Iona L. Meyer

Date of Award

11-1992

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Geography and Geology

First Advisor

Dr. Rolfe Mandel

Second Advisor

Dr. Jeffrey Peake

Third Advisor

Dr. Joseph Benak

Abstract

A small gully network developed across a pasture in the Dissected Till Plain of northeastern Kansas was monitored for one year to assess gully evolution in non-loessial materials. The objectives of this investigation were to identify stable and unstable drainage elements within the gully network; identify zones of net erosion and deposition; estimate the volume of sediment removed or deposited during the monitoring period; determine rates of headcut advancement; determine processes that advance and widen gullies, and to determine the historic development of the gully network.

Portions of the gully network were measured after every rain event exceeding 1.5 cm in a 24 hour period. A series of reference points and/or transects were established at selected gully elements to determine headcut advancement rates and detect changes in gully volume. Historic growth rates were determined by examining aerial photographs.

Results of this investigation indicate that the upper reach was a zone of net erosion, whereas the lower and middle reaches were zones of net sedimentation. Although considerable erosion occurred during the monitoring period, with sidewalls accounting for 92.0% of all erosion, sedimentation was the dominant process, resulting in a net decrease in gully volume of about 2.77m3. It is likely that a portion of the sediment was contributed by adjacent slopes that are experiencing sheet and rill erosion.

Gully headcut advance ranged from 4 to 69 cm/yr, with advancement apparently controlled by surface deposits and soils. Headcuts migrated fairly rapidly when advancing into former gullies that are filled with sediment. The gully fills are marked by permeable, low strength silt. However, headcuts advancing into the in-situ glacial till had slower advancement rates due to till having a higher clay content, thereby imparting greater resistance to erosion.

Headcuts migrating into gully fills were subject to advancement by failure at the toe of headwalls, and by toppling, whereas headcuts migrating into the till-derived soils advanced primarily by rill enlargement. Gully widening resulted from sidewall failure, which was largely controlled by soil moisture conditions, undercutting, and cattle.

Examination of aerial photographs suggest that portions of the gully network have rejuvenated and infilled since 1937. This evidence is supported by the existence of late­ Holocene gully fills at the study site. Cut-and-fill cycles play an important role in river basin evolution, and appear to be an important factor of gully evolution at the study site. Headcuts migrating into gully fills can be expected to advance quickly. Hence, soils and terrain analysis may be used to locate gully fills, allowing land managers to isolate areas prone to rapid gully development.

Comments

A Thesis Presented to the Department of Geography/Geology and the Faculty of the Graduate College University of Nebraska In Partial Fulfillment of the requirements for the Degree Master of Arts University of Nebraska at Omaha. Copyright 1992 Iona L. Meyer.

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