The BoogieDopp: a New Instrument for Measuring Discharge in Small Rivers and Channels

The BoogieDopp is a new instrument for measuring discharge in small rivers, streams and channels. It consists of an Aquadopp Current Profiler mounted on a 1-m long boat (made by OceanScience) that looks like a boogie board. It is designed for tethered operation in small channels and shallow rivers and it transfers data through radio modems. By collecting data from tethered instruments, the BoogieDopp does not need to measure velocity via bottom-tracking, which simplifies the system and eliminates many of errors and biases associated with bottom tracking. The BoogieDopp minimizes the cell size (about 10 cm), immersion depth (nominally 2 cm) and flow interference, all of which enable accurate data to be collected close to the surface. Discharge measurement is conceptually similar to traditional current meter measurement in that the user stops at 10-25 positions (verticals), measuring for typically 40 s at each position. Measuring this ways simplifies the physical assumptions necessary for extrapolation into the bottom and surface. While individual profiles vary wildly, long-term mean profiles closely match model hydraulic profiles (i.e. the 1 /6 power law). Holding station for a while allows time for averaging, and it ensures that physical conditions remain stationary during the average. This paper summarizes the methods used to obtain data and to compute discharge, provides a simple model for measurement uncertainties, and presents results from a variety of channels and rivers ranging in discharge from 0.2 to 100 m 3 /s. We conclude that the BoogieDopp is able to measure discharge in these channels with an uncertainty of a few percent. 1. Overview The BoogieDopp is a new system designed to measure flow in small rivers and channels. Moving-boat Doppler-based instruments for measuring river discharge have been available now for more than a decade (c.f. Gordon, 1989). The BoogieDopp takes a different approach, blending the old and the new, and adding a few twists of its own. Based on the Aquadopp Current Profiler, its small size, long cylindrical shape and ability to work in shallow water enable it to work in applications that have not been well served up to now. It mounts on a small board, which makes it easy to carry and easy to get into tight spaces. It uses two beams instead of three, relying on the board to keep the beams aligned with the flow. With only two beams, it is able to position itself closer to the walls of narrow channels. It adds a forward-looking beam to measure velocity close to the surface. An important difference is that the BoogieDopp does not use bottom-track velocity. Instead, it holds fixed positions, much like traditional current meter measurements. This means that the BoogieDopp avoids difficult errors associated with bottom tracking. In particular, the BoogieDopp eliminates errors caused by “moving bottoms”.