제주 도심하천의 강우분석 및 홍수량 산정방법 연구

Abstract

A water control project are established to prevent flood damages from typhoons and localized heavy rain. When establishing water control projects, flood volume plays an important role in determining size of the hydraulic structure. Flood volume is calculated according to the Guideline for Calculating Design Flood Volume (Ministry of Land, Infrastructure and Transport, 2012). However, the Guideline for Calculating Design Flood Volume fails to properly reflect hydrologic characteristics of Jeju Island because it was written based on the conditions of inland areas of South Korea. For the analysis and evaluation of flood volume in rivers of Jeju Island, it is necessary to develop a flood volume calculation method for Jeju based on river observation data taken from Jeju Island. Accordingly, this study was conducted to calculate flood volume that reflects topographic and hydrologic characteristics of rivers in Jeju Island by improving the parameters presented in the Guideline for Calculating Design Flood Volume. In addition, flood volume of urban rivers in Jeju Island was reviewed using hydrologic component survey data observed at river sites over many years. When calculating areal rainfall, the Thiessen polygon method cannot account for changes in rainfall according to altitude (mountain effect). Also, since there is no areal reduction factor (ARF) appropriate for Jeju Island, the Thiessen polygon method was determined to be inadequate for calculating areal rainfall of mountainous rivers in Jeju Island. The applicability was checked by comparing with areal rainfall using the isohyetal method. Areal rainfall calculated by the Thiessen polygon method can be partially applied to rivers in Jeju Island depending on altitude, but this method is inappropriate for mountainous rivers in Jeju Island because errors are created by altitude. Therefore, the isohyetal method is a more appropriate method that can account for the location of rainfall observatories and the effects of mountainous areas without creating errors from altitude. Urban rivers in Jeju Island do not have large basin area and are characterized by sharp slopes. When flood runoff occurs, it occurs at a fast flow rate of 7m/s or above. In addition, as topographic characteristics according to altitude and changes in land use are shown clearly, flood volume was calculated by applying the parameters considering topographic and hydrologic characteristics of rivers. In comparison to the Guideline for Calculating Design Flood Volume, the accuracy of peak runoff rate was increased by 1.2% according to runoff characteristics. Also, the   value of the runoff hydrograph was increased by 20.6% compared to observed flood volume. When combined with the parameters reflecting river characteristics of Jeju Island, flood volume was calculated more accurately compared to the conventional method.