LISTENING TO STONES ROCK AND ROLL AT HYDROPOWER INTAKES Northwest Hydraulic Consultants (NHC) has recently demonstrated the benefit of using hydrophones (underwater sound recording systems) to monitor the effectiveness of sediment flushing operations at hydropower facilities. Sediment flushing is needed to reduce the amount of sediment entering the penstock, but it often requires a plant outage and results in lost generation revenue. Optimizing sediment flushing requires nearly real-time information on the magnitude and timing of movement of stones through the facilities, as operators want to ensure flushing is conducted long enough to be effective, but not longer than necessary to avoid the lost power production that flushing requires. NHC scientists and engineers are providing operators of AltaGas and Innergex hydropower facilities with this information by monitoring the sounds produced from moving stones.

NHC recently installed autonomous hydrophone systems at the intakes of two run-of-the-river hydroelectric facilities: the Forrest Kerr on the Iskut River and Upper Lillooet on the Lillooet River. These simple, inexpensive systems consist primarily of a hydrophone sensor (i.e., sound recorder), which is mounted underwater near the entrance of the facility's sluiceway. The hydrophone captures the sounds produced by the stones as they move through the sluiceway. The sounds are enhanced by an amplifier and communicated to a remote computer, which stores them as sound files and processes them. The processed sound data is then transmitted to the plant Programmable Logic Controller (PLC) via the MODBUS data communications protocol and NHC Aquarius TimeSeries database for uploading to NHC's web portal (Figure 1). The processing is performed by custom software that NHC developed, which filters and processes the sound files to determine the number of impacts produced by stones, among other statistics (Figure 2).

The effectiveness of the hydrophone in detecting sediment movement was demonstrated during a recent test sluicing at the Upper Lillooet River facility on 17 May 2018. Comparing sound files recorded before and during the sluicing event showed that the stone movements can clearly be detected. The extent of stone movement was also quantified as up to 10,000 stone impacts per minute during the flush.

Our experience clearly demonstrates that hydrophones can be useful in assessing the movement of sediment in rivers. They provide hydroelectric operators with another operational tool to optimize their sediment sluicing activities. Specifically, operators can use the hydrophones to determine when sediment begins to move during operations or flushing and when sediment is no longer being moved during flushing. The hydrophone, together with continuous bed monitoring using sonar and suspended sediment monitoring in penstocks, can provide a more complete understanding of sediment movement at hydro facilities.

For more information on these technologies, contact Andre Zimmermann via email or at 604-980-6011.

Figure 1. Components of the autonomous, remote hydrophone system at Upper Lillooet hydro project

Figure 2. Screenshot of the results from analyzing the sound file developed by NHC for
remote acquisition and processing

Figure 3. Number of stone impacts recorded by the hydrophone before, during, and after the 17 May 2018 flushing at the Upper Lillooet hydro facility