Performance evaluation of three DEM‐based fluvial terrace mapping methods

The availability of high‐resolution digital elevation models (DEMs) derived from airborne light detection and ranging (LiDAR) surveys has spurred the development of several methods to identify and map fluvial terraces. The post‐glacial landscape of the Sheepscot River watershed, Maine, where land‐use change has produced fill terraces upstream of historic dam sites, was selected to implement a comparison between terrace mapping methodologies. At four study sites within the watershed, terraces were manually mapped on LiDAR‐DEM‐derived hillshade images to facilitate the comparison among fully and semi‐automated DEM‐based procedures, including: (1) spatial relationships between interpreted terraces and surrounding natural topography, (2) feature classification algorithms, and (3) the TerEx terrace mapping toolbox. Each method was evaluated based on its accuracy and ease of implementation. The four study sites have varying longitudinal slope (0.0008–0.006 m/m), channel width (< 5–30 m), surrounding landscape relief (20–80 m), type and density of surrounding land use, and mapped surficial geologic units. All methods generally overestimate terrace areas (average predicted area 210% of manually defined area) with the most accurate results achieved within confined river valleys surrounded by the steep hillslopes. Accuracy generally decreases for study sites surrounded by low‐relief landscapes (predicted areas ranged 4–953% of manual delineations). We conclude with the advantages and drawbacks of each method tested and make recommendations for the scenarios where the use of each method is most appropriate. Copyright © 2016 John Wiley & Sons, Ltd.     

Hillslopes,rivers, plows,and trucks: mass transport on Earth's surface by natural and technological processes

The surface of the earth is being transformed by a new force in the form of technological systems and processes that move significant quantities of mass large distances. Because movement of mass is perhaps the most basic geomorphic process, and because the continuing rise of technology appears to characterize a new epoch in earth evolution (the Anthropocene), it is of interest to compare technological and natural mass transport mechanisms. A purely dynamical ‘mass‐action’ metric, representing the product of mass displaced, distance moved, and mean speed of displacement, is used to compare the transport effectiveness of selected systems. Systems with large mass‐action tend to be advective, and systems with small mass‐action diffusive. Local environments are conditioned by mass‐action through the introduction of transport corridors, such as roads and rivers, which put constraints on mass transport by embedded diffusive systems. Advection also subjects local environments to externally determined time scales, such as the times for delivery of unit mass of water or sediment to a river mouth, and supports the emergence of associated dynamical processes there, for example those of human activity or delta construction, that are too rapid to be sustained by diffusion. Most of the world's mass‐action is generated by the motion of fluids of global or continental extent, as in atmospheric circulation or river flow. Technological mass‐action exceeds that of all land‐based geomorphic systems except rivers. Technological systems with large mass‐action tend to be comprised of discrete, self‐powered units (e.g. trucks). Discretization of transported mass reflects the different locomotion strategy required for transport of solids on land, compared with the transport requirements of spatially extensive fluids in nature. The principle of maximum entropy production may provide a framework for understanding the emergence of advective, technological mass‐transport systems. Copyright © 2010 John Wiley & Sons, Ltd.