Estimation of surface runoff using NRCS and rational method.

Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, storm water, meltwater, or other sources, can no longer sufficiently rapidly infiltrate the soil. This can occur when the soil is saturated by water to its full capacity, and that the rain arrives more quickly than the soil can absorb it. The objective of this study is to determine the surface runoff using NRCS and Rational methods. In this study Chaktai-Rajakhali watershed in Chattogram city is taken a study area. The study area is further classified into nine (9) sub-catchments or drainage sub-basin based on land use patterns. The average rainfall received by the watershed is about 3378 mm that is substantially higher than the country's annual average of 2300 mm and rainfall is mostly occurs between May to October. In this study, there are two major methods that followed are NRCS and Rational method. The curve number method helps us to generate the curve number depending on the land conditions of our watershed. From the outcomes of this study, the average curve number of this study area is found about 79.29. In return periods of 2 years to 100 years maximum possible average discharge is found about 37.20 m3/sec to 85.41 m3/sec and the maximum possible average runoff would be 3331.03 mm to 7726.52 mm in this catchment. In conclusion, if this urbanization trend is going on tremendously in Chaktai-Rajakhali will face devastating flood in the future. [ABSTRACT FROM AUTHOR]