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The term "mitigation" in land development context implies that a not-so-desirable condition will be offset or lessened by human action. Webster’s dictionary says that to mitigate is to make something less severe or painful, to make a condition or situation milder. The Federal Emergency Management Agency’s Mitigation Division says that mitigation is "the ongoing effort to lessen the impact disasters have on people’s lives and property through damage prevention and flood insurance" so that "the impact on lives and communities is lessened." None of this discussion assures complete protection, but merely a lesser degree of damage when a risk threatens.
"Prevention" and "lessening" are difficult to assess in dollars. How do we determine how much was saved when damage did not occur, and lives were not lost? Proving a negative is never easy. Can we estimate that loss was less than expected based on past experience? What is the value of a human life not risked or even lost, whether it be that of the rescuer or the rescuee?
It takes a cumulative approach rather than a piecemeal or tunnel-visioned approach to development within a watershed to reduce risk. One of the great difficulties with the current processes of issuing individual construction permits or even individual Letters of Map Amendment and Revision for flood maps is that the relatively small effect of paving over scattered sites throughout the watershed adds up to a much larger impact on the properties at the bottom of the slope. There is more than one substance that flows downhill. Some of the less liquid forms include litter, drowned animals, motor vehicles, fertilizers, and pesticides. The effects are water pollution, impact damage to structures, and instability of structures due to erosion.
The Association of State Flood Plain Managers (ASFPM) advocates an approach it calls "No Adverse Impact," meaning that thou shalt not do something to your land that adversely affects thy neighbor’s property. ASFPM measures "adverse impact" in terms of increases in flood peaks, flood stage, flood velocity, erosion, and sedimentation. The ultimate goal of "No Adverse Impact" is assessment of the cumulative effects of each change to a watershed, but application of the concept is currently being phased in by some communities more gradually, looking only over the common property line. Municipalities sometimes fear inverse condemnation claims, and also seek that careful balance between generating income and killing the goose that laid the golden egg.
FEMA established the Hazard Mitigation Grant Program (HMGP) to assist property owners in protecting their structures by making them less vulnerable to natural disasters. Retrofitting, elevating, and razing are part of the process. By taking people out of harm’s way, the nation will ultimately reduce the cost of disaster recovery in both dollars and lives. The current federal Administration has slashed the funds available for this program, as its past successes are among the "difficult to measure" returns on investment.
Increasing development has altered the amount of permeable surface in southeastern Pennsylvania, and the watercourses that have not been forced through pipes or filled in are bearing the additional load of surface runoff. Upstream development continues to sprawl, heedless of the repercussions downstream. One of the downstream areas affected by this situation is the Darby Creek, a tributary to the Delaware River that overflows its banks with great regularity in Darby Borough, suffering so many repetitive floods that the Borough decided a few years ago to participate in FEMA’s HMGP buyout program. This was not an easy decision. The owners of the handful of homes backing up to the creek loved the stream when it behaved, an idyllic setting in the suburbs of Philadelphia. Leaving their homes meant uprooting memories, breaking up their community, re-planning their futures. The peace of mind gained by not having to watch the weather and not having to shovel out feet of debris and sediment from their homes was not an equal balance for some. Nonetheless, the Borough did resolve to participate, and the homes were bought out and removed.
In their place, an open space to preserve an unobstructed floodplain became the site of a new park. Supported by the local Riverkeeper organization (part of a network devoted to restoring and preserving the ecological integrity of waterways while protecting citizen rights to enjoy water resources), the scarred landscape was planted with water-tolerant trees and staked for "no mow" protection of the hoped-for meadow. The Delaware Riverkeepers support a riparian buffer program to help communities protect their watercourses while protecting themselves from those same streams. The community becomes involved in the planning and planting of the buffer areas, and the Riverkeepers find a volunteer to monitor the condition and evolution of the new buffers. Since this particular park is my "adopted buffer," I am intimately familiar with the "before" and "after" aspects of its redevelopment as green infrastructure. I’ve monitored the succession of plants taking root (some not so welcome, such as Japanese knotweed and purple loosestrife), mucked through the debris after storms to assess bank stability, and reported on the success and failure of planted saplings, whether due to drowning or deer browsing.
Last fall, when a series of hurricanes battered the area, Darby’s mayor was quoted in the local paper as saying that the buyout and open space did not work–the area still flooded. But that had not been the point. Had there still been a street-full of houses, they once again would have been under water. As it was, the force of the water was sufficient to uproot boulders that had been installed as part of the weir and baffles system meant to redirect the water from its straightest, most scouring route. The sediment deposited by floodwaters extended over the park area and out into the adjoining street. But no homes were damaged, no lives had been risked.
Unfortunately, the phrase "sustainable development" has gained the green allure of mold rather than of meadows, despite its good intentions. Perhaps it is time to replace it with a new phrase that does not cause so many people to tune out what is perceived as regressive rather than progressive. "Mitigation" and "no adverse impact" are aspects of "sustainable development" whose time has come. Can we phrase them in a way that is seen as beneficial to all parties involved?
Wendy Lathrop is licensed as a Professional Land Surveyor in NJ, PA, DE, and MD, and has been involved since 1974 in surveying projects ranging from construction to boundary to environmental land use disputes. She is a Professional Planner in NJ, and a Certified Floodplain Manager through ASFPM.
A 243Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE