Original paper

Geomorphic characteristics of riffle-pool spacing in a low order stream with high rates of bank erosion in Fairfax County, Virginia

Kang, Ranbir Singh


The riffle-pool sequence is a fundamental characteristic of river systems. Formed by alternating bed topography, pools are characterized by slow moving deep water while riffles are channel units with fast and shallow water. Therefore, these channel units are significantly heterogeneous in their morphologies. In general, a distinct riffle-pool sequence is suggested for higher order gravel bed streams with the pool spacing between five to seven times the channel width. Most of these findings are based on channel width measurements at either bankfull stage or bed level. It is not clear whether a well defined riffle-pool sequence with similar spacing is maintained in low order streams especially with high rates of bank erosion. This study addresses that gap by analyzing the geomorphic characteristics of riffle-pool sequence in Thompson Creek, a low order stream experiencing high rates of bank erosion in Virginia, USA. Field surveys were conducted at both bed and bankfull widths from the beginning points, midpoints and tails of riffles and pools. The statistical comparison of riffles and pools revealed minimally significant differences among widths, spacing, and ratios of spacing with widths. These channel units in Thompson Creek have considerable homogeneity possibly due to high rates of bank erosion. These results suggest that riffle-pool sequences can exist in low order streams with high rates of bank erosion, however, they have minimal geomorphic contrasts and their spacing is below the usually expected five to seven times channel width.