Integrated model for estimating sediment discharge to coastal area from river basin - A case study of Sakawa river

In this study an integrated model to estimate total sediment discharge from a river basin to coastal area is proposed. The model consists of soil erosion estimation and transport mechanism components and one-dimensional river profile change component. Sakawa river basin that has an area of approximately 570 km² is selected as a case study. The basin boundary is delineated from the Digital Elevation Model (DEM) data using GIS software. The input parameters for the model were derived from rainfall data, land use/land cover data, soil data and elevation data. The average annual sediment discharge to the river mouth is estimated to be about 6.7 × 10⁴ ton/yr. The simulated sediment discharge at the river mouth is also compared with the measured sediment at the river mouth and the results show reasonably good fit. Also the effect of land use and climate change to the sediment yield is analyzed. The land use data derived from remotely sensed images of 1976 and 1997 is used as the basis for comparison to see the effect of land use change. It was observed that using the land use data for the year 1997, total sediment discharge to the coastal environment increased as compared to the year 1976; this is mainly due to the increased agricultural areas and residential areas and also decreases in forest area. For analyzing the effect of climate change, HadCM2 model is used to generate mean daily precipitation for the month for the period 2040-2050 and then daily rainfall amount is generated from this data using exponential distribution. The results of the sediments discharge to the coastal environment using this generated data show a decrease in the average annual sediment discharge.