GUEST OPINION: Preserve director has different view of Searsville Dam

By Philippe S. Cohen

Given the scope and importance of the issues raised by Matt Stoecker's guest opinion in the Almanac February 16, as director of Jasper Ridge Biological Preserve, I am compelled to respond. The article contained some factual errors and I would like to cast a different light on some of the assertions he made.

At the outset, I want to make clear that I am agnostic about the removal of Searsville Dam. It is not clear to me what the best path is nor do I think we have enough information (or knowledge of the risks) to make an informed or appropriate decision at present.

Issues, both upstream and downstream, and the preserve's educational and research interests, present a more complex set of circumstances than the article depicts. Mr. Stoecker may ultimately be right, but it is certainly not because our collective understanding of the issues clearly point to a particular solution or strategy.

There are a number of factual errors that need correcting. First, Stanford University did not have the dam built. It was constructed by the Crystal Springs Water Company (today, the San Francisco Water Dept.), and was not acquired by Stanford University until about 20 years after the dam was completed.

Second, it is not at all clear that the dam has contributed to the threatened extinction of tiger salamanders, red-legged frogs, or sticklebacks. In fact, I am unaware of any evidence suggesting that sticklebacks are at risk as they are in Southern California. There is reason to think that sticklebacks have never made it as far as the dam's location due to natural instream barriers.

I'm also unaware of any evidence suggesting that there was ever a significant run of salmon in the San Francisquito Creek watershed. Also, all the evidence points to Searsville Dam having considerable earthquake integrity. Not only did it survive the 1906 and 1989 earthquakes with no structural damage, but recent analysis of the dam confirms its continuing structural integrity and safety.

Finally, I know of no evidence for the claim that Searsville Lake will be a meadow when it fills in. There is simply insufficient information at this time to know how the filling in of the Lake will play out.

Factual errors aside, Mr. Stoecker makes assertions that are not self-evident. For instance, it is not obvious that the water leaving the lake is having the temperature and dissolved oxygen impacts described. For example, data collected on the preserve of water entering and leaving the lake show no such differences.

While Mr. Stoecker is correct that as a rule standing bodies of water generate increased water temperatures and reduced dissolved oxygen, Searsville Lake is not just a standing body of water. One reason for this is that the reservoir discharges in the winter when there is little temperature stratification in the lake. It discharges over an aerating spillway, and in fact, the water leaving the lake may have a higher dissolved oxygen content than the inflow. Another significant difference is that water resides in the lake for such short periods of time during the rainy season and the lake's total capacity is so low, that its real impact on downstream water quality is minimal at best.

Mr. Stoecker's description of how sediment might be removed from the lake basin as the dam is being lowered raises a host of other issues. First, there is the question of how the increasing sediment will impact downstream hydrology.

This is not at all obvious and needs considerable investigation before asserting that the dam's removal will somehow enhance public safety.

Second, the prospect of regular disturbance of adjacent preserve lands as the dam is lowered presents many ecological risks. Add to that the annual exposure of sediment as the dam is lowered, and we may be creating conditions rife with potential non-native species invasions.

Yellow starthistle, French broom, Pampas grass, and many other plant species could become established or their presence on the preserve significantly expanded. In addition, the disturbance to surrounding habitat on the preserve in order to manually remove sediment could be substantial and further undermine the integrity of Jasper Ridge habitats and therefore, undermine our teaching and research mission.

It is certainly not obvious to me that Searsville Lake is just a liability. From the preserve's perspective, the lake provides many important educational opportunities as well as significantly enhancing avian diversity. It supports a substantial wetlands community that is itself a disappearing habitat type. In addition, hundreds of Stanford undergraduates use the lake and its0 associated environs each year for field classes.

I certainly agree with Mr. Stoecker that how we manage Searsville Dam's future (or lack of one) provides many important research and precedent- setting opportunities. But removal as the best and most reasonable option is by no means obvious nor should we assume or expect that "this task could easily be accomplished."

While Mr. Stoecker is obviously trying to explore ways to improve watershed health and address important issues, these ends will not be achieved if we fail to recognize what we don't know as well as what we think we know. In other words, it's not an obvious, easy decision as to what should be done about Searsville Dam and how that should be accomplished.

Philippe S. Cohen is director of Stanford University's Jasper Ridge Biological Preserve