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Calculation of Roughness Coefficient in Gravel-bed River with Observed Water Levels

실측 수위에 의한 자갈하천의 조도계수 산정

  • Kim, Ji-Sung (River & Coast Research Division, Korea Institute of Construction Technology) ;
  • Lee, Chan-Joo (River & Coast Research Division, Korea Institute of Construction Technology) ;
  • Kim, Won (River & Coast Research Division, Korea Institute of Construction Technology)
  • 김지성 (한국건설기술연구원 하천.해안연구실) ;
  • 이찬주 (한국건설기술연구원 하천.해안연구실) ;
  • 김원 (한국건설기술연구원 하천.해안연구실)
  • Published : 2007.10.31

Abstract

The purpose of this study is to analyse the characteristics of Manning's roughness coefficient according to change of discharge by using observed data obtained from a stable gravel-bed river and to investigate the applicability of the relevant existing empirical methods to it. Observed water level and discharge data are used as input data for the USGS computer program NCALC model for calculation of the roughness coefficient. Calculated values are compared with roughness values which are estimated with four widely used methods. The results show that though the empirical methods are able to give similar roughness values only for flood flow, they seem to have rather high uncertainty because of necessity of subjective judgement and differences of resultant values. Roughness coefficients for normal-low flow cannot be estimated from the existing empirical formulae. Especially, using the Manning equation for calculating them should be careful as this provides a wide range of estimated values in normal-low flow. The relations between the roughness coefficient and characteristic size of bed materials are different from them in flood flow even though they have a close relations.

본 연구는 자갈하천에서 실측한 자료를 사용하여 유량 변화에 따른 조도계수의 변화를 분석하고, 기존 조도계수 경험식의 적용성을 검토하는 것이 목적이다. 실측자료를 이용한 조도계수의 산정을 위하여 미 지질조사국의 NCALC 모형을 이용하여 대상구간의 조도계수를 산정하였고, 산정된 결과를 4가지 경험적인 방법에 의해 산정된 조도계수와 비교하였다. 분석결과 기존의 경험적 방법들은 홍수기에 국한하여 근사적인 해를 제공할 수 있으나 판단의 주관성, 방법에 따른 결과의 차이 등으로 인하여 산정결과의 불확실도가 높을 것으로 판단되었다. 평저수기의 조도계수는 기존 경험적 방법으로 산정이 어려울 것으로 나타났으며, 특히 Manning 공식을 이용하여 조도계수를 산정하는 경우, 상한치와 하한치의 범위가 크므로 사용 시 주의가 필요함을 알 수 있었다. 그리고 평저수기에도 조도계수와 하상입도가 상관성이 있는 것으로 확인되었으나 홍수기의 상관성과 다르게 나타남을 확인하였다.

Keywords

References

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