Introduction to Stream Restoration - Hydro-Environmental Analysis: Freshwater Environments - page 215

ian zones in the southwest, and 40% of U.S. waterbodies currently do not meet water quality
standards.
In addition to channel alterations, watershed impacts such as those due to urbanization, agricul-
ture, or forestry practices also directly impact the functioning of rivers and streams. For example,
urbanization usually results in increases in impervious areas (roads, parking lots, etc.) that may
increase cumulative runoff lows and the rate of runoff. Individual changes in land uses or the
cumulative impacts of land uses in a watershed directly impact receiving waters. Wesche (1985)
describes the chain of events that lead to (FISRWG 1998) (Figure 8.4):

• Changes in land use that lead to changes in geomorphology and hydrology

• Changes in stream hydraulics, sediment transport and storage

• Changes in the functions of stream habitats

The potential effects of changes in land use activities as tabulated by the Federal Interagency
Stream Restoration Working Group (FISRWG 1998) are listed in Figure 8.5a,b.
The lack of natural and unimpaired streams and rivers introduces an additional complexity to
restoration in that since there are so few undisturbed streams, many of the characteristics of natural
systems, such as the natural low regime, are only poorly understood and quantiied. In addition,
determining the extent of impacts and establishing restoration goals are often based on a compari-
son of existing conditions in a stream or river with some reference stream or river considered to rep-
resent an undisturbed or acceptable condition. The paucity of undisturbed streams makes locating
representative reference conditions dificult.

Changes in
land or stream
corridor use

Changes in
geomorphology
and hydrology

Changes in
stream
hydraulics

Changes in function
such as habitat,
sediment transport,
and storage

Changes in
population,
composition, and
distribution,
eutrophication,
and lower water
table elevations

FIGURE 8.4 Chain of events due to disturbance. (From FISRWG, Stream Corridor Restoration: Principles,
Processes, and Practices , Federal Interagency Stream Restoration Working Group, 1998.)