Runoff Change Study Using Remote Sensing and GIS in Southern Taiwan

Taiwan has been experiencing fast economic development and population growth for the past twenty years. This development has put pressure on the agriculture and overall hydrology of the nation. To cite but few, 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 study employing remote sensing for obtaining periodic regional updates of runoff model parameters through land cover analysis, together with geographic information system (GIS) for handling and performing the image processing and runoff curve number estimation, was performed in two, one static (Mei-Nong) and the other developing (Niao-Song) basins in Kaohsiung, southern Taiwan. Landsat 30-m resolution imagery from 1990, 1995, and 2000 was processed to land-cover maps. Ground truth data was collected from field survey and historical aerial photos. GIS analysis of this land-cover, together with soil map data, was used to estimate spatially-distributed United States Department of Agriculture, Natural Resources Conservation Service-Curve Number (USDA-NRCS-CN) on a 30-m grid, and to compute runoff depths. Results of the study indicate that, integrating remote sensing and GIS for tracking the land cover change hence runoff response was helpful for understanding the trends and possible impacts of the dynamics of the change in land use on the overall hydrology of the two study areas. Niao-Song basin has experienced changes in land cover hence runoff response more than the Mei-Nong basin. Over the 10 years of study, the runoff depth has changed much attributed to an increase in residential areas and reduced agricultural areas. The results of the study will be useful in planning, managing and anticipating the potential change in the runoff response of the irrigation areas as a result of possible changes in land use.