Introduction - Living Roofs in Integrated Urban Water Systems - page 6

Evapotranspiration Rain

Irrigation

Water
collection

Living Roof
Social amenity

Evapotranspiration

Toilet
ushing

At-grade garden/
urban agriculture

Irrigation

Cistern Pump

promoting urban biodiversity, contributing to carbon neutral or mitigation strate-
gies, noise pollution (acoustics) dampening, social and amenity value, absorption
of atmospheric pollutants, and stormwater runoff reduction. Indeed, living roofs
are one of the few technologies that may provide multiple functions for environ-
mental management.

Figure 1.2
Living roof: a tool with
multiple beneits

1.2.1 A stormwater control measure
In rural to suburban or urban transformations where land is readily available,
holistic stormwater approaches often center around opportunities for runoff to
soak (iniltrate) into the ground, usually via vegetated SCMs. Many cities currently
aim to densify accommodation and ofice space in the downtown and regional
cores, yet city boundaries still expand. In these dense urban areas ground-level
SCMs may be impractical, ineffective, infeasible or cost-prohibitive. Land prices,
poorly drained subsoils (due to repeated earthworks, shallow topography, high
water tables or clay soils) and signiicant underground development (such as
subways) are challenges for SCMs designed to discharge water into the ground.
Conversely, rooftops provide productive opportunities for stormwater mitigation
while creating amenity and architectural value.
The greatest contribution of living roofs to stormwater control is the contribu-
tion to mitigating runoff hydrology. At the site or building scale, studies show
that runoff is often eliminated altogether for small to medium sized precipitation
events (usually considered < 25 mm of precipitation, but this igure depends on
location). When runoff is generated, low rates are substantially less than a com-
parable conventional roof surface and hydrograph (the variation of low with
respect to time in a storm event) timing is modiied (Carpenter and Kaluvakolanu
2011; Carson et al. 2013; Fassman-Beck et al. 2013; VanWoert et al. 2005; Vil-
larreal 2007; Villarreal and Bengtsson 2005). Even during large (> 25 mm) or
back-to-back storm events, living roofs can provide measurable reductions in
runoff potential, and reliable peak low attenuation (Carpenter and Kaluvakolanu