Extreme weather can result in a violent act of nature, and in the past year much attention has been paid
to the disastrous impacts of flooding during the spring and summer. For example, residents of cities and
agricultural farmland found themselves at odds when the Army Corps of Engineers wrestled with
opening floodgates to channel water away from the metropolitan areas of New Orleans and Baton Rouge
in May 2011, and instead direct the floodwaters to small Louisiana towns and farms.
Water became the enemy, but it might have been an unnecessary role.
"The relationship between flood conditions and the spatial distribution of urban development has been poorly studied,
often because of limitations on available data about stream flow or the common use of generic watershed models
in urban hydrologic modeling," said Glenn Moglen, professor of civil and environmental engineering at Virginia Tech.
Moglen has spent years studying the issue of limiting impervious surfaces such as pavements
that act as impenetrable materials to water. He has called for planners "to allow
a safety margin when regulating land based on imperviousness, to steer development
to already urbanized locations and away from relatively undisturbed locations, and
to take advantage of situations that mitigate the deleterious effects of imperviousness on stream ecology."
Moglen's expertise garnered him an appointment as a special guest editor of an issue of
the American Society of Civil Engineers' Journal of Hydrologic Engineering.
And he has current funding from the Federal Emergency Management Agency to calculate flood magnitudes
as part of the agency's efforts to modernize its maps.
In addition, Moglen and his former Ph.D. student, Alfonso I. Mejia, of Washington, D.C.,
who has now graduated from the University of Maryland, have developed a number of distinct models of
urbanization that show patterns of impact from both sprawl and clustered development that
reduce impacts to water resources. Their work was published in the April 2009 Journal of Hydrologic Engineering.
Moglen said their approach differed from previous studies because they looked at distributed effects
within a watershed and not the aggregate results at the watershed outlet. They also focused
on impacts generated by the spatial forms of urban patterns.
In the article, they cast doubt on land management policies promoting a fixed threshold of
impervious surfaces. They show that this can result in the unintended consequence of
favoring sprawl-type development. "Those within the planning community who espouse
threshold-based controls on land development" should be concerned, they wrote.
In another study for the U.S. Geological Survey (USGS), Moglen and Dorianne Shivers,
of Takoma Park, Md., who also worked with Moglen when she was a student, used data from
78 urbanized stream gages across the U.S. for a study on urban flood frequency.
They compared their models to previous results, and a key finding was a new method for estimating floods
at ungaged sites using common, easily obtained data. This method eliminated the need to
perform costly site visits in order to make urban flood estimates."
Their USGS study also indicated which mathematical models on peak discharges of water were
the best performing — an imperviousness distribution model and a population density
distribution model. "These models depend on three predictors each: rural discharge, imperviousness or
population density, and imperviousness or population density uniformity. The imperviousness or
population density predictor serves to scale up the rural discharge, and the imperviousness or
population density uniformity predictor scales down the discharge. This uniformity predictor
quantifies the homogeneity of the development in a watershed," they concluded.
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