Posts Tagged ‘san francisco bay’

Guest Speaker: Megan Prelinger 
7pm, Monday April 18th, 2016
FREE Green Apple Books on the Park, 1231 9th Ave, San Francisco, CA 

In 2010, Megan Prelinger and collaborators Rick Prelinger and Stacy Kozakavich were invited by the Exploratorium to develop exhibits for the Museum’s planned Bay Observatory gallery. The Bay Observatory opened to the public in 2013, featuring dozens of research-based exhibits that combine the Museum’s legacy imperative to integrate art and science for the benefit of public understanding with a fresh imperative to explore the waterfront and the natural environment. In response to the Exploratorium’s prompt to “animate the Library in the service of understanding San Francisco Bay,” Megan and her collaborators created a series of graphic atlases that explain that histories of the watersheds and the shorelines, both natural history and the built environment. Watersheds and Shorelines are two of five atlases that also include Islands and the two urban atlases, San Francisco and East Bay. All are installed as permanent exhibits in the Bay Observatory, along with a public access mini library of Bay Area landscape history. In her April 18 presentation, Megan will show slides and discuss the research and outcomes behind the Watersheds atlas and the Shorelines atlas. Watersheds traces the flow of water from the mountains to the mouth of the Bay, and Shorelines traces the landscape of the water’s edge of both San Pablo Bay and San Francisco Bay.

Megan Prelinger is a cultural historian and naturalist. She is co-founder along with Rick Prelinger of the Prelinger Library and architect of its information design. The library is an independent landscape-based research library in San Francisco that has been open to the public since 2004. She is the author of several books, most recently Inside the Machine: Art and Invention in the Electronic Age (W.W. Norton, 2015), and the 2013 and 2014 Watersheds, Shorelines, and Islands historical atlases, all permanent exhibits in the Exploratorium’s Bay Observatory gallery.

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Brenda Goeden of BCDC and Ian Wren SF Bay Keepers joined us on August 19th, 2015 at the Exploratorium to to talk about what gets dredged out of the San Francisco Bay.

Most of the dredging that goes on in the bay is for navigation. This is mostly through mud — 80% of the Bay is fine grain mud, and it is dug out to allow deep draft vessels to come through, and keep waters by marina’s clear. The dredging aka mining of sand is mainly for the construction industry – it becomes cement, asphalt, road-base, sub-base and general fill. The grains of sand are grains (.002 to .08 inches in diameter) bigger than mud, and smaller than gravel. it gets mined on demand, not necessarily day in, day out.

There are two main areas whether the sand comes from: Suisun Bay and the Central Bay. Suisun Bay is a finer grain of sand which is often used for back fill in trenches. The coarser sand of the the Central Bay is used for cement. Sand is only found in the high flow areas of the Bay where the water has enough energy to carry the sand. Mud is taken out to the slow wide sides of the Bay.

Sand Flow in the Bay - Barnard et al. 2013

Sand is important for a number of reasons outside of its commercial uses — it helps build marshes and beach. It provides shoreline protection as it takes more energy to move, it provides a particular kind of habitat, and on the shore provides a place for recreation and having a place for viewing wildlife.

The amount of historical sand, and sand in the Bay is difficult to measure. Most of the sand in the Bay comes from the Delta and the larger watershed (40% of California’s watershed drains into the Bay), and estimated 1.2million cubic yards, with another 300+ thousand cubic yards coming from local streams. Where not blocked, the rivers and creeks, slide and bounce the sand along into the Bay.  Storms and other high flow events are key in moving the sand along and into the Bay and beyond.

The sand also is carried out into the ocean, and large dune field lays under water past the Golden Gate Bridge. This was once a wide delta of sand, but has been slowly growing smaller. This changing shape of this sand has affected how sand flows both inside and outside the Bay. The pattern of sand dispersal on Ocean Beach has meant the northern end of the beach has been gaining sand, and the southern has been losing sand leading to fast erosion of the shore. The bay itself is also losing some protection from ocean waves in this process as well. Crissy field on the other hand has benefited, gaining sand from both flows headed out to sea, and sand coming in along the shore.

There’s not a lot known about the habitat underwater in these sands. The Central Bay sand area is the deepest in the Bay 90′-300′ deep where the water is salty, deep, cold, and fast. Aka difficult to study (there has been some studies monitoring what is brought up by the sand miners). We know there are wondrous things going on down there, like the migration of Dungeness crabs — marching in to lay eggs, and then marching out again — but no one has ever seen it or knows the pathways.

Suisun Bay is shallower, warmer, and less salty. The two areas are pretty different, but in both cases these are deserts compared to the meadows of mud. The organisms living there tend to be smaller, efficient, and highly adapted.

Humans have had a huge impact on these fields of sand — the biggest being the pulse of sand brought down from the Sierra’s by gold miners, and estimated 10x the usual flow of sand. Before that, and before many of the rivers and streams were dammed. The flow might have been around 2 million cubic yards. The sand from mining continued to pulse through the system and is only recently pretty much all gone. Now a large portion of the pool of possible erodible materials is trapped behind dams and the delta tunnels.

We still have sand, and we still have sand coming in, but the question now is how much sand do we have, and how much can we afford to take out. Mining has been happening since the 30s, peaking in the years 1949-79. Much of the sand is used locally shipped to different dispersal points around the Bay.

Dredge mud goes to different places, a lot gets shipped and dumped out at sea, or dumped at certain disposal sites in the Bay itself (inside the bay this can disperse contaminants, cause turbidity). These are not the preferable options — that favored option (by BCDC) is helping restoration efforts, filling land that has sunk below sea level on the other side of levees. This is the unfortunately the most expensive option, which there are not a lot of funds for, and small marinas don’t tend to have funds to support that kind of work, and dredging for ports is an expensive enough business that any additional fees would likely be too onerous.

San Francisco Bay Keeper is involved in the issue, hoping to bring in the perspective of the overall health of the Bay and nearby waters, and the sand being an important part of it. The sand taken is not replenished, there is a net loss, and they want to make sure we keep relic sites, and keep mining more in active parts of the flow. They are also looking to insure there is proper compliance and that companies don’t end up taking more than they should. They are looking through commenting on proposals and active litigation to reduce the amount of sand mining going on — to being sand mining to a sustainable level.

On the flip side, if local industries turned to external sources for sand, there may be equally damaging impacts — leaving aside where the sand is being mined from, the carbon costs of shipping that sand by barge or truck would not be small.

The biggest question we seemed all left with was the complicated nature of the question. A unknown or at least unseen, but super valuable resource here in the Bay below us. How much is there? and how much can we afford to take out?

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picture from Golden Gate Cetacean

Return of the Harbor Porpoises
Guest Speaker:  Bill Keener
7:30pm, Thursday, March 15th, 2012
FREE at the Randall Museum, 199 Museum Way, San Francisco, CA 

Bill Keener, cofounder of Golden Gate Cetacean Research, created to study the porpoise, will tell us of their disappearance by the 1940′s, the mystery of their unexpected return in recent years, and how you can help by reporting your porpoise sightings.

Bill’s experience includes work as a field observer for the harbor porpoise population study in the Gulf of the Farallones National Marine Sanctuary from 1987-1989.  He is an environmental lawyer and the former Executive Director of the Marine Mammal Center.

Read more about Bill and porpoises in Bay Nature magazine, Jul-Sep 2011, Safe Harbor, Welcoming Porpoises Back to San Francisco Bay.

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White Sturgeon in San Francisco Bay

The Sturgeon in San Francisco Bay:
How critical can a 10,000 year old Bay be for a 100 million year old fish?

Guest Speaker:  Michael McGowan
7:30pm, Thursday, February 16th, 2012
FREE at the Randall Museum, 199 Museum Way, San Francisco, CA 

Michael McGowan, fisheries oceanographer and aquatic ecologist, will discuss his research on how the ecology of the green and white sturgeon differ in their life history and in how they use the Bay.

White sturgeon are the largest fresh water fish in North America that can live over a hundred years and can grow to 20 feet long, and weigh 1500lbs. (more info)

Green sturgeon, up  to 7 feet long and 350lbs, seem to be a little more mysterious on the web, they are probably migratory salt water fish that probably spawn in fresh water. (more info)

Michael will fill in the details for us.

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