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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

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