New watershed classification based on distance to the drainage divide



[1] Models of watershed behavior are beginning to incorporate lidar (light detection and ranging) topography measurements with resolutions of the order of 1 square meter, but this increase in the availability of high-quality data is outpacing the ability to make the best use of them. At issue is the conceptual lens through which the data are analyzed, particularly when investigating hydrologic behavior at different scales. Scaling parameters are used to break down the masses of data into groupings that fit within certain constraints that can then be analyzed for trends, and watershed research has traditionally used either stream order—a measure based around how many tributaries a body of water has—or the upstream catchment area to make these divisions. To best make use of the available high-resolution topography data,Gangodagamage et al. propose a new scaling parameter based on what the authors refer to as the “directed distance from the divide.” The technique involves calculating, for each point in a watershed, the longest distance from that point to a drainage divide, taking into account variations in topography and recognizing that water only flows downhill. When two of these paths converge, the shorter is treated as a tributary to the longer, with this process being repeated until the entire watershed culminates in one major river. From these calculations the watershed can be broken down and analyzed using ensemble statistics based on flow paths of different lengths. (Water Resources Research, doi:10.1029/2010WR009252, 2011)