ASSESSMENT OF STREAM MIGRATION RATES TO ESTIMATE BANK EROSION ON THE LOWER CHEYENNE RIVER

Total suspended solids (TSS) constitute part of EPA requirements for regulated waterbodies in the United States. The Cheyenne River is currently on the 303(d) Impaired Waters list due primarily to exceeding the defined acceptable TSS parameter. It is suspected that these elevated TSS values are due to high TSS quantities in tributaries originating in the Badlands rather than anthropogenic influences. Understanding the sources of TSS are critical in establishing an obtainable plan for remediation of the impairment. An ensemble of methods were used to understand the unique conditions of this waterbody including an analysis of river channel movement over time to estimate the amount of sediment moving through the system. The river channel below Angostura Reservoir was delineated using digital aerial photography for two time periods, 1991-1998 and 2008. The delineated river channel movement was estimated by characterizing meander bend parameters and measuring the distance moved using GIS. The length of movement was divided by the time period between the two aerial photography data sets to get an average migration rate. Visual interpretation was used through four reaches to determine the length of reach affected by lateral migration. Cross sectional geometry of the channel was available from a physical habitat assessment done at 13 sites along the Cheyenne River main stem. Multiplying the rate of movement by the channel geometry (primarily bank height) and the length of channel reach affected, an estimate of bank erosion was made. The average annual bank erosion was then compared with FLUX estimates of average annual sediment loads to estimate the percentage of annual sediment load due to lateral channel migration and bank erosion.