MODELING STREAMFLOW FOR CHANNEL AND BANK STABILITY

Spearfish Creek flows in a narrow, incised canyon in the northern Black Hills resulting in high velocity flows that place increased stress on channel banks and bottom. Potential results include damage to existing roadways and bridges as well as channel widening and damaged fish habitat. Thus, it would be desirable to predict locations where increased bank and/or channel stress would be expected under varying flow conditions. An approximately 1.6 km reach was surveyed using a laser-digital transit. Channel cross-sections were measured every 30 m producing a detailed topographic map of the channel, banks, and limited floodplains. Flow modeling was performed using discharges that were based on current stream-flow and known historic flood flows. The stream was modeled as segments, using SMS, where inflow to each segment occurred at the upstream boundary. The segment containing Squaw Creek tributary had two inflow boundaries. Results indicted high stress at numerous points along the entire stream channel as a function of river channel morphology. Areas of concern included sections that contained bends or narrowing of the channel. Where the highway was closest to the potential channel scour zones, damage might be expected under severe flow conditions causing immediate damage to the fishery. These results will allow highway engineers and fisheries personnel to maximize efforts to sustain existing roadways and to provide and maintain quality fisheries within Spearfish Canyon.