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Archived News Release from 2005

For Immediate Release

Silt Buildup to be Studied in Redwood Shores Lagoons; Need for Cleanout to be Determined

Redwood City, CA - March 7 , 2005 - Approximately 150 acres of lagoons help define the Redwood Shores community, and continue to be a source of beauty, pride, and quality of life for the people who live there. However, a great deal of silt has been accumulating for many decades, and as a result today the lagoons are not in the prime condition that is desired. Redwood City is hiring a consultant to map the lagoons’ underwater contour through a process of hydrographic surveying, to help determine the level and quantity of silt on the floor of the lagoons.

Water in the lagoons needs to ‘flush’ (to be periodically replaced through tidal action) at least once every seven days to avoid potential problems associated with lack of proper water movement. Some parts of the lagoons meet that standard, but there are other areas that are flushed considerably less-frequently. When silt builds up on the floor of the lagoons, it can prevent the water from flushing with the tides. When that natural flushing doesn’t occur, the result is a serious overgrowth of bacteria and algae (propagated in part by an accumulation of fecal matter from the local fowl population). It also causes an increase in the stubborn widgeon grass, which reduces the natural flow of water and leaves an accumulation of debris when it dies out.

These elements contribute to lagoon water that is cloudy and unclean, that can have bacteria and algae at higher-than-desired levels, which may have an unpleasant odor, that is unsightly, and which in general does not reflect the value and pleasant appearance of the surrounding Redwood Shores homes.

The City’s consultant will use sonar and GPS (global positioning system) to map the contour of the lagoons’ floor. From that mapping, the City staff can calculate the total amount of silt involved and identify possible solutions and costs. One option is a combination of installing pumps to force the water from certain areas, and removal of large amounts of the silt from other areas.

The City is NOT considering draining the lagoons as that could cause problems with the sensitive slopes on the shoreline of the waterway, nor would any traditional dredging occur (i.e., a barge-mounted shovel system). The current technology for silt removal of this nature consists of pumping the silt out through large hoses for deposit elsewhere.

The City’s hydrographic surveying consultant is expected to begin work by the end of March. For a period of about two weeks, residents in Redwood Shores may see one or two small boats moving very slowly throughout the lagoons as they map the floor. The consultant’s report should be completed by early summer, and with that information City staff can begin work to determine the most effective way to proceed, depending on silt quantity, location, and overall costs associated with cleaning out the lagoons. As staff proceeds with this project, information will be provided to residents and their input will be sought through community meetings.

Visit Redwood City’s award-winning website at www.redwoodcity.org for information about the City and its services, the community, recreation programs, education, and City government.

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Contact:
Paul Willis
Associate Engineer
650-780-7219

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