본 연구는 하상마찰의 척도인 등가조고를 이용하여 자갈하천의 하상저항을 산정하는 것이다. 이를 위하여 국내 8개 자갈하천에서 실측을 통하여 마찰계수 f를 산정하였고, 하상재료의 누가입경분포를 조사하였으며, 각 단면의 실측 마찰계수를 나타내기 위하여 대수 연직유속분포를 가정하여 계산된 평균 등가조고와 누가입경분포를 이용하여 계산된 구간 등가조고를 비교하였다. 더불어 등가조고를 사용하여 계산된 Manning 계수를 Strickler 유형의 기존 경험식에 의한

In this study, we estimated the equivalent roughness using an estimation model, which considered grain distribution on the bed and the protrusion height of the grains. We also reviewed the appropriateness of the estimated equivalent roughness at the Goksung and Gurey station in the Seomjin River. To review the appropriateness of this model, we presented the water level-discharge relation curve applying the equivalent roughness to the flow model and compared and reviewed it to observed data. Also, we compared and reviewed the observed data by estimating the Manning coefficient , the Chezy coefficient , and the Darcy-Weisbach friction coefficient by the equivalent roughness. The calculation results of the RMSE showed within 5% error range in comparison with observed value. Therefore the estimated equivalent roughness values by the model could be proved appropriate.

Flow resistance in a natural stream is caused by complex factors, such as the grains on the bed, vegetation, and bed-form, reach profile. Flow resistance in a generally stable gravel bed stream is due to protrudent grains from bed. Therefore, the flow resistance can be calculated by equivalent roughness in gravel bed stream, but estimation of equivalent roughness is difficult because nonuniform size and irregular arrangement of distributed grain on natural stream bed. In previous study, equivalent roughness is empirically estimated using characteristic grain size. However, application of empirical equation have uncertainty in stream that stream bed characteristic differs. In this study, we developed a model using an analytical method considering grain diameter distribution characteristics of grains on the bed and also taking into account flow resistance acting on each grain. Also, the model consider the protrusion height of grain.