The Western Lowlands of Arkansas Potential Natural Vegetation

The Western Lowlands correspond to that portion of the White River basin that lies within the Mississippi Alluvial Valley.  It is bounded on the west and north by the Ozark escarpment, on the west and south by the Grand Prairie, and on the east by Crowley’s Ridge. Part of this area is located in southeast Missouri; however, this map covers only the Arkansas portion of the Western Lowlands, which includes more than 4.5 million acres.

Various streams enter the basin from the western uplands in Arkansas, including the Black, Current, Spring, White, and Little Red Rivers.  The Cache River and Bayou De View originate within the lowlands on the eastern side of the basin.   All of these streams drain to the White River, which discharges to the Arkansas River. 

All of the major streams in the basin are flanked by relatively narrow floodplains with recent (Holocene) landforms that are typical of meandering river systems, including poorly-drained backswamps, better-drained point bars, and well-drained natural levees.  Abandoned channel segments form crescent-shaped oxbow lakes and depressions.  However, most of the Western Lowlands region is made up of much older features that are higher in the landscape.  These are a series of terraces made up of glacial outwash that flushed into the Mississippi Valley during periods of waning Late Wisconsin continental glaciation.  Sometimes called “valley train” terraces, they are composed of relatively unsorted, coarse materials deposited in a braided-stream environment, and are very different from the later fine-grained, well-sorted deposits of the modern meandering streams. They form several distinct terrace surfaces in the Western Lowlands, with the oldest and highest being 30 feet or more above the modern floodplain.  On the lower and younger terraces, the remnant outwash channels are often distinctly visible, and may carry smaller modern streams within them.  Some of the valley train surfaces are covered with extensive dunefields made up of wind-blown sands deflated from younger outwash channels and deposited on adjacent older surfaces. 

This complex landscape of old and young deposits of various origins historically was subject to frequent flooding in the low-lying areas, and the higher terraces were prone to long-term ponding of precipitation in many places.  Flooding has been reduced in the past century by federal projects that included levee construction, channel straightening and deepening, and upstream reservoir construction.  Local interests have effectively drained many of the areas that were subject to ponding during wet periods.  However, the lower White River remains subject to backwater inundation from the Mississippi River during major floods.