April 5, 2021
Davis Open Space and Habitat Commission
Re: Proposal for habitat restoration/public access project along the South Fork of Putah Creek east of the City’s South Fork Preserve
I recommend that you approach the proposal with great caution and offer these questions and comments. There is no objection to weed control, riparian planting, and modification of water diversion methods. But the largest part of this proposal is to modify channel form, and that is of great concern. It’s been tried before on Putah Creek in Winters at great cost and great loss to fish and wildlife and riparian forest resources.
The stream channel filling and alteration part of this proposal is premised on these erroneous ideas about the existing stream condition:
On the contrary, the existing stream, floodplain and riparian habitat evolved naturally under the new water flow and sediment regime after the construction of Monticello Dam. A new channel and floodplains developed from within the old wider active channel, and evolved to a stable and functional form existing today, consistent with current post-dam flow and floods. It is supporting a healthy population of fish and wildlife. There are a variety of channel widths and depths, varying with the bed and slope, and the variety yields habitat diversity and resilience.
The idea that a stream should somehow be a 30-foot wide meandering stream is better fitted to a mountain valley setting, not here in the central valley. And the proposed stream narrowing will in no way revert the fish population from non-native to native. It will instead reduce open water habitat by 50% just by stream narrowing. I suggest you consult with a fisheries biologist such as Dr. Moyle at UC-Davis on the false idea that channel alteration will somehow bring native fish back to dominance.
There is one essential aspect of the proposed channel alteration to understand: A bulldozer does not build like flowing water does. Flowing water builds up horizontal layers of sediment, naturally sorted and stratified between fine and coarse layers. Bulldozers mix sediments rather than sort, and build monolithic and compacted fills. In the natural floodplain with a stratified floodplain, groundwater flows horizontally and easily through the coarse layers to sub-irrigate the floodplain. In the bulldozer-built floodplain, there are no coarse horizontal strata connecting the channel and the floodplain, and water flow is blocked. InWinters where the channels were extensively filled by a similar project, the floodplain trees died for lack of water, plantings died too, and 10 years later there are large areas of floodplain desert.
Bulldozer geomorphology destroys the natural anatomy of floodplains and blocks groundwater flow. Narrow 30 foot channels are not the “natural” form. The stream is healthy. Massive earthmoving will not improve it.
Jeffrey Ten Pas