Glossary Culvert: A drainage pipeline located underground Flood Plain: The area near a creek that is naturally subject to flooding 100-Year Flood: A significant flood that has a 1-in-100 chance of occurring in any given year (also called a one-percent flood) Infrastructure: System of built structures and facilities that serve a central purpose, such as flood control Line: Another term for a creek or flood channel. For example, Mission Creek is called Line L by District staff. Pump Station: A facility that lifts stormwater, after it is collected in channels, creeks, and pipes, to an elevation high enough to allow the water to flow by gravity into San Francisco Bay Watershed: The region drained by a creek or river, or manmade drainage system, such as a culvert or channel Wetland: Land, characterized by particular soils and vegetation, that is often or always under water and may serve as a natural habitat Zone: Administrative area designated by the Alameda County Flood Control District for flood control system design and maintenance

Flood FAQs

» What is a flood plain?

A flood plain is a naturally-occurring feature near a river or creek that floods periodically. When development brings pavement, roofs, and other hard surfaces, rainfall percolates less into the ground. Runoff to the nearby river or creek increases, and the development within the flood plain can be subject to flooding.

 

» What does FEMA have to do with flood plains?

FEMA, the Federal Emergency Management Agency, carries out emergency management programs that help communities nationwide to prepare for disasters, including floods, and deal with their aftermath.

To determine the risk of flooding, and thereby reduce flood damage, FEMA maps flood plains and prepares study to identify areas of likely flooding based on existing and planned development and existing flood control facilities. Areas with a 1 percent (1 in 100) chance, or more, of flooding in any one year are in a 100-year flood plain. In other words, the area is expected to flood at least once in a 100-year period. These 100-year flood plains are mapped as Special Flood Hazard Areas.

 

» What are FIRMs?

Flood Insurance Rate Maps (FIRMs) identify Special Flood Hazard Areas and are used to identify flood insurance requirements for an area. Although a 1 in 100 chance of flooding each year may seem remote, the likelihood of flooding increases over the life of a typical 30-year mortgage. Lenders require flood insurance for homes located in a Special Flood Hazard Area.

 

» What is the National Flood Insurance Program?

FEMA administers the National Flood Insurance Program, which provides flood insurance and flood disaster assistance for communities that meet its requirements to reduce flood risk. The Alameda County Flood Control and Water Conservation District, in corporation with the county and its cities, complies with these requirements.

» I understand how rain flows downhill through natural creeks. But how does it flow through low-lying communities along the Bay without flooding most of the time?

Once rain water reaches low-lying shoreline and residential areas, the Flood Control District's 22 pump stations help "lift" the water so it is discharged to San Francisco Bay. The work of pump stations is especially important in period of high tide, when Bay water levels are much higher than the level of flood control channels.

Most of the District's pump stations were built by individual cities, then turned over to the District for operation and maintenance. So, each pump station varies in design and size. Keeping pump stations in good working order requires time, expertise, and carefully planned preventive maintenance.

» What is SCADA?

All of the pump stations in the Districts are now monitored using SCADA, which stands for Supervisory Control and Data Acquisition. SCADA systems interface with District computers to alert staff of operational problems. The technology saves time money by pinpointing malfunctions and minimizing staff time to shut off general alarms for non-critical situations. District staff also use SCADA to review long-term equipment use and efficiency data to improve overall station performance. Trend data can be used for better engineering when replacing or rehabilitating District pump stations.

» What are some of the maintenance activities undertaken by the Flood Control District to keep waterways clear?

Maintenance and Operations field crews regularly inspect and clear obstructions from over 330 miles of creeks within the Flood Control District. Each year, thousands of cubic yards of items from shopping carts to mattresses and other trash are removed from waterways — a time-consuming and expensive process.

The public can help lower the cost of removing trash, and the resulting damage to natural waterways, by remembering the motto, "Only Rain in the Drain."

Vegetation posing a fire hazard or obstructing storm water flow must also be removed by waterways. Typically, this is accomplished by hand, natural biological means or the application of herbicides by state-certified personnel.

Flood Control District staff must keep silt from clogging flood control channels and reservoirs. Silt is an ongoing by-product of nature. During heavy storms, eroded soils wash into fast-moving creeks. The silt is carried downstream where it settles out in low-lying channels. Along the shore, silt is carried into bayside creeks and channels at high tide. When the San Francisco Bay's salt water mixes with fresh water, silt settles out.

Desilting projects are critical to keeping stormwater flowing unimpeded. However, these projects require a number of environmental permits from state and local agencies.

The District is working to minimize the amount of silt that reaches flood control channels by implementing erosion control projects along area creek banks. Preventive measures reduce the need for costly, time-consuming desilting projects and minimize work conducted in natural creeks.

For more information on the importance of keeping natural waterways clean, visit the following Web sites:

• Alameda Countywide Clean Water Program
• San Francisco Estuary Institute
• Urban Creeks Council of California
• The Oakland Museum of California Creek and Watershed Information Source

» What is bioengineering? Can a creek be made better, naturally?

Bioengineering is the name for technology that employs plants and other natural materials, rather than concrete and steel, to reinforce and stabilize creek banks so that waterways remain open and silt deposits are minimized downstream.
Some specific bioengineering techniques are:

• Live cribwall: Logs placed in an interlocking pattern and planted with cuttings
• Live stakes: Willow, or other plant cuttings, packed into soil
• Rootwads: Logs, with their rootball still attached, installed into a creek bank
• Tree revetment: Trees anchored along a bank for reinforcement
• Soil lifts: Layers of coconut fiber wrapped in soil and anchored on the creek bank

Selecting native plants and natural materials, such as tree stumps and rock, can lower construction costs. Maintenance costs, however, are usually higher because living materials require trimming and other care.

Overall, natural materials are the favored choice. They blend into the creekside environment and they are likely to thrive when the work is complete because they are already acclimated to local soil conditions.

» What's the difference between Alameda Creek, in Zone 5, and Old Alameda Creek, in Zone 3A?

The first waterway to be named Alameda Creek was one of several channels that crossed Zone 3A's coastal plain to reach San Francisco Bay.

From 1965 to 1975, a manmade flood control channel was constructed to dramatically increase flood protection for the area. This channel was termed the Alameda Creek Federal Project or "New Alameda Creek."

Today, the manmade channel is referred to as Alameda Creek, and the natural channel in Zone 3A is called "Old Alameda Creek."

For more information on Alameda Creek, visit the Alameda Creek Alliance.