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<br />level during normal flow, and at stations 198 and 213 it was lower than the
<br />stream bed.
<br />
<br />Because of the low gradient and low water velocities at the Blacksmith
<br />Fork dredged site gravel deposition has raised the river bed and water table
<br />to a point where the adjoining agricultural lands may often be too wet to
<br />cultivate in late spring and early summer. To alleviate this problem the
<br />landowners periodically deepen this section of river.
<br />
<br />Cross sections were surveyed along the entire basel ine, from 0 to 1123 m in
<br />January, 1975 (Figure 17). In late March, the river was altered with a backhoe
<br />between stations 335 and 860. Cross sections of the altered area were surveyed
<br />in April. The lower half of the altered area (stations 335 to 481) was surveyed
<br />again in Hay immediately prior to spring runoff. In June, following runoff,
<br />cross sections were surveyed from stations 0 to 1123. Landowners again made
<br />stream alterations beginning on August 28, 1975 using a bulldozer and backhoe
<br />between stations 335 and 789. Cross sections were surveyed in this area in
<br />September, 1975, and January, April and June, 1976.
<br />
<br />Changes at the downstream end of this study site, between stations 335 and
<br />375, were limited to removal of a long gravel bar on the eastern, convex depo-
<br />sition bank during both alteration operations. After removal of the bar in
<br />March, 1975, gravel was deposited in the same general area during the spring
<br />runoff, but the bar was not restored to its previous height. Removal of the
<br />bar again in August increased the stream width 1.2 m more than the March alter-
<br />ation. By January, gravel hap already been deposited along the inside of the
<br />bend, and by June, 1976, the bottom contour was virtually the same as measured
<br />in June, 1975. Furthermore, the cross sectional area at station 375 varied
<br />only five percent from 1975 to 1976.
<br />
<br />Nearly 60 m upstream, at station 434, a similar experience was observed.
<br />At this location, downstream from a horseshoe bend, the thalweg hugged the east
<br />bank and a long gravel bar extended for more than 30 m along the west bank. The
<br />gravel bar was removed during the March, 1975 alteration, restored by the spring
<br />runoff, removed again in August, and again restored by the spring, 1976 runoff.
<br />At this site, the stream bottom was slightly eroded instead of being raised by
<br />the deposition that usually occurs at low water flovls in late winter and early
<br />spring. During the same period, a large deep pool just downstream at 390 was
<br />slowly filled in, until by June, 1976 it disappeared. Although the deepest
<br />portion of the pool was filled during the alterations in March, 1975, the
<br />subsequent high water scoured the streambed and recreated the pool. Apparently
<br />some subtle change in the conformation of the stream allowed the streambed
<br />material to deposit during the low flow periods of fall and winter, and the
<br />high flows in the spring, 1976 were either insufficient to scour out the pool
<br />or the change in the streambed redirected the energy of the spring runoff.
<br />
<br />Immediately after each alteration the maximum depth of this profile was
<br />less than the January, 1975 level, but subsequent rearrangement of streambed
<br />materials by the current restored the previous depth. The maximum depth in
<br />June, 1975 was a few cm greater than in January, and by June, 1976, the maximum
<br />depth was about 23 cm greater than in January, 1976. The cross sectional area
<br />was 24 percent greater in June, 1976 than in January, 1975.
<br />
<br />31
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