A thesis submitted in pa1tial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 2006

Urbanization continues to expand; rural areas have become sub-urban areas and have finally become urban areas. A major percentage of their surfaces are hardened and impervious which change runoff characteristic. Runoff in urban areas reacts quickly to rainfall as compared to rural areas due to the significant impervious areas. As a result, increased runoff causes flooding of lowlands in urban area. These areas required drainage structures to prevent flood problem. Design storms are most frequently applied to the calculation of runoff peak flows for the sizing of drainage structure. For this purpose, the best design storm should be selected. The main objectives of this study are to study rainfall characteristic using rainfall data at AIT meteorological station and to derive design storm pattern and then compared to historical storms and field rainfall to determine the most appropriate design storm pattern for AIT. Historical rainfalls at AIT meteorological station were analyzed based on annual maximum rainfall and based on storm duration to develop Depth-Duration-Frequency (DDF) curve and Intensity-Duration-Frequency (IDF) curve. Three design storm namely; Chicago, Yen and Chow and Sifalda design storm were developed from DDF and IDF curve for the duration of 30 minutes to 2 hour depending on historical rainfall which was selected for comparison. These design storms were compared to historical rainfall based on their shape, time to peak and peak intensity. In general, it has been found that Chicago design storm was the most suitable design storm. However, it always gave an overestimation of peak intensity