contribute to its filling. A large part of the stream-born sediments finer than sand entering 

 the lagoon also probably remains in the lagoon. The USGS studies show that the lagoon's 

 circulatory pattern is nearly inoperative as a self -flushing, self -maintaining, dynamic system. 

 (Gilroy, 1970b.) 



Although the Marin County Parks and Recreation Department (1971) recognizes that 

 there are areas in Bolinas Lagoon of pollution, poor circulation, and increased 

 sedimentation, no recommendation has been made to correct a situation which can only 

 lead to an increase in the sedimentation rate in the lagoon and consequent deterioration of 

 the system. To correct this undesirable condition, it would appear to be ideal to apply the 

 principal proposed by O'Brien (1971) to improve the interior channels as follows: 



"Dredging shoals between LW and HW in the shallow upper reaches of a 

 lagoon or estuary will not only aid in the maintenance of navigation channels, but 

 will also improve the water exchange and flushing of the lagoon or estuary." 



Fine sediments resulting from cliff erosion on the outer coast enter the lagoon on the 

 flood tide. Some of these sediments are carried well into the lagoon, and contribute to its 

 silting. 



As emphasized by Ritter (1969) and Gilroy (1970b), nature, with some assistance from 

 man's operation on the watershed, will transform Bolinas Lagoon by sedimentation into a 

 muddy meadow. As mentioned in the General Comments in Section II, a tidal lagoon inlet 

 may be closed completely by the forces of wave action long before the tidal prism is 

 reduced to zero by sedimentation processes in the lagoon. J. R. Ritter, (19 Sept. 1972, 

 private communication), estimates that Bolinas Lagoon will become filled to highest high 

 water in about 500 years, if the present rate of filling (16 acre -feet per year) continues. This 

 rate is based on the rate of deposition over the 29-year period between the bottom surveys 

 by the Corps of Engineers, 1939 and the Bolinas Harbor District, 1968. C. Wahrhaftig 

 (Conservation Foundation, 1971) estimates that the lagoon will be converted to dry land in 

 500 to 2,000 years if the past average rate of sedimentation were to continue. Actually, the 

 lagoon entrance will probably close completely long before the lagoon is filled with 

 sediment to the highest high water level. The time to closure, however, cannot be estimated 

 because the closure criterion (the ratio of wave power to tidal power) for natural lagoons 

 has not been established. Of interest, however, are the following lagoons along the northern 

 California coast which appear to be always closed. 



Lagoon Surface Area (ft 2 ) 



Lake Earl 10 X 10 7 



Freshwater Lagoon 1 X JO 7 



Stone Lagoon 2.6 X 10 7 



Big Lagoon 6.8 X 10 7 



Abbotts Lagoon 0.9 X 10 7 



41 



