EM 1110-2-1100 (Part V)
31 Jul 2003
Insurance Rate Maps (FIRM's) prepared by FEMA. A storm surge elevation at the one percent exceedance
level (100-year recurrence interval) plus waves is employed to determine risk and insurance rates for
individual properties located on the flood maps. Insurance rates are much lower for structures elevated above
the 100-year flood level and is a requirement for all new construction in the coastal, high-hazard zone
(including waves). In effect, these regulations become floodplain zoning laws applicable to individual
property owners and have resulted in a reduction in Federal government expenditures for insurance claims
and disaster assistance benefits (National Research Council 1990).
(2) Setback limits. A second way to adapt is to limit construction close to the shoreline. The NOAA has
identified land-use planning and construction siting as the most effective means to reduce coastal storm
hazards, particularly on eroding coasts. Here, the mechanism to require change in old construction practices
is the Coastal Zone Management Act (CZMA) of 1972. Through the CZMA, the NOAA provides funds to
individual states to help solve their own coastal hazard problems. As a result, many states have developed
coastal construction setback lines and zones that include historic erosion rates at each site. The methods,
definitions, widths, etc., vary from state to state as summarized in Part V-8. A key element is the historic,
average erosion rate at each site. Presently, FEMA does not include delineation of erosion zones and erosion
hazards on its flood maps. Methods to incorporate both coastal erosion (National Research Council 1990)
and beach nourishment (National Research Council 1995) in the national, flood insurance program have been
proposed but have yet to be formally adopted. Clearly, coastal erosion increases the risk and beach
nourishment reduces the risk of coastal flood and wave damage.
Retreat is the final adaptation option. Relocation here also considers abandonment and demolition. To some,
retreat is the only option. But practically, all constraints (economic, environmental, social, legal, etc.) must
be evaluated for this alternative as well as for all others as previously discussed. This approach may be
employed by the Corps as the Federal government agency designated by Congress to protect the nation's
shores from the chronic effects of erosion and coastal flooding. Two examples illustrate the USACE's
approach and focus on why the retreat alternative was selected.
(1) Cape Shoalwater, Washington. The northern shoreline of the inlet to Willapa Bay, Washington, has
been receding at an average rate of 30 to 40 m/year for over 100 years (Terich and Levenseller 1986).
Erosion of this area (Cape Shoalwater) has been faster and has lasted longer than any other site on the U.S.
Pacific Ocean coast (Komar 1998). Natural, northern migration and progressive deepening of the channel
inlet are the two main factors responsible for erosion of the cape. A few homes have been lost, a lighthouse
destroyed, the main road moved inland and a historic, pioneer cemetery relocated in this rural area.
(a) In the 1960s and 1970s, the USACE studied the construction of a jetty to stabilize the inlet location
and reduce the erosion of the cape. They concluded that a structural solution was not economically feasible
to the Federal government. The USACE recommended that if Federal government funds were available at
this site, they should be used to purchase land threatened by future erosion. However, no Federal project for
relocation could be justified based on the relative benefits and costs to the Federal government.
(b) The rural area (low benefits) and extremely high erosion rate (high costs) were responsible for this
outcome, as may have been expected. At other sites, this result is not as obvious.
(2) Baytown, Texas. The northern, upper end of Galveston Bay on the Gulf of Mexico includes Burnett,
Crystal, and Scott Bays and low-lying areas that are part of Baytown, Texas, about 24 km east of Houston.
Flooding occurs routinely from minor storms and is compounded by subsidence of the ground surface.
Withdrawal of oil and gas and groundwater for the metropolitan area of Houston produced 2.5 m (9 ft) of
subsidence between 1915 and 1975 (U.S. Army Engineer District, Galveston, 1975).
Shore Protection Projects