Big Pine Creek Ditch Revisited: Insight into the Initiation and Evolution of Meandering

Abstract:

The initiation of meandering of rivers remains an important unresolved problem in fluvial science, despite an extensive body of research that has addressed this issue. Given that many rivers meander, investigating the development of meanders in an initially straight channel has been viewed as an important approach to understanding both why and how meandering occurs. The vast majority of previous research of this type has involved the formulation of mathematical and conceptual models of meander initiation or experimental work on meander formation in straight, erodible laboratory channels. Few studies have explored how meanders develop in straight rivers, particular over long timescales. This study examines the development of meandering in Big Pine Creek Ditch, which was straightened through a channelization project in 1932. The adjustment of this creek to straightening was first reported in a classic study of response to channelization by Barnard and Melhorn (1982). That study involved manual analysis of channel change using historical aerial photographs for three different years between 1938 and 1971. The present research uses GIS-based methods to reanalyze channel change between 1938 and 1971 using five sets of historical images and also updates the analysis using another five sets of historical images for the period 1971 to 2018, thereby providing information on meander development in an initially straight channel over an 86-year period. Results demonstrate that the initiation of meandering was highly spatially variable along the straightened channel and that recovery of sinuosity in reaches that remeandered has occurred more quickly than predicted by Barnard and Melhord (1982). The study provides insight into the timescale over which meandering develops, spatial variability of this timescale, patterns of meander evolution, and the rate of increase in sinuosity over time.