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PNW Ecosystem Research Consortium
Longitudinal Patterns - RevetmentsS. Gregory L. AshkenasD. Oetter K. Wildman
138
Revetments and banks that have been armored present both negative
and positive implications for restoration of large rivers. From a river man-
agement perspective, the areas with low amounts of bank revetments are
important resources to protect and opportunities to resist the trend to sim-
plify the river and reduce its natural dynamic processes. They allow the river
to function more naturally and, as a result, maintain ecological functions
through natural processes of channel formation. These reaches are important
for conservation and restoration, particularly when considered in comparison
to the heavily armored sections of the river, which offer reduced ecological
functions.
From a restoration perspective, areas with high amounts of revetments
but less intensive human development offer potential opportunities for
modification or removal of revetments. In this illustration of approaches for
The Willamette River has been straightened, channelized, and armored
along its length by federal and state agencies, municipalities, and private
citizens (see Revetments, pages 32-33). The more urban and industrialized
area near Portland tends to have 40-60% of the river banks in revetments and
bank control structures. Other cities along the river also tend to restrict
movement of the river by bank armoring and other structures designed to
control the path of the river. Upper reaches of the Willamette River between
Albany and Eugene are more geomorphically complex. These areas contain
intermediate amounts of channel control structure, largely associated with
attempts to prevent erosion of agricultural lands in the complex floodplains
(Fig. 44, p. 32). The lands along the river between the Portland metropolitan
area and Salem and between Salem and Albany have some of the lowest
amounts of bank protection.
prioritization of river restoration, we will consider revetments to be oppor-
tunities for restoration, though we acknowledge that the revetments lower
the current ecological condition of the river. River reaches that once were
dynamic and complex can be restored to higher levels of ecological function
by reconnecting existing but isolated side channels. Riprap and pilings can
be removed completely or modified to maintain some stability but still
allow higher flows to reconnect with the side channels. Efforts to reconnect
historically complex river channels are greatly affected by hydrologic
regimes. High flows are necessary to maintain open flow through side
channels. Efforts to lower these high flows with flood control reservoirs
reduce the ability of rivers to maintain off channel habitats. Restoration of
channel complexity through modification of bank control structures will be
increased if flood management strategies also allow for more natural flood
regimes. Careful attention to concerns of private citizens and local commu-
nities is essential for constructive discussions of restoration options related
to restoring the dynamic processes of the Willamette River and its flood-
plain.
Figure 188. Blockage of historical side channel and armoring with
riprap in the upper Willamette River.
Figure 191. Fringe of native riparian vegetation with riprap to stabilize
the lower bank in Corvallis.
Figure 187. Bank revetment used to repair a slump that
occurred on the river bank of the Willamette River in
Corvallis during the flood of February 1996.
Figure 190. Development of docks and bank armoring with riprap
on a steep bank near the Portland metropolitan area.
Figure 189. Bank protection and drainage for new
apartment buildings in the riparian area of the
Willamette River in Salem.
Introduction
Willamette River Basin Atlas
2nd Edition
RIVER RESTORATION Revetments
139
S
N
Portland Metro Salem/Keizer Albany Corvallis Eugene/Springfield
Portland Metro
Salem/Keizer
Albany
Corvallis
Eugene/Springfield
Scale: 1:1000000
0 mi 10 mi 20 mi
0 km 10 km 20 km 30 km
SN
1995 Urban Growth Boundaries (UGBs)
Slices which intersect UGBs
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
105
110
115
120
125
130
135
140
145
150
155
160
165
170
175
180
185
190
195
200
205
210
215
220
225
kilometers0.0 0.01 - 0.080.09 - 0.250.26 - 0.460.47 - 0.700.71 - 1.081.09 - 1.591.60 - 6.63
Percent
0.01.1 - 2.93.0 - 7.98.0 - 13.914.0 - 22.923.0 - 29.930.0 - 38.838.9 - 70.1
80
0
1
2
3
4
5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
105
110
115
120
125
130
135
140
145
150
155
160
165
170
175
180
185
190
195
200
205
210
215
220
225
20
40
60
0
Figure 192.
Length of revetments
in 1995.
Figure 193.
Percentage of river
banks with revet-
ments in 1995.
Note: 1 kilometer equals .62 mile