Analysis of Influences of High-turbidity River Water on Groundwater Level in the Tedori River Alluvial Fan Using a Lumped Hydrologic Model

High turbidity water that followed huge landslides in the upper area of the Tedori River in 2015 brought out the serious problems of sedimentation in paddy fields and bed of the river. Groundwater level in the alluvial fan area increasingly lowered just after the occurrence of turbid water and it had continued for several years. Therefore, a conceptual and lumped hydrologic model was developed to evaluate the impacts of turbid water on groundwater level. At first, the model parameters were determined using the data of 2002-2010. The calculated groundwater level coincided almost with the measured one and validity of the hydrologic model was proved. In the next step, the model was applied to the years of 2011-2020 to verify the model performance and investigate the impacts of turbid water. As a result, great difference between the measured and calculated level was found just after the occurrence of turbid water in 2015 and it continued for several years, while the both levels showed similar fluctuation in 2011-2014 before the occurrence. The great difference indicates the possibility of impacts of turbid water on groundwater and it is considered that the lowering of groundwater level was caused by decrease in paddy filed percolation and seepage from river due to sedimentation of soil particles.