H41E-1366
Multiscale controls on water surface roughness and implications for remote sensing of rivers
Thursday, 17 December 2015
Poster Hall (Moscone South)
Brandon T Overstreet1, Carl J Legleiter2, Lee Harrison3, Lincoln H Pitcher4, Jonathan Ryan5, Asa K Rennermalm6 and Laurence C Smith4, (1)University of Wyoming, Laramie, WY, United States, (2)University of Wyoming, Department of Geography, Laramie, WY, United States, (3)NOAA Santa Barbara, Santa Barbara, CA, United States, (4)University of California Los Angeles, Los Angeles, CA, United States, (5)Aberystwyth University, Aberystwyth, SY23, United Kingdom, (6)Rutgers University New Brunswick, New Brunswick, NJ, United States
Abstract:
Remote sensing has emerged as a viable and efficient tool for studying river systems and facilitating their rehabilitation. While many remote sensing applications utilize spectral information from the substrate and water column, light reflected from the water surface is often a significant component of the total at-sensor radiance. As water surface roughness (WSR) increases, a greater proportion of surface facets become oriented so as to reflect, rather than transmit, light. As a result, WSR exerts a primary control on the amount of surface reflected light measured by a remote sensor. WSR in rivers is a function of flow hydraulics, channel form, slope, bed roughness, and wind. While the relative influence of each of these components on WSR changes with scale, understanding these relationships could lead to methods for obtaining hydraulic information from image-derived metrics of WSR (i.e., surface reflectance). We collected field data on flow depth and velocity using an acoustic Doppler current profiler and simultaneously measured WSR using a custom built ultrasonic distance sensor on a diverse set of rivers ranging from a 15 m wide supraglacial river on the Greenland Ice Sheet to 100 m wide gravel-bed rivers in Wyoming and Oregon. Simultaneous multi- and hyperspectral image data sets indicate that image-derived surface reflectance is strongly correlated with WSR. Temporally distributed point measurements of flow depth, velocity, and WSR on the supraglacial river capture a threefold range in discharge (6 m3/s to 17 m3/s) and indicate that flow velocity is a primary control on WSR in smaller channels, even in the absence of sediment-induced bed roughness. Spatially distributed field measurements from large gravel-bed rivers suggests that spatial variability of WSR in the thalweg corresponds with geomorphic facies while WSR along the channel margins is more significantly influenced by grain size, relative submergence, and bank geometry. These findings suggest that controls of water surface roughness are scale dependent. Image-derived metrics of WSR provide information on channel hydraulics that could be used to define geomorphic units (i.e. pool/riffles), refine flow model inputs, and delineate aquatic habitats.
