Stream Flow Generation for Simulating Yearly Bed Change at an Ungauged Stream in Monsoon Region

Woong Hee Lee,Heung Sik Choi,Dongwoo Lee,Byungwoong Choi

doi:10.3390/w13040554

Abstract

The stream flow generation method is necessary for predicting yearly bed change at an ungauged stream in Monsoon region where there is no hydrologic and hydraulic information. This study developed the stream flow generation method of daily mean flow for each month over a year for bed change simulation at an ungauged stream. The hydraulic geometries of cross-sections and the corresponding bankfull indicators of the Byeongseong river of 4 km reach were analyzed to estimate the bankfull discharge. The estimated bankfull discharge of the target reach was 77.50 m3/s, and the total annual discharge estimated 3720 m3/s through the correlation equation with the bankfull discharge. The measured total annual discharge of the Byeongseong river was 3887.30 m3/s, which is greater by 167.30 m3/s of 4.3% relative error. The volume and bed changes over a year by the Center for Computational Hydroscience and Engineering Two-Dimension (CCHE2D) model simulated using the measured discharge during 2013 and 2014 coincided with the surveyed in the same period. Estimated total annual discharge was used for the scenarios of stream flow generation. The generated stream flow using the flow apportioned to each month on the basis of the flow percentage in an adjacent stream simulated the river bed most appropriately. The generated stream flow using the flow based on the monthly rainfall percentage of the rainfall station in the target stream basin also simulated river bed well, which is confirmed as an alternative. Quantitatively, the root mean square error (RMSE), mean bias error (MBE), and mean absolute percentage error (MAPE) in-depth change of thalweg between the measured and the simulated were found to be 0.25 m, 0.04 m, and 0.44%, respectively. The result of the simulated cross-sectional river bed change for target reach coincided well with the surveyed. The proposed method is highly applicable to generate the stream flow for analyzing the yearly bed change at an ungauged stream in Monsoon region.

Highlights

Bed change analyses are classified into short-term bed change analysis, in which the aspects of erosion and deposition including local scours in the surroundings of a stream structure or at a curved channel are analyzed, and long-term bed change analysis, in which the occurrence of erosion and deposition caused by the change in the sediment transport form over time is analyzed
A two- or three-dimensional model is commonly used to analyze the characteristics of local erosion and deposition around river structures, otherwise a one-dimensional model is used for the prediction of long-term bed change
The effective discharge is defined as the flow rate that moves most of the annual similar amount over the years and is calculated using the flow rate-frequency distribution curve and the similar amount curve

Summary

Introduction

Bed change analyses are classified into short-term bed change analysis, in which the aspects of erosion and deposition including local scours in the surroundings of a stream structure or at a curved channel are analyzed, and long-term bed change analysis, in which the occurrence of erosion and deposition caused by the change in the sediment transport form over time is analyzed. Observed hydraulic data and hydrologic data are important and fundamental to predicting and analyzing bed changes. It is time-consuming and expensive to acquire the hydraulic data and hydrologic data and investigate the bed changes of many streams in various regions. The hydraulic data and hydrologic data are collected mostly in large-scale rivers, and most of small-sized and medium-sized streams are not gauged. Long-term bed change analyses using a two- or three-dimensional model have disadvantages in that the simulation takes a long time, and an incorrect simulation result may be obtained unless an accurate boundary condition and sediment transport formulas are used when applying the model. Most of the bed change analyses using a two- or three-dimensional model are short-term bed-change analyses when flooding

Methods

Results

Conclusion