Analysis of River Bed Variation Based on Hydrological and Hydraulic Models: A Case Study on Hosan Stream Watershed, South Korea

Abstract

These days, the irrigation facilities and the facilities in the vicinity of river are classified into different categories and managed based on the purpose of low flow and high flow, and are constructed according to the plans designed to maximize economic effects. Both hydrologic analysis and hydraulic analysis need to be conducted as part of preliminary basic investigation and analysis before these facilities are installed. The hydrologic analysis has been taken to an advanced level through many applications. On the other hand, the hydraulic analysis was based on hydraulic model experiment and therefore much difficulty was involved in its application in Korea. However, the advancement of computers in contemporary era has helped resolve those problems to some degree, enabling the hydraulic properties to be analyzed based on numerical model. This study presents a prediction of river bed variation in near future on assumption that the changes in upstream flow rates and past flow rates. For that, the hydrological analysis of Hosan Stream Basin was conducted first, which was followed by the analysis of hydraulic properties based on the 2-dimensional numerical model by using the daily discharge, derived by the hydraulic analysis, and the observed precipitation as the input data. In this study future changes in river bed were forecasted under the assumption that flow velocity of past and changes in flow rate at upstream river due to construction of large-scale artificial structures downstream occur in the future. Therefore, the long-term runoff volume from the downstream part of Hosan Stream was estimated using the SSARR (Stream Synthesis and Reservoir Regulation Model). Changes in the river bed were simulated using hydraulic models named; RMA-2 and SED-2D. As a result, it was found that the river bed variation is significantly affected by the inclusion of sediment in flood flow at upstream. In this regard, there is a need to devise measures to mitigate future flood damage to artificial structures by reflecting sedimentation trends downstream before the construction of large-scale artificial structures at downstream of river.