Agriculture Reference
In-Depth Information
Property damage, loss of life
250
Approx. range channel
forming lows
200
150
Approx. range for water quality
100
1-year, 24-hour
Approx. range for recharge
50
90%
12mm
0
0
10
20
30
40
50
60
70
80
90
100
Percentile rainfall event
extensive land use restrictions, altogether increasing cost for marginally
increased beneit.
In hydrologic terms, the 75th-95th
percentile events are considered small to
medium sized storms, for which living roofs are very effective at controlling the
runoff volume and peak low rate (
Section 2.5.1
). Since the vast majority of all
rainfall events are in this category, living roofs can make a large contribution to
planning for comprehensive stormwater management. In some receiving environ-
ments, this may sufice for regulatory compliance. Elsewhere, living roofs should
be seen as a complement and mechanism to reduce the size of conventionally
designed ground-level or subsurface SCMs.
Figure 2.1
Example rainfall
frequency spectrum for
Minneapolis, Minnesota
(Rainfall spectrum
retrieved from Minnesota
Pollution Control Agency
[2013]. Indication of
approximate impacts are
superimposed by this
book's authors).
Quantitatively, addressing the range of stormwater impacts from frequently
occurring rainfall events presents a signiicant departure from conventional SCM
and drainage design procedures embedded in many municipal codes. Living roof
design professionals face an uphill battle where regulatory requirements enforce
only historical perspectives on stormwater management, or where quantitative
GSI design procedures have not yet been adopted.
Conventional stormwater management approaches apply an end-of-pipe
design approach to capture and treat urban runoff, once generated, with little
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