Measuring streambank erosion due to ground water seepage: correlation to bank pore water pressure, precipitation and stream stage

Abstract

Limited information exists on one of the mechanisms governing sediment input to streams: streambank erosion by ground water seepage. The objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow/erosion with precipitation, stream stage and soil pore water pressure. The streambank site was located in Northern Mississippi in the Goodwin Creek watershed. Soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity (K s ) with depth, but differences between lateral K s of a concretion layer and the vertical K s of the underlying layers contributed to the propensity for lateral flow. Goodwin Creek seeps were not similar to other seeps reported in the literature, in that eroded sediment originated from layers underneath the primary seepage layer. Subsurface flow and sediment load, quantified using 50 cm wide collection pans, were dependent on the type of seep: intermittent low-flow (LF) seeps (flow rates typically less than 0·05 L min − − − − −1 ), persistent high-flow (HF) seeps (average flow rate of 0·39 L min − − − − −1 ) and buried seeps, which eroded unconsolidated bank material from previous bank failures. The timing of LF seeps correlated to river stage and precipitation. The HF seeps at Goodwin Creek began after rainfall events resulted in the adjacent streambank reaching near saturation (i.e. soil pore water pressures greater than − − − − −5 kPa). Seep discharge from HF seeps reached a maximum of 1·0 L min − − − − −1 and sediment concentrations commonly approached 100 g L − − − − −1 . Buried seeps were intermittent but exhibited the most significant erosion rates (738 g min − − − − −1 ) and sediment concentrations (989 g L − − − − −1). In cases where perched water table conditions exist and persistent HF seeps occur, seepage erosion and bank collapse of streambank sediment may be significant.

Calculating the sediment budget of a tropical lake in the Blue Nile basin: Lake Tana

“…The seepage from the subsurface flow to the stream channels unlike earlier application of the model (Tilahun et al, 2013a), base and interflow have a small sediment concentration early in the rainy phase (Fox et al, 2007;Fox and Wilson, 2010;Tebebu et al, 2010).…”

Bank‐collapse processes in a valley‐bottom gully, western Iowa

“…Sometimes smaller, localized collapse at the base of a gully wall ( Figure 6C) undercut the unsaturated alluvium above, leading to its eventual collapse. Bradford et al (1978) observed these small collapses, calling them alcove or pop-out failures and noting that they may be caused by sapping (see also Fox et al (2007) and Wilson et al (2007)). Observations of vigorous seepage 1·5-2·0 m below ground level during rainfall events ( Figure 6D) also highlighted the potential role of groundwater flow in instigating mass wasting.…”

“…Our general goal was to determine through monitoring over a 2-year period whether positive pore pressures associated with subsurface water flow were alone sufficient to instigate bank failures. The role of subsurface water in the failure of gully and river banks has received considerable attention (e.g., Bradford and Piest, 1977;Osman and Thorne, 1988;Higgins et al, 1990;Hagerty, 1991;Darby and Thorne, 1996;Casagli et al, 1999;Simon et al, 2000;Collison, 2001;Simon and Collison, 2001;Amiri-Tokaldany et al, 2003;Dapporto et al, 2001Dapporto et al, , 2003Rinaldi et al, 2004;Darby et al, 2007;Fox et al, 2007;Wilson et al, 2007), and some authors have isolated effects of reduced matric suction in the unsaturated zone (e.g., Fredlund et al, 1978;Casagli et al, 1999;Rinaldi et al, 2004). This study, motivated by observations of bank failures seated below the water table, focuses on only the saturated zone.…”

Budgeting suspended sediment fluxes in tropical monsoonal watersheds with limited data: the Lake Tana basin

“…Unlike in the Tilahun et al ( 2013a) model application, in our model formulation the subsurface flow contains some sediment in the rainy phase (Fox and Wilson, 2010;Fox et al, 2007;Tebebu et al, 2010).…”