Corps and Santa Paula Creek
- The US Army Corps of Engineers has been working this year to 'clean out' Santa Paula Creek, a tributary to the Santa Clara River. Flood control projects require the regular removal of sediment from the streambed and concrete channels. This project is the source of cobble for the Surfers Point Managed Retreat Project, set be begin soon.As the article below suggests, the pending approval of yet another large development project has the potential to further constrict this creek - increasing the flood risk in Santa Paula. It will also increase the taxpayer burden of constructing and maintaining flood control structures and 'bailing out' the future victims of flooding... Thanks to Alasdair Coyne for publicizing this issue!
Studies show high flood risk for S.P.
Saturday, September 25, 2010
Three new studies cast serious doubt on the adequacy of current flood protection provided by the Army Corps of Engineers for residents of Santa Paula, adjacent to lower Santa Paula Creek.
n A 2006 hydrology study of the Santa Clara River and its tributaries project that a 100-year flood in Santa Paula Creek will be 36 percent larger (from 28,000 cubic feet per second (cfs) to 38,000 cfs). The 2005 flood was an actual 27,500 cfs event.
n A 2009 Geological Society of America Bulletin, entitled “Sediment yield from the tectonically active semiarid Western Transverse Ranges of California,” describes annual rainfall and the sediment flows in the creek as the highest in the Santa Clara River watershed. Santa Paula Creek, and the lower Santa Clara River basin, produces 58 percent of the entire watershed’s sediment flow.
n A new study, now available to the Ventura County Watershed Protection District in draft form, but not yet available to the public, will provide further analysis of sediment movement in lower Santa Paula Creek.
It has already been disclosed that the sediment flow in Santa Paula Creek is greater than previous estimates, and that much of it is deposited on what is left of the creek’s original alluvial fan at the creek’s junction with the Santa Clara River, adjacent to the city.
In our last Keep Sespe Wild newsletter, we described how the Army Corps of Engineers proposed to construct a second fishladder at the upstream end of the channelized section of Santa Paula Creek, next to the one destroyed by the 2005 floods. This was to cost $7 million, which funds had to be committed by the end of the month.
River groups meet
In April, CalTrout, Friends of the Santa Clara River and Keep Sespe Wild wrote to California’s two U.S. senators asking them to oppose the construction of a second costly fishladder, which would also be at risk of being battered by boulders and filled with sediment.
The Army Corps of Engineers still wants to set aside funding for flood control on lower Santa Paula Creek. The funds will not be used to construct facilities. According to Dr. Josephine Axt, the Army Corps of Engineers chief of planning for the Los Angeles District, the funds will be used for “geotech work, hydrology and hydraulics, design, an environmental assessment, and a biological assessment for steelhead.”
In late July, CalTrout, Friends of the Santa Clara River and Keep Sespe Wild met with county of Ventura staff, including the head of county Public Works, Jeff Pratt, and Martin Hernandez, who works for Supervisor Kathy Long, as well as Dr. Axt.
The draft Santa Paula Creek sediment report, due to be released by the end of of this month, indicates that sediment would be deposited downstream of the concrete-walled flood control channel, causing flooding which would leave the Highway 126 access roads under five feet of water, and Highway 126 only 12 inches above the water level.
The development of additional flooding at this location will not occur quickly. Even though it is now established that the volume of flow in a 100-year flood will be 38,000 cfs (not 28,000 cfs, as previously estimated), the Army Corps of Engineers is not allowed to use this new, higher number in their planning, without federal legislation to authorize that change!
The Army Corps of Engineers will next prepare a general re-evaluation report on Santa Paula Creek, along with the county of Ventura. This will be part of their budget in fiscal year 2012, and then it will take from 2013-2015 to complete.
Alternative flood control needed
The only effective solution to a flood control hazard caused by the Army Corps of Engineers’ too-narrow flood channel for current and projected estimates of water and sediment flows in lower Santa Paula Creek, is to restore the former width of the too-narrow channel.
At the upstream end of the existing flood control channel, the east bank is set to be developed by Limoneira Co., as East Area One, with approximately one square mile of new homes and streets. But Limoneira’s environmental impact report failed to perform any analysis of the current flood hazard.
The increased volumes of both water and sediment now estimated for a 100-year flood event on lower Santa Paula Creek pose an immediate flooding threat to properties adjacent to the creek. If the channelized creek is to be widened to allow a larger volume of water and sediment to pass downstream, such an approach must be pursued while much of the northeastern creek barrier is still undeveloped orchard lands. If Limoneira builds right to the current, inadequate concrete channel, a flood disaster will be likely in a 100-year flood.
If Limoneira reduces the western, creekside edge of their proposal somewhat, to allow more channel space for water and sediment to pass downstream, the flood risk there will be lessened for existing development in the city of Santa Paula and the proposed Limoneira East Area One development.
Limoneira’s last hurdle for their East Area One development is to go before the Local Agency Formation Commission later this fall, to formally annex the East Area One property, currently county land, to the city of Santa Paula.
The worst-case scenario would be a 100-year flood shortly after a forest fire in the creek’s watershed. The National Marine Fisheries Service estimated in January 2010 that a watershed-wide burn would increase hillslope sediment delivery by a factor of seven.
The soundest long-term solution to this flood-hazard area is to allow more channel space for water and sediment to pass safely downstream. While it is not possible to restore Santa Paula Creek’s entire original alluvial fan, since much of the city of Santa Paula is built on it, the more space dedicated to the creek channel, the safer the residents of Santa Paula will be in a 100-year flood.
— Alasdair Coyne of Ojai is conservation director of Keep Sespe Wild.