From: <Bobgmoss@aol.com> Subject: Flood Dangers, Matadero & Barron Creeks Date: Sun, 12 Oct 1997 13:16:17 -0400 (EDT) Message-ID: <email@example.com> To: bpa@Sunset.AI.SRI.COM (current address: firstname.lastname@example.org) cc: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
Flood Control Issues - Barron & Matadero Creeks
Bob Moss - Chair, BPA Creeks Committee
As reported previously, the flood control projects in Barron Park and just downstream were designed and built correctly. They do in fact provide protection against a 100 year flood for all of Barron Creek, and for Matadero Creek down to about Alma. Below there protection on Matadero Creek is only a 50 year level. There are 5 options for corrective action from SCVWD staff. Presently we are in Option 5 - do nothing. The staff recommendation is Option 1 - reduce the amount of water diverted from Barron Creek into Matadero Creek, resulting in increased protection to the 100 year level on Matadero Creek, and reduced protection to 20 years on Barron.
The problem is the bridge at Louis which is not high or wide enough to allow 100 year water levels to pass. Flows greater than about 2900 cfs cannot go under or around the bridge. That is slightly less than a 50 year event (50 years at the Louis bridge = 3060cfs, 100 years = 3500 cfs). Therefore the water will surge back upstream until the high water reaches Waverly, where it will break over the flood walls with great force and flood the area from Waverly to 101. The concerns at SCVWD about this overtopping at Waverly are 1) properties flooded by such an event are not on the flood hazard maps now, so SCVWD could be accused of making a previously safe condition unsafe. 2) if there is an overtopping and breakout at Waverly it will be sudden and violent, occurring in a few minutes and dumping 500 to 600 cfs onto the streets. This kind of flow is considered a safety hazard as well as a flood hazard. 3) About 3000 homes are threatened by a 50 year flood from the inadequate bridge at Louis vs. about 1000 homes (all in Barron Park) threatened by a 20 year flood on Barron Creek. Thus the staff proposal to approve Option 1, and increase the probability of Barron Creek flooding in exchange for reducing the probability of Matadero Creek flooding.
We made a number of suggestions and proposals which greatly reduces flooding risk from Barron Creek, and still increases protection to Matadero Creek. Barron and Matadero are very different creeks with respect to both capacity and rate of rise and fall during storms. Barron Creek rises and falls very rapidly, in minutes compared to Matadero which rises and falls over hours. Modification of the operation of the Barron Creek diversion gates at the Gunn settling pond should be done so that the amount of water diverted may be adjusted as required. That can give 70 year protection or better for both creeks. Greater levels of protection, up to the 100 year flood, are possible if the 2 streams are managed to optimize flow diversion. This is a variant of SCVWD staff Option 2.
It is important to understand that the difference between 100 year flood protection (760 cfs at Foothill) and 20 year flood protection (460 cfs at Foothill) for Barron Creek is about 300 cfs. The same 300 cfs on Matadero Creek at Louis is the difference between about 50 year (3060 cfs) and 70 year (about 3250 cfs) protection. Greg Zlotnick and the BPA representatives noted this significant difference in risk at Barron Creek for a relatively small difference in flow on Matadero Creek. It is hoped that the combination of varying flows and rates of rise in the 2 creeks, plus the differences in sensitivity to changes of a few hundred cfs in the 2 creeks will provide a solution which protects both creeks as much as reasonably possible. An adjustable diversion gate at the Gunn settling basin tied to upstream creek flow gauges will provide the best chance to balance flows between the 2 creeks without creating disproportionate hazards to either creek.
Installation of stream flow gauges and flood warning devices on Matadero and Barron Creeks is not a new idea. The BPA applied for a $20,000 Federal grant for this purpose in 1984-85, but it was denied.
Installing stream flow gauges creates potential problems with State Fish & Game and Federal Wildlife organizations because of possible impacts on the Red Legged Frog. A full investigation of frog impacts could take months and effectively prevent any actions this rainy season. Greg Zlotnick noted that this is a situation that is best addressed by our elected representatives since it is their job to remove bureaucratic impediments.
Another suggestion was to design any diversion blockage so that the maximum possible flow goes into the bypass tunnel, and only the highest flows would be blocked and flow down Barron Creek. SCVWD staff seemed willing to accept this proposal.
Both SCVWD and Public Works will provide greater than usual levels of service to Palo Alto to try to minimize damage. Glen Roberts, Director of Public Works, made it a point at the SCVWD Board meeting to ask for additional sandbag sites, more sand and sandbags, and rapid response to remove any trash or debris in creeks which might interfere with flows. At the Friday meeting this was expanded to include perhaps pre-filling some sandbags, and having organizations such as CCC and Scouts do sandbagging for those who are unable to do it themselves such as seniors, physically handicapped, etc. The BPA will try to identify those who would need assistance, and provide lists of those needing assistance to Public Works and SCVWD, as well as other possible helpers. Neither Public Works nor SCVWD will commit to providing such help directly, but they can work with others such as CCC and Scouts to help with sandbagging.
We also requested tools such as grappling hooks and poles to aid in removal of debris from creeks, especially the trash rack at Barron Creek and Laguna. SCVWD will provide the tools to us for this use.
Public Works agreed to aid in removal of several stumps in Barron Creek, and to be available for assistance during storm events, as a supplement to SCVWD crews. This arrangement has been effect for years and appears to work quite well.
We also proposed use of temporary flood walls such as inflatable tubes, sandbags, plywood barriers, or any other practical method of providing high enough capacity to contain high flows in Matadero Creek. SCVWD has used the inflatable tubes on San Francisquito Creek, but had 2 of them vandalized at a cost of $16,000. They are reluctant to risk the same fate on Matadero Creek. Also, blockage of overflow at Waverley can cause flooding at other streets such as Cowper and Ross, so those areas also would need some protection. SCVWD staff will re-evaluate this option to see how practical it may be. If the inflatable tubes are used it may require commitments from nearby residents to watch them and work to prevent any vandalism. They of course will be motivated since if the tubes are vandalized and fail to prevent flooding, those neighbors would be most at risk.
The long term solution to the undersized capacity at the Louis Bridge is to change the size and shape of the channel from angled walls to vertical walls. This design is used on Adobe Creek, and can be seen at Adobe Creek and Charleston, Louis or Meadow. SCVWD staff estimates that the work can be completed before the 1998-99 rainy season, so the risk should exist only for this year.
Some general comments about the meetings next week at Rickey's Hyatt at 7:00PM Wednesday and the Holiday Inn 7:00 PM Thursday. While it is understandable if people are upset and frustrated, bashing SCVWD staff is not necessary. They have been bashed adequately already (SCVWD Directors were not amused by the screw-up) so it would be more productive to adopt the posture taken by the BPA Board, and try to fully understand the existing situation, look at the options offered at this time, and be willing to suggest other practical short-term corrective actions. Then we all will have to decide what balance of risks we are willing to accept for the overall good of the entire community, and make our desires known to SCVWD.
I look forward to seeing the meetings next week.