Tomoko Minagawa

Comprehensive flood control involving citizens in a Japanese watershed

In July 2009, the city of Fukuoka, Japan experienced a flood disaster along the Hii River, which runs through densely populated, concrete-covered areas of the city. The drainage system was overwhelmed and the river overflowed due to heavy rainfall and rapid runoff. The event led citizens in its watershed to plan and implement comprehensive flood control. The plan aims not only to mitigate floods but also to revitalize the river environment and populated communities in urban areas. This study reports the activities led by the citizens. They organized and carried out civic forums, workshops, and fieldwork to share views as to how the flood disaster was caused, how floods in the watershed should be controlled, and how the river environment should be rehabilitated. This study illuminates how people, including the flood victims and municipal engineers, can change drastically and communicate effectively in the course of discussing and implementing the comprehensive flood control measures.

Factors of Water Quality and Feeding Environment for a Freshwater mussel’s (Anodonta lauta) Survival in a Restored Wetland

Wetland plays important roles in river ecosystems. However, the area of wetland decreased considerably due to excessive construction and land use with economic development. For recovering river ecosystem, the wetland named Azame-no-se was restored in the Matsuura River, which is located in Saga Prefecture in Kyushu, Japan. Anodonta lauta, a freshwater mussel that lives in the lentic water of wetlands, played an important role in a river. However, A. lauta lost its habitat and became endangered in Japan. A. lauta was found surviving in the Azame-no-se Wetland; however, only recently researchers have begun to understand the mechanisms that allow this mussel to now prosper there. This study investigated mussel survival mechanisms in the restored Azame-no-se Wetland. Mussel motility, coverage of Trapa japonica (an aquatic plant) and water quality were investigated in three pools (Shitaike, Ueike, and Tomboike) of the Azame-no-se Wetland and in still water in the Matsuura River (May 2011–2012). A feeding behavior experiment was also conducted in Ueike Pool two times in 2012. Results showed that this pool had abundant nutrients (thanks to its high flood frequency) that supported the growth of certain phytoplankton species possibly important for A. lauta. Dissolved oxygen was another important factor. Although Shitaike Pool shared similar conditions with Ueike Pool, the mussel became extinct when the dissolved oxygen decreased because of the lush growth of T. japonica in Shitaike Pool. This study indicated that the factors essential for A. lauta’ survival in the restored wetland were dissolved oxygen (DO), nutrients, and phytoplankton species. These results could be helpful for understanding functions of restored wetland and further offer suggestions for managing river–floodplain system.

Study of sediment transport and deposition in the Kuma River and tidal flat for evaluation of environmental impact associated with removal of the Arase Dam

本研究で対象とする球磨川は,熊本県南部の人吉盆地 を西に貫流し,山地狭窄部を北流,八代平野を経て八代 海に至る,流路延長115km,流域面積1,880kmの1級河 川である(図-1).流域の大部分は急峻な山地であり,河 床勾配も八代平野を除いて概ね 1/1000以上と急流であ る.球磨川が流出する八代海は,潮位差が最大で4mで あり,沿岸には2,947haの広大な砂・泥干潟が存在する. 球磨川本川の横断構造物としては,人吉盆地上流の市房 ダムと幸野ダム,その下流の山地狭窄部に位置する瀬戸 石ダムと荒瀬ダム,という計4つのダムがある.さらに, 荒瀬ダム下流には,出水時にゲート開放がなされる遥拝 荒瀬ダム撤去影響評価に向けた球磨川及び河口干潟の 土砂輸送・堆積特性の把握 Study of sediment transport and deposition in the Kuma River and tidal flat for evaluation of environmental impact associated with removal of the Arase Dam

Study on Water Quality of Rivers from the view point of Scenery

The purpose of the study is to evaluate the water quality of rivers from the view point of the human sense by image test of river water. The result indicated 1) The image of “Clear water” has less relation with the value of BOD. 2) The image of “Clear water” has strong relationship with the image of “Transparent”. 3) The image of “Transparent” has strong relationship with “Transparency by cylinder test”, and is explained by “Transparency by cylinder test” and “depth”. 4)“Water color” reflects “Clear water”.And its showed that “Transparency by cylinder test” is presumed from the optical absorbance of SS at 610nm, which is percolated with filter papers from river water.

A study of color perception for color planning of structres

1. はじめに 朝みかけた橋の色が昼間全く違って見えたり、眼前 に広がるカラー舗装があまりにもどぎつくあざやかに 見えることを時々経験する.こ れらは光の条件の違い や面積の広がりによる効果と考えられる.屋 外の構造 物の色彩計画を行う場合、屋外という光の条件下で色 がどのように見えているか、また、面積効果はどのよ うに現れるか等の色彩の基礎的な認知特性は考慮すべ き項目であり、特に面積効果(彩 色面積が大きくなる と色彩の明度・彩度は小面積の場合より高く見える現 象)は 、大きな面が出現する土木構造物において重要 となると考えられる.し かし、これらに関する知見は 少なく、色彩計画に反映できるほどの定量的データは 得られていないのが現状である. そこで本研究では、屋外の光の下で実際に見える色 を「みかけの色」とし、JISで 規定されている物体の表 面色の測定方法により測定される色、すなわち標準光 の下で測定される色を「JIS色」として区別し、面積効 果による「みかけの色」の変化に着目する.

How dose a person evaluate natural landscape on a river: in case of Agano river

This study made clear evaluation of “Nature” of river from landscape point of view. The results are as follows;1. The evaluation of “Nature” of river landscape is highly related to the evaluation of “Nature” of river terrace. The evaluation of “Nature” of river terrace depends upon the situation of river terrace mainly.2. People are apt to think that the river terrace is quite natural if the terrace is “natural vegetation”, however people think it not so natural if the terrace is covered by artificial vegetation such as lawn and field.3. People are fond of the neat vegetation from point of view, and not fond of messy vegetation when the vegetation is highly natured.This study also mentions that is important to establish the new landscape evaluation method which includes ecological knowledge.