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United States Department of Agriculture

Agricultural Research Service

Research Project: Technologies for Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research Unit

Title: In situ soil pipeflow experiments on contrasting streambank soils

Authors
item Midgley, Taber -
item Fox, Garey -
item Wilson, Glenn
item Felice, Rachel -
item Heeren, Derek -

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 30, 2012
Publication Date: March 1, 2013
Citation: Midgley, T.L., Fox, G.A., Wilson, G.V., Felice, R., Heeren, D. 2013. In situ soil pipeflow experiments on contrasting streambank soils. Transactions of the ASABE. 56(2):479-488.

Interpretive Summary: Erosion caused by water flowing through large soil pores called soil pipes has been suggested as a cause of levees, dams, and streambanks to fail. Very little research has been conducted under field conditions to measure and model flow through soil pipes and the erosion inside soil pipe using either natural or artificially created soil pipes. This research used soil pipes created in a streambank from the bank face back to a trench with a constant water level to study soil pipe in two contrasting streambanks: Dry Creek in northern Mississippi and Cow Creek in northern Oklahoma. Experiments included “open pipes” where the soil pipe was directly connected to the trench and open at the streambank face and “clogged pipes” which involved plugging the outlet of the soil pipe using soil from the bank face next to the soil pipe. Tensiometers were used to measure soil water pressures in the soil next to the “open” and “clogged” pipes. When pipeflow occurred, the flow was sampled to measure sediment concentrations and erosion of the soil pipe. Flow and sediment data were used with a turbulent flow erosion model to estimate erosion properties of the soils, which were subsequently compared to properties measured using the jet erosion device. “Clogged” soil pipes resulted in pore water pressure increases in the soil adjacent to pipes. The pressures generally remained below saturation during these experimental periods, except locations close to the plug. Depending on the density of the plugged soil material, the “clogged” soil pipes either burst open, resulting in turbulent flow through the soil pipe or were manually punctured to reestablish flow. Calibrated erosion properties from the turbulent flow and erosion model matched those observed from jet erosion tests for the less erodible soils on the Dry Creek streambank. At dry Creek, sediment concentrations were consistently below 2 g/L even with fairly high water levels maintained in the trench on the soil pipe. For the more erodible soils of Cow Creek, there is a need for improved pipe flow modeling that better accounts for interactions between the pipe and the adjacent soil. These interactions lead to cases of steady flow rates but increased sediment concentrations during the early stages of pipe flow.

Technical Abstract: Soil piping has been attributed as a potential mechanism of instability of embankments and streambanks. Limited field work has been conducted on quantifying and modeling pipeflow and internal erosion processes in the field with either natural or artificially created soil pipes. This research utilized an innovative constant-head trench system to conduct constant head soil pipe experiments in two contrasting streambanks: Dry Creek in northern Mississippi and Cow Creek in northern Oklahoma. Experiments included “open pipes” where the soil pipe was directly connected to the constant-head trench and open at the streambank face and “clogged pipes” which involved plugging the outlet of the soil pipe using soil excavated adjacent to the pipe. A tensiometer network was used to measure soil water pressures surrounding “open” and “clogged” pipe outlets on the streambank face. When pipeflow occurred, flow and sediment samples were collected using flow collection pans to quantify sediment concentrations and pipe enlargement. Flow and sediment data were used with an existing turbulent pipeflow and internal erosion model to estimate erodibility and critical shear stress properties of the soils, which were subsequently compared to similar properties derived from jet erosion tests. “Clogged” soil pipes resulted in pore water pressure increases in the soil adjacent to pipes, which generally remainedbelow saturation during these experimental periods, except locations close to the plug. Depending on the density of the plugged soil material, the “clogged” soil pipes either burst resulting in turbulent pipeflow or were manually punctured to reestablish pipeflow. Calibrated erodibility and critical shear stress from the turbulent pipeflow and internal erosion model matched those observed from jet erosion tests for the less erodible soils on the Dry Creek streambank where sediment concentrations were consistently below 2 g/L even with fairly large hydraulic gradients on the pipe (0.3 m/m). For the more erodible streambank soils of Cow Creek, there is a need for improved pipeflow modeling that better accounts for pipeflow and soil matrix interactions leading to cases of steady flow rates but increased sediment concentrations during the initial stages of pipeflow.

Last Modified: 8/1/2014
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