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