Abstract
Huge landslides in the upper reaches of the Tedori River have caused a long period of high turbidity in the river, predominant since May 2015. This turbidity has caused concerns about recharge of groundwater in the downstream alluvial fan. In this study, the measurements of paddy percolation and underflow water, before and after the occurrence of high turbidity, were used to examine its influence on groundwater recharge functions. The measurements included water requirement rates in an area covering the Tedori River alluvial fan and river discharge observations in the section of the river that flows through the alluvial fan. The results revealed that the amount of paddy percolation decreased significantly in response to the elevated turbidity, and the volume and width of the riverbed underflow water were reduced. The amount of groundwater recharge was estimated based on these measurements, which revealed that groundwater recharge from paddy percolation was reduced by 270 mm/year (36%), and the recharge from riverbed underflow water was reduced by 591 mm/year (61%). The total groundwater recharge was reduced by 861 mm/year (36%), a value that corresponded favorably to the empirical groundwater level measurements.
