Study On The Effect Of Channel Leakage On Flood Routing Of Dagu River

Dagu River is the longest river in Jiao Dong Peninsula,its main stream is 179.9km long,the basin area of Dagu River in Qingdao city is 4850.7km~2.The bed of Dagu River belongs to wide-shallow sandy bed,its cross section is very irregular,and the bed penetration is quite strong.Usually,the river channel is dry in most time of year.Main stream channel is almost dry mostly except the floods takes place in rainy season each year.The leakage recharge of Dagu river directly influences flood flow and the quantity to groundwater recharge.In addition,several rubber dams established in upper reaches are used to impound surface water.The regulation of flood is more complicated than common stream flow.Therefore,it would be inaccurate by using traditional flood evolution model to predict flood movement.In the prediction process, river channel leakage must be considered to flood evolution.While the researchment that the effect of Dagu River leakage to river channel flood evolution is operated deeply,it may have much significance to predict flood movement and to use groundwater resources optimally in river basin.This work is funded by "Study on the Effect of Channel Leakage on Flood Routing of Dagu River" of Qingdao Water Special Researchment.Through on-site hydrological observation and field infiltration test,we researched the penetration regulation of Dagu River channel and calculated stable leakage flux in every river section.Based on these works,we built a one-dimensional river channel flood evolution model using MIKE 11 software considering river channel leakage.And also, the reliability of model is validated in the simulating process.To sum up,we obtain some new and valuable understanding and conclusions,it as follows:(1) The change law of infiltration flux is determined in different locations of upstream,middle stream and downstream of Dagu River through field on-site test. The test results also reveal that infiltration flux could be divided into two stages. Infiltration flux is large initially,and then it becomes stable as time passes.In addition, infiltration flux in upper reaches of Dagu river is larger than middle stream.At the same time,we found that permeability of unsaturated zone becomes better and infiltration flux gets larger in upstream when it's closer to river channel.In this work, three on-site tests were done.Test results show that the stable infiltration flux in Yujiaxiaoli near upstream bank is 24.2 m~3/(d·m~2),8.6 m~3/(d·m~2) in Wangbi Village far from upstream break,and 19.9 m~3/(d·m~2) Nanshaliang Village near middle stream bank respectively.(2) Based on these field tests,time of unsaturated leakage is very short while the river channel is dry initially.Due to small proportion of unsaturated leakage in total infiltration flux,river channel infiltration flux in the period of flood discharge could be approximatively replaced by stable infiltration flux thus without the need to consider the effect of non-saturation leakage process.In the process of flood progression,river channel infiltration flux could be calculated by stable leakage coefficient relevantly in some river sections.As a result,this measure can not only simplify model but also do not affect the precision of flood evolution modeling.(3) We simulated the remote water transfer instance in Dagu River basin.These real data could date back to April,2003.The results show that the value of water flow and water level in each observation section coincide with measured value.And the results also reveal that calculated value of leakage quantity coincide with measured value basically.It shows that the established model could simulate preferably flood evolution process in main stream of Dagu River considering river channel leakage.(4) We use calibrated model to analyze various factors on the impact of river leakage quantity.The results show when increase leakage coefficient calibrated by model by 25%or decrease it by 25%while remain other parameters unchanged in the model,the leakage quantity increases by 770,000 m~3 or decreases by 780,000 m~3 respectively.The river bed leakage quantity is proportional to leakage coefficient. Meanwhile,when retain other parameters unchanged,the river leakage quantity is proportional to river bed roughness too.But the result also shows that the influence degree of riverbed roughness on river channel evolution time is larger than leakage coefficient.