The main subject of this study is to decide the optimal time distribution of rainfall in order to estimate the optimal design flood for the ChangChon basin.
In the past, probability rainfall which was estimated through frequency analysis played a very important role in estimating the optimal design flood, but recently the shape of design rainfall and the size of design flood around the target area have become also important. Therefore, the necessity has arisen for an optimal rainfall distribution shape reflecting the characteristics of the flood area in oder to estimate the optimal design flood.
This study conducted a basic work of extracting geographical factors by dividing the flood area and producing a river network based on the GIS data around the ChangChon basin. Data on annual maximum rainfall by random duration period measured by JinJu and SanCheong observation posts were collected and used in constructing the basic data by estimating the probability rainfall with a rainfall analysis program, FARD2006. The study distributed design rainfall over a 24-hour duration period by utilizing the constructed data with main time-distribution rainfall models such as the alternating block method, the Huff method and the Mononobe method. For comparison and analysis of these data, extraction analysis was conducted with an extractor program, HEC-HMS, and the design flood and flood data by estimated time-distribution rainfall model were used in comparing estimated flood amounts of the DeokCheon River Maintenance Plan.
Four parts of the Huff method were compared and Huff 4 was the largest in the peak discharge. To select the optimal Huff part, the third quarter was chosen since it was not affected by the initial loss and had a large peak discharge.
As a result of comparing flood amounts based on the time distribution of rainfall, the peak discharge was the largest with the alternating block method, and was the minimum in the third Huff quarter. In addition, in the analysis of the discharge amount by duration period, the discharge amount in the Huff 3 method was not distributed around the center as much as the alternating block method or the Mononobe method.
When compared with the peak discharge estimated in the DeokCheon River Maintenance Plan, the alternating block method and the Mononobe method yielded excessive estimates, whereas the Huff 3 method showed the closest estimate to the peak discharge in the DeokCheon River Maintenance Plan.