• Under the Influence of Large Woody Debris: A Survey of the La Crosse River In the Upper Midwest Driftless Area

      Prise, Adam (2012-10-19)
      Streams are dynamic environments driven by the force of gravity and shaped by local climate, geology, and vegetation. Large woody debris (LWD) can have important influences on stream processes. The main influence of LWD on these systems is a resistance to flow; this added roughness induces a multitude of channel adjustments. Despite the importance of LWD, streams have been heavily managed by humankind, often involving the removal of debris to improve flow. Recent studies have highlighted the significance of large woody debris in mountain streams, particularly in the Pacific Northwest of the United States and Canada. However, there has been little research on the influence of LWD on streams in the Upper Midwest. This study will specifically investigate a stream (the La Crosse River) in southwestern Wisconsin’s Driftless Area. This area remained untouched by glaciers during the Last Glacial Maximum, but outwash from melting glaciers was deposited here, making the main bed material coarse sand. Combining stream survey methods (channel cross-sections) and a wood census, the influence of LWD was determined through statistical analysis of measurements of stream (velocity, depth, and width) and LWD (total counts, length, DBH, and volume) characteristics, in conjunction with qualitative analysis of detailed cross-sections. LWD are present in the study reach, but few relationships proved statistically significant, while local influences (initiation of scour and deposition) are clearly seen. Explanations of human, regional, historical, and bed form influences are explored.