Topography Battles Surface Texture: An Experimental Study of Pool-riffle Formation
Abstract
Pool-riffles are perhaps the most common streambed shape found in streams and rivers, and not surprisingly, they are essential to salmon ecology, and are a central focus of many restoration actions. Yet, when an applied earth scientist or engineer is faced with developing a pool-riffle design, there is a lack of clear and rigorously developed design guidelines. Given the volumes of money spent annually within the restoration industry, this is a real problem. Recognition of this problem is growing, however, and an increasing level of attention has been directed to questions of pool-riffle formation in the past decade. At this point and given certain landscape characteristics, it is well established that streamwise gradients in channel width are associated with pool-riffles. Specifically, pools are associated with negative gradients in width, and riffles with positive gradients. Importantly, these associations have now been documented from field-derived data, as well as via experimental and numerical investigations. There is much to build from the present knowledge base, and central to this are questions related to (a) how pool-riffles evolve during the formative process, (b) what are the basic set of ingredients necessary for pool-riffle formation within systems characterized by relatively non-erodible channel margins, and (c) do pool-riffles persist, once formed, under a broad range of forcing conditions? We have completed four physical experiments examining the process and evolution of pool-riffle formation under a large range of upstream boundary, as well as physical channel conditions. We will report on two of the completed experiments. Our work will highlight two new non-dimensional channel evolution numbers, derived to help describe and characterize bedform development, as well as response to perturbations from near-equilibrium conditions. The channel evolution numbers lay the foundation for development of a new regime diagram, which quantifies the basic ingredients needed to drive pool-riffle formation, as well as formation of other types of gravel bedforms. We believe our work holds promise for application in identifying suitable conditions for pool-riffle construction, and natural maintenance over typical restoration project time frames.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMEP53C0986C
- Keywords:
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- 1824 Geomorphology: general;
- HYDROLOGYDE: 1825 Geomorphology: fluvial;
- HYDROLOGYDE: 1826 Geomorphology: hillslope;
- HYDROLOGYDE: 1886 Weathering;
- HYDROLOGY