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Title: Predicting streambank seepage flows: sensitivity to soil properties and layering

Author
item HEEREN, D - Oklahoma State University
item FOX, G - Oklahoma State University
item CHU-AGOR, M - Oklahoma State University
item Wilson, Glenn

Submitted to: Proceedings of the World Environmental and Water Resources Congress Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/1/2009
Publication Date: 5/17/2009
Citation: Heeren, D.M., Fox, G.A., Chu-Agor, M.L., Wilson, G.V. 2009. Predicting streambank seepage flows: sensitivity to soil properties and layering. Proceedings of the World Environmental and Water Resources Congress Conference. Great Rivers. 342:3753-3762.

Interpretive Summary: Streambank failures result in loss of land and increased sediment and nutrients in streams. Computer models that predict subsurface flow have been combined with models of bank stability to predict bank failure. Understanding the degree of characterization of the soil properties necessary to predict when seepage contributes to bank failure is needed. This research examined how sensitive predictions of seepage were to soil properties and the effect of soil layers. A groundwater flow model was used to predict velocity (v) of seepage from a streambank. Another model, ROSETTA, was used to estimate soil properties for various levels of soil data ranging from knowledge of only soil texture to knowing the actual percent sand, silt, and clay and also knowing the saturated hydraulic conductivity (Ks); and bulk density (BD) of the streambank. Results suggested that Ks and/or percent clay measurements are necessary to adequately predict seepage. A layered bank was also simulated with several combinations of soil types. Results indicated that only one order of magnitude difference in Ks (equivalent to a resistance ratio of 10) may be necessary to induce perching and seepage from the top layer. This research suggested that, if a field survey is performed to locate streambanks susceptible to failure by seepage erosion, simply identifying soil layers by soil type may not be adequate as Ks and/or bulk density measurements are necessary.

Technical Abstract: Streambank failures result in loss of land and increased stream sediment loads. Variably saturated flow models integrated with bank stability models are being used to predict bank failure; however, understanding of the level of soil characterization necessary to predict when seepage contributes to bank failure is needed. ROSETTA, a pedotransfer function, was used to estimate hydraulic parameters for various levels of soil data (from texture class to saturated hydraulic conductivity, Ks). A two-dimensional groundwater flow code, SEEP/W, was used to model a hypothetical streambank and estimate seepage velocity. Results suggested that Ks and/or percent clay measurements are necessary to adequately predict seepage. A layered bank was also simulated with several combinations of soil types. Results indicated that only one order of magnitude difference in Ks (equivalent to a resistance ratio of 10) may be necessary to induce perching and seepage from the top layer. This research suggested that, if a field reconnaissance is performed to locate streambanks susceptible to perching, Ks and/or bulk density measurements are necessary to indicate the presence of a restrictive layer.