Estimating Erodibility Parameters for Streambanks with Cohesive Soils Using the Mini Jet Test Device: A Comparison of Field and Computational Methods

The jet test device has been predominantly used for in situ critical shear stress (τc) and erodibility coefficient (kd) measurements of cohesive streambanks/beds using three analytical procedures: the Blaisdell method (BM), the iterative approach (IP), and the scour depth approach (SDP). Existing studies have reported that τc and kd estimates can be influenced by the computational procedure, time intervals for scour-hole depth measurements, and the pressure head selection. This study compared estimates of τc and kd among the three computational procedures using single and multiple pressure settings (SPS, MPS). A new method is introduced applying incrementally increasing pressure heads, hypothesizing depth-averaged erodibility parameters would be generated that better represent bank and fluvial erosion. Estimates of τc applying the MPS-BM procedure were greater by 17% to 100% compared with SPS-BM procedures and kd estimates were lower with less variability (σ = 3.54) compared with other procedures from 126 jet tests among 21 Tennessee stream sites. This finding supports the hypothesis of increasing τc and decreasing kd with greater soil depths into the bank, suggesting the MPS-BM procedure can improve the estimation of τc and kd using the mini-jet test device. Overall, this study demonstrates the need to standardize field and computational procedures