A Study On The Simulation Test And Water Quantity Calculation Method Of Groundwater Flow Pattern In The Natural Filter Bed

Natural filter bed seepage water intake technology is a kind of technology which can make clean water with high efficiency and low cost that has been widely applicated in recent years.It depends on the purification and adsorption function of natural filter bed, by the percolation way to achieve the cleaning effect, compared with the traditional methods greatly reduces the cost and simplify the process. In the water intake process, due to the weak permeable bed surface membrane, when the water intake rate faster than the water supply rate, a wide range unsaturated zone will appeared in the aquifer which would both make the water quantity significantly reduced after and the groundwater flow no longer saturated. Thus the result calculated by the traditional method which neglecting the effect of unsaturated zone will be wrong, meanwhile the engineering not up to the design water quantity, this phenomenon is the result of many factors, but the existing research, without explicit quantitative analysis to the influence factors of water intake, the study on the variation characteristics of the groundwater flow near the water intake pipe due to the unsaturated zone is always fuzzy and blank.Through the conceptual model established by Beipiao seepage water intake engineering, builded the indoor simulation test model. Based on the principle of underground water dynamics, simulated the water effects under the different influencing factors, analysis of the characteristics of groundwater flow change. Compared the actual amount of water obtained from the experiment with the amount of water obtained by the traditional method, discussed the applicability of various computing methods. Based on the above analysis, using Visual Modflow simulated the flow field in typical water intake chamber of Beipiao engineering. Analysis the influencing factors of the groundwater flow field, discriminated the critical conditions for the production of unsaturated zone and the effect to the flow field.According to the above research content and methods, the following conclusions are obtained:(1) The groundwater flow field in the natural filter bed is a three dimensional saturated unsteady flow, the river recharges groundwater through weak permeable layer in seepage way, groundwater movement characteristics can be viewed as Non complete well motion with leakage recharge.(2) The river as a source of water filtration water, the water level higher, the head difference is bigger, more infiltration recharge, more water intake, instead of low river water level, the water infiltration recharge is limited,even increase the drawdown, water intake increased slightly.(3) Along with the increase of the depth of the well, the water intake around lower part of the river bed is also gradually increasing, but with the continuous pumping time, the drawdown is too large, the amount of water is no longer increased or even decreased.(4) When the aquifer appear the frozen layer on the surface, will greatly reduce the water intake, under the condition of the same water level and the same drawdown, the quantity of water is far less than that in the non frozen layer, because the water infiltration recharge is blocked cause the frozen layer, soon to reach the aquifer of the maximum amount of water.(5) Due to the lower pumping rate is faster than river recharge rate, non saturated zone first formed in the saturated zone under the aquifer surface, step by step extension, the aquifer water centent reduces from the upper part extend to the lower part, Aquifer total water center cut down, the unsaturated zone reaches the maximum in the aquifer, at this point the amount of water to reach the limit. Before the non saturated zone formed, with the intake process, water intake is content increasing during aquifer water centnet cut down, however, in the non saturated with extended to the whole of the aquifer, the aquifer water content decreased rapidly, and water intake also subsequently decreased, but the water intake has been downward trend before.(6) Established Beipiao water percolation numerical model by Visual MODFLOW software, simulation analysis groundwater flow field characteristics near the mouth under different influencing factors, determine the critical condition of non saturated with numerical simulation method, the established model accord with water filtration principle, determine the established numerical simulation method can provide theoretical basis for the calculation of percolation water intaking engineering design. Simulation results have reference value.