The formulation and implementation of a plan is composed of four phases:
1) Planning. Prepares the ground for the next three phases by preparing a community's profile that includes information such as population and main economic activities, and identifying key players who will work together to develop the plan.
Public involvement is important because it brings perspectives from multiple disciplines, provides an opportunity to understand residents' concerns, draws from the experience of long-term residents, and fosters communitywide communication.
2) Risk assessment. Identifies potential hazards, associated damages, and consequences. Risk is determined by the probability of a particular disaster; consequences include physical damage to infrastructure and buildings as well as economic losses to the community.
All participating parties evaluate risk to critical facilities, defined by FEMA as “those essential to the health and welfare of the population, including hospitals and medical emergency facilities, fire and police stations, power generation facilities, water and wastewater supply systems, shelters, and schools.”
Main arteries and thoroughfares are considered critical if they're essential to recovery efforts; for example, when public works and utilities need certain roads to access and restore basic services such as water, sanitary sewer, and electricity.
3) Mitigation plan development. Defines concrete actions, both structural and nonstructural, that must be taken to reduce the risk.
Structural activities are those that require construction — building a levee, reinforcing a building, or relocating equipment such as water pumps and utility vehicles. Nonstructural activities provide guidelines or prohibit certain activities for future development; for example, zoning ordinances to prohibit specific activities in floodplains or adopting more stringent engineering codes for buildings.
4) Implementation. The plan is adopted by elected officials, the proposed actions are implemented, and the plan's performance is reviewed and evaluated annually.
Hazard mitigation planning helps Houston
Both the city and nonprofits get grants as a result of their partnership.
Hurricane Alex tore through Houston in June, drenching the nation's fourth-largest city in 14 inches of rain over two days. When it was over, news reports mentioned that the Texas Medical Center had used the Harris Gully gage to decide to implement its Stage 1 disaster-mitigation preparation by closing the flood doors at several hospitals to prepare for the worst.
After Hurricane Ike hit Texas in 2008, nonprofit organizations under the city's hazard mitigation action plan (HMAP) submitted projects to the Mitigation Section of the Texas Division of Emergency Management to compete for federal funding.
Separate money from the direct Federal Emergency Management Agency 404 HMGP and 406 PA was set aside by the Stafford Act to aid in mitigating future recurrence of damages from natural and manmade disasters. The city submitted projects for both city-owned facilities and to support nonprofit organizations identified in the city's plan.
Those nonprofit institutions that had their own HMAPs have incorporated them into the city and county plans.
These storm sewer improvements provide relief to Harris Gully, a major tributary to Brays Bayou and one of the streams most heavily impacted by the flooding of Tropical Storm Allison in 2001. The storm lines provide relief to the main system with two diversions and a 120-inch parallel line.
The diversions are a 78-inch line that routes a portion of the watershed to a point downstream of the original outfall and a 100-square-foot box sewer that diverts the upper portion of the watershed to a point upstream of the original outfall. The projects were funded by disaster mitigation funds following Tropical Storm Allison.
The grants from Hurricane Ike have just begun to be released, but several projects — including the Houston project — have been awarded to local nonprofit organizations to help them prepare for the next event.
Plans must be updated every five years and as new information becomes available.
For example, the performance of Chile's buildings that meet U.S. engineering codes is being analyzed using data from February's earthquake. Hurricanes Ike and Rita prompted substantial changes in sea-level frequency curves and surge-level projections for Texas; recalculating the frequency curves produced higher elevations for 100- and 500-year hurricane events.
Another example of data that must be incorporated into mitigation plans is the recent revision to the Saffir-Simpson scale used to classify hurricanes in five categories according to intensity.
While the previous version based classification on wind speed and storm surge, recent data show that storm surge doesn't always correlate with wind speed. The new scale, named Saffir-Simpson Hurricane Wind Scale, uses only wind speed and provides estimates of the expected impact due to high winds only.
The process of tracking a hurricane is much better than decades ago, and warning systems such as flash flood alerts and real-time modeling and flood inundation mapping are becoming increasingly popular. For mitigation planning, more sophisticated modeling can be used to evaluate the performance of specific flood control structures under hypothetical storm situations or after a real event.
— Penland (firstname.lastname@example.org) is executive director of civil engineering services for Walter P Moore; Salazar (email@example.com) is team director for Walter P Moore's hydrology & hydraulics services.