Adobe Creek Collaborative Meeting
Hillview Community Center (Room A)
97 Hillview Avenue
Los Altos, California
Website:
6:30 to 8:30, Wednesday, February 15, 2006
Meeting Purpose
A.Update on status of project
Meeting Notes
1. Welcome and Introductions - [10 min.] Jitze Couperus
1.a, b, c, d, e
Jitze introduced Henry Louie, Director of Public Works for the Town of Los Altos Hills, who will be representing the Town at the Collaborative.
2. Project Update – [15 min] ACWG
Jitze suggested the District report be presented first to provide the background necessary for the residents’ update to make sense, and to avoid redundancy.
3. District Report - [report 45 min]
3.a.Small group meeting to discuss results of HEC-RAS analysis (1/23)
Tony reported that Susan, D.J., and Richard met with the District to go over the results of the HEC-RAS analysis of the revisions to Alternative 7 that Dr. Annable suggested, and to discuss the analysis of an additional alternative Dr. Annable is being requested to consider. In December, Dr. Annable had requested additional HEC-RAS analyses to be run and sent to him. The steering committee will be kept in the communication loop with Dr. Annable regarding feedback on the Alternatives.
3.bStatus of Dr. Annable's review of HEC-RAS analysis
Tony stated that Dr. Annable has as yet been unable to attend to the Alternatives because of his involvement with a grant due the middle of February. He indicated February 14 that he would be able to start work on the new Alternatives that week.
3.c.Field meeting to review site conditions for geotechnical review of project (2/8)
Tony reported that Susan and Richard attended a field meeting to review the geotechnical information for the project. Two reports are being used. One was prepared in 1999 and contains boring data from W. Edith to the Robleda storm drain taken along the Los Altos Hills side. The second report was the 1986 geotechnical report done for the Robinwood Pool property. The geotechnical staff reviewed the reports and came to the site to check field conditions and determine whether those two reports were still applicable. The staff concluded that the two reports are still applicable. They will now produce a memo evaluating the actual data and the plans for the project and provide a recommendation on how to proceed. Additionally, they will recommend how to retain the existing hardscape, primarily the gunite on the Los Altos side. They will also determine if additional evaluation of the existing hardscape is required. Once the memo is received it will be shared with the Collaborative.
Susan requested a summary of the revised Alternative 7 and the additional Alternative discussed at the small group meeting so that the people who were not in attendance would understand what Dr. Annable is currently evaluating.
Tony provided drawings of a representative cross section from each of the two Alternatives to illustrate the concepts. Dr. Annable’s first recommendation was to strike a constant slope from Edith to Foothill. The first cross section is what was devised for the stretch from Edith to the storm drain outlet by striking that constant slope. The HEC-RAS calculations were run using that cross-section. Some of the variables used to measure whether or not a cross section is stable are stream power, velocity, and shear stress. These were discussed at the January 23 meeting. The profile for the revision of Alternative 7 was available to be viewed after the meeting. The other alternative being considered involves reducing the slope of the bottom of the channel in the first 500 feet downstream of the Edith Ave. Bridge, and concentrating the drop structures in the downstream portion. The second cross section on the bottom of the page is associated with that alternative. It is based on the bankfull and two bankfull channels and uses side slopes angled at a one-to-one ratio.
Richard noted that the scales on the two cross section drawings were distorted, so the one-to-one slope is not visually apparent.
Bernice asked for the dimensions of the width of the cross sections measured between the red dots.
Tony interpreted the first cross section to be 20 meters or 60 feet in width. The bottom cross section looked to be 10 to 11 meters in width. These typical cross sections would occur between Edith and the storm drain outlet. Tony preferred to present the cross sections in connection with the profiles of their associated alternatives at a later time.
Beau summarized that Tony had run the models for both alternatives and provided that information to Dr. Annable. He is waiting to hear Dr. Annable’s comments on stability. The top cross section shows a wider top width and the banks look closer to an slope of one-to-one. The bottom cross section is narrower at the top, stays within the blue lines, but has a much steeper slope. Dr. Annable will come back with his comments on the two alternatives. The top alternative does not stay within the blue lines, but the bottom alternative does.
Tony thought Dr. Annable would be able to respond within two weeks. Either he would determine that the alternatives were acceptable as submitted to him, or there might need to be some back and forth to refine them to be acceptable. The models for both alternatives were run for several flow rates: 30, 500, 800, 1200, 1600, 2000, and 2400 cfs. There were 10 different flows altogether.
Libby wondered what volume of water the top alternative would carry, and what volume the bottom alternative would carry. The volumes appeared to be different to her.
Saeid clarified that the difference between Dr. Annable’s recommendation and Dr. Sen’s is that the top cross section contains 2400 cfs within the channel. That is the recommendation Dr. Annable was trying to look at; in order to contain all the flow and have safe energy, what kind of width is needed? It doesn’t really apply as one of the alternatives because it doesn’t recognize the constraints of this project. We are just trying to get the information from that situation to apply to the feasible alternatives.
Jitze explained that until recently the Collaborative had been focused on one number, cubic feet per second. In reality, we need to consider two numbers, the conveyance number and the stability number. To him, the conveyance number is how many cubic feet per second will flow down the creek before it starts to overflow its banks. Two years ago we all agreed we don’t need or want a 100 year solution. The stability number is different, indicating a flow below which the creek won’t get totally eroded or destroyed. It’s possible to have a conveyance number of a certain value completely different from the stability number. The stability number indicates whether the creek requires widening. The conveyance number indicates when the creek will overflow its banks. There may not be any relationship between the two. For each of them there is a range of numbers that can be discussed, either based on observations or analysis.
Saeid said that Dr. Annable’s recommendation was to stabilize the invert by maintaining a uniform slope from Edith to Foothill, and then to identify what width in the upper reach would be necessary to establish a stable channel. He would then take that information and use it in the analysis to come up with the preferred alternative.
Jitze stated that the stability was critical so that the creek wouldn’t be wiped out in the first three or four years. Having established the level of stability, then we can look at the conveyance, whether it overflows every five or ten years, and how that matches with the stability.
Tony said he’d like to talk about the detailed calculations of how he came up with the cross sections and what was sent to Dr. Annable after the meeting.
3.d.Small group meeting to discuss design flow criteria for preferred alternative (2/10)
Tony reported that the small group discussed what the channel should convey, and at what flow the channel should be stable. The risk considered was that if, for example, the 100 year flow is 2400 cfs, and we choose stability for a maximum flow of 2000 cfs, if a 2400 cfs flow occurs, what do we do? The group agreed on a design flow for conveyance of 1100 cfs for whatever alternative we choose, meaning 1100 cfs has to be conveyed within the channel. Other key criteria were that the same capacity as or better than what currently exists must be maintained throughout the project.
Richard clarified that 1100 cfs was presented down to the step pools, and then the number changed to 2400 cfs, which is the existing capacity.
D.J. added that Jason reconfirmed in writing that the project will not make any situation worse than what currently exists. Secondly, the 1100 cfs came from observed data. Over the past 90 years, the highest flow observed was estimated to be 1000 cfs. So the 1100 cfs is somewhat over that highest number.
Richard clarified that the 1100 cfs was the channel capacity of Dr. Sen’s alternative. Tony confirmed that.
D.J. reiterated that 1100 cfs is more than the creek has ever seen in the last 90 years. If we chose 800 cfs and we had experienced 900 or 1000 cfs a few times, then we would have a problem. 1100 cfs hasn’t been observed since 1920.
Susan confirmed that, as far as we know, that is true. She added that apparently Reaches 5 and 6 haven’t experienced more than 630 cfs.
D.J. said that the 1100 cfs applied only to the conveyance, and that the bank stability would be more than that, maybe 2400.
Tony said that with the alternative that is flatter in the first 500 feet and concentrates the step pools near the lower portion of the project, the channel is stable in the flatter section at 2400 cfs. The next step is to determine the stability of the channel in the cascading step pool section. The stability will be related to rock size. Determining a realistic rock size will be part of the process for determining that the channel will be stable at X flow and that it will convey X flow. Dr. Annable is aware that the community has agreed to limit the conveyance capacity to 1100 cfs. The streampower is related to the amount of flow to which the analysis is limited.
Richard asked whether the bankfull channel in Dr. Sen’s alternative was computed using 2400 or 1400 cfs to get the 15 foot sizing.
Tony said the bankfull channel is based on the reference reach in the Manresa area. There the bankfull channel is about 15 feet wide. Dr. Sen measured the flow for the bankfull channel. it is about 80 to 85 cfs. All the written reports size the bankfull flow to be about the 1.1 to 1.5 year event. 80 to 85 cfs falls within that range.
Saeid said the bankfull channel is about the 2.3 year event. It has nothing to do with the 100 year or 10 year events.
Susan asked if the bankfull channel was based on the statistical 2 year event or the observed 2 year event.
Saeid said it was based on the reference reach, which is what actually happened. The mark in the creek can be seen.
Tony stated that as a result of Dr. Annable walking the creek toward Foothill, he included a picture in his report that he identified as the prime example of what the channel should look like. That bankfull channel measures 15 feet. When Dr. Annable made his recommendation on the cross sections being evaluated, one of his key points was to not change the bankfull channel. That part of the design is fine. The reference reach is located near Manresa.
Henry Louie asked for the location of the 1100 cfs channel, whether or not the 1100 cfs refers to existing capacity, and for the return year to which it was equivalent.
Tony answered that the 1100 cfs refers to the proposed capacity of the new channel downstream of Edith Avenue, and that 1100 cfs is close to the 10 year flood event.
D.J. clarified that the 10 year event estimate is based on a computer simulation. Based on observed data, 1100 cfs is a much larger event.
Henry asked for the location of the 2400 cfs channel. He asked for clarification that the two cross sections presented were proposed cross sections.
Saeid said the existing capacity of the channel downstream of the stormdrain is 2400 cfs.
Tony said the cross sections presented will change after running more numbers and taking into consideration the recommendations Dr. Annable will suggest. The purpose of the cross sections is to provide an illustration of the work the District has done so far to develop the numbers that were sent to Dr. Annable.
David mentioned the significance of the blue lines in the development of a solution.
Richard suggested that Henry look at the website to review some of the more important background documents produced by the Collaborative.
Beau suggested that Henry meet for an hour with a couple of Collaborative members to come up to speed.
D.J. was puzzled as to why the bankfull channel would be based on the observed data, while the 1% event is being based on the computer simulation. Logically, one would think both quantities would be calculated using the same method.
Tony stressed that the bankfull channel was based on the reference reach. Walking the creek from Hidden Villa, past Manresa, all the way down to Foothill, the stable cross section of the bankfull channel is about 15 feet wide.
D.J. stated that taking twice the width of the bankfull channel and extending it toward the top of the creek would produce a dimension at the top different from the number calculated using the computer generated worst case scenario.
Tony said that that involves flow, which is different.
3.e.Project staffing, organizational structure, and schedule update
Tony presented the organizational structure of the project team. The big block of main importance is the QA/QC team, which includes a lot of other people who provide input on the project. The geotechnical staff, for example, is part of that team. Whenever particular expertise is needed in any department, that team can be drawn in. It’s a lot bigger section than it appears to be.
Susan asked for the difference between the line with the arrows and the line without.
Tony continued that the project owner, Beau in this case, puts together a project proposal. That’s why in the beginning Jason was working closely with Beau on all the details. Once the proposal becomes a project, based on funding, then it moves to the Capital Programs Services Division. Katherine leads that as Assistant Operating Officer. A Senior Project Manager is assigned to the project, in this case Saeid. Then the team is put together. The arrows indicate the owner and his representatives. The owner’s representatives come to the project meetings and report back to Beau on the status of the project. Tony said he works mostly with Saeid, and Saeid reports back to Beau. The two parts are the owner, and the Capital Programs Services Division, which actually does the project.
Tony added that Kristen O’Kane would be going on maternity leave in three weeks. Lee Ellis works on the budget and the schedule.
Saeid said the actual schedule is worked out among himself, Tony, and Katherine. QA/QC includes a lot a people, including Dipankar, who can be called on depending on what needs review: geotech, hydrology, hydraulics, or other areas.
Susan asked whether the role of QA/QC was to evaluate a product that had been produced elsewhere in the organization, or if QA/QC produced that product themselves before reviewing it.
Tony said that in Dipankar’s case, his role extended beyond QA/QC, but that Dipankar’s function fell within QA/QC in the organizational chart.
Saeid said hydraulics and hydrology are specialized fields, and those teams act as consultants. The project team goes to them as experts when they are needed.
Jitze summarized that in addition to QA/QC, a bubble should be shown on the organizational chart labeled “talent pool”.
Beau added that Dipankar became engaged in this project because he had a separate project looking at the practice of geomorphology and how it could be integrated into maintenance. He conferred on this project while charging to that other project. He is associated with that other project and acts as advisor to this one. There are other capital projects also using this methodology and being evaluated as less than 1% flood protection projects. As needed, the project team uses hydrologist, geologist, legal, and real estate groups. They have hours budgeted for this project. The core team stays on the project. Saeid has eight other projects for which he is responsible. The QA/QC group doesn’t work on the project as it’s being put together. They are there to critique the quality of the project and send it back to the project team. The team then makes adjustments before it moves forward to the next stage. The typical key stages are the draft EIR, final EIR, Engineer’s Report, and 30%, 60%, and 90% reviews. All of those go through QA/QC for comments. With this project, the smaller pieces are being released that haven’t gone through the full QA/QC process. The Collaborative process disrupts the normal flow of the project. The review by Dr. Annable has been added as QA/QC on this small piece. The usual QA/QC wouldn’t review these individual pieces. They wait until the whole package is put together.