When you hear on the radio or TV that there is a “Flood Watch” or a “Flood Warning it’s already too late to begin preparing for the high water. Please prepare for the possibility of flooding ahead of time. Following are some things to do now as well as resources and links to helpful information:
- Rake your leaves and place into your green bin (keep out of gutters and storm drains)
- Sign up to receive emergency calls, text, and/or email notification alerts using AlertMarin, the Marin County Sheriff's Office of Emergency Services emergency notification system.
Sign up for AlertMarin.
- To check where to purchase sand bags in your area, please visit the Sheriff's Office of Emergency Services webpage. To obtain further information on training and education to keep you and your family safe, warm, and fed in the event of a flood please visit the website readymarin.org.
- Buy a NWS radio (see below for a recommendation) to be ready for weather updates
- Put a flashlight, radio and spare batteries in an easy place to find if the power goes out
- Remove hazardous materials (paints/chemicals, etc.) from flood prone areas such as garages and sheds
The National Weather Service recommends having a NOAA weather radio, such as the Midland WR-100B SAME Weather and All Hazards Alert Monitor. NOAA weather radios can be purchased online or at a local electronics store.
Flood Control Zone Winter Preparedness Updates
The Flood Control District prepares for every year as though it is an “El Niño year.” Although two major flooding years in Marin's history occurred during years with El Niño episodes (1997/98 and 1982/83), it is not unusual to experience major flooding in the absence of El Niño, such as in 2005/06. Flooding can even occur during a drought year such as 2015, when the County suffered some of its worst flooding damage since 2006.
The District follows a consistent system of facility and creek maintenance each year which mitigates the risk of flooding. We conduct regular inspections of the creeks, floodwalls, and levees within our jurisdiction, and frequently test our pumps, motors, and generators. Creeks, drainage ditches, pipes, trash racks, and pump wet wells are cleared of vegetation, sediment, and trash in the fall and throughout the winter as needed.
How can we protect ourselves from flooding?
There are many ways to reduce flood risk. Generally, multiple strategies are employed simultaneously. Possible approaches depend on the type of flooding, the physical setting, cost-benefit considerations, available funding, legal and permitting implications, and the support of the local community.
Away from the Channels
Hold Back Stormwater
Stormwater detention in basins or vaults captures stormwater before it enters the creek and releases it slowly to reduce downstream flooding. Finding the space for stormwater detention facilities can be difficult and expensive in urban areas.
Stormwater pipes or channels bypass water from flood prone areas to a location downstream. New pumps and/or tide gates may be required depending on where the bypass flood waters are discharged.
Pipe Stormwater Underground
Conveying stormwater in underground pipes creates space for streets, homes, and other urban features. Well-maintained pipes may quickly move water downstream but underground infrastructure can be difficult to inspect and troubleshoot. Over time, land settles and pipes age, clog, and break. Downstream tides or flooding limit how fast water is able to exit the drainage pipe, so larger pipes do not necessarily improve drainage. Many stormwater pipes are located on private property.
Regular inspections, pipe flushing, repair, and eventual replacement of old or failed pipes are all necessary to reduce the risk of stormwater overflow. Tide gates and pump stations can improve stormwater drainage efficiency in low-lying areas.
Raise or Flood-Proof Buildings out of the Floodplain
Structure elevation is a reliable flood risk reduction strategy. It can be expensive and must be weighed against the expected damage and frequency of flooding to get a true picture of the costs and benefits. While it may raise a building above floods, it does not necessarily improve access from that building to nearby roads and resources that may be underwater or cut off by flooding.
In and Along the Channels
Vegetation trimming and targeted sediment removal within creeks and channels can help reduce flood risk, although the benefits can be short-lived. Creek maintenance is typically performed annually. Excessive vegetation or sediment removal can harm wildlife, water quality, and bank stability.
Increase Creek Flow Capacity
By replacing bridges or utility crossings, increasing the size of culverts, or widening the creek channel, we can increase the amount of water that can flow in a channel during floods. It can also provide space for habitat and promote bank stability. It is expensive because creek widening is constrained by buildings, roads, and property lines
Stabilizing creek banks and channel bottoms reduces erosion, stabilizes habitat, and protects infrastructure. This activity includes vegetating eroding slopes with native plants and sometimes re-grading bank slopes. Depending upon the location of infrastructure, the strategic placement of rocks, wood and/or installation of an engineered structure may be required to stabilize the creek banks.
Levees and Floodwalls
Levees and floodwalls constructed alongside the creek or bay confine floodwaters. While effective, levees and floodwalls must be contiguous throughout the area of flooding, require space and material, and may require pump stations and drainage pipes to move water over or through them and into creeks.
Habitat Enhancement and Restoration
Habitat enhancement and restoration to improve habitat for flora and fauna while reducing flood risk. Projects that remove obstructions to flow or allow flood waters to be absorbed by wetlands can reduce flood risk and improve critical habitat. Closer to the bay, strategic wetland restoration can absorb floodwaters and reduce the impact from storm-related waves.
Near the Mouth of the Channels
Pump Stormwater from Low-lying Areas to Creeks
In the baylands, the District operates eight pump stations to move water out of low-elevation neighborhoods constructed on former marshlands. Rainfall from these areas drains to a point lower than the adjacent levees or creeks. Large pumps move ponded water into adjacent creeks where it can drain to the bay. Opportunities may exist to increase pumping capacity at currently-operated pump stations. Pumps are effective at protecting low-lying areas but they are expensive, require regular maintenance, and consume a lot of energy.
Adjustable tide gates can extend across channels or attach to outfalls of stormdrain pipes that drain to creeks and channels. They are designed to keep tidal waters out of the stormdrain system during high tides and protect low-lying areas. They are prone to being stuck open by debris and require regular maintenance. Larger gates are manually operated increasing the burden to deploy them successfully during forecasted high tide events.
Who is responsible for flood risk reduction?
Everyone has a role to play. The “Whole Community” approach to flood risk reduction requires communities and government agencies to work together to understand, assess, and identify flood risk reduction needs and solutions. The collaboration and shared understanding creates communities more resilient to flooding and better able to adapt and respond when floods occur.
The Marin County Flood Control and Water Conservation District (District) maintains 3.6 miles of channels (17% of the total channel length) and related flood control infrastructure in the Southern Marin Watershed. Maintenance activities include regular servicing of eight pump stations, multiple tide gates, miles of levees and drainage ditches, and an annual vegetation maintenance program. Work is limited to areas where the District has permission to perform maintenance – on its own lands or where it has acquired easements.
Flood Control Zones partner with municipalities and other agencies to provide flood risk reduction. Each zone has an advisory board of residents who are appointed by the District Board of Supervisors. The zones have authority to construct, operate, and maintain stormwater basins, levees, pumping stations, culverts, drainage ways, and creeks.
Property and special taxes (if approved by a majority of voters) support work in the zones. All revenues in the District are collected through the zones and must be spent in the zone providing the funding. The annual work program is coordinated by the zone engineer and the budget for the work program is reviewed annually by the advisory board prior to being adopted by the District Board of Supervisors.