Spatial variations in river channel adjustments : implications for channel management in South-East England

Downs, Peter W (1992) Spatial variations in river channel adjustments : implications for channel management in South-East England. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Hydrogeomorphological research in the last twenty years has increasingly provided results with practical applications to river channel management and can potentially be further developed to provide guidelines for schemes of `integrated river basin management'. However, this potential level of application is not yet realised, partly because no method has been developed to explain spatial variations in river channel adjustment. Such variations may be expressed by `river channel sensitivity' for which four interpretations are proposed. One practical and attainable interpretation of sensitivity involves changes in the balance of disturbing and resisting forces causing thresholds between particular styles of channel morphology adjustment to be crossed. Two approaches for assessing this notion within the Thames drainage basin are investigated. The first approach involves summarising the process mechanisms involved using stream power. Estimates of stream power at 318 cross-sections within the channel network of the River Ray (Wiltshire) separate channels with, from those without, periodic deposition at around the 7.5 W.m^-2 threshold. However, the separation is only exclusive for 45% of the data set illustrating the difficulty in reducing experimental variance to a level at which subtly differentiated adjustments in a lowland channel can be distinguished. The second approach to sensitivity directly relates channel adjustments to the drainage basin characteristics which may control them in the form y = f(a₁x₁, ax₂,...a_nx_N) where y represents categories of river channel adjustment, x₁...x_n represent the potentially influential drainage basin characteristics, and a₁...a_n express the relative sensitivity of each adjustment to the incorporated influences. Evidence for channel adjustment was collected by field surveys using a structured checklist of observations which was proved to be robust after tests in the Burstow Stream basin and on the Monks' Brook (Hampshire). Subsequently, the technique was utilised to estimate adjustments in 250km. of channels in the Lambourn, Ravensbourne, Roding and Sor basins. Ten resulting categories of adjustment suggest that 63% of channels show some form of morphological adjustment.