PNNL

Abstract

As part of phase I of the EED LDRD project \#85141, Characterizing Clallam Bay for Wave Energy Device Testing, PNNL staff performed on-water survey work collecting water velocity measurements in Clallam Bay in May 2025. Clallam Bay is a semi-sheltered bay on the northern coast of the Olympic Peninsula being considered for marine energy device testing, wave energy converters in particular. This work utilizes the existing PNNL programmatic permit authorizations in the area from consultation with regulatory agencies and the Makah Tribe. The goal of this survey is to measure the spatial variability of water velocity across a broad swath of PNNL’s permitted zone. This information is useful for understanding the spatial hydrodynamics of the area, how it relates to the local bathymetry, and to inform the design of equipment for future studies. The secondary goal of this survey is to determine, based on the velocity distribution, the best zones to deploy the ADCP, a hydrophone, and an anchored Spotter wave buoy in phase II of this project. From the collected survey data, it was found that flood tide currents are short and swift, while ebb tides are slower and longer lasting. Slack water is nearly nonexistent; rather, ebb tide currents increase and decrease in speed in a single cycle. This results in a flood tide that is a progressive wave and a double ebb tide that is approximately a standing wave. Spatially- and depth-averaged flood tide currents peak at 1.3 m/s and are nearly continuous across the survey area. These currents generate localized areas of sand dunes, observable in bathymetric data provided by NOAA. During ebb tide, the underwater ridgeline extending offshore from Slip Point generates a ~0.9 m/s jet that dissipates across the bay, slowing to 0.3 m/s at the western side of the survey region. The presence of a strong flood current complicates the design of floating platforms in Clallam Bay, as these platforms must have enough buoyancy to counter the drag exerted on mooring systems, while the mooring system itself must be designed with enough compliance to not compromise platform stability in rough seas.