8150

• UCREFRP Catalog Number: 8150
• Author: Wydoski, R. S.
• Title: Realistic Management of Endangered Species--An Overview.
• USFW Year: 1977.
• USFW - Doc Type: \
• Copyright Material: YES

232

C. H. THEILING

Off-Bank Revetments
Channel~

Natural Bank

Unmodified Bank

Channel

. Rock

Figure 5. Schematic ilIustrations of three common bankline configurations in the Upper Mississippi River System

current velocity and structurally complex habitat south of the Missouri river. They attract or support large
numbers offish (Farabee, 1986; Baker et aI., 1991) and also provide substrate for invertebrates. Organic drift
trapped in dike-created eddies may help support local invertebrate and fish populations, though the
ecological importance of the effect has not been fully evaluated (Sparks, 1991).

Wing dikes
Stone dikes (wing dikes) extending perpendicular from the bank were constructed to constrict flow to the
main channel during periods of low discharge (Chen and Simons, 1986). Sediment accumulation between
dikes caused rapid river bed aggradation and terrestrial conversion in lentic habitats between dikes (Neimi
and Strauser, 1991). Loss of lentic habitat has reduced fish habitat value throughout the reach below the
Missouri River.
Experimentation with dike alterations started with notches of various sizes, shapes and locations cut in
existing structures (Neimi and Strauser, 1991). Scouring downstream of the dike was expected to reduce bed
agradation. Physical evaluations of dike modifications showed unexpected results in that topographic/
bathymetric diversity was greater than expected (Neimi and Strauser, 1991). Cursory ecological evaluations
of modified structures (Atwood, E. R., Illinois Department of Conservation pers. comm.) and extrapola tions
from similar structures (Farabee, 1986; Baker et al., 1991) indicate they at least support a greater number of
fish species, and usually higher abundances, compared with other available habitats.

Bank revetments
Bankline revetments (rip-rap; Figure 5) are used to eliminate the tendency for the main channel to migrate
within the floodplain because channel movement can disrupt commercial navigation. Standard revetments
use coarse grade rock to stabilize bank positions by eliminating downcutting (River bed erosion) at the base
of the bank. Typical installation requires substantial bank clearing and grading that is both expensive and
environmentally damaging (Neimi and Strauser, 1991). An alternative bank stabilization being tested is off-
bankline revetments (Neimi and Strauser, 1991).