Estimating discharge in gravel‐bed river using non‐contact ground‐penetrating and surface‐velocity radars

Abstract

Discharge measurement is a critical task for gravel-bed channels. Under high-flow conditions, the elevation of the riverbed changes significantly by intensive torrential flow. The stage-discharge relations commonly used for stream discharge estimation may no longer be adequate. The contact-type velocity measuring is also subject to measurement errors and/or instrument failures by the high-flow velocities, driftwood, stumps, and debris. This study developed a new real-time method to estimate river discharge in gravel-bed channels. A systematic measuring technology combining ground-penetrating radar and surface-velocity radar was employed. The rating curves representing the relations of water surface velocity to the channel cross-sectional mean velocity and flow area were established. Stream discharge was then deduced from the resulting mean velocity and flow area. The proposed method was examined in a steep gravel-bed reach of the Cho-Shui River in central Taiwan. The estimated stream discharge during three flood events were compared to the prediction by using the stage-discharge relation and the index-velocity method.The proposed method of this study is capable of computing reasonable values of discharge for an entire flood hydrograph, whereas the other two methods tend to produce large extrapolation errors. Moreover, when the computed discharge is used in 2D flood flow simulation, the proposed method demonstrates better performance than the commonly used stage-discharge and index-velocity methods.

Real‐time monitoring and estimation of the discharge of flash floods in a steep mountain catchment

“…It also validated the efficiency and reliability of the proposed noncontact method in this study. Previous researchers (Chen, ; Chen & Chiu, ; Chen & Chiu, ; Hong et al, ; Moramarco et al, ) found that the maximum velocity generally occurred at or close to the water surface located in the open‐channel thalweg (Figure ), which was similar to the measured results of the vertical velocity profiles of the channel cross section. This observed behaviour was a confirmation of open‐channel hydraulics and was mainly affected by the in situ geometry of the selected cross‐section and channel roughness (Rantz, and 1982b).…”

“…Direct current metre measurements during the peak of flash floods were usually impractical and even impossible for personal safety and technical time‐consuming reasons (Chen, ). For example, traditional contact monitoring instruments, such as the propeller current metre, electric magnetic velocity metre, acoustic Doppler velocimeter, and acoustic Doppler current profile (Hong, Guo, Wang, & Yeh, ; Ran, Li, Liao, Hl, & Wang, ), were always installed into the river water to estimate these hydrological parameters and were easily destroyed by the devastating flash flood, especially in a steep watershed with rapid flows. Meanwhile, the extrapolated rating curve under common flow conditions was limited and not reliable (Bihan, Payrastre, Gaume, Moncoulon, & Pons, ).…”

Evaluation of discharge measurements methods in a natural river of low or middle flow using an electromagnetic flow meter

“…where y is the average depth of the whole cross section. and b. by the surface velocity (Hong et al, 2017)…”

“…More recent studies have proposed that entropy theory should be integrated into a method calculating the river discharge (Alimenti et al, 2020; Bechle & Wu, 2014; Farina et al, 2017; Moramarco & Singh, 2010). According to this theory, velocity is considered as a probabilistic variable and the ratio of mean to maximum velocity is stable for a certain cross section (Ammari et al, 2017; Chen & Chiu, 2004; Chen, Yang, Hsu, & Kuo, 2012; Hong et al, 2017). This ratio is known as the entropy parameter and does not depend on any flow conditions.…”

Study on the Characteristic Point Location of Depth Average Velocity in Smooth Open Channels: Applied to Channels with Flat or Concave Boundaries

“…Bretheim et al [15] used the restricted nonlinear (RNL) model to simulate wall turbulence and obtained the real mean velocity distribution in the channel at a low Reynolds number. Hong et al [16] employed a systematic measuring technology combining ground-penetrating radar and surface velocity radar and established the rating curves representing the relation of water surface velocity to the channel cross-sectional mean velocity and flow area. Then, stream discharge was deduced from the resulting mean velocity and flow area.…”