258 The Barcelona Region’s land mosaic
vegetationalong the gullies is a major determinant of how much enters the
groundwater, and how much becomes downstream flood hazard (Decamps and
Decamps2001). Trees with scattered shrubs and debris from previous floods,
and even herbaceous vegetation, provide friction against flowing water, which
increases absorption into the ground. However, a good shrub cover (e.g., ofSalix
willow) along gullies and streams in the upper portion of a stream system is
an especially effective way to reduce flood hazard downstream. Poplar (Populus)
forwood production, if combined with shrub cover, can provide effective fric-
tion. In the GBRegion two factors tend to remove valuable shrub cover, browsing
bygoats, sheep, etc. and family-food gardening, especially in the long stretches
between towns and villages. Both lead to greater downstream flooding.
The lower portion of a stream system receives the water from upstream and is
thekeyflood hazard area (Decamps and Decamps2001). Floodwaters may cover
thefloodplain valley and cause property damage including bridge washout.
Rich wildlife habitat and biodiversity here are enhanced by: (1) shrub cover;
(2) uprooted floating plants being widely deposited across the lower floodplain;
and (3) diverse surface micro-topography that creates variations in groundwa-
terand surfacewater conditions present. Important recreation benefits can vary
from walking paths near small streams to promenades and ‘‘people parks” by
rivers.Industries, streams, and rivers
Traditionally industries were established along rivers and major streams,
around which villages and towns grew. Today electric power, fuel supplies, and
watersupplies reach across the land and support modern industry. The gradual
removal of old industries from the streams and rivers of the Greater Barcelona
Region would produce an enormous cumulative benefit to natural systems and
people (Color Figure43).(Heavy industry [discussed later] and industrial sites
of exceptional architectural/cultural heritage value of course are special cases.)
Without the existing almost-non-stop stair-stepped sequence of small dams and
elongated ponds, and without the associated need for industrial evaporative-
cooling, less direct evaporation from the stream surface would occur. A more-
natural rapidly flowing and winding river with stretches of splashing riffles that
oxygenate the water would appear. Aquatic habitat heterogeneity would increase,
and more normal-period water flows in the lower portions of rivers would be
restored.
Furthermore, without the input of industrial byproduct wastes, such as met-
als and toxic organic substances, stream and river water quality should greatly
improve. In principle, light, medium, and heavy industries clean their water, e.g.,
in waste-treatment ponds, and pour reasonably clean water back into the stream