Rainfall-Runoff Simulation of Radioactive Cesium Transport by Using a Small-Scale Portable Rainfall Simulator

Abstract

Soil pollution with radioactive cesium (134Cs and 137Cs) has been considered one of the major environmental issues of agricultural farmlands after the nuclear power station incident which occurred in Fukushima Prefecture on 11th March 2011. A small-scale portable rainfall-runoff simulator was developed to conduct the rainfall-runoff experiments in the laboratory using the radiocesium contaminated soil in Fukushima. This study describes and demonstrates the operation method and performance of a portable rainfall simulator as well as runoff, sediment discharge, radioactivity, and contaminant transport. The rainfall simulator is able to produce the rainfall intensity from 30 to 70 mm h−1 with Christiansen’s Uniformity varied from 72 to 91%. The simulated rainfall kinetic energy rates were accounted for about 45, 58, and 74% of the kinetic energy of the natural precipitation for different rainfall intensities of 30, 50, and 70 mm h−1, respectively. The applicability of a small-scale portable rainfall simulator for the rainfall impacts on runoff, soil erosion, and the transport of radioactive cesium is investigated. The total radioactive cesium (134 + 137Cs) measured in runoff sediments ranged up to 6847 Bq kg−1 and they were in the ranges that have been reported in the literature. The results revealed that the average total radioactivity average of cesium in the discharged sediments was found to be higher (up to three times) than the average rates determined in initial soil in lysimeters of all Fukushima sites before the experiment. The results have proved that a small-scale portable rainfall-runoff simulator system is a useful tool for investigating rainfall-runoff phenomena and contaminant transport in the laboratory.