Use of radars to monitor stream discharge by noncontact methods

Abstract

[1] Conventional measurements of river flows are costly, time-consuming, and frequently dangerous. This report evaluates the use of a continuous wave microwave radar, a monostatic UHF Doppler radar, a pulsed Doppler microwave radar, and a groundpenetrating radar to measure river flows continuously over long periods and without touching the water with any instruments. The experiments duplicate the flow records from conventional stream gauging stations on the San Joaquin River in California and the Cowlitz River in Washington. The purpose of the experiments was to directly measure the parameters necessary to compute flow: surface velocity (converted to mean velocity) and cross-sectional area, thereby avoiding the uncertainty, complexity, and cost of maintaining rating curves. River channel cross sections were measured by groundpenetrating radar suspended above the river. River surface water velocity was obtained by Bragg scattering of microwave and UHF Doppler radars, and the surface velocity data were converted to mean velocity on the basis of detailed velocity profiles measured by current meters and hydroacoustic instruments. Experiments using these radars to acquire a continuous record of flow were conducted for 4 weeks on the San Joaquin River and for 16 weeks on the Cowlitz River. At the San Joaquin River the radar noncontact measurements produced discharges more than 20% higher than the other independent measurements in the early part of the experiment. After the first 3 days, the noncontact radar discharge measurements were within 5% of the rating values. On the Cowlitz River at Castle Rock, correlation coefficients between the USGS stream gauging station rating curve discharge and discharge computed from three different Doppler radar systems and GPR data over the 16 week experiment were 0.883, 0.969, and 0.992. Noncontact radar results were within a few percent of discharge values obtained by gauging station, current meter, and hydroacoustic methods. Time series of surface velocity obtained by different radars in the Cowlitz River experiment also show small-amplitude pulsations not found in stage records that reflect tidal energy at the gauging station. Noncontact discharge measurements made during a flood on 30 January 2004 agreed with the rated discharge to within 5%. Measurement at both field sites confirm that lognormal velocity profiles exist for a wide range of flows in these rivers, and mean velocity is approximately 0.85 times measured surface velocity. Noncontact methods of flow measurement appear to (1) be as accurate as conventional methods, (2) obtain data when standard contact methods are dangerous or cannot be obtained, and (3) provide insight into flow dynamics not available from detailed stage records alone.

Conventional Point-Velocity Records and Surface Velocity Observations for Estimating High Flow Discharge

“…In the first case, the sampling concerns only a small part of flow area so that it is possible to minimize the sampling time and the contact with the surface water. In the second case, the velocity measure is obtained without any contact and safety conditions [8,9]. Moreover, recent developments in Interferometric Synthetic Aperture Radar (InSAR) techniques make possible new scenarios where the river surface velocity can be inferred from space.…”

Estimación del caudal a partir de la evolución del nivel del agua en un estuario con onda de marea estacionaria

“…Más recientemente, mediciones continuas de la velocidad superficial a partir de métodos de no contacto mostraron ser útiles para estimar la descarga [25][26][27][28][29][30][31][32][33][34][35][36][37]. El desafío consiste en relacionar la velocidad medida en superficie con el flujo subsuperficial.…”

“…El desafío consiste en relacionar la velocidad medida en superficie con el flujo subsuperficial. Típicamente, la velocidad superficial es convertida a velocidad promediada en profundidad vía una constante multiplicativa (conocida como índice de velocidad) [26], despreciando la variabilidad de los perfiles del flujo estuarino a lo largo del ciclo mareal y la presencia de gradientes baroclínicos.…”

Three Methods for Estimating the Entropy Parameter M Based on a Decreasing Number of Velocity Measurements in a River Cross-Section

“…Such an operation would be unfeasible using conventional gauging techniques. In this regard, Costa et al [18] demonstrated the monitoring potential of "no contact" radar sensors directly installed on a bridge or mounted on an arm connected to a pole positioned on the riverside [19]. Moreover, the application of remote sensing and satellite information to study the range of surface velocities in a river has drawn a great deal of interest in recent years [20][21][22].…”