Environmental Engineering Reference
In-Depth Information
19. Capture-reuse can be achieved using a subsurface storage reservoir that
provides temporary storage of stormwater runoff. The stormwater storage reser-
voir may consist of clean uniformly graded aggregate or premanufactured struc-
tural stormwater storage units. This type of system is very similar to a subsurface
infiltration system except that infiltration is prevented with a waterproof liner or
the presence of a restrictive soil layer, and a way to reuse the water must be
provided (e.g., pump well, manhole, sump).
Volume Reduction
Based on the area of the roof structure, the potential annual yield can be estimated.
The seasonal variability and demand cycle(s) must be developed to optimize the
storage capacity required. After the water need is determined, choose a structure
that is large enough to contain the amount of water needed. The amount of storage
in the container is equal to the volume reduction.
Peak-Rate Mitigation
Overall, capture-reuse takes a volume of water out of site runoff and puts it
into storage, effectively removing the volume of the rooftop rainfall from the
site runoff. This reduction in volume will translate into a lower overall peak rate
for the site. The proportional reduction is dependent on the size of the rooftop
as compared to the total site impervious cover. In many sites, the use of this
system will meet the regulatory requirements for volume reduction. However,
the potential for pollutant production from the surrounding site landscape and
impervious surfaces should not be neglected and may well warrant additional
water quality mitigation measures, such the use of porous pavements and rain
gardens.
Water Quality Mitigation
The water quality of rooftop runoff will vary with location, type and age of
roofing material, and proximity of localized air pollutant emissions. Pollutant
removal takes place through the settling of particulate matter in the storage unit
and subsequent filtration and disinfection prior to consumption in the case of
potable use. For nonpotable uses, filtration or disinfection is usually not required.
In most locations, roof runoff is as clean or cleaner than surface waters and should
serve well as a source of raw water.
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