Two pool-to-pool spacing periods on large sand-bed rivers

A few months before I left HEC, I worked with Stan and others on a study of the Madeira River in Brazil. The Corps (Flood and Coastal Research and Development) was working with the Brazilian Government (Mobile District Brazilian initiative) on a sediment study on the Madeira River between Manicoré and Porto Velho in Northern Brazil. During the project, the study team discovered some interesting geomorphic patterns in the location and regularity of deep pools in the Madeira River. Basically, we found that pool-to-pool spacing in the Madeira has two distinct periods. First, we found evidence of “rhythmic” pools, features developed by macro-turbulent feedbacks with the classic spacing of 5-7 channel widths. This wouldn’t ordinarily be very special, except for the fact that this period does not correspond to the actual river planform—this section of the river is actually quite straight, and meanders are much less frequent. Second, we found evidence of periodic, extremely deep “mega pools” at ~40 channel widths, which we refer to as “forced” features driven by encounters with bedrock. However, the regular spacing of these megapools is more a coincidence of regional geology than anything else. It’s a fun paper to read and has a lot of background information on the Madeira that hasn’t been published before, so check it out!