2. • Depth vs. Edge Condition
• Native Plants in a non-native
condition
• Safety considerations
• Treatment options can attract
invasives
• Maintenance considerations
• Can you address a sense of
place?
Integrating Treatment
with Design
Considerations
9. Natural materials, create transition
into surrounding landscape.
This fits perfectly with the client’s
greater image, treats stormwater
and meets LEED criteria, by
integrating the design into the site
we can create an amenity out of a
necessary function.
10. Consider construction
and survival of plant material.
Graphic obtained: Landscape Architectural Graphic Standards - Leonard J. Hopper, RLA, ASLA
Considerations for damage
Bio-retention areas/ Rain Gardens
should never double as
snow storage areas.
12. Gravel Wetlands
Considerations:
• Great for retro-fitting old quantity detention ponds
• Great for Nitrogen Removal
• Generally less impacted by temperature
• Soils are not a factor as it is fully lined
• Better suited for limited outlet conditions 4-8”depth vs. 30”depth
• Cost is generally higher than pond and similiar to underdrain soil filter
clogging and will prevent flows out of the filter. The geotextile fabric shall be Mirafi
170n or equivalent.
8” (20 cm) minimum
thickness of wetland soil
24” (60 cm) minimum thickness
of 3/4” (2 cm) crushed stone
(gravel)
3” (8 cm) minimum thickness of
graded filter (i.e., pea gravel) if
needed
Low permeability soil or
liner if underlying soils are
very permeable
Figure 3: Diagram of typical gravel wetland construction.
Gravel Wetland Drain Design
13. Gravel Wetland Design Specifications Page 1 of 10
Stormwater Manual - City of South Portland, Maine www.southportland.org
primary outlet. To maintain the system in its saturated condition, it must be situated in low
hydraulic conductivity soils or lined below the gravel layer. Because infiltration is not designed
to occur, separation from groundwater is not required and the GWs are sited much like
stormwater ponds.
Figure 1: Diagram of a gravel wetland. Source: UNH Stormwater Center.
How does it work?
UNHSC
Subsurface Gravel Wetland
Design Specifications
June 2009
Image and Figure from:
University of New Hampshire Stormwater Center
• Treatment comes through uptake of plants rather
than infiltration
• Underlayer is always wet.
• Aesthetics around the basins to create better
sense of natural environment
