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Riparian Vegetation Reduces Stream Bank
and Row Crop Flood Damages1
Donald Roseboom and Kenneth Russe11
2
Abstract.--Large alluvial stream valleys in the
prairies of western Illinois have been channelized to increase the size of row crop fields. Fish surveys at thirteen sites in the 61,760 acre watershed documented the elimination of large game fish in old channelized stream segments when upstream segments contained smallmouth bass up
to 2.7 lbs. Channelized stream banks contributed much of
the sediment, which eliminated instream habitat.
INTRODUCTION
and residential land management types were planimetered from ASCS aerial photographs for the entire
watershed. Agricultural land uses were row crop
(corn and soybean), pasture, and wooded pasture.
Row crops were the largest single land use in the
watershed (49 percent of the area).
The Soil Conservation Service has desigLated
33 Illinois counties in the Mississippi and Illinois River basins of western Illinois as critical
sediment producing areas (Crews, 1983). Western
Illinois streams have highest instream sediment
yields in the state (Bonini et al., 1983). Nonpoint pollution is generally regarded as the most
common cause of stream degradation in Midwestern
streams (Judy et al., 1984).
The topography and soil types in the watershed
were determined during the Wisconsin Glacier Age.
Glacier deposits not only formed the flat prairie
of western Illinois, but torrential runoff from
melting glaciers formed very large stream valleys
with extremely steep bluffs. Present day streams
meandered down the wide floodplains formed by
glacier runoff. Fehrenbacher et al. (1977) described the upland prairie and floodplain landforms
of waterways in western Illinois. Soil types have
developed as dark upland. prairie soil, lighter
timber soil along the bluffs, and alluvium from soil
deposition in the old glacier valleys. Row crop
acreages are confined to the relatively flat upland prairie and the floodplain. Pastures and
wooded pastures are found on bluffs bordering the
floodplain because the steep slopes and infertile
soils preclude other agricultural uses. Strip·mined land is also very steep and is almost entirely
pasture.
From 1980 to 1983, the Illinois Department of
Energy and Natural Resources funded a study by the
Illinois State Water Survey to determine the effects of land use on water quality in a 97.5
square mile watershed in western Illinois. By
determining the extent of different land uses in
16 large subwatersheds during two years of stream
sampling, the influences of agriculture, stripmining, urban activities, and stream modifications
were assessed in watershed streams.
GEOGRAPHIC AREA
Court Creek flows east along the southern
boundary of the watershed from Galesburg, IL to
the Spoon River at Dahinda, IL. Three major tributaries (Middle Creek, North Creek, and Sugar
Creek) drain 65 percent of the watershed from the
north. .Ten land uses of agriculture, stripmining,
METHODOLOGY
Sixteen stream sampling stations were established on Court Creek and its tributaries. Subwatersheds are the watershed areas between sampling
stations. The extent of each subwatershed area
determined from U.S. Geological Survey topographical maps developed in 1978. Each quarter section
of land use was placed in a subwatershed on the
basis of topographic maps. The extent/ of land uses
were measured for each quarter section of watershed
from 5 sets of aerial photographs taken between
1940 and 1979. By this method the extent of agriculture, stripmining, residential housing, and
stream length reduction was determined in each
subwatershed.
lPaper presented at Riparian Ecosystems and
their Management. University of Arizona, Tucson,
April 16-17, 1985.
2Donald Roseboom is Associate Professional
Scientist, Illinois State Water Survey, Peoria, IL.
Kenneth Russell is District Fishery Biologist,
Illinois Department of Conservation, Galesburg,
IL.
241
residential land uses to the major water quality
problems at C2.
Stream flow gages were established at nine of
the 16 subwatershed sampling stations. Flows at
ungaged sampling stations were calculated on the
basis of watershed area. A continuous stage recorder was placed at the C2 sampling station.
Flow-duration curves of staff gages were adjusted
to the flow-duration curve of the C2 continuous
stage recorder. Stream samples were obtained
with a USGS depth-integrating DH-59 sampler.
The M3 subwatershed is 71 percent row crop
(3093 of 4320 acres) and had the highest annual
sediment and nutrient yield of the three upland
prairie subwatersheds. However, the agricultural
subwatershed between the Ml and M3 sampling stations
is only 40 percent row crop (834 of 2080 acres) but
had much greater stream sediment and nutrient yields.
The Ml subwatershed had annual sediment and nutrient
yields similar to the net annual yields for the entire watershed at sampling station C2.
Annual stream loadings were calculated by
means of a flow-duration curve and a sediment or
nutrient discharge curve. Stream loadings for individual storms were determined by sampling each
event during the rise and fall of flood waters.
Each stream sample represented a stream flow and
a sampling time period. Sediment and nutrient
loadings (lbs.) per sampling period (min.) were
determined as the product of stream flow (cfs), sample concentration (mg/L), time period (min.) and a
factor of 0.003747. The storm loadings were the
sum of the sampling period loadings.
During April of 1983 the amount of sediment
and nutrients transported during a single storm
(storm loadings) were determined. The Ml subwatershed contributed 74, 74, and 66 percent of the sediment, phosphorus, and ammonia loadings, even though
it represents only 33 percent of the combined Ml and
M3 subwatersheds. The peak stream flow at Ml was
320 cfs from 2.4 inches of rain while the peak
flow at M3 was 76 cfs from 2.1 inches of rain.
Fish survey sites were established on stream
segments representing the upper and lower sectors of
the principal streams in the watershed. Illinois
Department of Conservation personnel performed the
fish surveys and identified the collected fishes.
Fish were collected Pith a rotenone-potassium permanganate technique with a blocking net at the
lower end of the site. Each site contained a pool
and riffle. Stream habitat evaluations for instream habitat, water depth, stream bed materials,
and riparian vegetation were made by experienced
Illinois Department of Conservation personnel.
An analyses of the Ml and M3 subwatersheds revealed 58 percent of the Ml subwatershed and only
25 percent of the M3 subwatershed had steep slopes
(>15 percent). Bluffs along the floodplain become even steeper in lower segments of Middle Creek.
This steep topography increases the rate of storm
water runoff as indicated by greater peak storm
flows at Ml. A comparison of aerial photographs
between 1940 and 1979 found a 7 percent stream
length reduction in the Ml subwatershed. Channelization further increases the rate of storm water
runoff. Even more importantly, 25 percent of Ml
subwatershed lays in the floodplain below the steep
bluffs. Since row crop fields are the dominant
land use in the relatively flat floodplain, this
cultivated land occurs downstream of areas in which
storm water runoff reaches high velocity. The primary complaint of land owners in floodplain subwatersheds is damage to row crop fields from high
velocity stream flows, not submergence of crops.
Channelization efforts in the floodplain during the
1980's were attempts to divert high velocity stream
flows from rwo crop fields. Either the stream is
straightened (thus increasing stream velocity) or
diverted into the bluff (eroding large earthern
cliffs).
RESULTS
The C2 sampling station represented the combined effects of all land uses in the entire watershed (table 1). At the C2 station, sediment, total
ammonia, and total phosphorus were the most pronounced water quality effects. The bulk of the row
crops were in the flat upland prairie surrounding
the headwaters of streams as in the M3 subwatershed. The sediment and nutrient yields of upland
prairie subwatersheds are compared with yields from
one floodplain subwatershed and the total watershed
in Table 1. The three upland prairie subwatersheds
of M3, S5, and Cl2 represent, respectively, the
contribution of agriculture, stripmining, and
Table 1.
Landform
type
Land
use
Upland
prairie
Residential
Annual stream yield on a per acre basis.
Upland
prairie
Upland
prairie
Floodplain
alluvium
Mining
Agriculture
Agriculture
Total
watershed
at C2
Sediment
tons/ac/yr
0.7
1.0
1.7
9.2
7.5
Ammonia
lbs/ac/yr
1.8
1.4
2.5
4.6
3.7
Phosphorus
lbs/ac/yr
2.9
2.0
7.4
14.0
14.2
242
Downstream floodplain subwatersheds had even
greater annual sediment yields of 52.2, 26.8, 23.4,
46.5, and 21.0 tons/acre/yr. On North Creek, the
lower 25 percent of the watershed contributed 50
percent of the annual sediment yields. Stream
nutrient yields for floodplain subwatersheds are
closely correlated with sediment yields. As in
Middle Creek, these floodplain subwatersheds are
bordered by very steep bluffs, which have high
rates of surface water runoff.
Table 2.
Type of
yield
Stream lengths in downstream floodplain subwatersheds have been reduced by an average of 15
percent since 1940. Stream reduction as great as
25 percent were determined from 1940 and 1979
aerial photographs. The broad floodplain of Court
Creek had similar stream length reductions. Stream
reconnaissance of floodplain subwatersheds found
major bank erosion sites occurring at the sites of
former stream meanders in the floodplain, especially sites bordering row crop fields.
Percentage of storm yield eroded from
seven bank erosion sites
Storm
date
Sediment
(tons)
12/2/82
12/24/82
4/1/83
13387
13206
33293
1391
639
2551
10.4
4.8
7.7
T.
Ammonia
(lbs)
12/2/82
12/24/82
4/1/83
4569
3524
8470
166.9
76.7
306.1
3.7
2.2
3.6
T.
12/2/82
Phosphorus12/24/82
(lbs)
4/1/83
37858
29311
53381
7511
3451
13775
19.8
11.8
25.8
1 Weights are
unit weight
erage total
trations of
Bank erosion measurements were begun during
the second year of sampling when analysis of the
1981 annual sediment yields found large increases
of sediment yield from the floodplain subwatersheds. In the eroding banks, Soil Conservation
Service (SCS) personnel identified a sandy overburden of recent origin, a well developed soil
layer developed over thousands of years, and a
sandy glacial outwash dating from the glacial ages.
A 48 inch steel pin was driven into each bank
layer following the method described by J.M. Hooke
(1979). Six foot wooden stakes were driv.en vertically into the stream bed and bank to mark the pin
positions. The location of each set of three pins
was marked by a wodden stake placed 15 feet from
the edge of the bank. Bank erosion measurements
were made with a steel surveyors tape after each
storm. The weight of the eroded bank was the product of the length of the section, the height of
the bank, the depth of erosion into the bank, and
a unit weight of 90 lbs/cu. ft. SCS personnel
from the Knox County soil survey estimated this
unit weight during the inspection of the eroding
banks.
Amount
Percent of
eroded from storm yield
Storm seven bank from eroded
yield
sites 1
banks
calculated from bank soils with a
of 90 lbs. per cubic foot with avammonia and total phosphorus concen60 mg/kg and 2700 mg/kg respectively.
veys of Court Creek and its three tributaries,
these seven sites are not estimated to contribute
more than 10 percent of the total bank erosion
occurring during major storms.
In July of 1982, flood waters eroded as much
as 1150 tons of soil from a single bank erosion
site during one storm. These storms also caused
the extensive uprooting of very large trees, which
hung up on sand bars and diverted much of the stream
flow into stream banks and across row crop fields.
In an attempt to correlate the contribution of
eroding stream bank~ to the sediment budget of
large streams, the amount of bank erosion at seven
sites was measured during the next three storms.
The amount of bank soil eroded from all seven sites
during the three storms is shown in column 4 of
Table 2. Chemical analysis of bank soils for total
ammonia and total phosphorus permitted the determination of the amounts of ammonia and phosphorus entering the stream with bank soil.
Storm yields for the three storm events are
also given in Table 2. Bank erosion from just
seven bank erosion sites represents a significant
proportion of the sediment, phosphorus, and ammonia leaving the entire watershed at C2. Given the
extent of bank instability found during stream sur-
243
Fish surveys revealed instream habitat degradation in channelized floodplain stream segments,
even though channelization occurred at least 20
years earlier. The habitat degradation and its
effects on fish populations are illustrated by two
fish survey sites on Court Creek - C3 and C6 (table
3). The C3 site was located below 72 square miles
of watershed while the C6 site had a watershed area
of 35 square miles. Both water depth and instream
habitat at C3 were severely reduced by the deposition of fine sands. Stream banks had very little
woody riparian vegetation and large bank erosion
sites were present upstream. Approximately 20 percent of bank soils at major bank erosion sites
were fine sand. Much of the sand was located in
the lowest layer of bank soil.
The C6 fish survey site was characterized by
deep pools with instream cover of snags and exposed
tree roots. High gradient riffles provided coarse
gravel and large rock rubble. Large mature trees
increased bank stability and provided shade. Stream
fish populations reflected the habitat differences
between C3 and C6. The standing crop of fish at
C6 was 303 pounds per acre while the C3 site had
only 100 pounds per acre even though both sites
contained over 2600 fish. At C3 forage species
represented 95 percent of the crop by number and
55 percent of the crop by weight. Bluntnose minnows
and sand shiners were the most abundant species.
Game fish comprised only 4 percent of the C3 crop
by weight.
At the C6 site, forage species comprised 88
percent of the crop by number but only 10 percent
by weight. Game fish, mainly smallmouth bass, comprised 22 percent of the crop by weight. Eighty
Table 3. Species and number of fishes found in
unstable channelized stream site C3 and the stable
site'C6.
Species
C3
Largemouth Bass
Smallmouth Bass
Bluegill
Green Sunfish
Channel Catfish
Yellow Bullhead
Stonecat
River Carpsucker
Quill back
Whit'e Sucker
Golden Redhorse
Carp
Stoneroller
Hornyhead Chub
Emerald Shiner
Striped Shiner
Bigmouth Shiner
Red Shiner
Sand Shiner
Suckermouth Minnow
Bluntnose Minnow
Fathead Minnow
Creek Chub
Johnny Darter
Orangethroated Darter
Logperch
No. of Fish
No. of Species
and scrub timber. Except for the constant filling
of eroded banks by the local land owners, such
field damage would be more appraent on aerial photographs.
C6
22
8
29
19
11
12
7
Now the major reason for channelization is to
divert floodwaters from eroding into floodplain
fields. Erosion of floodplain fields also occurs
as scour in areas away from the stream bank. Channelization is often practiced without legal authorization as the only method available for the local
land owner to limit flood damages to fields. Aerial
photography and bank erosion measurements suggest
channelization is a short term solution, which results in long term damages to streams and surrounding row crop fields.
10
87
15
11
9
33
38
26
14
40
9
76
107
35
116
37
24
9
56
3
93
59
2
Individual land owners are attempting to stabilize stream banks, but are having limited success. Between areas of extensive bank erosion, certain channelized stream segments demonstrated remarkable stability. These stream segments were
characterized by a well developed stream border of
woody vegetation, which reduce stream flow velocity
and prevent bank erosion. These green belts of
trees act on high velocity water in the same manner
that wind breaks of trees act on high velocity
winds. They reduce erosion by decreasing the velocity of the flood waters at the surface of bank
soils. They reduce the effects of upstream erosion
since sedimentation occurs among the trees and forms
a natural levee. Sand is deposited along the banks
and not as sand bars in floodplain fields.
3
134
360
769
3
928
3
23
7
1963
31
6
3
1
2646
22
2607
23
LITERATURE CITED
seven smallmouth bass were found with weights up to
2.7 lbs. Pool depth and instream habitat were the
most important habitat differences found between
the C6 and C3 survey sites. The major bank erosion
sites upstream of the C3 site contributed tons of
sand to the stream during flooding. The deposition
of this sand is the major cause of stream degradation in the watershed.
DISCUSSION
Floodplains in Knox County have served as
sediment traps for upstream erosion for thousands
of years; indeed floodplain soils are characterized
as alluvium. Forests in western Illinois were confined to the floodplain bluffs and large valleys
formed by glacial melting. The major land use
changes'in these floodplain areas has been theremoval of forests and the channelization of streams
to maximize row crop fields and increase the rate
of storm water runoff. The Court Creek study suggests this land management practice has been too
extensive.
A comparison of 1940 and 1979 aerial photographs of C2 subwatershed revealed the complete erosion of a small field at bank erosion site III. An
average of 2000 tons of soil was eroded every year
from 600 feet of bank. The soil deposited over
thousands of years was replaced by sand, gravel,
244
Bonini, A.P., N.G. Bhowmik, R.L. Allgire, and D.K.
Davie. 1983. Statewide instream sediment
monitoring program for Illinois. SWS Contract
Report 318A, 45 pp. IL. St. Water Sur.
Champaign, IL.
Crews, W. 1983. Erosion in the upper Mississippi
River system: an analysis of the problem.
17 pp. Upper Mississippi River Basin Assoc.
St. Paul, MN.
Fehrenbacher, J.B., I.J. Jansen, B.W. Ray, J.D.
Alexander, and T.S. Harris. 1977. Soil associations of Knox County, Illinois. Spec.
Publ. 46. 27 pp. University of IL, College of
Agriculture, Urbana, IL.
Hooke, J.M. 1979. An analysis of the processes of
river bank erosion. Jour. Hydro!. 42:39-62.
Judy R.D., P.N. Seeley, T.M. Murray, S.C. Svirsky,
M.R. Whitworth, and L.S. Ischinger. 1984.
1982 national fisheries survey val. I technical report: initial findings. 140 pp. FWS/
OBS-84/06. Fish and Wildlife Service.
Washington, D.C.
Roseboom, D.P., R.L. Evans, J.E. Erickson, and L.G.
Brooks. 1982. An inventory of Court Creek
watershed characteristics that may relate to
water quality in the watershed. Doc. No. 83/
23-A. 95 pp. IL. St. Water Survey. Peoria,
IL.