Introduction to the Physical Geography of Medium-Sized Rivers, Focusing on the Southeastern and South-Central United States

Abstract

This set of eight papers, four in this special issue of Physical Geography and four in the forthcoming issue (Vol. 32, No. 6), resulted from a special session on the geomorphology and physical geography of medium-sized watersheds at the meeting of the Southeastern Division of the Association of American Geographers (SEDAAG) held in November 2010 in Birmingham, Alabama. Medium-sized rivers are generally large enough to contain multiple zones, in which different geomorphic processes may be dominant. In their headwaters, known as Zone 1, low-order streams dominate and have a unique signature in terms of water quantity, water quality, hillslope sediment, and nutrients provided from local contributing areas (Schumm, 2005). As tributaries converge into higher-order rivers, the Zone 2 or transfer zone takes on greater relative importance. Geomorphic investigations in this zone require integration of multiple inputs from the larger drainage area and consideration of lag times, from initial landscape disturbance to changes in sediment delivery and channel and floodplain morphology. Generally, sediment input can equal output if a stream is stable in the transfer zone, but it is usually disrupted when anthropogenic disturbances are prevalent, a theme that is explored in a number of the papers in this issue.In medium-sized watersheds, one substantial problem encountered in efforts to relate landscape condition to channel and floodplain change is that a wide variety of disturbances can be occurring, as was the case in many of the rivers discussed in this issue. In some cases, the dominance of a particular activity or the timing of geomorphic and sedimentary responses may suggest the drivers of change to the system. The downstream transmission of fluvial disturbances in Zone 2 can eventually result in a diversity of sedimentation patterns and rates in Zone 3, the lowermost depositional zone in the areas of lowest gradient.Although the initial common theme was scale of watershed, an unplanned common theme of human impacts was central to most of the papers and has become a recurring theme in geomorphology (James and Marcus, 2007). Human disturbances were associated with early and recent land cover and land use changes. The three papers that focus on mining in the southeastern and south-central United States are important additions to the literature, in that mining is more often associated with the western states. Lessons learned from the changes in morphology and sedimentation associated with these disturbances provide insights into the needs and strategies Downloaded by [Umeå University Library] at 21:12 18 November 2014 394 MOSSA AND HEITMULLER for watershed and river restoration, and for best management practices in disturbed watersheds.Because of the scale of the watersheds, a variety of methodologies were employed. Some that are widely used included application of hydraulic and water-budget models, flood frequency analysis, cross-sectional surveys, and analysis of historical stage, discharge, and land use records. Some of t...