The Ever Changing Muddy Waters of Bolinas Lagoon

Derbridge, Jonathan

This report is a history of Bolinas Lagoon, its ecology, human impacts, and plans for the future. Bolinas Lagoon is a tidal estuary on the west Marin coast. Like any tidal estuary, it is subject to an ever-increasing level of sedimentation. Unlike most estuaries, however, Bolinas Lagoon sits directly on the San Andreas fault, and is subject to major earthquakes every 200-300 years that act to lengthen the life of the estuary by lowering its floor. The lagoon and its watershed have been the focus of much human activity in the past 150 years, and more recently, the focus of intense study and debate. Since humans have been active in this area, the sediment levels in the lagoon appear to have changed. Although this is a natural process, it has been argued that logging and grazing in the area have significantly increased the rate of sedimentation and that the lagoon will eventually turn into a marsh. An influential group of concerned residents in the Bolinas area managed to get Congress to fund a United States Army Corps of Engineers (USACE) study into what should be done. In 2002, the USACE recommended an 8 to 9 year dredging plan to remove 1.5 million cy of sediment, at a cost of $100-$130 million in order to prevent the closing off of the lagoon’s inlet by 2050. Marin County rejected that proposal when it was shown that there had been insufficient work done to demonstrate that the USACE’s predictions were accurate. Members of the public and local scientists with an interest in the natural history of the area also expressed a great deal of concern over what effects a drastic solution like dredging such a huge amount of sediment might have on the lagoon’s ecosystem. The county has since hired a team of highly respected hydrologists and ecologists, and an independent scientific review group to come up with data that will show what is likely to happen to the lagoon over the next 50 years. The results from this study are still pending, and an Adaptive Management Plan will be put in place so that a constant monitoring program can inform the scientists studying the lagoon of the ongoing changes within it. The conclusions of this paper found certain human perspectives led to erroneous assumptions that there was a problem that needed fixing, but it is becoming increasingly clear that there are no real threats to the health of the ecosystem. Bolinas Lagoon has been changing and evolving, filling with sediment and then becoming deeper after major earthquakes for the last 10,000 years. Such timescales are not what humans are used to thinking in, but if people connected to Bolinas Lagoon want to find a long-term resolution to the question of what to do with it, they must adjust their perspectives.