ABSENCE OF PREFERENTIAL FLOW IN THE PERCOLATING WATERS OF A CONIFEROUS FOREST SOIL

✍ Scribed by B. G. RAWLINS; A. J. BAIRD; S. T. TRUDGILL; M. HORNUNG

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 193 KB
• Volume: 11
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/(sici)1099-1085(199705)11:6<575::aid-hyp478>3.0.co;2-z

✦ Synopsis

Evidence for the functioning of macropores and the presence of preferential ¯ow in forest soils is equivocal. This is partly because many workers use only one diagnostic technique to indicate whether or not macropore ¯ow occurs. In this paper three lines of evidence are used to suggest that preferential ¯ow does not occur in the percolating waters of a coniferous forest soil under the range of hydrological conditions that prevail in the ®eld. To simulate ®eld conditions, realistic rainfall intensities were used in conservative solute transport experiments on four undisturbed soil columns.

A method is described in which breakthrough data can be used to calculate the percentage of antecedent water displaced from a soil column during frontal-type breakthrough experiments. Calculations based on this method using the experimental data show that as little as ®ve percent of the antecedent water was immobile. The simple form of the functional advection±dispersion equation, based on a single value for linear velocity and the dispersion coecient was ®tted to two of the breakthrough curves with reasonable accuracy, further suggesting that preferential ¯ow did not occur in the experiments. Finally, soil moisture characteristic curves were determined for replicate soil samples from the forest soil. The operational water contents of the columns during the breakthrough experiments were compared with the soil moisture characteristics and it was found that pores exerting pressure heads greater than À0Á5 kPa did not appear to contribute to ¯ow through the columns, again suggesting an absence of preferential ¯ow.