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Off Deadline: Searsville proposals muddy San Francisquito Creek flooding questions

 

After an exhaustive multi-entity review of what to do about the Searsville Dam and the mostly silted-up flood plain behind it, Stanford University has proposed a compromise to resolve the longstanding dilemma of what to do about the dam.

There has been a strong push by the group Beyond Searsville Dam to have the dam removed entirely, citing environmental damage to fish and other factors.

And there is an equally long-running concern about downstream flooding every decade or so of San Francisquito Creek, even though it's a bit odd to be discussing floods in flatland Palo Alto, Menlo Park and East Palo Alto during the middle of a major drought.

The dam and the flooding potential of the "volatile" creek are inextricably linked, as the dam's existence has provided some slowdown of the surge of water coming down from steep, short canyons during heavy rains.

The volatility of the creek can sometimes be measured in hours, from a mere trickle to surging whitewater threatening to spill over into residential areas of the three downstream communities. I have personally witnessed the surge a number of times when I resided in The Willows area of Menlo Park and reported on the bitter feelings between the cities when they each were accusing the others of trying to unilaterally raise banks on one side or the other of the creek.

The latest big overflow in 1998 sluiced through north Palo Alto neighborhoods on its way to flood lowlands Palo Alto with several feet of muddy water, causing about $28 million in damage, endless complications with insurance and repairs, and hard feelings all around. In this case, the overflow was at the infamous Pope/Chaucer Street Bridge separating Palo Alto and Menlo Park. Demands to remove the bridge reached a crescendo, along with some lawsuits.

But had the bridge not been there, there might well have been serious flooding into Menlo Park and potentially deadly flooding into some really low areas of East Palo Alto, where water from a levee break could reach a reported 8 to 10 feet deep — drowning depth.

There were a reported 17 "overtoppings" of the creek's banks in addition to the big one at Pope/Chaucer.

Creek anecdotes abound. There was a flood precipitated by heavy rain in the mid-1950s, during which the late Dr. William Clark — en route at night to aid a patient having a heart attack — drove into an icy 3-foot-deep pond in the then-new Oregon underpass at Alma Street. Dr. Clark waded away from his stalled car. The patient died.

Circa 1970 then-City Manager George Morgan was up in the early hours actually helping crews use poles to push tree trunks through the too-small arch opening at Pope/Chaucer Street Bridge.

Along the way, Santa Clara County raised creek banks and built low concrete walls along lower areas of the creek, which helped prevent some floods over the decades. But the patchwork wasn't enough for 1998 and falls far short of protecting against a proverbial "100-year flood" — a misnomer, as it actually means a flood that has a 1 percent chance of occurring in any year. Well, maybe not a drought year.

The 1998 flood was just a "45-year flood," a relative trickle compared to a 100-year flood.

The 1998 flood prompted creation of the Joint Powers Authority for the creek in 1999 by the three downstream cities and San Mateo and Santa Clara counties, resulting in the unpronounceable SFCJPA shorthand.

Its first executive director, Cynthia D'Agosta, helped forge the agency and supplant some of the harder feelings and suspicions between the communities. Her prior experience with the about 100 entities along the Los Angeles River (famous for chase scenes in movies) helped with the thorny challenge, but slogging through federal, state and regional water-related agencies proved tough.

When current director Len Materman took up the challenges, he focused successfully on getting a local funding package put together with contributions from the five agencies represented on the JPA's Board of Directors. The package will pay for major projects — including replacing the Pope/Chaucer Street Bridge! — from Middlefield Road out to the baylands.

He also has pushed hard to move a federal study along relating to the creek's volatility, which would be severely worsened if the surge occurred during a high tide. Results of that study may still be years off, but it's continuing.

But what does all this have to do with Searsville Dam?

A lot. Stanford University is the largest landowner along the creek's watershed, including the Searsville Lake area, now referred increasingly as the Searsville Reservoir — part of Stanford's Jasper Ridge ecological study area.

Yes, the dam and flood plain behind it do play a role in reducing the downstream volatility of the creek, chiefly by creating a slowdown of the surge while water flows away downstream.

Stanford's plan, outlined in a 41-page report, is to stop short of removing the dam through two methods. What to do with the silt is a huge concern, being debated vigorously in online comments on the story.

Stanford officials say their proposed alternatives would not make potential downstream flooding worse. Some add-on alternatives, such as creating large overflow areas upstream, could cost millions of dollars.

But not making things worse may not be enough for the SFCJPA agencies.

Materman said in a telephone interview that some outside funding for upstream improvements would be likely when the federal study is completed and a comprehensive program adopted.

Such funding would not be likely unless there were some real improvement in the flooding risk, he indicated.

Former Weekly Editor Jay Thorwaldson can be emailed at jthorwaldson@paweekly.com and/or jaythor@well.com. He also writes periodic blogs at PaloAltoOnline.com.

Comments

Like this comment
Posted by resident 1
a resident of Adobe-Meadow
on May 8, 2015 at 8:43 am

Thank you for providing more Palo Alto specific data to this topic which as you have noted is being discussed in another thread.
It needs to be noted that bayland assets - the baseball park, golf course, and PAO are directly aligned with the flood channel at the bottom end into the bay.

The PAO is now owned by the city as an enterprise effort which records profit and loss specific to the airport operations. You all will note the number of planes that are housed at PAO. If responsible action is not carried through here then I am sure that a legal action will occur.

Action - or LACK OF ACTION - will be duly noted.

Other city related actions are clearing of the growing amount of vegetation in the creek, as well as broken tree parts - all of which will create the "beaver dam" effect in a climatic trauma. Those parts move down to the bridges where they catch and create flooding.

The Adobe Creek has been overhauled and works very well, and is regularly cleared of growing vegetation. That is important with the tunnel under the highway open - you can see the build up of vegetation that needs to be skimmed from the tunnel channel waterway.

Foe those that walk the baylands at the end of San Antonio Road you will note that Mountain View has many deep water collection areas so that in the event of high tides there are water catchment areas. They are good planners for their Shoreline Park area.

It is hoped that the City is actively engaged in this planning activity. Yes we have commissions, etc. but I do not think they have fiscal responsibility in the event of a crises - possibly they do - not sure on that. I think what is missing in this whole equation - who is on the hook for what in a crises.


Like this comment
Posted by Rain-Rain-Go-Away
a resident of Another Palo Alto neighborhood
on May 9, 2015 at 10:16 am

> The 1998 flood was just a "45-year flood,"
> a relative trickle compared to a 100-year flood.

Statements like this are meaningless unless the actual rainfall data, and the analysis of the data, can be provided. It is a shame that the author did not provide the source of his 45-year claim (possibly the USGS?).

When engineers/scientists do a rainfall/flood analysis trying to make an estimate of what the rainfall/flood levels would be for the elusive 100-year storm, they typically use some sort of regression scheme to convert the random rainfall/flood level data into a model that offers a simple linear equation that can be used to make predictions beyond the range of the data available. While it is possible that in a given situation a 100-year rainfall/flood level might be twice as much as a 45-year rainfall/flood level—it is much more likely to not be the case. The 100-year value will necessarily be greater than the 45-year value, but each situation is different and no generalizations can be applied.


Like this comment
Posted by resident 1
a resident of Adobe-Meadow
on May 9, 2015 at 11:37 am

I believe that the Insurance industry has already worked those numbers - that is why people in the lowlands of PA - defined as below El Camino Blvd. have 100 year flood insurance. It is a requirement of your mortgage. And you need to be registered with FEMA. I think all of the work has been done on this already. Call your insurance agent - make him work for his money.
The Bottom line is that you are required to have flood insurance whether it rains or not.


Like this comment
Posted by Rain-Rain-Go-Away
a resident of Another Palo Alto neighborhood
on May 9, 2015 at 12:06 pm

> The Bottom line is that you are required to have flood
> insurance whether it rains or not.

True for federally insured/backed mortgages, but not other money sources, unless so specified. Probably a good idea, although the cost could come to $30K-$50K over the life of a mortgage.

If the extent of the flood plain were to be reduced via work on the Creek, then people no longer in the flood plain would see the need for this flood insurance go away.


Like this comment
Posted by Matt Stoecker
a resident of Another Palo Alto neighborhood
on May 28, 2015 at 1:48 pm

Thanks Jay.

I agree that funding (and permitting) will be more likely if the eventual project shows a net benefit to flood protection in the watershed. The same can be said for the proposed project showing a net benefit for ecosystem health, and in particular star and federally listed steelhead restoration. For these reasons, we believe that the proposed plan to leave the dam with a hole in it will not generate enthusiasm to either fund or permit the project. However, we believe this announcement from Stanford signals that dam removal is closer at hand than ever before.

On the flooding front, it is import to note a few things: 1) The dam is currently causing flooding of private residents upstream of the reservoir in Family Farm / Woodside and this will get worse as more sediment is trapped over time. 2) The ongoing presence of the dam (even one with a hole in it) continues to present a significant dam failure risk to downstream communities. The US Army Corps of Engineers, State of California, and San Mateo County have all identified Searsville as a "High Hazard" dam whose failure would likely result in loss of life. Cutting a hole in a 125 year old dam that has 3 huge cracks in it and sits adjacent to the active San Andreas Fault is not without serious risk to downstream resident; a situation that dam safety officials and Stanford recognize. The ongoing structural integrity of the dam, and safety of this particular hole-in-dam proposal, are unknown. 3) Dam removal eliminates dam failure and upstream flooding issues and risks. 4) The Searsville study process we just finished, and previous efforts, identified multiple options that can be employed alongside dam removal to reduce downstream flooding including: the off-stream detention basins you mention, restoring and enhancing the historic floodplain and flood attenuation function of Confluence Valley currently submerged by the dam and reservoir, modifying the upper marsh areas at Searsville to seasonally fill with flood waters, as well as needed downstream flood protection projects identified by the JPA.

On the ecosystem front, the hole-in-dam proposal seems at first blush to solve many problems associated with the dam such as fish passage, downstream flows, water quality, non-native species, preventing beneficial sediment from reaching Bay wetlands. However, many issues remain and new issues would be created by such a project. Consultants have acknowledged that fish passage through a hole in the 60-foot thick base of the dam, and extensively engineered creek channels upstream and downstream, would be "experimental" and the effectiveness unknown. This proposed design is also a single-species (steelhead) effort that would not ensure other native fish and wildlife migration. The hole would require extensively engineered internal baffles to slow water and provide resting areas for migrating steelhead; conditions that are know to also trap woody debris, block flow, and cause premature filling of the reservoir area with water and sediment. This situation can change the timing and eliminate the usefulness of storing water for flood protection at the correct time. As you note the "100-year" flow happens far more frequently than every 100 years. Removing debris jams from the hole in the dam and the resulting sediment deposited upstream is expensive and results in problematic siltation issues downstream. Santa Barbara County operates several such flood protection dams with holes in them and the National Marine Fisheries Service just issued them a Jeopardy Decision finding, which says these facilities are causing excessive harm to listed steelhead and Critical Habitat downstream under that are protected under the Endangered Species Act. The State Water Board has already told Stanford that they support dam removal and that they question whether any other option is feasible (including the hole-in-dam and fish ladder approaches).

Recent and highly successful dam removal efforts around the country that have combined progressive flood protection measures and ecosystem restoration have received broad funding and permitting support. The situation here is no different. Thankfully, Stanford's plan is surprisingly close to being a good one. For over a decade we have pushed for the reservoir to be eliminated, for non-native reservoir habitat to be eliminated, for Stanford to instead divert water further downstream at their existing dam less diversion, to instead store water in their off-stream Felt Reservoir, to use a hole-in-the-dam strategy (or gradual notching) to safely transport sediment downstream, and to restore sediment transport to the SF Bay for wetland replenishment and coastal community protection from rising seas. Stanford's hole-in-dam proposal agrees to do all of this, except take the final step of removing the dam. Now, Stanford just needs to including removing the dam once the sediment has been safely stabilized and transported downstream and identified flood protection measures have been committed to downstream. A widely supported Searsville Dam removal, flood protection, and ecosystem restoration project is increasingly close to becoming a reality.

Matt Stoecker

Director
Beyond Searsville Dam


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