Methodology for evaluating post harvest erosion risk for the protection of water quality

Authors: Edwin A. Christopher, Rien Visser
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2007, Issue N.Z.J.For. 52(2) 2007, pp 20-25, Aug 2007
Publisher: New Zealand Institute of Forestry

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Abstract: Poor forest harvesting practices can accelerate soil erosion, impact site productivity and decrease water quality. Postharvest monitoring for the protection of water quality using visual inspections provides one rather subjective means for compliance monitoring. This study develops a method for quantitative analysis of potential erosion rates post-harvest using a Universal Soil Loss Equation (USLE) modified for forestry. To carry out an on-site inspection, the harvested area is divided into five disturbance areas: 1) landing area, 2) skid trails, 3) access roads, 4) cut-over, and 5) stream crossings. Erosion rates are estimated using the USLE in each of these areas, then combined to present a weighted average erosion rate for the whole harvest site.

The methodology was tested on 54 harvest sites in Virginia, USA, harvested between one to eight years ago, divided equally among three regions in Virginia. These regions are defined as Coastal Plain, Piedmont and Mountains. The weighted estimated erosion rates were significantly higher for the harvested areas in the Mountains (4.4 Mg/ha/yr) compared to the Piedmont (2.7 Mg/ha/yr) and Coastal Plain (2.5 Mg/ha/yr). In the mountains, the disturbance area contributing the greatest amount of potential erosion was the skid trails (54% of total), while the greatest potential contribution in the Piedmont came from the access roads (39%) and skid trails (39%). In the flatter coastal plain the cut-over area produced 74% of the estimated total erosion.

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