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2025 Vol.58, Issue 10

Research Article

Estimation and field applicability analysis of the velocity index for non-contact discharge measurement

비접촉식 유량 측정을 위한 평균유속환산계수 산정 및 현장 적용성 분석

Tae-Hee Leea*
,
Seung-Ho Parkb
,
Jung-Hwan Chunc
,
Tae-Woong Okd
이 태희a*
,
박 승호b
,
천 정환c
,
옥 태웅d
aPrincipal Researcher, Hydrological Survey Department, Korea Institute of Hydrological Survey, Goyang, Korea
bResearcher, Hydrological Survey Department, Korea Institute of Hydrological Survey, Goyang, Korea
cResearcher, Hydrological Survey Department, Korea Institute of Hydrological Survey, Goyang, Korea
dResearcher, Hydrological Survey Department, Korea Institute of Hydrological Survey, Goyang, Korea
a한국수자원조사기술원 수자원조사본부 책임연구원
b한국수자원조사기술원 수자원조사본부 전임연구원
c한국수자원조사기술원 수자원조사본부 전임연구원
d한국수자원조사기술원 수자원조사본부 전임연구원
*Corresponding Author
31 October 2025. pp. 835-846
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Abstract

Due to the increasing frequency and intensity of floods driven by climate change, the importance of reliable discharge measurements during flood events is growing. In particular, under high-flow conditions, conventional contact-type methods are often impractical, leading to the increasing adoption of non-contact techniques such as Surface Velocity Radar (SVR) systems. However, converting surface velocity to depth-averaged velocity requires an accurate velocity index (α), w.hich is known to vary significantly depending on site-specific hydraulic and morphological characteristics. This study investigates five sites along the Wicheon Stream, a major tributary of the Nakdong River in Korea. Surface and depth-averaged velocities were measured using SVR and Acoustic Doppler Current Profiler (ADCP) under various flow conditions. The velocity index α was estimated using three approaches: the Log Law, Power Law (Qrev-based extrapolation), and direct Surface velocity–Mean velocity comparisons. The results showed that α ranged from 0.76 to 1.20 depending on site and method. In particular, the direct comparison method using co-located SVR and ADCP data allowed quantitative determination of optimal α values via R2-based optimization, revealing that using a default α of 0.85 can lead to discharge estimation errors exceeding 40% in some cases. Furthermore, the discharge values computed using different α values affected the shape of the stage–discharge relationship curves, suggesting that fixed α values can introduce significant errors in long-term hydrologic records and design flood estimations. This study highlights the need for site-specific calibration of velocity indexs and offers practical approaches to improve the accuracy of non-contact discharge measurement in rivers.

Keywords
Non-contact discharge measurement
Surface velocity
Mean velocity
Velocity index
ADCP
SVR

최근 기후 변화로 인해 홍수 발생 빈도와 강도가 증가함에 따라, 홍수기 유량 측정의 중요성이 강조되고 있다. 특히 고수위 조건에서는 접촉식 유량 측정이 어려워 비접촉식 기술, 그중에서도 전자파표면유속계(Surface Velocity Radar, SVR)를 이용한 표면유속 기반 측정이 주목받고 있다. 그러나 표면유속으로부터 평균유속을 환산하기 위해서는 신뢰성 있는 평균유속환산계수(Velocity Index, α)의 적용이 필수적이며, 하천 특성에 따라 α값이 크게 달라질 수 있다는 점에서 환산계수의 정밀한 산정이 요구된다. 본 연구에서는 낙동강 제1지류인 위천의 5개 지점을 대상으로, ADCP (Acoustic Doppler Current Profiler)와 SVR를 이용해 다양한 수위 조건에서 유속을 측정하고, 세 가지 기법(대수 법칙, 멱함수 법칙, 표면유속–평균유속 직접 비교)을 통해 평균유속환산계수를 산정하였다. 분석 결과, α값은 지점별, 방법별로 0.76에서 1.20까지 분포하였으며, 조도, 하상재료, 유속 분포 특성에 따라 상이한 값을 나타냈다. 특히 SVR과 ADCP를 동일 위치에서 비교 측정한 결과, 결정계수 기반 최적화 분석을 통해 각 지점의 α를 정량적으로 도출할 수 있었으며, 단순 고정값(0.85)을 적용할 경우 최대 40% 이상의 유량 산정 오차가 발생할 수 있음이 확인되었다. 또한, 산정된 환산계수를 기준으로 유량을 계산한 결과, 수위–유량관계곡선의 형상에도 유의미한 영향이 나타났으며, 이는 장기 수문자료 구축 및 홍수량 산정 시 오차를 유발할 수 있음을 시사한다. 본 연구는 다양한 하천 조건에 따라 변화하는 평균유속환산계수의 특성을 정량적으로 분석하고, 비접촉식 유량 측정의 정확도 향상을 위한 환산계수 적용 방안을 제시하였다는 점에서 의의가 있다.

키워드
비접촉식 유량측정
표면유속
평균유속
평균유속환산계수
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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 :10
  • Pages :835-846
  • Received Date : 2025-04-21
  • Revised Date : 2025-07-28
  • Accepted Date : 2025-08-07
  • DOI :https://doi.org/10.3741/JKWRA.2025.58.10.835
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