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Step-by-step guide for Siting and Operating Surface-water Velocity Radars

The goal … To collect channel velocity and cross-section data on Monday and operationally transmit real-time stage, velocity, area, and discharge on Tuesday regardless of (1) how surface-water velocities were measured (LSPIV or radar) or (2) the hydraulic conditions that existed on Monday.

Introduction

The United States Geological Survey (USGS) and Environment and Climate Change Canada (ECCC) are exploring the use of velocity radars to measure surface-water velocities and compute real time mean-channel velocity and discharge in streams and rivers. Velocity radars can (1)  deliver real-time discharge at new stations where stage-discharge, index-velocity, or slope-discharge ratings are not available; (2) extend ratings; (3) corroborate indirect measurements; and (4) provide an alternative for measuring discharge at sites with complex ratings .  The ultimate goal of this effort is to transition the use of surface-water velocity radars from a proof-of-concept to an operational mode and to more clearly determine operational limitations.

Backstory

These guidelines are an extension of the non-contact methods initiated by HYDRO 21 (Costa et al., 2006). The USGS Hydrologic Instrumentation Facility (HIF), Project Chiefs from 6 USGS Water Science Centers (WSCs), and two vendors (Stalker and Hydrological Services of America; HSA) participated in proof-of-concept testing. Fourteen (14) sites, which exhibited different hydraulic flow regimes, were identified and collocated with existing USGS streamgages. Laboratory testing was conducted in parallel with field deployments by the HIF (Fulford, 2015) and the Switzerland Federal Institute of Metrology (METAS).  Testing at the HIF and METAS was conducted in the spring 2015 using standard methods including flumes, carriage-tow tanks, and tuning forks with known frequencies. Stalker and HSA offered their units gratis in exchange for an assessment on their performance. Similarly, OTT Hydromet (OTT) offered their radar for testing; however, the unit is still under development.

Quick Start Guide

You’ll need to acquire a small amount of velocity and channel data beyond what a normal field trip demands. Data should be collected at the cross section-of-interest and in the vicinity of the radar footprint. Keep in mind that the radar’s ability to return a surface-water velocity is influenced by (1) the quality of scatterers or waveforms on the water surface, (2) the air gap or the distance between the bridge deck and the water surface, and (3) the potential noise imposed by wind drift, eddies, secondary flows, and macro turbulence.

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