Influence of Underground Weir on Water Withdrawal of Infiltration Gallery

Infiltration gallery is an artificial structure installed below the riverbed including perforated in gravel to collect subsurface runoff in riverbed. The main advantage of the infiltration gallery is stably supplying clean water. If we build an underground weir downstream of infiltration gallery, in addition to avoiding riverbed erosion and extend the life of the infiltration gallery, it can also raise groundwater level around the infiltration gallery and increase water-intake from infiltration gallery. The aim of the research is investigating the influence of underground weir on infiltration gallery, and focused on groundwater level and water-intake. First, this study design a simple case and conceptualize infiltration gallery and underground weir to confirm that the usability of boundary conditions set in FEMWATER numerical model, and then discusses the rationality of the variation of groundwater level around infiltration gallery by setting different configuration of infiltration gallery and underground weir. Second, this study collected observations about Ai-Liao weir to establish a numerical model of groundwater flow, and then use the established model to conduct three numerical tests, including: (1) Before Ai-Liao weir built, (2) After built Ai-Liao weir and then (3) Built Ai-Liao weir and infiltration gallery. After the groundwater level risen by underground weir has been confirmed, this study collected observations about Er-Feng infiltration gallery to establish and calibrate a numerical model of groundwater flow. Finally, this study use the model has been calibrated to establish an optimization model. The objective of the optimization model is the maximum annual value of net benefit. The decision variables including the depth of infiltration gallery and underground weir. The results shows: (1) By a virtual case study results that this study combined FEMWATER mode, underground weir and infiltration gallery boundary conditions setting can be reasonably simulated groundwater level changes; (2) The test results from the FEMWATER numerical model of groundwater in Ai-Liao weir shows that groundwater level upstream of the Ai-Liao weir has risen after built Ai-Liao weir and the location of infiltration gallery has effect on water intake from infiltration gallery; (3) When Er-Feng infiltration gallery has built, the annual value of net benefit is 302.2 million and the optimal depth of weir is 17.3m. If there is no structure in the wild, the annual value of net benefit is 513.0 million, the optimal depth of infiltration gallery and underground is 18.6m and 21.5m.