What City Officials Need To Know About Flood Control and Development

July 2005

by Marci Coglianese

Marci Coglianese is the former mayor of the City of Rio Vista, former assistant city attorney of Fairfield and the immediate past chair of the League’s Environmental Quality Policy Committee. Currently, she serves on the Bay-Delta Public Advisory Committee to the CalFed process. Coglianese was the League’s representative on the state’s Floodplain Management Task Force.

Two trends - rapid population growth and mounting flood risk - are about to collide in the fastest growing regions of our state. Lower land costs increasingly drive Californians inland to the Sacramento and San Joaquin Valleys in search of more affordable housing. Urbanization of the Central Valley’s agricultural and open space lands may ease the housing crisis, but it could also add to the state’s growing flood crisis by placing even more people and property in harm’s way.

Lester Snow, director of the California Department of Water Resources, the state agency charged with flood control, describes the growing flood threat in the Central Valley as "a ticking time-bomb." His recent white paper, "Flood Warnings: Responding to California’s Flood Crisis," calls for formation of a Central Valley Assessment District to finance new investment in the valley’s deteriorating flood control system, and for improvement in local land use planning to keep new development out of flood-prone areas. But knowing just which developing areas may be flood prone presents a big challenge for growing cities.

The state’s urgent need to reduce flood risk became apparent after the New Year’s Day flood of 1997, the largest and most extensive flood ever experienced in California. From the Oregon border to the Southern Sierra, many flood control systems were overwhelmed as flooding spread over 300 square miles. More than 120,000 people were forced from their homes and 30,000 residential and 2,000 business properties were damaged or destroyed. Forty-eight counties were declared disaster areas with estimated economic losses totaling $5 billion. Surprisingly, damage occurred in many areas not normally subject to flooding.

FEMA Funds at Risk

California’s costly repetitive flood losses have grown to the point that the Federal Emergency Management Agency (FEMA) has warned the state to improve floodplain management or risk losing federal funding for disaster recovery and floodplain improvements. In an effort to head off future flood catastrophes, federal, state and local flood experts have proposed a variety of technical solutions to the problem, including improving le-vees, increasing capacity in bypasses and floodways, and re-operating reservoirs to better manage flood flows. But the state is also emphasizing the need for better floodplain management and is calling for local government to join the effort.

In 2002, Governor Gray Davis, on the recommendation of the Legislature, convened a broad-based stakeholder task force to develop recommendations for reducing the impacts of flooding through better coordination of floodplain management decisions. The 33 signatories to the Floodplain Management Task Force’s final report represented state and local government, special districts, the building industry, agriculture and environmental groups. Remarkably, in less than a year, the diverse group was able to reach consensus on 65 recommendations in three areas:

1. Improve the quality and accuracy of flood risk information;

2. Foster multi-objective management; and

3. Provide local assistance and funding to improve floodplain management.

Good Flood Maps Are Hard to Find

A key finding of the task force was that local governments rarely have access to accurate floodplain maps needed to make good land use decisions. Nearly all California cities and counties participate in FEMA’s National Flood Insurance Program (NFIP) so that federally subsidized flood insurance is available in their communities. But most local FEMA Flood Insurance Rate Maps (FIRM) are seriously out of date and haven’t kept up with watershed changes, such as upstream urbanization, that may cause the size and location of a floodplain to shift. And many areas along the urban fringe proposed for development have never been mapped by FEMA and may be in a floodplain.

The task force found another problem with relying on FEMA maps to make land use decisions. The designation "Special Flood Hazard Area" or "100-year flood zone" is commonly misinterpreted to mean a low, once-in-100-years risk of flooding. The designation actually means a 1 percent chance of flooding in any given year, which translates into a 26 percent chance of flooding over the life of a typical 30-year mortgage. So even if a 100-year flood zone were accurately mapped, a city might site a development there without fully appreciating that the new homes will be subject to a flood risk that is greater than anticipated.

Increasing the Margin of Safety

To limit catastrophic flood damage, the task force recommended that the state plan for higher future flood flows, recognizing that new development will increase runoff and a changing climate may produce more rain and less snow in winter. One practical step cities can take to compensate for uncertainties about mapping accuracy and future flood flows is to increase the "margin of safety" for new construction in the 100-year flood zone. The task force recommended increasing the minimum elevation of the lower floor of structures to at least one foot above the base flood elevation (BFE), the estimated water height during a 100-year flood. Currently, FEMA only requires that the lower floor be "at or above BFE."

The task force also suggested that cities not rely solely on FIRMS but instead plan for the "the reasonable foreseeable" flood event, the flood that is realistically probable in the area based on all the information that is available. This can include historical records and photographs, flood damage data and the educated observations of long-time local residents who have a practical understanding of the local hydrology. Environmental impact reports for new development projects also can be valuable sources of updated hydrology data that cities can use to better define the reasonably foreseeable flood event and to make a flood map revision request to FEMA.

The MOM Approach

The second group of task force recommendations urged adoption of a multi-objective management (MOM) approach to floodplain management. Recognizing that floodplains provide multiple benefits - groundwater recharge, wetland and wildlife habitat, agricultural production, recreation and open space - the task force recommended that these important resources be considered when managing floodplains to reduce flood risk. A multijurisdictional watershed approach will normally be the most effective way to achieve MOM because floodplains typically extend across jurisdictional boundaries. For example, a multiobjective watershed or integrated water resources management planning process funded by Proposition 50 could also address floodplain management.

The final task force recommendations are grounded in awareness that most local governments lack the resources to effectively implement floodplain management strategies. They urge the state to fill the need by offering more public information and education about flood hazards and available mitigation measures. Also recommended is more technical assistance to local communities, especially those experiencing rapid growth. The task force also favored expansion of DWR’s floodplain awareness mapping program to include all areas planned for future development. Floodplain awareness maps, already available for some parts of the state, provide a cost effective screening level assessment of flood-prone areas that can alert cities to potential flood hazards. While not all task force recommendations have been implemented, DWR’s website does provide a number of new tools to improve floodplain management.

With California’s population projected to rise from 37 million today to 46 million by 2030, the state is urging cities to streamline their development processes and build more housing. But building new houses without improving floodplain management is a recipe for a flood disaster, which the state and local governments must work together to avoid.

More Information Online About Floodplains

The Department of Water Resources (DWR) website (www.water.ca.gov) provides a number of new tools to improve floodplain management. You can also find links to the websites for the Federal Emergency Management Agency and the Floodplain Management Association, an organization dedicated to providing newsletters, conferences and training to local governments. Guidance for incorporating floodplain policies into a general plan, floodplain awareness maps and the DWR white paper on the flood crisis are on the DWR website. The full report of the Floodplain Management Task Force also is posted on the DWR website at http://fpmtaskforce.water.ca.gov.