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HYDROLOGY, MORPHOLOGY AND WATER QUALITY IN CONSTRUCTED OPEN-DITCH CHANNELS

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  701P0904,  . (doi: 10.13031/2013.17441)
Authors:   J.S. Strock, R.T. Venterea, J.A. Magner, W.B. Richardson, and P.H. Gowda
Keywords:   

Open-ditch channels are potential transporters of considerable loads of nutrients, sediment, pathogens, and pesticides from agricultural land to small streams and larger rivers. An open-ditch research facility incorporating a paired design was constructed near Lamberton, MN during 2002. Our objective was to compare hydrology, ditch channel morphology, and water quality between two experimental open-ditch channels both spatially and temporally. Channels were constructed with a 0.1% slope. A 200-m reach of existing drainage channel was converted into a system of four parallel channels. The facility was equipped with water level control devices and instrumentation for flow monitoring and water sample collection on upstream and downstream ends of the system. Hydrographs from base- and storm-flow periods are presented along with water quality data. Longitudinal profiles along the horizontal length of each open-ditch were made every 3 m. In addition, eight longitudinal cross-sections were measured in each open-ditch. Hydrographs from simulated flow during 2002 indicated flow between channels at upstream and downstream monitoring locations were similar. Cumulative outflows were 60 and 85 m3 for channels A and B, respectively. Channel cross-sections near the upstream end of the facility generally exhibited a trapezoidal shape whereas cross-sections near the downstream end tended to exhibit a parabolic shape. The parabolic shape coincided with an area of increased gradient (0.7%) in the channel bottom. Base- and storm-flow water samples were analyzed for sediment, nitrate plus nitrite, ammonia, orthophosphate, and total phosphorus. Stable isotopes of nitratenitrogen, 15N and oxygen, 18O, were used to assess the source of nitrate-nitrogen and the magnitude and mechanisms of nitrogen transformation processes in these open-ditch channels. Results from two years of data collection are presented, and our plans for future experimental work at this facility are described.

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