Quantifying the coevolution of bedload transport and bed topography in mountain rivers: field and flume experiments using smartrocks

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Quantifying the coevolution of bedload transport and bed topography in mountain rivers: Field and flume experiments using smartrocksThe bottom of most steep mountain rivers is composed of coarse sediment (gravel to boulders), and the morphology (slope, width, depth, sediment size distribution, surface roughness) of a given channel develops over time due to size-dependent sediment transport and sorting. Conversely, transport rates of both water and sediment are controlled (in part) by channel morphology. The overall goal of this project is to better understand key feedbacks among sediment size, sediment transport rate and channel bed topography, in order to more accurately predict all these factors in natural rivers. A field experiment in river bed evolution will be conducted in which part of a mountain river channel (Reynolds Creek Experimental Watershed, Idaho) is modified using construction equipment. Starting from this artificially smoothed and straightened channel reach, the coevolution of bed topography and bedload transport rate will be measured over time. Complementary experiments will be conducted in laboratory flumes (artificial rivers in which variables can be precisely controlled). Hypotheses will be evaluated using unique data sets collected in both the field and laboratory by applying new and developing technologies. Methods include custom "smartrocks" (gravel and cobbles embedded with accelerometers) and clast tracking using radio frequency identification (RFID) tags. Channel bed morphology will be measured over length scales from centimeters to kilometers by combining airborne and ground-based laser topography surveys (LiDAR).Understanding river bed topography and bedload transport has many practical applications with broad significance to society. Mountain rivers are economically important (for example, cattle ranching takes place along one of the field sites at Reynolds Creek). Predicting how a river will respond to a flood of a given size depends on understanding channel stability, which in turn depends on the channel feedbacks being studied. River restoration efforts require a stronger scientific grounding to be able to engineer channels that will be stable over a given range of floods. Dam removal planning depends strongly on predicting channel feedbacks that occur while river discharge, sediment transport rate and channel morphology are all rapidly changing. In many rivers, transported sediment is also regulated as a pollutant, and better predictions of transport rates are critical for scientifically informed land-management decisions. Finally, the bed topographies of engineered and natural river channels form specific ecological niches, such as for spawning salmon that are sensitive to sediment sizes on the channel bottom.