| The temporal and spatial distribution of Weihe River basin runoff is uneven. In the flood season, the drastically increased river runoff, threats the safety of river course and the downstream city. However, river runoff decreases sharply in the dry season, which causes a series of deficiencies to river ecological base flow and the deterioration of ecological environment around the river. In the non-flood season, Ecological base flow of Weihe mainstream encounters a severe lack of water in dry years and extremely dry years, which is unable to meet the demands of river ecological base flow and especially true for Lincun where the river runoff is only 25% to 39% of ecological base flow in dry years and 3% to 7% in extremely dry years. Ecological base flow loss also happens to Weihe branch in various degrees. For example, in the non-flood season, Huluhe’s runoff only takes 4% to 19% of ecological base flow in extremely dry years. According to statistics, 99% of Weihe River drainage area depends on the groundwater recharge. In the non-flood season, when Weihe River runoff cannot match the ecological flow base, mainstream and branch groundwater take 72% and 47% of the river runoff respectively. Therefore, the Weihe River basin groundwater plays an important role in ensuring the river ecological base flow and maintaining the river ecosystem health. To ensure a healthy Weihe River, it must strengthen the groundwater recharge to the river ecological base flow.Based on the water circulation rules of Weihe River basin, ensuring the river ecological base with flood underground regulation flow as a goal, this dissertation is to make a systematical research on the theory and key technology of stormwater underground regulation is used to ensure the river ecological base flow from the aspects such as theoretical research, technology exploration, engineering practice, benefit evaluation and so on. The main research results are as follows:(1)Study the relationship between the runoff, basic flow and ecological base flow of Weihe River and its tributaries, determination of the important guarantee foundation of Weihe River ecological base flow- groundwater. In some months, the runoff of Weihe Rive and its tributaries cannot meet the demand of ecological base flow, so it is necessary to guarantee the river ecological base flow in the non-flood season through some regulating measures. Although cross-basin water transfer and surface reservoirs can effectively allocate the surface water resources and meet the demand of river ecological base flow in the non-flood season, this two commonly used methods have an obvious defect which brings some negative effects on environment. 34% to 58% of Weihe River runoff comes from groundwater recharge, especially in the non-flood season it almost covers the whole. That is to say, groundwater can well guarantee the river ecological base flow and maintain the river ecological health through regulating stormwater during the flood season.(2)Making a system research and summary of basic theory and method of stormwater underground regulation to guarantee the river ecological base flow. Basic theory mainly involves three aspects: regulating water conditions, geological conditions and regulation models. When the river flow is more than two times of the ecological base flow during the flood season, it could be defined as flood flow. Weihe River has a rich flood resourcesproviding sufficient water for stormwater underground regulation to guarantee the river ecological base flow. The geological conditions of regulation mainly consider the regulating location, hydrogeological conditions, aquifer permeability and thickness and so on. Proposal of four regulation modes: underground reservoir, mountain-valley, water resources by the river, city rain and sewage reuse, based on the necessity and feasibility of stormwater underground regulation. Morever, the composition content and applicable conditions of each regulation mode are determined.(3)Study on the factors influencing stormwater underground regulation to ensure the river ecological base flow. As a result, the eliminate clogging technology and ecological remediation are chose to be the key research fields. Usinglaboratory simulation of flood regulation clogging process and numerical simulation method to study the eliminate clogging technology, the sediment threshold via recharge coarse sand could be confirmed: when the infiltration rate maintains 50%( K/K0=0.5 in stable time), the sediment concentration of regulation water is 0.213kg/m3; when the infiltration rate is 90%( K/K0=0.9 in stable time), the sediment concentration of regulation water is 0.032kg/m3, and in this situation, it is hardly blocked. When the sediment concentration maximum of regulation water via medium sand is 0.025kg/m3, medium sand system could hardly be blocked. For the river ecological environment, on the basis of water safeguard, it requires manual repair and maintaining the integrity and species diversity of the river ecosystem in order to maintain the sustainable development of river ecology. So this dissertation proposes the ecological remediation technology consisting of ecological restoration technology and regulating facilities landscaping.(4)Carrying out the engineering practice of the mountain-valley regulation mode and stormwater underground regulation mode. The engineering practice of the mountain-valley regulation mode is carried out on the left bank of the Jinling River. The result shows that the flood storage is around 27815.3m3, while the increment of river ecological base flow goes to 10104.83 m3 and the time of flood retention is 180 days. Based on the regulation area of Jinling River demonstration project, the comparison of the multi-scheming security effect has been made. The results also shows the dispersive layout of ditches and the pipeline infiltration are more conducive to the protection of the river ecological base flow by raining flood storage, while the pipeline infiltration placed along the edge has the worst security degree. Therefore, in the stormwater underground regulation, infiltration facilities are supposed to be spread evenly in the layout. Taiping River flood underground regulation project uses the engineering practice of underground reservoir regulation mode. According to the practice, the experiment cumulative quantity of pumping is 131754m3, while 91427m3 of the water that holds 69.39% of total quantity of pumping was discharged to the river and increases the Taiping River base flow by aquifer discharging, achieving an obvious recharging effect.(5)Building the technical index system of stormwater underground regulation to ensure river ecological base flow including Water circulation index, groundwater types, storage area index, vadose zone index, aquifer index, regulating water sediment index and water flow index. Firstly, stormwater underground regulation guarantees the river ecological base flow with the premise of setting phreatic water recharging. Secondly, storage sites are able to be selected on the first or second level terrace in the upper reaches of the river, at a horizontal distance from 500 m to 1000 m away from the river. Thirdly, the thickness of vadose zone in the storage site should not be less than 6m, while the permeability coefficient of aquifer should not be less than 10m/d. Finally, in order to avoid the occurrence of congestion, the flood could be pretreated according to the water sediment regulation standard, or the water flow rate could be controlled above 0.7m/s. |
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