Glossary - Living Roofs in Integrated Urban Water Systems - page 169

Hydrograph : the varying relationship between stormwater runoff low rate and
time resulting from a precipitation event. It is often presented as a graph of
low rate versus time for a given storm event.
Hydrological cycle : also known as a hydrologic budget or water balance, it
describes the distribution of water inputs, losses and storage for a given
system (watershed, drainage area, living roof, etc.). Components of the hydro-
logic cycle include precipitation (rain, snow, sleet, etc.), release of moisture
from plants, open water bodies, and soil to the atmosphere (ET), recharge of
deep ground water supplies, and shallow ground water low to recharge
stream base low, and storage (e.g., by soil moisture, atmospheric moisture
and SCMs). For a deined system, the luxes of water amongst components
must be in balance with the amount of water stored in the system, such that
an increase in one component must result in a decrease in one or more other
components.
Irrigation system : technology that supplements receipt of water to plants by
precipitation. In the urban context, preferably harvested rainwater or recycled
grey water is used as the supply source, but potable water can be used.
Several forms of delivery exist, including drip irrigation, basal supply and over-
head sprinklers. Irrigation eficiency on living roofs is substantially different
than at-grade landscapes due to the non-wicking nature of the living roof
growing media. Living roof irrigation should be activated according to the
moisture content of the growing media. Extensive living roofs typically need
little or no irrigation past establishment.
Impermeable surface : constructed surface that prevents rainfall or runoff from
soaking into the ground, generating surface stormwater runoff.
Lightweight aggregate (LWA) : lightweight, coarse granular material compris-
ing the majority of a living roof growing media, or used as a drainage layer.
LWA may be naturally sourced (e.g., pumice) or manufactured (e.g., expanded
minerals such as clay, shale or slate).
Living roof, extensive : a single or multilayered living roof system (drainage,
growing media and plants) designed individually or as composite, manufac-
tured system. The growing media depth may be 25-150 mm, while the
surface may be either level or graded with low topographic features. Extensive
living roofs are vegetated with typically low-growing plants.
Living roof, intensive : a multi-layered system (drainage, growing media and
plants) designed individually or as a composite, manufactured system. The sub-
strate depth is usually 150 mm, either levelled or with variable topographic fea-
tures. Although they are vegetated, they may also incorporate hard landscape
features like paving and structures like pergolas. Vegetation allows and includes
the whole palette of plants from herbaceous plants, to shrubs and trees.
Living roof, inverted assembly : the living roof assembly type in which the
insulation is installed above the waterprooing membrane. Water drains
through the growing medium. A portion of the water then runs above the
insulation to the drainage points. The remaining water drains vertically