| Abstract: | This paper provides an alternative method to describe the water retention curve over a range of water contents from saturation to oven dryness. It makes two modifications to the standard Brooks and Corey [1964] (B-C) description, one at each end of the suction range. One expression proposed by Rossi and Nimmo [1994] is used in the high-suction range to a zero residual water content. (This Rossi-Nimmo modification to the Brooks-Corey model provides a more realistic description of the retention curve at low water contents.) Near zero suction the second modification eliminates the region where there is a change in suction with no change in water content. Tests on seven soil data sets, using three distinct analytical expressions for the high-, medium-, and low-suction ranges, show that the experimental water retention curves are well fitted by this composite procedure. The high-suction range of saturation contributes little to the maximum capillary drive, defined with a good approximation for a soil water and air system as H(cM) = {???)/(o) k(rw) dh(c), where k(rw) is relative permeability (or conductivity) to water and h(c) is capillary suction, a positive quantity in unsaturated soils. As a result, the modification suggested to describe the high-suction range does not significantly affect the equivalence between Brooks-Corey (B-C) and van Genuchten [1980] parameters presented earlier. However, the shape of the retention curve near ‘natural saturation‘ has a significant impact on the value of the capillary drive. The estimate using the Brooks-Corey power law, extended to zero suction, will exceed that obtained with the new procedure by 25 to 30%. It is not possible to tell which procedure is appropriate. Tests on another data set, for which relative conductivity data are available, support the view of the authors that measurements of a retention curve coupled with a speculative curve of relative permeability as from a capillary model are not sufficient to accurately determine the (maximum) capillary drive. The capillary drive is a dynamic scalar, whereas the retention curve is of a static character. Only measurements of infiltration rates with time can determine the capillary drive with precision for a given soil. |
| Genre: | Article |
| ProdID: | 70021996 |
| Citation Author: | Morel-Seytoux, H. J.; Nimmo, J. R. |
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| Citation End Page: | 2041 |
| Citation Issue: | 7 |
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| Citation Language: | English |
| Citation Larger Work Title: | Water Resources Research |
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| Citation Number Of Pages: | 11 |
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| Citation Search Results Text: | Soil water retention and maximum capillary drive from saturation to oven dryness; 1999; Article; Journal; Water Resources Research; Morel-Seytoux, H. J.; Nimmo, J. R. |
| Citation Start Page: | 2031 |
| Citation Volume: | 35 |
| Citation Year: | 1999 |
| Type: | citation/reference |
| Text: | Soil water retention and maximum capillary drive from saturation to oven dryness; 1999; Article; Journal; Water Resources Research; Morel-Seytoux, H. J.; Nimmo, J. R. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1029/1999WR900121 |
| Date Other: | Fri, 1 Jan 1999 00:00 -0600 |
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