Sedimentological impact of a high magnitude, low-frequency flood in a braided river revealed from sequential GPR surveys

Abstract

Integrated aerial photography and GPR profiling has been used to explore the surface and subsurface evolution of braid bars within the South Saskatchewan River, Canada 2004-2007. Following a large flood in 2005, areas of a kilometre-long braid bar experienced incision and the creation of new unit bars. Subsequent low-magnitude, high-frequency flows during 2006 produced a further new central unit bar. Analysis of GPR profiles shows the presence of bar margin deposits in the subsurface relating to the unit bars produced in flood conditions and low-magnitude high-frequency flows. Quantitative comparisons of deposits reveal that the bar margin deposits formed during the large flood are similar in scale to the low-magnitude, high-frequency deposits with respect to the height and width of individual strata. However, stratal angles appear steeper in bar margin deposits produced by the low-magnitude, high-frequency events.