River Floodplains of Southeastern Minnesota
Series Description
Floodplain forest study sites were investigated along the major river systems of southeastern Minnesota. These include the Root, Cannon, Zumbro, Whitewater and Vermillion rivers, all tributaries to the Mississippi River. These rivers all originate on the cultivated glacial plains of southern Minnesota, wind slowly east, drop abruptly into wooded gullies and ravines, and ultimately meander through the deep gorges of Minnesota's unglaciated "driftless area".
Forest floodplain wetlands are occasionally inundated by flood waters, typically during the early spring thaw and wet season. River oxbows and shallow depressions along the floodplain retain water for extended periods, and provide habitat and breeding grounds for a wide array of organisms. Silver maple (Acer saccharinum), box elder (Acer negundo), hackberry (Celtis occidentalis),and black walnut (Juglans nigra) are common forest canopy trees, with a dense understory of herbaceous annuals, perennials, and ephemerals. Floodplain soils are alluvial soils, formed over long periods of time by river processes. These soils have been greatly affected by historic and current land uses, including the highly erosive agricultural practices of this region at the turn of the century.
Land use in southeastern Minnesota is predominantly agricultural. On the glacial plain where these rivers begin, row crops such as corn and soy beans are typical. The steep slopes of the driftless area are presently managed as hardwood forest, as part of the management practices adopted by Richard J. Dorer Memorial Hardwood Forest. Land use in the floodplains includes row crop agriculture (corn, soy beans), silviculture, grazed woodland and pasture, residential and commercial land uses. Public lands, such as wildlife management areas and state forest lands, are increasingly common. Urban land uses include impoundments and storm water conveyance systems commonly associated with human settlement and development.
Sites chosen for this study met the following criteria:
How sites were selected to form a land-use gradient:
Twenty eight sites were evaluated for inclusion in this series. Sites were identified from information provided by the Minnesota Department of Natural Resources (Ecological Services and local Wildlife management staff) and by staff of Soil and Water Conservation Districts. Sites were chosen to meet the above criteria and to represent a gradient from minimally impacted floodplains, with little channel and vegetation modifications, to highly impacted floodplains impacted by filling, floodwater engineering, and forest removal. Reasons for excluding sites from the study included: low stream order (and so no floodplain development), influence from the Mississippi River (sites close to their mouths), and close proximity to another selected site. Of those included, the Black Walnut (BW), Melnik (ME), and Hokah (HO) sites have highly modified channels. The Melnik site is along the historic channel of the Root River. A straightened diversion channel now carries most of the river flow. The Hokah and Black Walnut sites have been stabilized for crop production (sod and trees, respectively). These two sites also have ditched and graded floodplains. The floodplains of Cannon Highway (CH), Hastings (HA), and Rochester (RO) have been graded and filled. Hastings and Rochester sites are within a urban greenway and Cannon Highway has been developed for a bridge improvement. The Whitewater River sites (WS, WN) have been affected by flood diversion engineering, which routes high flow water away from the historic channel. Sites along the Zumbro River (ZK, ZB, ZT) are relatively unimpacted as are two along the Root River (RP and RM).
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