Wednesday, November 15, 2006 - 2:15 PM

Field and Laboratory Verification of Seepage Erosion Sediment Transport Models.

Garey Fox, Oklahoma State Univ, Dept Biosystems and Agric. Eng., Stillwater, OK 74078, Glenn Wilson, USDA-ARS, Nat'l Sedimentation Lab., 598 McElroy Dr., 598 McElroy Dr., Oxford, MS 38655, United States of America, and Andrew Simon, USDA-ARS Nat'l Sedimentation Lab., 598 McElroy Dr, Oxford, MS 38655.

Erosion by lateral, subsurface flow is known to erode streambank sediment in numerous geographical locations; however, the role of seepage erosion on mass failure of streambanks is not well understood. In the absence of an established sediment transport model for seepage erosion, the objectives of this research were to investigate the mechanisms of erosion due to concentrated, lateral subsurface flow and develop an empirical sediment transport model for seepage erosion of noncohesive sediment on near-vertical streambanks. Seepage flow and sediment concentrations were measured in situ along the banks of two deeply incised streams in northern Mississippi: Little Topashaw Creek and Goodwin Creek.  Subsurface flow and erosion was quantified at selected seep locations using lateral flow collection flumes installed into exposed faces of the streambanks.  Seeps at Little Topashaw Creek were predominantly characterized as seepage through a conductive layer overlying a water restrictive layer. Seeps at Goodwin Creek were unique from those at Little Topashaw Creek and were characterized as intermittent “low-flow” seeps primarily active following large rainstorm events and as a result of reverse bank storage, perennial “high-flow” seeps which developed the most significant headcuts, and “buried” seeps which eroded unconsolidated bank material from previous bank failures.   Laboratory experiments were performed using a two-dimensional soil lysimeter of a reconstructed streambank profiles.  From the lysimeter experiments, a seepage erosion transport model for conductive, noncohesive soil layers was derived based on a dimensionless sediment discharge and dimensionless seepage flow shear stress.  The advantage of this sediment transport model is that it relates sediment flux to seepage discharge from the streambank.  The application of this sediment transport model to the seep measurements at the two stream sites will be discussed.