Nafise Moghaddasi

By Nafise Moghadasi, Iman Karimirad and Vahedberdi Sheikh

Extensive flood damages all over the world necessitate flood risk mitigation. Land use changes affect hydrological characteristics such as total runoff and flood’s peak flow. This study investigates the impacts of land use change on flooding of the Boostan dam catchment in Golestan province, Iran. For this purpose, watershed modeling system (WMS) is used to compare different types of land uses between 1996 and 2006 using corresponding maps. After calibration and validation of the model in each period of time, flooding of the catchment was evaluated using two representative parameters of peak flow and volume of flood. Comparison of land use maps in 1996 and 2006 revealed the total rangelands have been increased while good rangeland areas decreased, fair rangeland increased, and poor rangeland remained relatively constant. It means the region faces decrease in high-quality rangelands in the catchment. Also the forest areas decreased. Both degradation of rangeland and deforestation intensify flooding. But peak flow and flood volume of the whole catchment have been mitigated. Because in spite of negligible change in total curve number (CN) of the catchment, rangelands in downstream and near residential areas converted to agricultural lands and upstream agricultural lands transformed to high- and medium-density rangelands. This means that distribution of land use changes was in such a way, influential upstream areas in flooding, associated with reduced CNs. So the implemented biological measures have reduced the flooding potential of the catchment. Sensitivity analysis of the model showed that 5% decrease in CN can cause 40% decrease in peak flow of the catchment and in contrast and 5% increase in CN can enhance flood peak flow up to 60%.

Part of the book: Natural Hazards