Induced channel enlargement in small urban catchments,Armidale, New South Wales

Surveys of stream channels in 14 small catchments within and adjacent to Armidale, northern New South Wales, revealed that urban affected streams were four times larger (on average) than adjacent rural streams. The enlargement of such channels is frequently attributed to increased urban storm runoff. In this case, however, there is no apparent linkage between the degree of urban development and the magnitude of channel enlargement. Rather, it appears that gullying is initiated by more direct disturbances to these channel boundaries, such as realignment and the building of road crossings. Once gullying has been initiated the degree of channel enlargement seems to be a function of slope; the enlargement of channels in the steeper headwater urban catchments being significantly greater than that in the lower reaches. For incipiently unstable channels such as these, the more conventional erosion control measures may be inadequate.