Introduction to Stream Restoration - Hydro-Environmental Analysis: Freshwater Environments - page 250

A third alternative for sinuosity and meander design (FISRWG 1998; Soar and Thorne 2001) is
to irst:

• Calculate a stable channel slope analytically on the basis of the sediment transport

• Compute the sinuosity and channel length

• Compute the meander wavelength

For example, a common engineering approach would be to use hydraulic and sediment transport
models to estimate the hydraulic characteristics (such as depths, velocities, etc.) and sediment loads
based on the design lows. From the hydraulic characteristics, shear stresses could be computed
for comparison with an allowable shear stress (one that would not cause degradation). The process
would iterate until an allowable channel design (e.g., channel slope) was determined (computed
shear stress < allowable). The sinuosity is then given as the ratio of the measured valley slope to the
channel slope and is, therefore, directly related to the sediment regime, which controls channel sta-
bility. The channel length can then be computed from the product of the sinuosity and valley length.
Once sinuosity has been derived, only the wavelength is required to determine the target planform
geometry. Meander arc lengths vary from four to nine channel widths (FISRWG 1998).
Once the channel meander design and design sinuosity are selected, the remaining steps include
computing the hydraulic characteristics (depth, etc.) at the design discharge, and then computing the
local morphological conditions, such as the pool and rifle locations, depths, and offsets (FISRWG
1998). See FISRWG (1998) and Copeland et al. (2001) for examples and equations.
Rivers with erodible boundaries not only tend to meander, but they also tend to migrate, and the
development and control of meanders are a major consideration in restoration projects. Meander
migration is not only a problem in areas with high slopes and velocities. Streams with lat slopes and
relatively low velocities also exhibit active meander formation and migration, such as in backwater
areas and upstream of conluences and reservoirs (USACE 1994).
Protection against migration is typically based on some form of bank protection. This may be con-
tinuous forms of protection such as revetment, or discontinuous forms such as groins. Intermittent
groins are usually more economical than continuous revetment and while they may be unacceptable
for some projects, such as where navigation is an issue, they may also have other beneits such as for
isheries. Short lengths of continuous revetment at points of active river attack are not usually effec-
tive in the long term since the attack usually shifts to other points and tends to outlank the short
revetments. Bank vegetation and root systems may also provide effective protection (USACE 1994).

8.4.19 M onItorInG b Iota and / or f Low
Monitoring data are critical to any restoration project for both evaluation and planning purposes,
particularly for projects dealing with low modiications or improvements of instream habitats or
biota. Monitoring is also needed to assess the effectiveness of the project (postaudit studies) over
time and under variable environmental conditions, as with postaudit monitoring, to determine why
and how techniques and practices work, and, equally important, why some fail (Saldi-Caromile
et al. 2004).
The monitoring of biota is needed to evaluate sites, plan for restoration, and evaluate the effec-
tiveness of restoration. For example, biota data can be used to evaluate the health or “biotic integ-
rity” of a system, as discussed in Chapter 7. Flow data are critical to restoration projects, both
base low and low variations, such as over seasons or during events. Flow data are also used (with
hydraulic models) to estimate the variations in the hydraulic characteristics (depths, velocities, etc.)
affecting aquatic habitats as well as the relationships between lows and vegetation. The streamlow
also directly impacts water quality, such as the concentration of dissolved materials. Often, his-
torical data are required to estimate the frequencies of lows, such as for use with the indicators of
hydrologic alteration (IHA) software or for determining the probability distribution for lood lows.