洪水氾濫シミュレーションによる農地の作物被害の推定

Abstract

洪水問題について考える場合，ハザード(洪水現象)の定量的な評価に基づくリスクの同定が必要であるという立場に立って，洪水氾濫シミュレーション(ハザードの同定)から作物被害(リスク)の推定を行った。従来あまり考慮されてこなかった湛水継続時間をも推定できるような氾濫モデルを本研究において構築し，浸水深・浸水時間と作物被害率の関係表を用いて作物被害率を推定し，単位面積あたりの作物収量と単位重量あたりの作物小売価格を利用して損害額を推定した。対象地域は滋賀県日野川流域とその流域内部の竜王町とした。本研究によって，降雨，流出，内水・外水氾濫，排水，被害という一連の過程を計算する枠組みが概ね完成できた。

Identifying the agricultural risk by flooding based on the quantified hazard is vital when addressing the flood disaster problem. This paper carries out the crop damage (risk) estimation by flood based on the flood inundation (hazard) simulation. The flood inundation model developed here can simulate not only the flood inundation by bank overtopping and rainwater, but also the drainage process through the river network system. After simulating the flood inundation process, the crop damage by flood is estimated using a vulnerability index, that is, the relationship among the crop damage ratio, the inundation depth and the inundation duration. Afterwards, the economic loss is estimated with the average crop yield per area and the retail price of the rice per weight (kg) of Shiga Prefecture. The Hinogawa River, Shiga, Japan and Ryuou Town in the catchment are selected as case study sites. This paper has established a framework to assess flood risk in a river basin from rainfall, rainfall-runoff, flood inundation, drainage and the economic loss estimation.