Evaluating Change in the Prevalence of River Anabranching Before and After Agricultural Development in the Upper Midwest, United States

Recent research has indicated that numerous lowland rivers in North America and Europe had multithread, anabranching channel patterns prior to widespread human modification of landscapes and that contemporary human activities have transformed many anabranching rivers into single-channel meandering rivers. Although lowland rivers in the upper midwestern United States are predominantly meandering, anabranching occurs locally. Whether anabranching of these river systems was uncommon in the past or intensive agriculture has resulted in near eradication of anabranching channel patterns remains uncertain. This article quantifies the prevalence of river anabranching within several watersheds in the upper midwestern United States prior to widespread European settlement in the early to mid-1800s based on General Land Office survey plat maps and field notes. It also compares this prevalence to the contemporary occurrence of river anabranching. Results show that anabranching reaches were somewhat more common historically (22 percent more reaches in the past compared to the present), but were still relatively rare, constituting only about 1 percent of the total length of streams in the study watersheds. Analysis of the geographic distribution of anabranching reaches reveals that historical spatial patterns generally are different than modern patterns. Thus, only a handful of historical anabranching reaches have persisted through time to the present. The findings place contemporary river anabranching in the upper midwestern United States within the context of past conditions and suggest that human modification of landscapes throughout this region has not substantially modified channel patterns of rivers.