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2025 Vol.58, Issue 12 Preview Page

Research Article

Estimation of manning’s roughness coefficients at automatic discharge gauging stations using the continuous slope–area method

연속 경사 면적법을 통한 자동유량관측소에서의 실측 조도계수 산정

Ikhan Leea
,
Dongsu Kimb*
,
Kyeongdong Kimc
,
Youngsin Rohd
이 익한a
,
김 동수b*
,
김 경동c
,
노 영신d
aMaster’s Course, Department of Civil & Environmental Engineering, Dankook University, Yongin, Korea
bProfessor, Department of Civil & Environmental Engineering, Dankook University, Yongin, Korea
cPost-doctoral Researcher, IIHR-Hydroscience & Engineering, University of Iowa, Iowa City, IA, USA
dPrincipal Researcher, Research and Development Department, Korea Institude of Hydrological Survey, Goyang, Korea
a단국대학교 토목환경공학과 석사과정
b단국대학교 토목환경공학과 교수
c아이오와대학교 박사후연구원
d한국수자원조사기술원 연구개발실 연구위원
*Corresponding Author
31 December 2025. pp. 1425-1438
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Abstract

River discharge is a key indicator for water resources management and flood forecasting, but the traditional single stage–discharge rating curve produces systematic errors under unsteady flow due to hysteresis. This study applies the inverse continuous slope–area (CSA) method at Naju Bridge on the Yeongsan River by combining H-ADCP (Horizontal Acoustic Doppler Current Profiler) measured discharges with upstream and downstream water-surface slopes. Time-series Manning’s roughness coefficients (n) were estimated at 10-minute intervals for the 2020 flood events, segmented by stage to reflect cross-sectional characteristics, and applied to recalculate and validate CSA discharges for the 2019 and 2021 events. The estimated n shows a common pattern: rapid decrease at low stages, convergence at intermediate stages, an inflection before rapid expansion, and increase again at high stages, converging to values higher than conventional empirical or design criteria (reaching n ≈ 0.08~0.09 during extreme floods). Using the segmented n, the CSA method reproduced hysteresis in six flood events with R2 ≥ 0.94 and peak error ≤ 3%, although nRMSE exceeded 10% under low-flow conditions. Overall, time-series estimation and stage-wise application of measured n significantly improve the performance of the CSA method and enhance the practical applicability of field-based roughness estimation and CSA-based discharge computation in natural rivers.

Keywords
Manning roughness coefficient
Continuous Slope–Area method
Discharge
Water surface slope
H-ADCP

하천 유량은 수자원 관리와 홍수 예보의 핵심 지표이나, 이를 산정하는 전통적 단일 수위–유량곡선은 하천의 비정상류 조건에서 이력현상으로 체계적 오차가 발생한다. 본 연구는 영산강 본류에 위치한 나주시(나주대교)에서 H-ADCP (Horizontal-Acoustic Doppler Current Profiler) 실측유량과 상·하류 수면경사를 결합하여 연속 경사-면적법(CSA)을 역산하고, 2020년 홍수사상에 대해 10분 간격의 실측 Manning 조도계수 n을 산정한 뒤 단면 특성을 반영해 수위별 구간화 후 2019, 2021년 홍수사상에서 CSA 유량을 재산정 및 검증하였다. n은 저수위 급감–중수위 수렴–급확대 직전 변곡–고수위 재상승의 공통 패턴을 보였고, 기존 경험식이나 설계기준에서 사용되는 고정값보다 크게(극한 홍수 시 n≈0.08~0.09) 수렴하였다. 구간화한 n을 적용한 CSA는 6개 홍수사상에서 이력현상을 효과적으로 재현하여 결정계수 R2≥0.94, 첨두오차 ≤3%의 성능을 보였으나 저유량에서는 nRMSE가 10% 이상으로 증가하였다. 결론적으로, 실측 n의 시계열 추정과 구간 적용은 CSA의 재현성을 유의하게 향상시켜, 여러 하천에서 실측 조도계수 산정과 CSA의 실무 적용 가능성을 한층 높일 수 있을 것으로 기대된다.

키워드
조도계수
연속 경사 면적법
유량
수면경사
H-ADCP
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Information
  • Publisher :KOREA WATER RESOURECES ASSOCIATION
  • Publisher(Ko) :한국수자원학회
  • Journal Title :Journal of Korea Water Resources Association
  • Journal Title(Ko) :한국수자원학회 논문집
  • Volume : 58
  • No :12
  • Pages :1425-1438
  • Received Date : 2025-08-28
  • Revised Date : 2025-11-20
  • Accepted Date : 2025-11-25
  • DOI :https://doi.org/10.3741/JKWRA.2025.58.12.1425
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