Geologic and hydrodynamic controls on the mechanics of knickpoint migration /
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1988.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | Recent changes in land use patterns within major stream basins have caused flooding in areas that were not previously considered to be flood prone. Rapid headward erosion in emergency spillways at the Corps of Engineer reservoirs of Grapevine, Saylorville, and Black Butte caused the Corps to take a serious look at the available methods used to predict erosion damage in unlined emergency spillways. The catastrophic loss of private and Soil Conservation Service reservoirs because of knickpoint migration in emergency spillway channels was additional evidence that the mechanics of knickpoint erosion were not clearly understood. Severe erosion was documented at several Corps spillways where the flow was less than one tenth of the designed capacity. Preliminary research revealed that the severe cases of knickpoint erosion were usually caused by the mass failure of large blocks of material and not by the tractive force scour of individual grains. The details of the mechanisms which actually caused the mass failures were largely unknown. The purpose of this research was to specifically study the knickpoint erosion phenomena with respect to the combined effects of the geologic and hydrodynamic controls. Sodium silicate and gelatin cemented gravel in combination with plexiglas were used to simulate knickpoints in layered rock. An hydraulic flume had to be modified to accommodate layered samples. The designed drop structure, which is constructed in streams or channels to dissipate erosive energy, was used as an analog to study the knickpoint phenomena. The research revealed that the potential for headward knickpoint erosion is controlled by the geometry of the knickpoint, the velocity of eroding water, and the pressure underneath the nappe. The geometry of the knickpoint is in turn controlled by the site specific geology. The erosion rate was found to increase significantly when the thickness of the erodible lower layer in a two-layer model exceeded the diameter of the back roller at the toe of the knickpoint. I t was found that headward erosion in the flume could be controlled or completely stopped by controlling the pressure underneath the nappe. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Geology." |
| Physical Description: | xvi, 198 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |