Thesis (M.Sc.)--Chulalongkorn University, 1999

The flood statistical analyses are used for delineation of several flooding factors by means of multiple regression and correlation equations. The results of flood statistical analysis in the Chumphon basin is primarily caused by heavy rainfall of tropical storm. Furthermore, the HEC-1 model, showing the variation in lag time and flood peaks, reveals various levels of land use pattern and urban development. The land use changing not only promotes the increase volume of discharge after heavy rainfall, but also shortens the lag time and increase the flood peak and river stage. The rainfall and flood frequency analyses have been carried out using the method of moment of parameter estimation for Gumbel Probability Distribution for the designed of 2, 5, 15, 25, and 100 years return periods. The flood prone areas are estimated from various designed flood events. The results indicate that large part of the flood prone areas are in the western part of khlongTha Taphao. The location of flood prone areas of different of return periods cover numerous Tumbons of Hat Phan Ktar, Bang luk, Na Cha-ang, Wang Mai, Wang Phai, Na Thung, Tha Taphao, Ban Na, Khun Krathing, Tak Daet, Bang Mak, Tha Yang, Pak Num, Thung Kha, Visai Nua, and Hat Sai Ree in Amphoe Muang. The flood prone areas of 2 years return period is about 184 square killometres, 5 years return period is about 212 square killometres, 15 years return period is about 244 square killometres, 25 years return period is about 253 square killometres, and 100 years return period is about 269 square killometres. The flood prone areas of 2, 5, 15, 25, and 100 years return periods cover 23.19%, 26.66%, 30.74%, 31.89%, and 33.92% of the total area of Apmhoe Muang, respectively. The flood prone areas of different return periods are critically important for the planning and management of the flood disaster in Amphoe Muang, Chumphon province.