ASABE Technical Library - Abstract
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ESTIMATING DRAIN SPACING OF INCOMPLETE DRAINAGE SYSTEMS
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Transactions of the ASAE. 40(2): 377-382. (doi: 10.13031/2013.21282) @1997Authors: V. M. Kurien, R. A. Cooke, M. C. Hirschi, J. K. Mitchell
Keywords: DRAINMOD, Optimization, Random tile drains, Nitrate, Drain spacing, Hydraulic conductivity
Determination of nitrate loading per unit area from a field to a subsurface drain requires an estimate of the
area contributing flow to the drains. In random drainage systems or systems with irregularly spaced drains, the
contributing area is often unknown. Presented are the development and application of a method for using drain outflow
rates to estimate drain spacing for incomplete drainage systems that in effect drain most of the intended area. An
optimization routine is used to determine the drain spacing that minimizes the difference between observed and
DRAINMOD-simulated tile outflows.
The method was used to determine the effective spacings of tile drains installed in four fields in the Little Vermilion
River watershed in east-central Illinois. The drain spacing information estimated the nitrate loading rates for regions
within the watershed. Under the prevailing conditions of the watershed, DRAINMOD performance was relatively
insensitive to surface storage, the depth of the impermeable layer from the ground surface, diameter of the tile drains, and
the lateral hydraulic conductivities in all the soil layers of the soil profile, with the exception of the layer in which the
drains were located. Random tile drains in the agricultural fields on Drummer/Flanagan soils in east-central Illinois have
an effective region of influence of 100 m. Effective drain spacing was not site specific, whereas hydraulic conductivity was
highly variable and site specific.