Acoustic Doppler Technology for Streamflow Data Collection Don Hayes Richmond, Va.

History Vane Electro-magnetic Velocity Meter Acoustic Velocity Meter Acoustic Doppler Current Profilers

Acoustic Doppler Current Profilers

ADCP Applications Instantaneous Discharge Measurement Continuous Measurement—fixed mount Hydrographic Survey Calibrate and Validate Two-Dimensional Hydrodynamic Models Estimating Sediment Concentrations Using Acoustic Backscatter

Why do people want to use ADCP’s? More accurate measurements Better science (model calibration, water quality studies, etc.) Safety and Efficiency

Theory of Discharge Measurements

Conventional Discharge Measurement Velocity Width Depth This slide illustrates the method used to make conventional discharge measurements (using a Price AA current meter). Mid-Section Method Question for the class: Can someone tell me what the name of the method used in the US (USGS) for Qm’s? Answer: Mid-section method Prior to the 1950, we used a method called the mean-section method, before a study by Young (1950) concluded that the mid-section method was easier to compute and more accurate. Width is computed as half the distance from the current section to the previous section, plus half the distance from the current section to the next section. Therefore the mid-section method. This width is then multiplied by the depth measured to compute an area. Then Q= V*A. In Europe other methods are used – including full profiles using horizontal axis current meters.

Acoustic Profiler Discharge Measurement ADCP Discharge Measurement Discharge is the total volume of water flowing through a given cross-section of water per unit of time. With an ADCP and WinRiver the total volume discharge is computed for each ADCP ensemble (vertical) from a moving boat. There is no need to stop and make individual measurements. ADCP Measures Flow through some arbitrary surface An important feature of this system is that discharge can be measured over an irregular path. Instead of measuring flow through a PLANE like we do with Price AA measurements, with an ADCP (irregular weir) we are measuring flow through a SURFACE. If you project the ship track onto the bed, imagine a surface rising vertically above that projected ship track. The SOFTWARE is computing flow through THAT surface.

Measured and Unmeasured Areas Top estimate Triangular Shore estimate Measured The top and bottom of the profile cannot be measured for the reason just discussed. As the ADCP approaches the edge of the channel the depth of flow will become too shallow for the ADCP to profile. Or in the case where a vertical wall forms the edge of water, the beams from the profiler may impinge on the wall, causing erroneous measurements. Regardless of the type of edge of water, it is necessary to estimate the discharge on both shores and add them to the measured discharge to obtain an accurate estimate of the total discharge. Vertical Shore estimate Bottom estimate

It is not magic Quality Assurance is important

Progression of ADCP Use

Indiana’s Original Tethered Boat Electronics box Handle Foam floats Original design was good –but it was more or less a home-made platform. Needed to have something that work in faster flows and provide a good platform for a variety of situations. Catamaran design Aluminum frame Wireless modems ADCP

OceanScience RiverBoat ADCP Cost is ~$2,500. Comes with ADCP cable and radio/power connectors Can be adapted to other profilers (SonTek) 47 purchased by USGS Slot for rudder

Tennessee Tethered Boat Cost: < $600 US

Nortek BoogieDopp Integrated radio modem interface Deployed from “boogie board” Discharge computation software runs on WinCE (PocketPC) Discharge is computed in real time, post-processing can be done at the office (review of data, velocity profiles) Nortek profiler portion of the project – profiler features

Remote Controlled Boat Prototype running at 18 ft/s

SonTek FlowTracker Keypad LED display 2/4 MB recorder Similar to Aquacalc Measurements stored as binary file (*.wad)

Questions?