Remote sensing and geographic information system in runoff coefficient estimation for irrigated regions.

Fast economic development and population growth has been the major impression in Taiwan for the past twenty years. However, the development has put pressure on the agriculture and overall hydrology of the nation. For example, peak runoff increases significantly in the urbanized area due to the increase of runoff coefficient, which was caused by the over-development of neighboring farmland, the construction of new houses, roads, factories, nursery and plastic-mulched farms. Furthermore, the drainage system has not been upgraded accordingly and, as a result, poor drainage and severe floods have occurred. A runoff and drainage estimation model should be developed. Major parameters in the model should include hourly rainfall (maximum hourly rainfall, daily rainfall, etc.), land use change, soil characteristics, irrigated area, and drainage facilities. The rainfall records in the weather stations can be used to model rainfall parameters at first. Later, real-time information from radar, lightning data and satellite cloud imagery can be used to model more reliable rainfall parameters. Soil characteristics can be derived from existing data. The land use/cover change and actual irrigation area, if based only on traditional gathering and analysis methods, will be time and labor consuming. The use of satellite data and Geographic Information System (GIS) to facilitate the solution of the problem should be studied, evaluated and applied soon. Remote sensing and GIS are excellent tools for acquiring and managing spatially distributed data. This is mainly due to the fact that a good rainfall-runoff model has to include the spatial and geomorphologic variation in the model. Early studies on remote sensing runoff estimation focused on the estimation of runoff coefficient values from satellite data, and then applied the Rational Formula or Soil Conservation Service (SCS) Curve Number method for runoff estimation. The developments of satellite and GIS technologies are the steps that the Taiwan government has taken in order to promote high technology and economy. There will be a tremendous benefit in bringing high technology to the Taiwanese people and the agriculture and water resources 1 Agricultural Engineering Research Center, Chung-Li, 32043, Taiwan, R.O.C. 2 Center for Remote Sensing, University of Florida, Gainesville, FL 32611, U.S.A. 3 Tsao-Jiin Agric. Memorial Foundation for R & D for Agriculture and Irrigation, Kaohsung, Taiwan, R.O.C. departments. There is an urgent need to integrate satellite data and GIS technology in estimating runoff for irrigation area in Taiwan. Therefore, the objectives of this study are 1) to assess the runoff coefficient varied with regions that have involved historically different land use changes; 2) to investigate the early drainage design and runoff model and evaluate their current applicability in Taiwan; 3) to study the widely used rational formula method and the USDA Soil Conservation Service Curve Number (SCS-CN) method, and develop parameters applicable for Taiwan’s irrigation field and; 4) to develop a model which integrates remote sensing and GIS for near real-time runoff estimation.