本研究の目的は，甲府盆地を流下する 1 級河川である笛 吹川における河川水質の縦断分布特性を明らかにすること である．本研究対象領域である甲府盆地は，近年，地下水位 が漸増傾向であり 1)，地下水涵養機構が変化している可能性 がある．地下水涵養機構を明らかにするためには，地下水質 のみならず，河川水質および降水水質といった涵養源と考え られる水質を測定する必要がある．これまでに甲府盆地の地 下水涵養源・流動の解明の研究は数多く実施され，甲府盆地 内の降水．釜無川や

　本研究は，山梨県西部を南流する釜無川を対象に，浸水の起こりやすさを考慮した水害リスク評価手法を提案することを目的とした．その為に、洪水浸水想定区域図の作成に用いられる破堤地点毎の氾濫シミュレーションデータからメッシュ単位で浸水区分毎の浸水回数を集計した．また洪水被害による建物被害額の期待値を指標としたリスク評価手法を構築し，対象地域の水害リスク評価を実施した．最後に構築した水害リスク評価手法を釜無川に適用し，釜無川の洪水浸水想定区域内における水害リスクの経年変化を分析した．分析の結果，対象地域での浸水頻度の違いを可視化し，期待値の考え方を用いることにより，浸水頻度の違いによるリスクの差を表現できることを確認した．また，対象地域では2000年から2005年の間に浸水頻度の高い土地で開発がおこなわれた可能性があることを明らかにした．

Flood hazard maps are quite useful for the aid to damage reduction and emergency operations for major flood crisis. In this paper, in order to derive flood hazard maps even for ungauged basins, we propose a simple method for assessing the flood inundation area based on purely topographical analyses of Digital Elevation Model (DEM), without meteorological data and hydrological models. The quality of the map derived from the proposed method is evaluated for the Fujikawa river basin against the corresponding maps given by Ministry of Land, Infrastructure, Transport and Tourism. Despite the crudeness of the model, the simulated maps are in good agreement with the reference maps. For the Chao Phraya River basin in Thailand, where an unprecedented flood disaster was caused during the 2011 monsoonal season, the simulated flood inundation map successfully reproduces the actual flooded land.

Recently traditional river works have been provided at various locations in Japan. But many of these were constructed without any technical background on stability of the structure. This paper shows one of possible measures for increasing stability of SEIGYU against flood flow. SEIGYU were constructed in 1999 to the Fuefuki River, one of the tributaries of the Fuji River that is a class A river in Japan. Three of these SEIGYU were washed away by the floods in June and August in the same year. The return period of the flood peak discharges of the floods was 2 years. The stability of the SEIGYU against sliding and tumbling is studied by applying an equation of power equilibrium. According to the calculation, it has been found that the stability of SEIGYU against tumbling is high but the stability against sliding is low. The stability of SEIGYU integrated with concrete blocks embedded under the SEIGYU is studied by applying the same equilibrium and it is found that such SEIGYU will stand against a river flow of which the return period is 10 to 30 years.