The County of Del Norte obtained funding for the project through the California
Department of Fish and Game’s Grants Program and through the California
Coastal Conservancy. Winzler & Kelly Consulting Engineers and Michael
Love & Associates were selected to develop a design suitable for the
site.
The County maintained stream crossing on Peacock Creek was a severe barrier to all salmonids. The crossing consisted of a steep and undersized culvert that was perched about 3.5 feet above the downstream channel. Physical site constraints included 7 feet of vertical drop over 80 feet of channel length, water intake wells approximately 70 and 110 feet upstream of the existing culvert inlet, State Parks land immediately downstream, the CalTrans Highway 197 road prism adjacent to the site, and another CalTrans culvert only 400 feet upstream. Although the upstream culvert currently provides passage, any headcutting and incision of the downstream channel could make the crossing a barrier and risk structural failure of the crossing. These constraints necessitated an alternate design solution.
The resulting design is a fishway resting on concrete strip footings connected by struts, allowing an open bottom structure. An innovated concrete “vortex weir” design is used with the intention of creating ideal conditions for upstream migrating juvenile salmonids. This weir shape also allows for the fishway to function over a wider range of flows and will better concentrate the plunging flow to increase scouring and avoid having the pools fill with sediment. The vortex weirs are 20 feet wide and spaced 10 feet apart, with 8 inch drops over each weir. To ensure that the downstream end of the fishway remains backwatered by the channel, a downstream boulder grade control weir was built into the channel bed. Observations were made throughout its first winter of operation, which included a flow exceeding bankfull. Qualitative results show good flow patterns over the vortex weirs, and resting pools remain sufficiently scoured.