Stu Clement: A longitudinal assessment of environmental and use impacts to Brisbane's Gap Creek Circuit mountain bike trail

A year-long study to monitor and assess Brisbane's Gap Creek Circuit mountain bike trail was undertaken from April 2009 to April 2010 to look for changes to transect profiles and used tread widths under measured use (about 31 passes per day) and rainfall conditions (1,135 mm for the study year).

Gap Creek Circuit is part of a 12 km network of purpose-built, mountain bike only trails in Brisbane's Mt Coot-tha Forest. The trail was selected because: (1) it was built in accordance with internationally-recognised trail construction guidelines for producing the most sustainable trails (published by International Mountain Bicycling Association); (2) the entire trail would be subject to the same use; and (3) it was not to be subjected to maintenance work during the course of the study.

Trail tread transect profiles at 20 randomly-selected points were measured on five occasions over the year. The measurements indicate that: fifteen (75 per cent) did not exhibit any change or showed minimal change (soil movement). A further two showed noticeable change (both with soil loss) and the remaining three (fifteen per cent) exhibited considerable change (all with soil loss).

Used tread widths (where an estimated 91 per cent of riders travel) were also recorded. Forty-five per cent showed no change, while 25 per cent narrowed noticeably and 30 per cent widened. None of the tread widths that changed did so outside the edge of the trail as built and hence none showed signs of tread creep.

At no transect was there evidence of gouging, deep wheel ruts or channels caused by erosion. While continual maintenance of trails is always required, maintenance is likely to be required more often in those parts of trails that deviate too far from the guidelines while trail sections built within the guidelines will consume much less of the trail maintenance budget.