Characteristics of Groundwater Level Fluctuations in an Alluvial Fan and Changes in Paddy Field Percolations due to High-turbidity Water

Abstract

  In the Tedori River alluvial fan, the groundwater level significantly decreased immediately after the occurrence of high-turbidity water. This study was conducted to clarify the temporal and spatial characteristics of groundwater level decline due to high turbidity water by comparing it with those caused by heavy groundwater use for snow melting. Furthermore, an experiment that replicated the impact of high-turbidity water and farming operations, using 1/2000a Wagner pots, was conducted to grasp changes in paddy field percolation rate following the occurrence of high-turbidity water. The results revealed that the impact of groundwater use for snow melting on groundwater level decline was limited to areas with high-density building sites and only in the short term. In contrast, the impact of high-turbidity water lasted about two years over a wide area around the Tedori River from the fan top to the fan center. And the replicated experiment showed that the amount of paddy field percolation was suppressed by the inflow of high-turbidity water before midsummer drainage. However, the suppression of paddy field percolation by high-turbidity water could be improved after midsummer drainage, depending on how the drying process formed the cracks.