4 Solutions for Stormwater
Do you have a strategy to minimize flood damage and stormwater fees?
Fierce debate continues over the cause and impact of climate change, but few deny that parts of the coun- try are experiencing fiercer weather and heavier bouts of damaging stormwater. Building codes and regula- tions are becoming increasingly strict about managing stormwater on site to avoid any runoff that overloads collection systems and pollutes the environment.
Facility managers should assess their property’s risk of
stormwater flooding. The assessment should evaluate not only
probable volume but velocity, as the force of stormwater can
cause its own damage.
FMs should also investigate any stormwater utility fees that
may apply to their facility. Typically they are calculated on the
impervious area of a property, including roofs, parking lots,
roads and driveways. Retrofitting these areas as part of a stormwater strategy minimizes the fees.
Think about Permeability
Look up to your roof as one possible stormwater solution. For
existing buildings, a modular vegetated roof may fit the bill.
Modular systems consist of interlocking trays with pre-grown
vegetation. They are mobile and able to be carried to the roof
for easy installation. Individual trays can be replaced without
disturbing the entire installation if vegetation is not growing well.
They can also be removed if roof repairs are needed.
A modular vegetated roof is particularly well suited to existing
buildings because of its comparatively light weight. Jennifer
Cooper, Landscape Architect in the San Francisco office of
Perkins+Will, explains that an engineer should be consulted
to determine roof load capacity. The weight of a modular roof
with 4 inches of topsoil is 32-35 pounds per square foot and
costs $20 to $30 per square foot.
Cooper recommends tray systems with water reservoirs
because these have capacity beyond that of the soil itself. The
trays hold an inch or so of additional water, reducing water
runoff and promoting deeply rooted plants because the roots
grow down to access the reservoir water. For rain storms that
are high frequency but low volume, the tray system’s soil and
water reservoirs can often hold or absorb all of the water without runoff.
Given that paved and pavered ground surfaces account for
a large area of many properties, they also play an important
role in a stormwater strategy. The joints in between permeable
pavers allow stormwater to pass around individual pavers and
into the ground. Pervious block pavers are interlocking grids
of blocks with cells or voids through which water can flow. The
voids can be seeded with grass. Porous pavement is a mix of
concrete or asphalt with pores that allow stormwater to flow
through the material. Each of these options has varying properties, costs and adaptability to specific applications. One factor
to consider is the volume of vehicle traffic expected.