montgomery county today
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When rain falls on
undeveloped
land
, half of it soaks into the
ground, replenishing groundwater or
soil moisture.
As land is developed, even at
rural
densities
, there is a loss of vegetation,
and an increase in hard surfaces.
In this scenario, runoff doubles, and
there is a corresponding loss of 10% or
more in infiltration.
Suburban style development
has even
more hard surfaces, in the form of
rooftops, roads, sidewalks, and
compacted soil.
Because of impervious surfaces, over
50% of rainfall can become runoff in
boroughs and older urban areas
.
Stormwater BMPs, like the raingarden on the
left and the porous pavement on the right, can
be used to capture runoff from impervious
surfaces. Once captured, the rainwater can be
allowed to infiltrate into soil, or it can be
released slowly to prevent flooding. Often the
stormwater that flows through a BMP is filtered
and cooled, so that impacts to the receiving
stream are minimized.
FIGURE 117:
Impacts to the Hydrologic Cycle from Development
