Fluvial Geomorphology Studies in Kansas

An interesting example was the Smoky Hill River in central Kansas for which both a downstream and upstream geomorphic response to the presence of Kanopolis Lake (completed in 1948) was indicated. Before the dam was completed, a downstream increase in the stage (i.e.,elevation of the water surface) for the mean annual discharge (hereafter referred to as the reference stage) of about one foot indicated deposition that may have been a result of the disturbance (and associated increased sediment load) caused by the construction of the dam. Once the dam was completed, the downstream reference stage decreased about six feet with most of the indicated erosion occurring during the first 30 years. During that 30-year period, the erosion was interrupted by an interlude of modest deposition that occurred during a prolonged drought in the 1950s (fig. 1). Upstream from Kanopolis Lake, changes in the reference stage indicated that the channel bed slowly aggraded for several decades before stabilizing (fig. 2) (Juracek, 2001). The aggradation likely was a response to the artificial base level created by the reservoir.

Figure 1.Post-dam channel-bed erosion as evidenced by changes in stage for mean annual discharge (300 cubic feet per second) of Smoky Hill River near Langley, Kansas (gage number 06865500), 0.8 mile downstream from Kanopolis Lake, 1940-1997.

Figure 2.Post-dam deposition on channel-bed as evidenced by changes in stage for mean annual discharge (200 cubic feet per second) of Smoky Hill River at Ellsworth, Kansas (gage number 06864500), upstream from Kanopolis Lake, 1949-1997.

Channelization Effects

Channelization typically involves several types of channel modification including realignment, widening, deepening, and straightening. Typically, channelization results in channel shortening that increases channel slope and flow velocity which can cause substantial channel degradation. The degradation can migrate long distances upstream from the original site of disturbance. In addition, channel aggradation may occur downstream.

Juracek (2004) investigated the geomorphic response of Soldier Creek, Kansas, to channelization using streamgage data. In the late 1950s, about 10 miles of the stream was channelized for the purpose of flood control in the vicinity of Topeka, Kansas. The project, which was completed in 1961, involved channel realignment, widening, deepening, and straightening. The channelization-caused disturbance resulted in channel-bed degradation that migrated several miles upstream.

At a gage located about 12 miles upstream from the upstream end of the channelized section of Soldier Creek, changes in the reference stage clearly indicated the geomorphic response of the channel to the downstream channelization (fig. 3). Initially, from 1958 to 1970, a relatively stable channel bed was indicated as the reference stage fluctuated in response to scour and fill processes. Following the construction of a low-water crossing downstream from the gage in 1971, the reference stage increased about 1.5 feet indicating deposition. Then, following the partial washout of the low-water crossing in 1978, the reference stage decreased about 6.6 feet by 1999 indicating a long-term period of channel-bed erosion (fig. 3). From 1978 to 1999, the decrease in reference stage indicated a channel-bed degradation rate of about 0.3 feet per year.

A question that sometimes arises is whether a decrease in stage with time for a specific discharge is caused by channel-bed degradation or another cause such as channel widening or increased flow velocity. In this case, the pronounced channel-bed degradation indicated by the progressive change in the stage-discharge relation (fig. 3) was confirmed by an assessment of temporal changes in the width-discharge relation for a range of in-channel flows. Specifically, a substantial decrease in the widths associated with the higher discharges (fig. 4) indicated that the channel had entrenched.

The correspondence of the beginning of channel-bed degradation with the partial washout of the low-water crossing indicated that the crossing temporarily may have prevented the upstream migration of channel-bed degradation that would have reached the gage site as early as 1971 or as late as 1978. This translates to a total travel time of 10 to 17 years for the degradation to migrate from the upstream end of the channelized section of Soldier Creek (located 12 miles downstream) to the gage site. Thus, the degradation migrated upstream at an average rate of 0.7 to 1.2 miles per year (Juracek, 2004).

Figure 3.Channel-bed deposition followed by erosion as shown by changes in stage for mean annual discharge (100 cubic feet per second) of Soldier Creek near Delia, Kansas (gage number 06889200), 1958-1999.

Figure 4.Channel entrenchment as evidenced by a change in the relation between discharge and channel width for Soldier Creek near Delia, Kansas (gage number 06889200), 1958-1977 and 1978-1999).

Soldier Creek near Delia, Kansas.(photo by Kyle Juracek, USGS)

Flood Effects

The geomorphic effectiveness of a flood can be defined as the amount of channel morphological change caused by the flood and the subsequent time required for the channel to recover (Wolman and Gerson, 1978). Geomorphic effects caused by floods, which may range from negligible to substantial, include channel widening, channel-bed erosion or deposition, and channel straightening (i.e., avulsion) (Baker, 1988; Knighton, 1998). Factors that can determine geomorphic effectiveness include channel bed and bank composition, channel morphology, channel slope, valley confinement, sediment load, flood duration, stream power, the temporal ordering of floods, climate, and vegetation (Baker, 1988; Kochel, 1988; Costa and O’Connor, 1995; Osterkamp and Friedman, 2000; Emmett and Wolman, 2001; Fuller, 2007).

The geomorphic effects (short-term change and subsequent recovery) of the record-setting 1951 floods in eastern Kansas were assessed using streamgage data for 23 sites in a study by Bowen and Juracek (in press). For the sites studied, the 1951 flood was the largest discharge for the period of record at least through the year 2000. Flood-related, channel-bed elevation change was indicated at 17 sites and a substantial increase or decrease in bed elevation was indicated for seven sites. Substantial channel widening was indicated for three sites.

At a gage located along the Kansas River at Wamego, Kansas, a sudden drop in the reference stage indicated that the channel bed was eroded about 1.5 feet as a result of the 1951 flood. Subsequently, the channel bed never recovered to its pre-flood elevation (fig. 5).

At another gage located along the Kansas River at Lecompton, Kansas, channel widening of 150 feet or more (about a 20 percent increase) was indicated for moderate flows following the 1951 flood. Subsequently, during the late 1950s, the channel width for moderate flows decreased by as much as 50 to 80 feet (fig. 6). Due to a lack of high flows during the mid-1950s, impacts at higher flows could not be assessed. Channel width then stabilized and remained relatively stable at least through 2007 (data not shown). Thus, channel width did not completely recover to its pre-flood width.

Figure 5.Flood-related channel-bed erosion as evidenced by change in stage for mean annual discharge (5,100 cubic feet per second) of Kansas River at Wamego, Kansas (gage number 06887500), 1940-2006.

Figure 6.Flood-related channel widening as evidenced by relation between discharge and channel width for Kansas River at Lecompton, Kansas (gage number 06891000), 1946-1951, 1951-1956, and 1956-1960. ).

Kansas River at Lecompton, Kansas, following the 1951 flood (reproduced from McCrae, 1954).

Ongoing Studies

John Redmond Reservoir, Kansas: Sedimentation, sediment quality, and upstream channel stability, 2009-2012.

In response to concerns about sedimentation in John Redmond Reservoir, this study was undertaken in cooperation with the U.S. Army Corps of Engineers with objectives being to: (a) determine the amount and quality of sediment deposited in the reservoir, (b) assess channel stability at selected sites upstream from the reservoir, (c) characterize sediment transport through an area of streambank stabilization, and (d) characterize the potential of altered reservoir management to decrease sediment accumulation in the reservoir.

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