San Carlos tackles flooding

However, many of these locations have storm pipes that discharge into creeks that have sediment and capacity constraints causing a backwater effect that further affects the pipe capacity, according to Walter’s report.

Due to the downstream constraints of the creeks, modeling shows that even with the recommended pipe improvement, flooding will persist in the 100-year design storm and also during the 25-year design storm scenarios, according to the report.

Another tier of projects to address lesser flooding areas in the city could cost an additional $18.4 million, according to Walter’s report.

The council is expected to adopt a resolution at its Monday night meeting to approve the Citywide Storm Drain System Master Plan.

Stormwater in San Carlos generally drains from the hills on the west side of the city, flowing east toward the Bay. Stormwater is conveyed to the Bay through open ditches and pipelines into the city’s four primary creeks: Belmont, Brittan, Cordilleras and Pulgas.

San Carlos has experienced periodic flooding over the years generally due to a combination of issues including storm drain inlet blockages from leaves and debris, stormwater volumes that are greater than the capacity of the city storm drain pipelines and backwater and overtopping from creeks.

In addition, the eastern portion of the city is mostly flat and at low elevation. The area is also subject to tidal influences and sedimentation, according to Walter’s report.

A list of capital improvement projects have been developed to address the flooding including in the southern portion of the city between Brittan and Cordilleras creeks. There are several known flooding areas in that part of the city. Three other projects include addressing flooding along the 1400 block of El Camino Real, Oakhurst Avenue and at the south end of Cedar Street.

Cost of these three projects alone totals about $15 million.

Flooding may be reduced in these areas by upsizing the pipes. The 12- and- 18-inch pipes would be upsized to 24 inches while 15-inch pipes will be upsized to 30 inches. Some 30-inch pipes would be upsized to 48 inches in diameter, according to Walter’s report.

Public Works crews have completed sediment dredging of the Belmont Creek culverts under Industrial Road, and the Holly East and West open channels. In preparation for the wet season, Public Works crews completed channel cleaning at various locations along Belmont, Pulgas and Cordilleras creeks. Also, there is an ongoing capital improvement project to improve and replace storm drain inlets to prevent debris from blocking storm flows, according to Walter’s report.

The San Carlos City Council meets 7 p.m., Monday, March 14, City Hall, 600 Elm St., San Carlos.