Implications of Best Management Practices on Channel Evolution within the Bad River Watershed: West Central South Dakota

Stream channel morphology is highly variable among different landscapes due to differences in geology, topography, climate, and land use. Understanding a river system’s channel morphology is particularly useful due to regional relationships between channel form and sediment conveyance. The Bad River located in west central South Dakota has chronic high sediment loads attributed to the surrounding fragile landscape coupled with historic overgrazing. High sediment loads coming from bed and bank erosion of severely incised tributary channels have been responsible for violating the suspended sediment criteria set for warm water fisheries, and reducing power generation of Oahe Dam. Estimates place the annual cost of these impairments at $12 million. These issues have led to the creation of a Total Maximum Daily Load (TMDL) and issuing of Environmental Protection Agency (EPA) 319 funding to implement best management practices (BMPs) in critical locations. The lower Bad River Basin has been identified as the major contributor of sediment to the Bad River main channel and Lake Sharpe, a Missouri River main stem reservoir, while the upper Bad River Basin has been determined to produce only a small proportion of the sediment load conveyed to the mouth of the Bad River. Huge contrasts exist between current channel morphology and bank stability within subwatersheds of the lower and upper Bad River Basin. The lower basin channels are typically incised and their banks contribute large volumes of sediment, while the upper basin channels are quite stable. Consequently, BMP efforts were strongly directed toward the lower basin. The objective of this effort was to determine if BMPs directed toward the lower basin were effective in reducing sediment delivery as reflected by patterns in channel morphology and bank stability. Channel morphology data of six subwatersheds were collected using Rosgen classification during the mid-1990’s (pre-BMP). Records from two of these watersheds were used to compare shifts in morphology following an extensive BMP effort in the lower basin. Burnt Creek, located in the upper basin, had stable channel morphology structure when assessed in 1996, while Ash Creek, located in the lower basin, had severely incised channels during assessment in 1994. Best management practices, including improved grazing systems, establishment of off-stream water sources, and notill row cropping were implemented and maintained. Channel morphology was reassessed (post-BMP) in 2010 (Ash) and 2011 (Burnt) and morphology succession patterns were compared among Ash and Burnt Creek watersheds. Channel morphology within both watersheds was highly dynamic as 70% and 54% of the total assessed channel length changed in Rosgen Class for Ash and Burnt Creek’s over the sixteen year period. However, Ash Creek underwent an overall shift in Rosgen Class proportions and tended toward those observed in Burnt Creek. Changes observed in Ash Creek indicated a basin-wide shift in sediment delivery. Basin-wide improvements in bank stability were measured in Ash Creek. Fewer eroding banks were measured during post-BMP assessment and channel sinuosity increased, indicating reduced gradient and sediment transport capacity. Improvements were highly correlated to presence of in-channel vegetation, specifically Spartina pectinata (prairie cordgrass, PCG), a tall native warm season grass. Dense and moderate PCG stands were found in 15 and 23 reaches respectively, but were absent in 64 reaches within Ash Creek. Channel morphology was characteristically different among three subjectively defined PCG classes ─ dense, moderate, and absent. Dense PCG sites were associated with low headcut density, wide bankfull widths, high width:depth ratios, wide floodprone widths, and channel succession events trending toward decreasing stream power. Sites absent of PCG were associated with the opposite channel characteristics. Locations without PCG were queried for channel morphology conditions typical of dense PCG sites using ArcMap and nine locations suitable for PCG establishment were identified. Basin-wide change in channel morphology occurred more rapidly than literature would suggest, indicating BMP implementation coincided with natural channel succession. Therefore, it is likely that BMP implementation occurred when the majority of channels were nearing critical bank height and beginning the channel widening phase. Understanding regional channel evolution patterns should be considered when designing channel morphology monitoring studies to make decisions on when monitoring should take place.

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Thesis - University Access Only

Discipline thesis:degree_discipline

Natural Resource Management

Year

2012

Author dc:creator

• Vande Kamp, Kendall L.

Contributors dc:contributor

• Nels Troelstrup

• Natural Resources and Conservation

Statement dc:rights

• Copyright © 2012 Kendall L. Vande Kamp. All rights reserved.

Language dc:language

en

Repository record dc:identifier

https://openprairie.sdstate.edu/etd/587

OAI identifier oai:identifier

oai:openprairie.sdstate.edu:etd-1587