Urbanization
leads to creation of impervious surfaces
which lead to an increase in surface runoff volume,
this in turn contributes to downstream flooding
and a net loss in groundwater recharge. Eventually
loss of recharge affects residential and municipal
water supplies.
Minimizing
the disturbance on an urbanizing watershed is
one way of ensuring continued water supply. Since
each land use has a different level of impact,
careful physical planning can minimize these impacts.
Although the impacts of urban sprawl on groundwater
recharge and surface water quantity and quality
are of considerable importance, many planners,
city managers and water resource professionals
lack the ability to provide estimates of the potential
hydrologic impacts of land use change.
Assessment
of the hydrologic impacts or urban land use change
traditionally includes models that evaluate how
land use change alters peak runoff rates, and
these results are then used in the design of drainage
systems. Such methods however do not address the
long-term hydrologic impacts of urban land use
change and often do not consider how pollutants
that wash off from different land uses effect
water quality.
Techniques
traditionally used to assess the impacts of land
use change on runoff typically focus on individual
short-term "design" storm events of specific recurrence
intervals, and are used to calculate peak discharge
rates and hydrographs.
Single
storm methods are suitable as engineering approaches
in estimating flood intensities for stormwater
facilities management, they do not address the
long-term, cumulative hydrologic impacts of land
use change.