THE CONTRASTING EFFECTS OF WILDFIRE AND CLEARFELLING ON THE HYDROLOGY OF A SMALL CATCHMENT

✍ Scribed by DAVID F. SCOTT

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 209 KB
• Volume: 11
• Category: Article
• ISSN: 0885-6087
• DOI: 10.1002/(sici)1099-1085(199705)11:6<543::aid-hyp474>3.0.co;2-j

✦ Synopsis

A wild®re in an aorested research catchment presented the rare opportunity to compare the hydrological eects of wild®re with the eects of clearfelling in the same catchment in the Jonkershoek Valley, in the south-western Western Cape Province of South Africa. The timber plantation, which occupies 57% of the 2 km 2 catchment, had been clearfelled and re-planted to Pinus radiata roughly ®ve years before the ®re. The eects of the two treatments on total ¯ow, storm-¯ow and quick-¯ow volumes, peak discharge and storm response ratio were determined by means of multiple regression analysis, employing the dummy variable method to test for the signi®cance of treatments. Both clearfelling and wild®re caused signi®cant increases in all the stream-¯ow variables analysed. But the clearfelling eect was dominated by large increases in total ¯ow (96% over three years), of which storm-¯ow and quick-¯ow volumes formed only minor parts. After the wild®re, by contrast, increases in total ¯ow were small (12%) but the storm ¯ow increases were three-to fourfold in the ®rst year and roughly double in the second year. The wild®re caused ®re-induced water repellency in the soils which led to overland ¯ow on mid-slope sites, where soil in®ltrability normally far exceeds local rainfall intensities. It is argued that these results support the hypothesis that stream-¯ow generation processes were changed by the wild®re in that overland ¯ow made a direct contribution to storm ¯ows, but that clearfelling had no such eect.