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Drainage from layered field soils: Fixed gradient models
Author(s) -
Sisson James B.
Publication year - 1987
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr023i011p02071
Subject(s) - mathematics , exponential function , hydraulic conductivity , mathematical analysis , power function , differential equation , soil water , hydrology (agriculture) , soil science , geotechnical engineering , geology
Fixed gradient models result when the gradient term in the soil moisture equation is assumed to vary only with depth (remains invariant in time). The fixed gradient assumption results in a first‐order partial differential equation that is transformable to a mathematical form identical to that for a uniform soil. When the transformation was applied to field data, all water content data were found to plot along a single curve. Assuming a fixed gradient and an exponential form for K (Θ) resulted in a fitted curve with an r 2 = 0.847 (d.f. = 405) when data from three sites and seven depths were used. Assuming a power function for K (Θ) resulted in a similar r 2 . Prior to applying the transform, hydraulic conductivity required 42, 42, and 63 parameters to fit data obtained at the 21 spatial points sampled, assuming a Davidson, Watson or Brooks and Corey function, respectively. With the transform 23, 23, and 24 parameters were required for the three K (Θ) functions, respectively.