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A Study on the Effect of Flow Variation on the Existing Stability Conditions at the Lower Mouth of Plum Creek Stanley County, South Dakota
Thesis - University Access Only
Master of Science (MS)
Department / School
Civil and Environmental Engineering
Plum Creek is a tributary of the Bad River watershed and is located in the lower basin, which itself is one of the tributaries of the Missouri River. In this study, prevailing stability conditions and river dynamics of the lower mouth of Plum Creek, near the Bad River were evaluated, and comparisons of these conditions were made to those that may exist due to flow variability. The first part of study was conducted to classify Plum Creek based on Rosgen classification system to find the present stream type at selected segments. Three segments of the lower Plum Creek were selected for the evaluation of existing stability condition and river dynamics from the delineated watershed using available 7.5 minute (1.3 arc-second) USGS Digital Elevation Model (DEM). Flow analysis was performed in HEC-RAS after geospatial analysis of the DEM in HECGeoRAS to create the required geometric data to analyze flow. Bankfull flow was determined analytically and used for flow analysis in HEC-RAS. Required hydraulic parameters to classify the stream and find the stability condition were obtained from flow analysis; and geomorphic parameters were determined processing the HEC-RAS result in HEC-GeoRAS in GIS environment. Discharge was varied according to flow variation to find if any changes on stream type, and existing stability conditions were observed. Overall stability of Plum Creek was evaluated based on Pfankuch stability evaluation method. Measured bed sediment size was taken from USGS station to find the flow dynamics of the Creek using Shield’s equation. Threshold depth and slope required to entrain 90th percentile size of bed material for the bankfull flow were calculated to determine if the existing depth and slope were sufficient to carry the available size of riverbed material without deposition. The study found the bankfull discharge to be 18 m3/s (640 fps) and flood prone discharge to be 210 m3/s (2260 fps). Lower Plum Creek was found to be a “C5c” type based on the Rosgen river classification, entrenchment ratio (ER) was greater than 2.2, width to depth (W/D) ratio greater than 12, and sinuosity was greater than 1.4 for all selected reaches. Pfankuch stability score was found to be in between 100 to 110. These results indicated that the selected reaches were in a moderately unstable, slightly entrenched, and meandered with high sinuosity, which indicates that, overall, the Creek is in a fair stable condition but inclined to poor condition. A change in flow is sufficient to change geomorphic parameters, however stream type and existing condition remains unchanged. Flow dynamics and competence analysis for known median d50 and d90 size showed that the available depth and slope for the bankfull flow was enough to carry the bed material without deposition under increased flow conditions.
Library of Congress Subject Headings
Streamflow -- South Dakota -- Plum Creek
Stream measurements -- South Dakota -- Plum Creek
Sediment transport -- South Dakota -- Plum Creek
River channels -- South Dakota -- Stanley County
Includes bibliographical references (leaves 101-107)
Number of Pages
South Dakota State University
In Copyright - Educational Use Permitted
Govinda, Karki, "A Study on the Effect of Flow Variation on the Existing Stability Conditions at the Lower Mouth of Plum Creek Stanley County, South Dakota" (2012). Electronic Theses and Dissertations. 1346.