Lithologic controls of drainage density: A study of six small rural catchments in New England, N.S.W.

Abstract

The term drainage density has been operationally defined by a number of parameters characterising both static and dynamic networks (eroded channel density, perennial flow occupance, flow net, wetted channel length). The present study examines the variation of flowing stream length on six catchments of contrasting granite and sedimentary lithologies. The basic influence of lithology is analysed at three scales: between catchments, within one network, and along specific channel sections. Flow length graphs demonstrate that the drainage density of flow is greater on sedimentary rocks and is associated with higher eroded channel densities. All basins displayed a wide range of flow net fluctuations which were highly related to rainfall increments. Phases of flow network evolution were traced for each basin during one large storm. On granite basins two other components of the wetted channel network were quantified and exhibited equally dynamic characteristics when compared to flow. These were linear changes of continuous stagnant water sections and saturated segments. Field observations of episodic flows on two contrasting lithologies indicate the variable influence of rock type in surface and subsurface runoff processes and the importance of relating channelled flows to stream channel morphology.