Stanford Favors a Flood-Control Fish-Passage for Searsville Dam
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| Photoshop mashup of Searsville Dam and the Pope-Chaucer Bridge culvert. Searsville photo by Matt Stoecker. Culvert photo from The Other Side of Pope-Chaucer. |
Stanford announced that it has preliminarily chosen to cut a culvert at the bottom of Searsville dam as its preferred option for allowing steelhead to travel past the dam. If the flows exceed the capacity of the culvert, the dam will begin to back up water and reduce flood levels downstream. Searsville water contributes almost half of San Francisquito Creek's flow.
"The key question is whether – and how – the sediment can be moved downstream," McCown said. "The possibility of releasing the sediment downstream presents a unique challenge that we must continue studying to ensure that we do the right thing, especially for the communities located downstream of the dam. "Our preferred approach does not preclude the possibility of someday removing the dam. But we have to be confident we don't need the check-dam function and that removal wouldn't cause unacceptable impacts in the watershed."
The sediment, the result of the nature of rocks in the Santa Cruz Mountains, has been the key concern for committee members since their study began in 2011. The sediment is both fine and coarse. The fine sediment would likely flow to San Francisco Bay, nourishing salt marsh habitat. However, the disposition of the coarse sediment, which stabilizes the marsh area upstream of the dam, must be managed to minimize the potential to reduce channel capacity.
Menlo Park resident Jim Wiley, who lives near the creek, was cautiously optimistic, saying "this appears to be a win-win solution, balancing neighborhood flood-control benefits with a range of ecological concerns, including steelhead trout passage,'' he said. "However, we need a better understanding what will happen as 125 years of accumulated sediment passes through our neighborhood creek and is released into the Bay." From Stanford announces future of Searsville Dam by Lisa M. Krieger, San Jose Mercury News.
The history and status of this proposal is nicely summarized in Off Deadline: Searsville proposals muddy San Francisquito Creek flooding questions by Jay Thorwaldson, Palo Alto Weekly
"The Searsville Alternatives process now begins an intensive new phase of public and environmental agency review. This process will be rigorous, particularly since many questions remain and details need to be fleshed out. There will be many opportunities for public engagement, and shovels in the ground will be several years away." From Guest opinion: Keeping Searsville dam in place a good solution by Shani Kleinhaus and Lennie Roberts, published in both The Almanac and Palo Alto Online.
"The key question is whether – and how – the sediment can be moved downstream," McCown said. "The possibility of releasing the sediment downstream presents a unique challenge that we must continue studying to ensure that we do the right thing, especially for the communities located downstream of the dam. "Our preferred approach does not preclude the possibility of someday removing the dam. But we have to be confident we don't need the check-dam function and that removal wouldn't cause unacceptable impacts in the watershed."
Menlo Park resident Jim Wiley, who lives near the creek, was cautiously optimistic, saying "this appears to be a win-win solution, balancing neighborhood flood-control benefits with a range of ecological concerns, including steelhead trout passage,'' he said. "However, we need a better understanding what will happen as 125 years of accumulated sediment passes through our neighborhood creek and is released into the Bay." From Stanford announces future of Searsville Dam by Lisa M. Krieger, San Jose Mercury News.
The history and status of this proposal is nicely summarized in Off Deadline: Searsville proposals muddy San Francisquito Creek flooding questions by Jay Thorwaldson, Palo Alto Weekly
"The Searsville Alternatives process now begins an intensive new phase of public and environmental agency review. This process will be rigorous, particularly since many questions remain and details need to be fleshed out. There will be many opportunities for public engagement, and shovels in the ground will be several years away." From Guest opinion: Keeping Searsville dam in place a good solution by Shani Kleinhaus and Lennie Roberts, published in both The Almanac and Palo Alto Online.
Thanks for raising the issue. Unfortunately, the photoshop effort is far from what Stanford is proposing. This rendition shows a natural-bottom arch culvert which would not be employed with the dam due to issues such as undermining the footing. Stanford has proposed to build a circular or box type culvert with concrete bottom and highly engineered internal baffles or other type of fish passage feature. This also requires extensive and highly engineered channel construction both upstream and downstream to address the "firehose" suction and expulsion of water into and downstream of the hole during peak flows. Such a proposal has not been shown to be feasible or carried out before in similar federally listed Critical Habitat for steelhead and other species. Besides adequate fish passage, the proposal would have major problems with woody debris blockage within the hole, clearing sediment/debris, turbidity downstream, inundation of upstream habitat and "restoration" areas, and challenging and unproven safety modifications and rapid filling and draining pressure. If the dam can be removed safely, provide more flood protection benefits, and achieve a much greater level of ecosystem restoration and protection, why would we and the agencies accept this lesser and unproven option? Thanks for considering.
ReplyDelete-Matt
Thanks for the additional information on what Stanford is proposing. One point: the Pope-Chaucer bridge arch used in the mashup does have a concrete bottom as shown in the last illustration at http://2savetheoaks.blogspot.com/2014/10/the-original-popechaucer-bridge.html
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