Looking Glass River Watershed Management Plan - Greater ...

Altered Hydrology
Stream flows vary in characteristic ways over time frames ranging from
hours and days to seasons and years. The flow regime includes such factors
as the magnitude and frequency of floods and low flow periods, the seasonal
occurrence of various flow rates, and the rates of change of flow. The flow
regime of a stream reflects the operation of the hydrologic cycle within its
watershed. Climate, topography, geology, soils, vegetation, watershed size
and shape, stream pattern, land use, water use, and dams all impact the
timing and pathways of water movement to and through stream and hence
the stream’s flow regime.
Altered hydrology is not a pollutant in the terms of heavy metals or
pesticides, but does affect biota and stability of streams and rivers. Changes
in hydrology typically increase the volume, frequency, and peak discharges
of the stream. These changes may cause streambank erosion, sedimentation,
and poor conditions for plants, fish and macroinvertebrates. In addition the
surface runoff from precipitation collects and transports various pollutants to
the receiving waters thus not only affecting the flow characteristics in the
receiving water but also the pollutant concentrations.
Sources
Hydrology changes in receiving water courses are due to a loss of infiltration
into the soil, a loss of evaporation, loss of storage or increased flow
channelization. These occurrences are typical of development regardless of
the new land use. For example in urban areas loss of infiltration, storage and
evaporation result as impervious surfaces are created and the soil is
compacted due to construction operations. Refer to the discussion on the
relevance of impervious cover in Section 3 for additional information.
Another key cause of changes in hydrology is the loss of storage such as
wetlands and floodplains. Wetlands are discussed in Section 2 and show
that the majority of the existing wetlands are located in the eastern half of the
watershed which is generally the less developed areas. The future land use
discussion, also in Section 2, indicates that significant growth is expected in
this same eastern half of the watershed potentially threatening the existing
wetlands and potentially exasperating the future hydrology concerns.
Table 5-3 summarizes various sources of changes to the hydrology. The
sources and causes were ranked by reviewing all of the collected data
(Section 2 and 3) and combining it with the knowledge of staff from the local
communities.
5-8 Looking Glass River Watershed April 2007