "sudden rise and steep drop" in hydrographs with large rainfall intensity and "slow rise and slow fall" in hydrographs with low rainfall intensity. When very heavy rainfalls happen, karst waterlogging is easy to occur due to the sinkhole’s limited drainage ability. On July 24, 2019 after a rainfall storm (86.5 mm in 3.5 hours), the water level (1.96 m) surpassed the open channel height (1.6 m) in the Longwan karst depression; (2) The Chey-Manning formula was used to transfer the water level of the open channel into flow, then the rainfall and the flow of the open channel was fitted by a mathematical equation to estimate the runoff threshold of the Liujiaba and Longwan depressions, yielding values of 7.4 mm and 10.6 mm, respectively; (3)Through the changes of soil moisture content and electrical conductivity before and after the rainfall event, the influencing factors of runoff threshold were analyzed, indicating the rainfall intensity decreases the runoff threshold, and large antecedent soil moisture could promote slope-runoff. In addition, the yield threshold is also related to the topographic slope and soil material of karst depressions, implying the yield threshold is a multi-factor coupling parameter.
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Key words:
- karst depression /
- concentrated recharge /
- water level response /
- runoff threshold
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