16 2Nature, food, and water
Lake10080604020(^0) Reservoir River Stream Groundwater
Ber+
Can•
Atl•
Te g•
Eas•
Kag•
Ott•
Chi+
Sto+
Sdt+
Bar+
Bam+
Phi+
Por•
Iqu•
Nai+
Bei
Mos
San
Lon
Seo*
Primary water-supply source for city
Natural vegetation cover on drainage area
for water-supply source (%)
Figure 6.16Natural vegetation cover on drainage area relative to type of
water-supply source. Drainage area refers to the general area around or upslope of a
watersource (see Color Figures 2--39) and may not correspond with a specific
drainage basin (watershed/catchment). See Chapter5 fornatural vegetation types,
and Figure 6.2 caption for city information.
afamiliar situation around the world. Also chemical pollutants can essentially
eliminate the usefulness of a reservoir (e.g., see large reservoir to the northwest
in Color Figure7).
Awater-supply source on a river is essentially always upriver of a city, since
thedownriver stretch is subject to urban pollutants. As urbanization spreads
upriver, the water-supply source may move further upriver (or elsewhere). There-
fore protection of extensive continuous natural-vegetation cover in areas sur-
rounding upriver and tributary stretches is important. Water treatment costs,
e.g., for lake and river sources, vary widely depending on how well or poorly the
upslope land is protected with natural vegetation. Stream-corridor vegetation
helps, especially for erosion/sedimentation and phosphorus inputs, but covering
the surrounding land with vegetation helps much more.