Glossary - Living Roofs in Integrated Urban Water Systems - page 168

Establishment : period of time required for the growth of plants to create full
coverage.
Evapotranspiration (ET) : the simultaneous release of water from plants and
evaporation of moisture from soil or growing medium. On a living roof, ET is
the process by which the assembly dries, or “empties” stored water (retained
rainfall), thereby enabling the system to capture the next rainfall event. ET
inluences the extent to which consecutive storm events may be retained, or
partially retained by a living roof system, as well as the overall appearance and
health of the plant community. Potential ET is the theoretical rate at which
water loss should occur if water were readily available, and is often deter-
mined using models derived from agricultural applications. In a living roof
environment, the rate of actual ET is strongly inluenced by the amount of
(usually limited) water present in the growing media at any given time.
Experiential design : design of a space or series of spaces that addresses the
experience of the inhabitant or occupant. Experiential design differs from pure
aesthetics in that it focuses on what a space does for the inhabitant rather
than how it appears. It is not design that constructs emotions, but rather
elicits, frames and supports them.
Field capacity : the maximum amount of water that a soil or growing medium
can store against gravity drainage. It is usually determined as moisture content
per unit depth of media.
Green infrastructure (GI) : in holistic urban design, a combination of natural
and engineered infrastructure to provide or restore ecosystems and ecosystem
services. The term green stormwater infrastructure (GSI) is speciically used to
identify approaches for runoff management. GI and GSI may be considered
similar to or synonymous with LID and WSUDs.
Grey infrastructure : inorganic, engineered infrastructure used for the convey-
ance of people, goods, energy and other resources. Grey infrastructure is
coined “grey” because of the concrete and steel of its typical makeup. In
stormwater management practice, grey infrastructure implies conventional
sanitary and storm sewers (often combined), culverts, dams, and other rela-
tively inlexible water holding and conveyance structures.
Greywater : wastewater typically comprised of water used in building services
(e.g., sinks, laundry, showers), excluding sanitary waste (i.e., from toilets and
urinals), that can be reused for non-potable water demand with little or no
treatment. In holistic stormwater management, greywater can be recycled to
irrigate rooftop and at-grade vegetation, avoiding the use of potable water.
Growing medium : in living roofs, the layer in which rooftop vegetation estab-
lishes its roots and where the majority of stormwater retention is provided.
The appropriate choice of composition of the growing media is crucial to the
performance of almost all aspects of the living roof system. It is typically a soil-
less engineered medium, and sometimes called substrate. High water-holding
capacity and permeability, and low organic content characterize minimum cri-
teria for appropriate growing media for extensive living roofs.