What is a floodplain?
A floodplain is a land area near a river or creek that floods periodically. Building surfaces, such as parking lot pavement, roofs, and sidewalks, are often impervious (meaning that water cannot seep through them). Stormwater runs off these surfaces when it cannot easily percolate into the ground. Instead, runoff to the nearby river or creek increases, and the development within the floodplain can be subject to flooding.
What does FEMA have to do with floodplains?
FEMA, the Federal Emergency Management Agency, carries out emergency management programs that help communities nationwide prepare for disasters, including floods, and deal with their aftermath.
To determine the risk of flooding, and thereby reduce flood damage, FEMA maps floodplains and studies this information 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 floodplain. In other words, the area is expected to flood at least once in a 100-year period. These 100-year floodplains 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.
How do pump stations help protect communities close to the bay?
Rain flowing downhill collects in flood control channels and natural creeks, which traverse low-lying communities to the bay. Once rainwater reaches low-lying shoreline and residential areas, the Flood Control District’s 22 pump stations help “lift” the water so that it is discharged to San Francisco Bay. The work of pump stations is especially important in periods of high tide, when bay water levels are much higher than the level of flood control channels.
Most of the District pump stations were built by individual cities, and 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 District 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 and money by pinpointing malfunctions and minimizing staff time to shut off general alarms for noncritical situations. District staff also uses 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.
How are waterways kept clear, and how can I help?
Alameda County Public Works Agency Maintenance and Operations field crews, which support the Flood Control District’s efforts, regularly inspect and clear obstructions from over 330 miles of creeks within the District’s jurisdiction. Each year, thousands of cubic yards of items, from shopping carts to mattresses, furniture, 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 stormwater 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.
For more information on the importance of keeping natural waterways clean, visit our Pollution Prevention page or the following websites:
What is desilting, and why is it important?
Flood Control District staff must keep silt from clogging flood control channels and reservoirs. Silt—particles of soil, sand, rock, and plant debris—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 San Francisco Bay’s salt water mixes with freshwater, silt settles out.
Desilting projects—meaning work to dredge and remove silt deposits—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.
What is bioengineering, and can it make a creek better?
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 as follows:
- Live crib wall. Logs placed in an interlocking pattern and planted with cuttings.
- Live stakes. Willow, or other plant cuttings, packed into soil.
- Rootwads. Logs, with their root ball 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 is the difference between Alameda Creek (Zone 5) and Old Alameda Creek (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 man-made flood control channel was constructed in Zone 5 to dramatically increase flood protection for the area. This channel was termed the Alameda Creek Federal Project, or New Alameda Creek.
Today, the man-made 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.