SF Examiner

Redwood City To Study Lagoon Floor for First Assessment Of Lagoon Silt.

Meridian To Develop Reverse-Contour Map Of Lagoon System.
Professional Land Surveyors in the San Francisco Bay Area.

By Josh Wein, Staff Writer, Published: Tuesday, March 8, 2005 12:14 PM PST

REDWOOD CITY — City officials are considering cleaning out the mud that has built up in Redwood Shores’ lagoons for the first time since the winding network of waterways was built.

The city has hired San Francisco-based Meridian Surveying to chart the lagoon’s murky waters and find out just how bad the silting has become. The lagoons are designed to completely circulate tidal water within seven days. But built up bird excrement, loose yard clippings and mud from the nearby sloughs can slow that process, leaving water in the system for longer periods.

This often leads to a smelly buildup of algae and widgeon grass, which quickly dies and floats around the lagoons in the form of a black mass.

“It smells like a really stuffy wet grass that’s been sitting for a while,” said Redwood Shores resident Christina Lai.

Redwood City ‘s Public Works Department currently makes two lagoon sweeps a year to harvest the widgeon grass. But engineers believe that reducing the accumulated silt could eliminate that problem.

“There are no serious signs this is a problem right now,” said Paul Willis, a city engineer. “But it’s sight-unseen. So you don’t really know how bad or good it’s going to be.”

Meridian’s contract calls for the company to develop a reverse-contour map of the lagoon system. It will allow the city to compare the current lagoon depths with the original plans and see just how much shallower the waters have become.

Once that’s done, engineers will develop a plan for removing the gray mud. Willis said the worst-case scenario involves massive dredging, and hauling the dredged silt away for disposal — a potentially expensive project.

In 2003, Foster City, Redwood Shores’ northern neighbor, completed an expensive and extensive lagoon-dredging project. Vacuum-equipped boats sucked more than 100,000 cubic yards of sediment from the lagoon floor.

Though residents might spot a small boat or two out on the lagoons over the next few weeks, no dredging or cleaning will take place yet.