Allocation Of Soil Water And Groundwater In Relation Dagu Watershed And Soil Water Optimization

Water is a precious resource for human beings. Survival of organisms, development of agriculture and industry and progress of society are all depended on water. Qingdao is one of water shortage cities in northern China. With the rapid development of economy and urbanization, city’s water consumption is increasing dramatically; water shortage and water pollution is coming along. Therefore, it is important to protect and save water resources for Qingdao’s sustainable development.This research relies on the special funds for public industry research of ministry of water resources and national natural science foundation of China, on the basis of a large number of field experiment and long-term observation in the farmland of dagu river basin in Qingdao, the soil moisture, groundwater level and buried depth, soil physicochemical properties, precipitation, irrigation, meteorological data and other basic information were acquired, the distribution characteristics of soil moisture were studied at the same time. Under the condition of different groundwater buried depth, the transforming relationship between soil water and groundwater was discussed, and then the exchange capacity of different tillage period in the farmland where the groundwater buried depth is shallow was calculated by using the simplified soil water balance equation. We also simulated the soil water movement through the Hydrus-1d model and use relevant data of farmland to calculate the soil water resources quantity and irrigation demand index, and then we put forward reasonable suggestions for agricultural water saving irrigation. It has great significance for the study of the transforming relationship between soil water and groundwater on the dagu river basin; it can also provide reference for the further optimization of agricultural water saving irrigation.The main conclusions are as followed:We chose ten long-term observation area which in the dagu river basin to monitor soil moisture and have got two years’soil moisture data in the farmland in which summer corn and winter wheat is planted. The result showed that, soil moisture in different areas had a degree of spatial variability due to the difference of soil texture and groundwater level. Soil moisture content changed regularly in the vertical direction and zero flux plane was between40～60cm soil layer. Affected by crop species, precipitation and meteorological conditions, the change of soil moisture could be divided into four stages. At the first stage (June to July) and second stage (July to early August), the soil moisture content was relatively higher and fluctuated dramatically. However, at the third stage (Mid-October to March) and forth stage (April to May), the soil moisture content was relatively lower and always in a relatively stable state.We analyzed the transforming relationship between soil water and groundwater in areas of different groundwater buried depth on the basis of precipitation, irrigation, groundwater level and buried depth, temperature, soil physical properties and other basic information we have. The result showed that exchange effect between soil water and groundwater was weak when the groundwater buried depth was deep, whereas there were obvious conversion relations between soil water and groundwater when the groundwater buried depth was shallow. Besides, we use the simplified soil water balance equation to calculate the exchange capacity in shallow groundwater farmland. Results also showed soil water and groundwater could supply with each other. During the the growth period of corn, soil water and groundwater exchanged frequently which made soil moisture leak more easily and the phenomenon of groundwater level’s fluctuation more violent. Nevertheless, during the growth period of wheat, there was almost one-way links mainly from groundwater to soil water without irrigation. Furthermore, the change of supplement of wheat turned out more stable than that of corn during the growth period.Using Hydrus-ld model, we simulated the soil water movement and evaluated soil water resources quantity of different areas on the dagu river basin in farming period with soil evaporation, plant transpiration and variation of soil water storage. And then the total amount of soil water resources which was2.994billion cubic meters was calculated. Finally, advices on joint management of soil water and groundwater resources were given according to the conditions of groundwater resources and dynamic regularity of precipitation. We should dewater the aquifer as much as possible during drought period. When wet season comes, we must change precipitation into groundwater resource as much as possible by rainfall infiltration and artificial recharge. Thus, soil water resource can be in full use, meanwhile, Dagu river groundwater fast regulating function of water resource can be exert to the utmost.Basing on Hydrus-ld model, water requirement of crops, net irrigation water requirement and irrigation demand index was calculated. On this basis, we proposed agricultural water saving irrigation scheme which could save about120mm water in summer corn-winter wheat rotation period. This has positive significance for further improving agricultural water use efficiency and alleviating water shortage condition in this city.