Environmental Engineering Reference
In-Depth Information
Water Body/Hydrologic Modification
Many stream restoration projects involve the realignment or reconfiguration of a stream channel
to mitigate the impacts of prior channel alterations. Sometimes there is a need to raise the bed
of an existing degraded channel using various channel improvement structures to restore the
hydrologic connectivity of a stream with its floodplain such that overbank flooding will occur at
appropriate frequencies. The same concept would apply to lake restoration. Other times, there
is only the need to return water to restore the project site. In these cases, control structures that
regulate the inflow and outflow of water are sometimes needed to compensate for altered site
conditions.
In coastal areas, the most common action is providing for the return of tidal flows. Once
breeching a levee, the distribution of the water over the newly flooded land needs to be regulated,
sometimes by channels or control devices that regulate elevation and duration of tidal inundation
because in many cases the land has subsided during the time period of being isolated from the
tidal waters. In these cases, it is important to have a hydrologist or surveyor determine the relation-
ship between land surface elevations and tidal elevations at your specific location. Some riparian
restoration projects involve the lowering of portions of a site adjacent to a stream channel or on a
floodplain to achieve a desired frequency of inundation by floodwaters or a desired elevation above
the shallow groundwater table. Vernal pool restoration projects sometimes involve excavating new
pools and then lining the pools with appropriate soil materials.
Landform Modification
Some restoration projects require significant reconfiguration of land contours prior to revegeta-
tion. Major site modifications are commonly associated with lands used for material extraction
(i.e., mining sites). Several decisions are required when working with abandoned material sites
or other similarly degraded lands. The issues of slope, aspect, and shape of the slopes all need to
be addressed when considering the vegetation to be introduced. Abandoned farmlands typically
range from very flat to rolling hills and lack sufficient microelevations that create microhabitats
important in providing for species diversity. The vernal pool ecosystem requires a very small scale
microrelief of shallow depressions and mounds in between with very shallow slopes.
In many cases, the land modifications required on a site may not involve the actual restoration
work planned but are required because the existing landform is a source of constant degradation.
Over the past half century, numerous techniques have been developed with the goal of stabilizing
slopes, affecting stream courses through natural means, enhancing in-stream fisheries habitat, and
providing erosion and sediment control. The use of these techniques requires following a series
of established procedures while using specific material to accomplish the desired goal. Topics in
this category include assessment techniques, biotechnical solutions such as soil bioengineering
and biotechnical slope stabilizations, and watershed stewardship. Many of these techniques have
been standardized to permit the development of manuals to increase repeatable results within
the parameters of the technique requirements. While standardized in how these techniques are
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