Agriculture Reference
In-Depth Information
600
Design storm depth (mm)
15 mm
20 mm
25 mm
30 mm
500
400
300
200
100
0
0
5
10
15
20
25
30
35
40
45
50
60
70
Plant available water (%)
For stormwater
retention, depth of a
inished living roof is
determined according to
the size of the design
storm and the growing
media's
PAW
Colorado, the design storm depth for water quality treatment is ~15 mm of rain-
fall (UDFCD 2010). In this case, with
PAW
= 25 percent, the calculated growing
media depth would be:
D
LR
=
DSD
PAW
=
15
_____
_____
0.25
= 60 mm
(4.2)
While 60 mm of this particular growing media may adequately retain the water
quality design storm, the semi-arid, continental climate zone means that plant
water stress will be signiicant. Increasing the growing media depth provides a
supplemental reservoir, and greater resilience against elevated temperatures. In
Pennsylvania, Thuring
et al.
(2010) demonstrated that the shoot production of
three varieties of succulents (two of which were sedums) responded strongly to
changes in growing media depth, while depth and drought conditions affected
biomass development for two herbaceous grasses.
For new construction, in order to encourage long-term survival of a broader
range of plants (with potentially minimal or no regular irrigation in temperate to
subtropical climates, except drought periods), a minimum of 100 mm of growing
media is encouraged. To bolster plants for winter survival in latitudes north of
40°N, Boivin
et al.
(2001) advocated a minimum of 100 mm growing media. In
retroit applications, the minimum depth criteria could be relaxed to approxi-
mately 50 mm, but a narrower plant palette is feasible with likely requirements
for periodic irrigation if the roof is visible.
At the upper end of the recommended growing media depth, empirical evi-
dence suggests that doubling media depth does not equate to doubling rainfall
capture for water-holding capacity greater than about 20-25 mm. If a growing
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