Glossary - Living Roofs in Integrated Urban Water Systems - page 171

Program : a particular function or use of a space or building. Spaces often have
multiple programs. The lexibility of a space is dependent on its users and also
on inherent lexibility of the designed space. For example, the program for a
living roof might be a recreational space for building users or inhabitants as
well as being a stormwater mitigation strategy for the site.
Rational method : widely employed in predicting peak runoff rates in the design
of urban drainage systems. The method is a simple empirical formula that
relates the peak low rate (Qp) to the drainage area (A), a constant rainfall
intensity (i) and a runoff coeficient (C).
Receiving water : a general term for a water body into which runoff and pollut-
ants are discharged. Runoff and pollutants may be discharged with or without
treatment to receiving waters via surface runoff or through networks of pipes
and channels.
Retention (of stormwater) : techniques used to reduce the total volume of
stormwater runoff discharging from a site (or watershed) into a downstream
receiving environment. Retention may be provided by stormwater control
practices such as living roofs, bioretention, permeable pavements, groundwa-
ter iniltration and cisterns with plumbing for rainwater harvesting and reuse,
among others.
Saturation : a soil or media moisture condition in which all pore space is occu-
pied by water. Appropriately designed living roofs should have adequate per-
meability such that they never reach saturation.
Scale (in the built environment) : the size of a space relative to another. Scala-
bility of a design solution (system or single entity, physical entity or strategy) is
a pertinent issue when assessing its viability, as not all design solutions operate
well at all scales. Living roofs, especially within a holistic stormwater manage-
ment framework, have the ability to operate at multiple scales - if designed
and constructed properly, they can fulill stormwater management and other
design objectives at the scale of a single building, and can also impact the
natural and social ecosystem positively at the neighborhood scale.
Sedums : a hardy variety of succulents, with an excellent ability to survive in
droughty, shallow growing environments, making them a popular choice in
plant selection for extensive living roofs. Many sedum varieties exhibit CAM -
some exclusively CAM, while others luctuate between CAM and C3 photo-
synthesis, rendering them highly adaptable to varying moisture availability.
There are over 600 varieties of sedums, offering a wide range of visual
impacts, although some species exhibit relative tolerances to climate.
Stormwater control measure (SCM) : built, engineered devices to reduce
stormwater runoff volumes, low rates and contaminant loads.
Stormwater management : the control of discharges of surface runoff, in this
book with reference to urban environments. In GSI, stormwater management
includes on-site retention to limit runoff volumes, temporary detention to
further reduce peak lows, and source control to prevent discharge or provide
treatment to reduce discharged amounts of a range of contaminants.