Agenda Date: 11/10/97 Group: Project Development

Zone: NW Project No. 102109 Name: Matadero and Barron Creeks (Palo Alto)

SUBJECT: Interim Remediation Plan to Provide Flood Protection for Matadero and Barron Creeks

RECOMMENDATION:

After consideration of all suggestions and new alternatives identified at the public meetings, staff recommends that the Board approve Alternative 3 as the interim remediation plan to provide 100-year flood protection on Matadero Creek and 20-year flood protection on Barron Creek.

RATIONALE:

On October 7, 1997, staff reported to the Board about the status of the Matadero Creek Letter of Map Revision and proposed interim remediation measures to provide the best interim flood protection on Matadero and Barron Creeks (Attachment 5) for this coming rainy season. The Board directed staff to inform the public, through public meetings, about the status of the project's level of flood protection and the Letter of Map Revision and seek input on the alternative interim measures. Staff conducted two public meetings with the residents living within the areas affected by Matadero and Barron Creeks and received numerous suggestions and responded to questions. Staff has now completed the review and analysis of these questions and suggestions, along with the consideration of the five alternatives previously developed. The purpose of this agenda memorandum is to summarize staff's responses to the residents' suggestions, present results of the alternatives analyses, and request the Board's approval of a recommended interim plan to implement prior to the coming winter season.

SUMMARY:

As directed by the Board on October 7, 1997, staff conducted two public meetings to inform the residents about the status of the project's level of protection, the Letter of Map Revision, and the interim measures to be taken prior to the rainy season. The first public meeting was conducted with the residents in the vicinity of Barron Creek on October 15, 1997. An additional meeting was held on October 16, 1997, with residents in the Matadero Creek area. In these meetings, staff informed the residents of the status of the project's Letter of Map Revision and the current level of flood protection provided by the recently improved Matadero and Barron Creeks, which provide a significantly improved level of flood protection as compared to preproject conditions.

Matadero Creek is now protected at 50-year level compared to a 13-year level under preproject conditions. Barron Creek has an increased flood protection from a 4-year preproject level to a 100-year current level of protection. Staff explained that the District's goal was to achieve a one percent protection, and learned that this was not achieved. The District currently has a 50-year protection on Matadero Creek, which can cause induced damages if a 50-year flood event is exceeded, and a 100-year protection on Barron Creek. To demonstrate the difference between a 50-year event and a 100-year event, the attached cross section (Attachment 4) of Matadero Creek approximately 100 feet upstream of Waverly Avenue shows a difference of nine inches of water which is a one percent chance of having an average of nine inches height of water above the current 50-year water surface elevation in the channel.

As discussed with the Board on October 7, 1997, the five alternatives for interim remediation were also described in detail to the residents with respect to the pros and cons, level of flood protection, and the number of homes potentially at risk for each alternative. A number of very good suggestions and concerns were raised during the discussions with the residents. The following summarizes, first, proposed actions and responses to the questions and suggestions made at the public meetings and, second, staff's analysis of the proposed alternatives and the recommended alternative for interim remediation for this coming winter season. A list of the questions and suggestions raised by the residents is shown in Attachment 1 for the Board's information.

I. Proposed Actions and Responses to Suggestions

In response to several comments and suggestions received from the public meetings, staff has taken several steps to implement appropriate actions and programs. Numerous suggestions have also been carefully evaluated to determine their viability as interim solutions. Some suggestions could not be implemented in the time available, but will be considered for the long-term solution.

In response to several suggestions made to perform creek cleanout work, the District's maintenance staff has removed flow blockages, such as sediments, vegetation, and debris, along Matadero Creek between Alma Street and Greer Road to maintain the channel at its maximum capacity. Recent maintenance work has been completed on Matadero and Barron Creeks, including vegetation removal from the Matadero Creek floodway downstream of Highway 101 for approximately 500 feet, and vegetation cutting and stomping between Highway 101 and Greer Road. The District has also worked with the land owners of the properties at Hillview Avenue to reach an agreement for them to maintain the creek adjacent to their property. This work will be completed by December 1997.

Additionally, the Barron Creek culvert between El Camino Real and Laguna Avenue was inspected and found to be free of blockages or defects. Also, Barron Creek was inspected jointly by the City of Palo Alto (City) and the District between Laguna Avenue and Gunn High School. Some vegetation will be removed by the City's maintenance crew.

Another suggestion was to allow local participation in flood fighting. The District has asked for participation from local resources such as residents and the City to alert and keep the District informed of any flooding problems as they appear. Staff gauges and the District phone number will be placed at selected bridges between Waverly Avenue and Greer Road on Matadero Creek to assist residents in reporting flood events at these bridges during this storm season. Signs with the District phone number will also be installed at the bypass basin, at Laguna Avenue crossing Barron Creek, and at the diversion of Matadero Creek. Staff gauges with reflectors for night viewing have been placed at the sediment basin, the Laguna Avenue trash rack, El Camino Real along Barron Creek, and at the Laguna Avenue crossing of Matadero Creek.

In response to concerns regarding the District's ability to respond quickly, additional maintenance and other District staff will be assigned to monitor and patrol the creeks to respond to the flood events this winter. The District will continue to monitor the status of debris and sediment and maintain good conditions.

Additionally, sandbag booklets to assist the residents on how to use the sandbags will be placed at all sandbag sites for pickup. The District is setting up “How to Use Sandbags” workshops for those who are interested. All residents are invited to attend these workshops. There are two sandbag pick-up sites established, one located at Herbert Hoover Elementary School and the other at the right side of the Palo Alto Airport Administration office on Embarcadero Road. Staff also recommends setting up flood proofing seminars as an extra effort to provide flood proofing information to interested residents.

In response to a resident's suggestion, hand tools will be loaned by the District to interested residents for their participation in debris removal. District employees will not be used to perform this work since the District does not have an easement or right of way between Gunn High School and the trash rack at Laguna Avenue on Barron Creek. To address this limitation, on November 4, 1997, the Board directed staff to work with private property owners for permission to remove trees and other debris that could impact the creeks, and if unsuccessful, to seek enforcement of a District ordinance that requires property owners to maintain creeks. Presently, staff is working overtime and using the San Jose Conservation Corps and James Boys Ranch to supplement District crews to clean up creeks throughout the County. The Board's guidelines will be followed in these situations.

Finally, a few residents suggested that the District purchase or reimburse homeowner's flood insurance for their property. This is not being recommended since the project is essentially an incomplete project at this point, and the District does not have provisions to purchase private property insurance for the homeowners in this circumstance. Purchase of flood insurance is the homeowner's responsibility. The District would provide information about flood insurance to homeowners upon request.

II. Alternatives Analyses

As discussed previously, staff has added three new alternatives to the five that were discussed with the Board on October 7, 1997, in response to suggestions by residents. A total of eight alternatives are presented in the attached Matadero Creek Interim Fix Alternatives table (Attachment 2) for the Board's consideration to implement as interim measures for this coming winter. The alternatives were evaluated based on constructibility, time constraints, technical feasibility, probability of flooding, health and safety, costs, and space availability.

One primary principle considered when evaluating the alternative methods of operating the flood control project for the 1997-98 storm season is that the District should seek to avoid introducing a risk of flooding to properties that were not threatened by a flood event before the project was constructed. Allowing a District funded project to threaten flooding on properties not previously at risk is inconsistent with District policy, its mission, and constitutional principles governing the taking of property for public use. In order to achieve the District mission to protect life and property from flooding, the District avoids operating in a way that induces damages on previously non-flood hazard areas. The exception is when there is a determination that there is a public need and necessity which requires the condemnation or purchase of private properties. The legal process to acquire property requires extensive time. This guiding principle is one of the key criteria considered in staff's recommendation for the interim plan.

As suggested by some residents, an additional column has been added to Attachment 2 showing a ‘weighted risk factor' for each alternative indicating the probable number of homes at risk of being flooded divided by the particular return period of the flood event that causes the risk. For example, for Alternative 1, there are 3,020 homes at risk of flooding during the 50-year event.

To help put the various flood events in perspective, Attachments 3 and 4 are a chart and a typical cross section showing the relationship between the flow rates in cubic feet per second and various flood events on both Matadero and Barron Creeks. The 1983 El Nino was a 17-year event which generated 2,100 cubic feet per second flow at Louis Road on Matadero Creek.

Alternatives 1 and 5 would provide Barron Creek with a 100-year flood event protection while providing Matadero Creek with a 50-year protection. However, they are not recommended because both would create flooding on new areas and pose health and safety risks for the residents on Matadero Creek.

Alternatives 2 and 3 reduce potential public health and safety threats and avoid flooding on new areas for the entire project area. Alternatives 2 and 3 would provide a 100-year protection for Matadero Creek while providing a 20- and a 5-year protection on Barron Creek, respectively. Induced damages may result on Barron Creek if the 20- or 5-year flood event is exceeded.

Alternative 4 would regulate the diversion flow in such a way that both Matadero and Barron Creeks will have an equal level of flood protection at approximately a 70-year level. This alternative would provide balanced protection for the two creeks, and it would cause flooding on new areas on Matadero Creek if the 70-year level flood event is exceeded.

Three additional alternatives, Alternatives 6 through 8, were identified and analyzed as a result of the two public meetings and are listed in Attachment 2. Alternative 6 is to fully or partially block the flows from Stanford Channel which has been historically draining its 200 cubic feet per second flow to Matadero Creek prior to the project. The goal would be to increase flood protection by allowing more flow diversion from Barron Creek to Matadero Creek with Matadero Creek protected at a 100-year event level. By restricting the Stanford Channel flow diversion, Barron Creek's level of protection will increase to somewhere between a 20- to 70-year level. However, induced flooding may result on more than 200 new properties adjacent to Stanford Channel which were not previously subject to flooding. In light of an increased public health and safety threat and placing new areas at risk on Stanford Channel, this alternative is not considered viable.

The goal of Alternatives 7 and 8 is to provide a 100-year flood protection on both Matadero and Barron Creeks.

Alternative 7 proposes either removal of the Louis Road Bridge or pumping the excess flood water to bypass the bridge and thus avoid pressure flow that causes sudden rising of water at other bridges located upstream. Some local flood relief may result from the bridge removal or a pumping bypass system. However, flooding of new areas at the Waverly Avenue Bridge still would likely exist since other hydraulic factors besides the Louis Road Bridge contribute to limiting the capacity of the channel. Removing the bridge would also impact the existing utilities that are very costly to relocate, as well as adversely affecting traffic patterns in the surrounding neighborhood.

Alternative 7 also considered attaining the 100-year protection by pumping water around the reach of channel with inadequate capacity. This would require pumping over 140,000 gallons of water per minute (equivalent to about 300 cubic feet per second) with six 150-horsepower pumps and three 30-inch diameter pipelines 2 miles long to bypass the excess flood water over all the bridges from Waverly Avenue to the San Francisco Bay. This is impractical and would not be able to be implemented within the interim period, and it is cost prohibitive.

Alternative 8 proposes installation of a temporary sandbag levee system to fill the inadequate sections of the levees and bridges to provide a 100-year level of flood protection for Matadero and Barron Creeks. Employing the sandbagging technique for flood proofing is only proven effective in a relatively minor scale of repair, such as local shallow flooding. It would be required to sandbag over several thousand feet of inadequate levees with up to 7 feet in height with limited space available on top of the levees. The width of levee between Louis Road and Middlefield Road on Matadero Creek ranges from 1 to 12 feet. Constructing a 6-foot high sandbag levee with 1? to 1 slope requires a base width of 19 feet. Due to these constraints, constructing a safe and stable sandbag system is technically unachievable.

An additional suggestion made at the meetings was to attempt to balance the depth of possible flooding between the two creek areas. This suggestion was not analyzed and is not feasible to implement in the short term because of the complex and time consuming nature of such an analysis and the extensive surveys needed to determine its viability. Moreover, depth of water is nonuniform and varies from area to area. For instance, in the area behind the railroad near Alma Street on Matadero Creek, the water typically reaches 2 to 3 feet deep as opposed to other areas in the floodplain where the water can be released and spread out. The only available information is the Flood Insurance Rate Maps by the Federal Emergency Management Agency that illustrate the depth of flooding only for a 100-year flood event.

One last suggestion was made to consider incorporating the capability of switching between alternatives during an event. Due to the unknown and unpredictable rainfall intensity, storm events, locations and timing of the flow peaks, and lack of response time to implement the switch of an alternative, this suggestion is considered unachievable.

In view of the above discussion of the alternatives, staff concluded that Alternative 3 is the most viable solution for the interim remediation as it avoids potential flooding on new areas for Matadero Creek and provides the highest level of protection with the lowest probability of being flooded as illustrated in Attachment 2. In addition, flood proofing seminars can be formulated at the Board's approval to educate the residents on how to improve and protect their properties against flooding.

At the Board's direction, if Alternative 3 is selected, the installation of the diversion flow blocking panel structure can be completed within a few days following the Board's approval. The estimated cost to complete this work is approximately $3,500.

FINANCIAL IMPACT:

The cost of implementing the recommended interim remediation will be from the funds budgeted in the 1997-98 capital budget for the Matadero Creek Letter of Map Revision project. The estimated costs, including the diversion flow blocking panel structure for the recommended alternative and to provide sandbagging workshops, are approximately $5,000. The flood-proofing seminars will be formulated if the Board approves it. The estimated cost is approximately between $10,000 and $15,000.