River Ecology and Restoration - River Dynamics and Integrated River Management - page 654

(a) (b)
Fig. 10.30 (a) Waste water from a factory is discharged into the Jialing River and seriously polluting the river water;
(b) A frog is killed due to the pollution
(a) (b)
Fig. 10.31 (a) Urban sewage polluting a stream flowing through the Dalian in northeast China; (b) Eutrophication
of the Lijiang River at Guilin, a famous tourism attraction for its beautiful landscape and streams
Urbanization —Urbanization in watersheds poses special challenges for stream ecological management.
Recent research has shown that streams in urban watersheds have a character fundamentally different
from that of streams in forested, rural, or even agricultural watersheds. Impervious cover directly influences
urban streams by dramatically increasing surface runoff during storm events by 2 to 16 times, with
proportional reductions in ground water recharge (Schueler, 1995). Figure 10.32 conceptually shows the
effects of different amounts of impervious cover on the water balance for a watershed.
The unique character of urban streams often requires unique restoration strategies for the steam
corridor. The peak discharge associated with the bankfull flow (1- to 2-year flood) increases sharply in
magnitude in urban streams. Since impervious cover prevents rainfall from infiltrating into the soil, less
flow is available to recharge ground water. Consequently, during extended periods without rainfall, baseflow