Gully initiation and implications for management of scour holes in the vicinity of the Jabiluka Mine, Northern Territory, Australia

A track across a burnt grass swale wasused intensively on the Jabiluka Mineral Lease (locatedadjacent to Kakadu National Park in the seasonallywet tropics of the Northern Territory, Australia)for a short time period during the 1998 dryseason. Repeated vehicle passes over the burntgrass increased soil bulk density and locally disruptedthe root and algal mat, lowering the critical shearstress for sediment transport. Overland flow duringthe next wet season was above average and erodedeleven discontinuous, flow-aligned scour holes inthe wheel ruts where the track crossed grassedsandy swales. Although the site was burnt againduring the next dry season, the scour holes did notcoalesce during the second wet season, which waswetter than the previous one, because infrequenttraffic bypassed the eroded section allowing grassto re-establish. Scour holes on vehicle tracks in theKakadu region are an intermediate but reversiblestage in the development of gullies in grassedswales. Treatment of scour holes by soil conservationworks may prevent gully formation.