Environmental Engineering Reference
In-Depth Information
after this period, except during prolonged drought or if a “fresher” appearance
is required. Ensure that the maintenance plan includes a watering schedule for
the establishment period and in times of extreme drought after plants have been
established.
2. While vegetation is being established, remove any weeds by hand (weeding
frequency should decrease over time, as rain garden plants grow).
3. Although plants may need occasional pruning or trimming, rain gardens
should not be mowed on a regular basis. Trim vegetation as necessary to maintain
healthy plant growth.
4. Replace dead plants. If a particular species is more prone to mortality, it
may need to be replaced with a different species that is more likely to succeed
in the rain garden.
5. Mulch should be reapplied when erosion is evident. In areas expected to
have low metal loads in the runoff, mulch as needed to maintain a depth of 2 to
3 in. In areas with relatively high metal loads, replace the mulch once per year.
6. Rain gardens should be inspected at least twice a year for sediment buildup,
erosion, and to evaluate the health of the vegetation. If sediment buildup reaches
25% of the ponding depth, it should be removed. If erosion is noticed within
the rain garden, additional soil stabilization measures should be employed. If
vegetation appears to be in poor health with no obvious cause, a landscape
specialist should be consulted.
Cost of Rain Gardens
Rain gardens often replace areas that would have been landscaped and main-
tenance-intensive, so the net cost can be less than the conventional alternative. In
addition, the use of rain gardens can decrease the cost for stormwater conveyance
systems on a site. Rain gardens cost approximately $5 to $7 per cubic foot of
storage to construct.
Vegetated Roof Systems
Design Considerations
1. The live- and dead-load bearing capacity of the roof must be established.
Dead loads should be estimated using media weights determined using a stan-
dardized laboratory procedure.
2. Waterproofing materials must be durable under the conditions associated
with vegetated covers. A supplemental root-barrier layer should be installed in
conjunction with materials that are not root-fast.
3. Roof flashings should extend 6 in. higher than the top of the growth medium
surface and be protected by counter flashings.
4. The design should incorporate measures to protect the waterproofing mem-
brane from physical damage during and after installation of the vegetated cover
assembly.
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