Attaining Sustainable Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 508

employed for science-based landscape planning (Section 15.3), including the flows
of matter and energy onto specific sites, and landscape stability assessment.
• Unconformities . Geologic maps can highlight unconformities which may serve as
preferred natural pathways for the migration of contaminants.
• Anthropogenic disturbance . These outputs often identify human-induced pathways
for contaminant migration.
• Soil characterization . The soil samples taken at environmental investigations can
characterize the soils within the watershed and update the county soil survey
maps. This information can be used to implement terrain-specific erosion control
measures and reduce the loss of soil and the accompanying transport of heavy
metals into aquifers and streams.
• Groundwater flow, recharge zones, and contaminants . Combining the outcomes from
geological investigations and geologic maps permits the identification of ground-
water flow paths and recharge zones near high levels of contaminants in soil. This
information can assist wellhead protection efforts within the watershed through
the determination of appropriate capture zones computed from the hydraulic con-
ductivities of the aquifer.
In addition to the opportunities for source control produced from parcel-scale geological
investigations, there is the potential to apply integrated source control measures to atmo-
spheric processes such as precipitation and sensible heat transfers at the watershed scale:
• Sample the precipitation and develop a map of the pH distributions throughout the
watershed . Without cooperation across watershed boundaries, it will be impos-
sible to restore the pH to natural levels (pH = 5.6). Nevertheless, knowing the
pH distribution can identify areas where lower-pH precipitation may mobilize
heavy metals in soil and release them to groundwater. Once identified, the risks
of metals migrating to groundwater in these areas can be reduced by adding
vegetation to increase interception and raising the organic content of the soils.
• Develop a micro-climate classification map for the entire watershed with the objective of
ameliorating the effects of heavy thunderstorms . Begin by identifying those areas emit-
ting excessive amounts of sensible heat. Follow this with a tree pattern analysis
using aerial photos and ground surveys. Trees should not be planted until a cer-
tified arborist and a geologist have been consulted to optimize new tree plant-
ing locations. Those areas selected should have soil suited to native species and
an ability to intercept significant precipitation. Other considerations include the
potential to increase infiltration rates and the placement of trees at locations where
they do not become conduits for contamination released at the surface. Certain
trees such as willows can evapotranspirate large amounts of water per day (Minor
2009), and this capability reduces ambient air temperatures. Wherever possible,
the sensible heat management strategies—such as green roofs—should be linked
to stormwater management efforts.
• Get vertical with stormwater management . Figure 16.1 shows the paths of stormwater
in an urbanized watershed.
The arrows between the paths indicate the primary direction for the water flow. With
the exception of the vertical roof to downspout flow, the remaining components transfer