Environmental Engineering Reference
In-Depth Information
Roof
Downspout
Driveway
Road surface
Curbs
Storm sewer pipes
Outfall (local water body)
FIGURE 16.4
Source control for urban stormwater on the land parcel (circled).
circle in Figure 16.4 indicates the step in the flow sequence where human intervention can
achieve negative feedback and help return the runoff system to equilibrium.
Retrofitting developed urban areas for stormwater source control follows a key principle
of science-based landscape planning—do not do anything until you evaluate the capabil-
ity of the landscape. Even in developed areas, there is substantial capability to store water
before building additional infrastructure. Many of the general source control measures
and micro-topographic opportunities for stormwater management were presented for this
type of landscape in Chapter 13.
Vertical routing of stormwater also provides a new opportunity to design engineering
approaches that use this water as an asset, instead of treating it as something to trans-
port away quickly. The major residential uses of water are for toilet flushing and lawn
watering—two uses not requiring municipally treated potable water. A combination
of cisterns, rain barrels, low-cost filters, and simple plumbing modifications can make
downspout water available for these uses.
•
Link performance standards to source control
. Performance standards specify an
environmental condition that must be met to achieve a broader set of goals, such
as reducing pollution. For example, one performance standard found in many
municipalities is “post-development runoff must not exceed pre-development
runoff.” When planning at the site scale, proposed developments lying within
zones of high water retention capacity should not be allowed to sacrifice this
capability. Information from geologic investigations can identify these locations.
Instead of building infrastructure such as detention ponds to meet a performance
standard, the natural capacity of the landscape to hold water can be preserved.
This approach is a win-win situation for environment preservation and economic
development, which often conflict. Developers, instead of having to dedicate valu-
able property to detention storage, can take advantage of the landscape's capacity
to store water and not use valuable real estate for stormwater control. Residents of
the development then do not have to worry about maintaining the ponds, which
are prone to sedimentation. The environment wins because detention ponds rep-
resent an end of the pipe treatment that disrupts the local hydrology by moving
water out of its natural path.
16.3.2 Preserve Undamaged and Minimally Damaged Land
Any attempt to attain a sustainable urban watershed should capitalize on the assets avail-
able. If what humans have done to the land creates the most contamination in urbanized
watersheds—then what we have not done to the land in these locations must become part
of the solution. Land that is undamaged or minimally damaged is an asset, because it
can provide a starting point for overcoming human impacts on stream channels, aquifers,
and watershed ecosystems. Properly applying this principle requires a thorough knowl-
edge of how specific landscapes were formed and how they were subsequently altered by
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