Bankfull Geomorphic Relationships and HECRAS Assessment in Small Catchments of the Cumberland Plateau Ecoregion

Hodges, Ryan

ABSTRACT: There is a great need for state governments to have effective watershed restoration and mitigation efforts to return degraded ecosystems to a stable, healthy condition. Given the growing investment in stream restoration efforts, there is an urgent need for tools to assess and improve the effectiveness of restoration efforts at local, state, and nationwide scales. In 2000 there was less than ten stream restoration permits provided by the state of Tennessee and has increased each year with almost forty permits issued in 2013. To better achieve successful stream restoration, appropriate channel designs must be used that reflect the hydraulic conditions of streams in the appropriate ecoregion. Regional curves describe the relations of stream channel conditions to watershed drainage. Robust design curves that span the spatial scale of restoration efforts in terms of drainage area do not currently exist for the Appalachian Plateaus region of Tennessee. The objectives of this study were to 1) develop regional curves for low-order stream geometry in the Cumberland Plateau ecoregion of Tennessee, 2) compare the developed regional curve relationships for the Cumberland Plateau of Tennessee with similar relationships developed for neighboring ecoregions and, 3) validate the application of combining shear stress modeling and the modified Shield’s diagram for predicting bed substrate size in restoration of low-order streams in the Cumberland Plateau of Tennessee. Regional curves for the Tennessee Cumberland Plateau ecoregion were develop and compared with the regional curves of Alabama Cumberland Plateau, North Carolina Piedmont, and Tennessee Western Ridge and Valley ecoregions. Statistical analysis on the regional curves determined that there is a significant difference between some curves at the 0.05 confidence level. Using HEC-RAS and the modified Shield’s Diagram, the predicted D50 was five to ten times greater than the field measured D50 and D84.