Hydrological Changes In Typical Catchments Of The Hai River Basin Under The Influence Of Human Activity

Hai River Basin is suffering from serious water scarcity, and its hydrologicalprocesses changed a lot under intense human activities, including water abstract fromrivers and reservoirs, land surface change and agricultural irrigation. Human activitiesinfluence water cycle in different ways for mountainous and irrigated area, and typicalmountainous catchment and irrigated area in the Hai River Basin were investigatedrespectively, to understand the characteristics of hydrological changes under humanactivity.Regarding the hydrological changes in mountainous region of the Hai River Basin,the upstream catchment of Miyun Reservoir was selected as the study area. Analysis ofthe observed data during1956~2005showed that runoff and rainfall in the catchmentwere decreasing, while mean temperature and direct water abstraction were increasing.The annual runoff had a stronger decreasing trend than the annual precipitation, and thereasons for its decrease came from two main aspects, which are impacts from climatechange and human activity. Using a comprehensive method of data analysis andhydrological model, the contribution of different factors to the runoff decrease wereevaluated quantitatively.Regarding the hydrological changes in the agricultural region of the Hai RiverBasin, the Weishan Irrigation District was selected as the study area. Analysis of theclimate data during1958~2007showed that rainfall and mean temperature in thedistrict were slightly decreasing and increasing respectively. Analysis of thegroundwater level data during1974~2007showed that, the groundwater level in thedistrict was mainly stable, but the the groundwater level near the end of the1st mainchannel showed a decreasing trend. The groundwater level within the district was higherthan outside, which indicated that the water from the Yellow River was the main factorin keeping the high groundwater level. Under limitation of water resources from theYellow River, the water cycle in the Weishan Irrigation District may change in future.Basing on hydrological simulation, together with the analysis of field observation data,changes in evapotranspiration and groundwater level was predicted under differentirrigation scenarios.Another aspect of the impacts of human activities in the Weishan Irrigation Districtis change of the water environment. Irrigation water from the Yellow River brought a large amount of salt into the field, and at the same time, irrigation as well as fertilizationhad obvious impacts on field nitrogen balance. Salt and nitrogen content at differentdepths was continuously measured from May to November2010in a typical field in theWeishan Irrigation District. The analysis based on the measured data showed that: saltcontent reached a peak value near the depth of120cm, while the nitrate contentdecreased with the increasing of soil depth. The ammonium content was quite low,indicating a very strong nitrification process in the field. Using a salt movement modelat field scale, the impact of irrigation on salt accumulation was discussed, and the riskof soil salinization under poor drainage condition was evaluated. By developing a modelfor field nitrogen transformation and movement, the nitrogen balance under theirrigation and fertilization conditions was analyzed, and the leaching amount of nitrateout of the root layer was evaluated.