Steady and transient sand bedform evolution at Clear Run, North Carolina, September 2009

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Raleigh L. Martin
Description:

The evolution of sand bedforms through time was observed through time-lapse overhead camera imagery at Clear Run, a small, sand-bedded stream in Wilmington, North Carolina, USA. These observations were made as part of a larger study of "hyporheic" (i.e., surface-subsurface) solute and fine particle exchange through the injection and tracking of tracer solutes and particles in the stream channel. In particular, two scenarios were considered for observing hyporheic exchange and associated bedform evolution: (1) steady background "base" flow conditions, and (2) time-varying "flood wave" conditions associated with the opening of an artificial dam upstream of the observation section on the stream. The overall study is described in Harvey et al. (2012, Journal of Geophysical Research 117, G00N11, doi:10.1029/2012JG002043). This dataset contains processed images for the steady and transient bedform evolution observed at Clear Run on September 18, 2009. The images provided here were captured with a Nikon D5000 camera looking downward from approximately 2.5m above the stream bed. Time-lapse images were captured every 30 seconds. The images were rotated to align with the stream channel geometry and cropped to remove the stream banks and other non-bedform components of the image. Steady-flow images were further processed to normalize for variation in lighting. Specific details for each set of images are provided here: (1) Steady base flow observations (individual .jpg images contained in folder "ClearRunSteady_CroppedRotatedNorm") Images numbered 12 to 588 (577 total images, numbers increasing through time) were captured at 30-second intervals during steady base flow conditions on 18 September 2009, starting at 11:00:32 AM local time (Eastern Daylight Time). In all images, flow is from left to right. The vertical (spanwise) extent of the images is 2664 pixels (175.0 cm), and the horizontal (streamwise) extent is 1520 pixels (99.9 cm), based on a conversion factor of 0.0657 cm/pixel. (2) Transient flood wave observations (individual .jpg images contained in folder "ClearRunFlood_CroppedRotated") Images numbered 1 to 300 (300 total images, numbers increasing through time) were captured at 30-second intervals during the artificially-induced dam-release flood wave on 18 September 2009, starting at 4:08:32 PM local time (Eastern Daylight Time). In all images, flow is from left to right. The vertical (spanwise) extent of the images is 2904 pixels (201.8 cm), and the horizontal (streamwise) extent is 1612 pixels (112.0 cm), based on a conversion factor of 0.0695 cm/pixel. An additional metadata file ("ClearRun_metadata.xlsx") provides timing information for each of the photos in the steady and transient flow collections.

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