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Quantifying Subsurface Drainage Rates for Research Sites

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

Citation:  2016 10th International Drainage Symposium Conference, 6-9 September 2016, Minneapolis, Minnesota  .(doi:10.13031/IDS.20162493719)
Authors:   R. Wayne Skaggs
Keywords:   Drainage Coefficient, Drainage Intensity, Drainage nomenclature, Kirkham

Abstract. It is proposed that technical papers on drainage research studies and engineered design projects should report standard coefficients/parameters that characterize the hydraulics of the system. The following coefficients define key subsurface drainage rates that could be used to quantify the hydraulics of a drainage system. 1. The steady subsurface drainage rate (cm/d) corresponding to a saturated profile with a shallow ponded surface. This subsurface drainage rate defines the length of time that water remains ponded on the soil surface following large rainfall events. It is proposed that this rate be called the Kirkham Coefficient (KC) in honor of Professor Don Kirkham who derived analytical solutions for saturated drained profiles for most soil and boundary conditions of interest. 2. Drainage Intensity (DI), which represents the drainage rate (cm/d) when the water table midway between parallel drains is coincident with the surface. The DI can be estimated by the Hooghoudt Equation and is dependent on the effective saturated hydraulic conductivity of the profile, drain depth, spacing, and depth of the soil profile or restrictive layer. 3. The hydraulic capacity of the system, often called the drainage coefficient (DC). This value is the rate (cm/d) that the outlet works can remove water from the site. It is dependent on the size, slope and hydraulic roughness of the laterals, submains, mains, and, in cases where the pumped outlets are used, the pumping capacity. Routine inclusion of these three coefficients in the documentation of research and design projects would be very useful to readers as they compare results of different studies.

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