River Ecology and Restoration - River Dynamics and Integrated River Management - page 690

Hinckley, 1982; Chapman et al., 1982). This type of information can be coupled to site moisture conditions
predicted by applying discharge estimates or flood frequency analyses to the inundating discharges of
sites in the riparian zone. The resulting relation can be used to describe the suitability of sites for various
plant species, e.g., relatively floodprone sites will likely have relatively flood-tolerant plants. Inundating
discharge is strongly related to relative elevation within the floodplain. Other things being equal (i.e.,
within a limited geographic area and with roughly equivalent hydrologic regimes), elevation relative to a
representative water surface line, such as bankfull discharge or the stage at mean annual flow, can, thus,
provide a reasonable surrogate for site moisture conditions. Locally determined vegetation suitability can
then be used to determine the likely vegetation in various elevation zones.
10.4 Restoration Strategies
“Leave it alone and let it heal itself.” In some cases, the best solution to a river ecological problem might
be to remove the stresses and “let it heal itself.” Unfortunately, in many cases this process can take quite
a long time. Therefore, the “leave it alone” concept is a difficult approach for people to accept (Gordon et al.,
1992). Restoration of the impaired river ecosystem is necessary. According to the U.S. National Research
Council (NRC, 1992), restoration should involve the return of a given ecosystem to a state approximating
that in which it existed prior to disturbances.
10.4.1 Design of Stream Restoration
Design of instream habitat restoration can be guided and fine tuned by assessing the quality and quantity
of habitat provided by the proposed design. It should be noted, however, that the best approach to habitat
recovery is to restore a fully functional, well-vegetated stream corridor within a well-managed watershed.
Man-made structures are less sustainable and rarely result in a stable channel. Over the long term, design
should rely on natural fluvial processes interacting with floodplain vegetation and associated woody
debris to provide high-quality aquatic habitat. Structures have little effect on populations that are limited
by factors other than physical habitat.
Newbury and Gaboury (1993) and Garcia (1995) adapted the following procedures to restore instream
habitat.
1) Select stream. Give priority to reaches with the greatest difference between actual (low) and potential
(high) fish carrying capacity and with a high capacity for natural recovery processes.
2) Evaluate fish populations and their habitats. Give priority to reaches with habitats and species of
special interest. Is this a biological, chemical, or physical problem? If a physical problem, do the following.
3) Diagnose physical habitat problems: Drainage basin —Trace watershed lines on topographical and
geological maps to identify sample and rehabilitation basins. Profiles —Sketch main stem and tributary
long profiles to identify discontinuities that might cause abrupt changes in stream characteristics (falls,
former base levels, etc.). Flow —Prepare flow summary for rehabilitation reach using existing or nearby
records if available (flood frequency, minimum flows, historical mass curve). Channel geometry
survey —Select and survey sample reaches to establish the relation between channel geometry, drainage
area, and bankfull channel-forming discharge. Quantify hydraulic parameters at design discharge.
Rehabilitation reach survey —Survey rehabilitation reaches in sufficient detail to prepare channel
cross section profiles and construction drawings and to establish survey reference markers. Preferred
habitat —Prepare a summary of habitat factors for biologically preferred reaches using regional references
and surveys. Identify multiple limiting factors for the species and life stages of greatest concern. Where
possible, undertake reach surveys in reference streams with proven populations to identify local flow
conditions, substrate, refuges, etc.