Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 455363
Title A drain-spacing equation that takes the horizontal flow in the unsaturated zone above the groundwater table into account
Author(s) Yousfi, A.; Mechergui, M.; Ritzema, H.P.
Source Irrigation and drainage 63 (2014)3. - ISSN 1531-0353 - p. 373 - 382.
Department(s) Water Resources Management
Publication type Refereed Article in a scientific journal
Publication year 2014
Keyword(s) steady - seepage - soil - transient - system
Abstract Most drain spacing calculations do not take the horizontal flow in the unsaturated zone above the groundwater table into consideration. In this paper, a solution is presented that includes the contribution of unsaturated flow above the groundwater table. Drain spacing calculated with the newly derived equation is compared to that calculated with the Hooghoudt equation and the two-dimensional Hydrus-2D model. Results show that drain spacing calculated with the new equation results in a wider value. The effects are most pronounced for tiles located close to the impervious layer, particularly in coarse, sandy soils. These effects rapidly decrease if the depth of the impervious layer increases. The effect of the unsaturated zone flow contribution is limited to sandy soils, for low infiltration ratios and tiles placed on top of an impervious layer. The maximum increase in drain spacing calculated by the new formula is about 30% higher, suggesting that inclusion of the contribution of the unsaturated zone flow in the computation of drain spacing may result in greater economy in the design of subsurface drainage systems. Moreover, the new equation is more general and is applicable for tiles lying on or far from an impervious layer.
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