Pilot Study on Optimal Design and Management of Small-Scale Irrigation Scheme with Rainwater Harvesting -Constructing a Pilot Scheme in Ghana/West Africa-

在半干旱的萨凡纳，水作为农业生产的一个限制因素，可以通过建造自给自足的灌溉水箱(微型水坝)进行小规模开发，直接从准备好的集水区收集和储存雨水，对环境的影响较小。坦克也可以成为村级农村社区的核心，以鼓励农业活动以及农民的交流。这项研究的目的是在加纳的一个试验点建立一个微型水坝，讨论雨水收集系统的最佳规划、设计和管理，以制定分散的小规模灌溉计划，并对农业生产灌溉水箱的效果进行试验性评估。利用安装在现场的气象机器人自动记录的气象数据分析了现场的气候特性。为了在地理信息系统的支持下分析汇水区的径流，提出了一种新颖的二维径流模型De…用有限体积法对其进行了进一步的发展。根据这些分析结果和现场地形、岩土勘察结果，精心设计了由微坝、输水渠道和农田组成的方案。研究发现，如果将设计要求和施工质量放宽到边际限度，并适当监督微型大坝的建设过程，就可以建造技术水平高、寿命长的微型大坝(溢洪道设计考虑100年泄洪)，这是加纳等发展中国家目前无法找到的。考虑到自流节水补充灌溉是一种适应农田土壤水分变化的供水方式，建立了一个复杂的数值模型，可以从水分管理和水分利用效率的角度对其进行评价，并对农业生产中灌溉水箱的效率进行量化。目前，仍在继续对在试点农田中种植玉米进行实地观察。通过对所得结果的综合分析，将对农业生产灌溉水箱的效果进行评估。较少

Water as a limiting factor in agricultural production in semi-arid Savannah could be developed on a small scale by constructing self-reliant irrigation tanks (micro-dams) that directly harvest and store rainwater from prepared catchment, having less impact on the environment. The tank could also be a core of village-level rural community to encourage agricultural activities as well as farmers' communication. The objective of the study is to build a micro-dam at a pilot site in Ghana, discuss optimal planning, design and management of the rainwater harvesting system for developing a decentralized small-scale irrigation scheme and experimentally evaluate the efficacy of the irrigation tank for agricultural production. Climatic properties of the site were analyzed using meteorological data automatically recorded by a weather robot installed at the site. For analyzing run-off from the catchment area with the aid of GIS (Geological Information System), an innovative 2-D run-off model was de … More veloped using the finite-volume method. Design practice for constructing the scheme consisting of micro-dam, water conveyance channel and farm land was made meticulously considering the results from these analyses and the in-site topographical and geotechnical surveys. It was found that a micro-dam of high technical level and long life span (100-year flood discharge was considered for spillway design), which cannot be found currently in developing counties such as Ghana, could relatively inexpensively be built if design requirements and construction quality are relaxed to their marginal limits and the process of micro-dam construction would appropriately be supervised. Considering that a gravity-fed water-saving supplemental irrigation, an adaptive water supply subject to soil moisture content in the farm land, is the best, a sophisticated numerical model was developed that can evaluate its effectiveness in terms of water management and water use efficiency and quantify the efficacy of the irrigation tank for agricultural production. Currently field observations for maize growing in the pilot farm land are continued. Through comprehensively analyzing the results obtained, the efficacy of the irrigation tank for agricultural production will be evaluated. Less