Rivers and Streams, Characteristics - Hydro-Environmental Analysis: Freshwater Environments - page 44

impervious area (such as due to paving and concrete) often increases, impacting the timing and mag-
nitude of runoff. Changes in riverine characteristics may also occur due to the impact of landscape
changes on evaporation and precipitation. Changes may also occur in river lows over time due to
development as usage patterns for groundwater change, with the resulting impacts on river recharge.
One consequence of these changes is that historical data, such as river lows, are often not good predic-
tors of present or future lows, which impacts the validity of design conditions for river management
estimated from historical data, as introduced in the previous paragraph and as will be discussed in
Chapter 3.
2.2.5 r eGuLated VerSuS u nreGuLated r IVerS
The goal of many projects is to restore the natural function of rivers. However, undisturbed or
unregulated rivers or streams are rare. If the stream channel itself is not altered (such as by “realign-
ment” or straightening), then hydraulic structures or other hydraulic modiications may impact the
lows. Changes in the watershed that impact lows and sediment loads may also cause systems
to be out of equilibrium with their sediment loads, resulting in bank sloughing and other factors
impacting channel evolution. The degree of modiication and the impacts of that regulation have
far-reaching consequences on river systems and their management. Some of the characteristics of
regulated rivers are discussed in Chapter 3.
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