Analyzing high resolution topography for advancing the understanding of mass and energy transfer through landscapes: A review

International audienceThe study of mass and energy transfer across landscapes has recently evolved to comprehensive considerations acknowledging the role of biota and humans as geomorphic agents, as well as the importance of small-scale landscape features. A contributing and supporting factor to this evolution is the emergence over the last two decades of technologies able to acquire high resolution topography (HRT) (meter and sub-meter resolution) data. Landscape features can now be captured at an appropriately fine spatial resolution at which surface processes operate; this has revolutionized the way we study Earth-surface processes. The wealth of information contained in HRT also presents considerable challenges. For example, selection of the most appropriate type of HRT data for a given application is not trivial. No definitive approach exists for identifying and filtering erroneous or unwanted data, yet inappropriate filtering can create artifacts or eliminate/distort critical features. Estimates of errors and uncertainty are often poorly defined and typically fail to represent the spatial heterogeneity of the dataset, which may introduce bias or error for many analyses. For ease of use, gridded products are typically preferred rather than the more information-rich point cloud representations. Thus many users take advantage of only a fraction of the available data, which has furthermore been subjected to a series of operations often not known or investigated by the user. Lastly, standard HRT analysis work-flows are yet to be established for many popular HRT operations, which has contributed to the limited use of point cloud data.In this review, we identify key research questions relevant to the Earth-surface processes community within the theme of mass and energy transfer across landscapes and offer guidance on how to identify the most appropriate topographic data type for the analysis of interest. We describe the operations commonly performed from raw data to raster products and we identify key considerations and suggest appropriate work-flows for each, pointing to useful resources and available tools. Future research directions should stimulate further development of tools that take advantage of the wealth of information contained in the HRT data and address the present and upcoming research needs such as the ability to filter out unwanted data, compute spatially variable estimates of uncertainty and perform multi-scale analyses. While we focus primarily on HRT applications for mass and energy transfer, we envision this review to be relevant beyond the Earth-surface processes community for a much broader range of applications involving the analysis of HRT

Describing Post-wildfire Geomorphic Response Using the River Styles Framework

Wildfires have profound, highly variable impacts on erosion, sediment transport, and stream channel morphology. Climate change and fuel management actions have altered the current fire regime relative to the historic fire regime. The Twitchell Canyon fire burned 45,000 acres in Fishlake National Forest, near the town of Beaver, UT in July 2010. Over 30% of the area burned at high severity and monsoonal thunderstorms in the summer of 2011 resulted in massive debris flows and sheetflow erosion that have potentially altered the main stream channels in the burned area. We present the results of a reach-scale geomorphic analysis for pre- and post-fire conditions, based on the River Styles classification framework. Pre-fire classifications indicate that most channels are variable sinuosity with continuous floodplain. Post-fire classifications indicate a massive influx of sediment with a shift in River Styles classifications to accommodate that sediment. We have also calculated the probability and volume of post-fire debris flows that may be acting either as sources of sediment or barriers to sediment flux. Both models consider slope, percent of basin burned at high severity, average intensity of a defined thunderstorm, and generalized soil properties (% clay content and organic matter). Evidence of debris flow activity was observed in the two main creeks that we present (Shingle and Fish Creeks) and the model predicted high probability of debris flows for all of the sub-basins in each watershed. We have not verified models results for volume estimations but we use those volumes as relative measures of the size of barrier that a debris flow may have created in the main channels of Fish and Shingle Creeks, where a barrier refers to a barrier to sediment and movement or streamflow. We use the barriers to explain the observed changes to the River Styles classifications