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

水作为半干旱萨凡纳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）来进行小规模开发，这些水箱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。该水箱也可以成为村级农村社区的核心，鼓励农业活动和农民交流。这项研究的目的是在加纳的一个试验点建造一个微型水坝，讨论雨水收集系统的最佳规划、设计和管理，以发展一个分散的小规模灌溉计划，并实验性地评估灌溉水箱对农业生产的功效。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征。为了利用地理信息系统（GIS）对流域径流进行分析，提出了一种新颖的二维径流模型，并采用有限体积法进行了开发。结合分析结果和现场地形、岩土调查结果，对微坝、输水通道、农田组成的方案进行了精心的设计实践。研究发现，加纳等发展中国家目前还没有技术水平高、寿命长（泄洪道设计考虑100年泄洪量）的微坝，如果将设计要求和施工质量放宽到其边际极限，并对微坝施工过程进行适当的监督，就可以相对便宜地建成。考虑到自给式节水补灌是适应农田土壤含水量的最佳补灌方式，建立了一个复杂的数值模型，可以从水管理和水利用效率两方面评价其有效性，并量化灌溉槽对农业生产的有效性。目前仍在继续对试验田的玉米种植进行实地观察。通过对所得结果的综合分析，评价灌溉水箱对农业生产的效果。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