Study on the method to estimate the subsurface flow in alluvial sandbars

点击翻译按钮获取中文摘要

The aim of the project is to establish the method to estimate the subsurface flow in riparian sandbars in order to evaluate the spatial distribution of habitat of riparian species in sandbar's material or to evaluate water exchange rate with surface flow to estimate the effect of water purification of sandbars in the future. Objects are, (1) subsurface flow in whole sandbar and local flow around small pools, (2 the water exchange rate and its temporal characteristics between subsurface water and unsaturated zone caused by rainfall or evapotranspiration.The methods have been summarized below :1.Development of a method to estimate subsurface water level, flow structure and water budgetThis method has two parts :1) Observation of subsurface water distribution by installing 50-100 wells2) 2-D numerical simulation of subsurface flowThese enable to estimate the subsurface flow structure, retention time in sandbar and water budget with surface water region.2. Development of a combined method … More to estimate subsurface flow around sandbar poolsThe following methods are developed and examined its efficiency.(1) Measurement of subsurface water level distribution around pools installing pipes(2) 2-D subsurface simulation around pools, which affect as inner boundary condition.(3) surface flow analysis to judge the continuity to main channel, and estimate flow condition in it during floods.3. Development of a combined method to estimate exchange rate between subsurface water and unsaturated zone.This method is useful to evaluate water budget of sandbar subsurface water adding to in/out flow at the surface flow boundary by combination of following method :(1) Experiment measurement of hydraulic characteristics of unsaturated soil(2) Core sampling of unsaturated zone to see layer structure(3) 1-D subsurface simulation to estimate water exchange rate at the boundary between saturated zone and unsaturated one.Applications to river Kizu showed that these methods can supply us overall of sandbar subsurface flow, its budget, water exchanging of pools. Less