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August, 2006


A Not So Simple Take Home Message About Bolinas Lagoon
By Don Slack

I wrote an article in the Coastal Post June 1 issue titled "A Simple Take Home Message About the Bolinas Lagoon." In the July 1 issue Gordon Bennett wrote an article taking exception to a number of my points. I'll attempt to address some of these. As Gordon said, we should "move forward on a solid basis of science." I believe this includes:
1. Weighing of different informed opinions. This should include data from the ACE (Army Corp. of Engineers) 2002 report as well as data from the PWA (Philip Williams Associates) report of 2006.

2. Direct observations is another part of scientific data. For example actual photos and statements of sea captains that a 10 foot draft schooner could enter Bolinas lagoon at low tide around 1880 should be reconciled with the PWA report that states the lagoon was always a shallow water body.

3. Separation of fact and theory. The fact that the lagoon is filling in at about 45000 cubic yards a year is a measured fact agreed upon by all. The prediction that this fill rate will decrease and reach an equilibrium value in 100 years or so is an idea or theory not agreed on by some experts who have studied the lagoon.

Oddly, at the last two public meetings about the lagoon PWA representatives have spoken but ACE representatives have not. For the public or our Board of Supervisors to proceed on a solid basis of science we need to heard from both ACE and PWA scientists and why some of their views differ regarding predictions and actions to be taken.

To more specifically address some of Gordon's comments he mentioned that, according to table 5.1, pg. 83, of the PWA report the total acreage of mud flats and salt marsh will increase less than 1% between 2000 and 2050. This is correct as far as it goes. What Gordon didn't mention is that the table has two listings for mud flats (frequently submerged and frequently exposed) The frequently submerged mud flats decrease 26%. The frequently exposed increase 24%. Gordon arrived at the less than one percent number by adding the increase in exposed mud flats and subtracting the decrease in submerged mud flats. However both numbers say the lagoon is drying up. They do not, as Gordon implied, cancel each other. Examining the table further, Salt Marsh increases 22%, Fluvial Delta increases 82%, subtidal shallows decrease 100%. In short, the lagoon is drying up. This correlates with the reported 45,000 cubic yards per year.

Regarding the Ramsar convention of 1971 that designated Bolinas Lagoon as a wetland of international importance. They were referring to the lagoon as it existed in 1971 not some future (current) condition. In 1971 the lagoon was substantially deeper, consistent with the reported 45,000 cubic yard per year fill rate. In 1971, unlike today Eel grass provided important fish habitat in the lagoon, the lagoon served more extensively as a Pacific Flyaway for migratory birds, and it serviced a number of diving bird species that we don't see today. In short, a deeper estuary, much rarer along the western seaboard, than shallow mud flat marsh areas.

Regarding lagoon mouth closure, Gordon referred to the PWA memo of 5/23/06 pg. 6. This does show the closure condition predicted by the O'Brian parameter (2.0 MCY/yr. tidal volume) occurring 119 years from now. However the PWA report of 2/10/06 part , pg. 7 states that under unusual conditions of tide and waves closure could occur at 2.5 MCY which PWA predicts will occur in 50 years. It further states that sand accumulation in the entrance could induce closure sooner. This sand accumulation is occurring according to local fisherman. The ACE reported 35 years to possible closure conditions. In short, the predictions of closure are guess work at best and 60 years is probably as good a guess as any. There is a distinct possibility that closure could be sooner due to sand accumulation at the mouth.

I think most of us agree, as I do with the contention in the PWA report that whatever project takes place we need to retain the vast majority of marsh, mud flats and other estuary ecosystems as they have existed within the last 30 years or so. Adaptive management, meaning observing effects of our action and making corrections as we proceed, as suggested by the PWA report is a necessary part of this project. However doing too little at this juncture is equally detrimental from an ecological standpoint as doing too much.

The PWA and ACE reports, public meeting and decision dates are available on CD or on-line by going to or calling (415) 499 6387.

Public comments can be directed to Steve Kinsey, District 4 Supervisor, Administration Bldg, 3501 Civic Center Dr., Ste 329, San Rafael, CA 94903.

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