Tunnel formation processes in the Riverina area of N.S.W., Australia

Soil and site characteristics associated with tunnel erosion are diverse. This contributes to difficulties in identifying areas of potential tunnelling and the reclamation of land affected by this form of water erosion. Soil, site, and tunnel characteristics at three locations having different morphological expressions of this erosion form were examined to determine which features were important in tunnel development in the Riverina Area of N.S.W., Australia. Soil dispersion was a dominant process at each site and is related to high levels of exchangeable sodium. Field and laboratory studies demonstrated the importance of dispersion and its effect on water movement, particle transport, and subsequent tunnel initiation. Tunnel initiation mechanisms differed between the sites but could be identified by morphological examination of the tunnels. Potential tunnel eroding sites are characterized by a dispersible layer, a gradient for water flow, and soil characteristics that promote water Sow in defined paths. Appropriate control techniques need to be formulated for each differing form of tunnel erosion.