CONTROLS ON LATE QUATERNARY TERRACE AND FLOODPLAIN DEVELOPMENT IN THE KANAWHA RIVER VALLEY, WEST VIRGINIA

Late Quaternary events on the Kanawha River reflect local base-level control by the Ohio River as well as complex response mechanisms acting within the Kanawha River basin. An influx of glacial outwash caused aggradation in the Ohio River Valley about 22 ka B.P., which raised the base level of the Kanawha River and resulted in a back-filling of the valley. Glaciers retreated from the Ohio River basin by 13 ka B.P., reducing sediment supply and triggering incision on the Ohio and Kanawha Rivers. The incision left a well-defined late Wisconsin terrace in the Kanawha River Valley. The tread of this terrace lies at about 600 feet in elevation at the mouth of the Kanawha River and has a much lower gradient than the modern floodplain. The low gradient of this terrace indicates that the volume of sediment provided by the New/Kanawha fluvial system was not sufficient to maintain a constant gradient during the rise in base-level at the river’s mouth.

An early Holocene terrace can also be identified in the Kanawha River Valley which probably formed because of a complex response initiated by late Wisconsin incision and early Holocene knickpoint migration. The sediment released by upstream incision caused renewed aggradation in the lower reaches of the Kanawha River and formed a terrace with an elevation of about 580 feet in elevation at the river’s mouth. Well-dated stratigraphic sequences at St. Albans and Dunbar show unconformities between Late Wisconsin and Holocene deposits.

Levee development was also an important component in the formation of the early Holocene terrace, and sedimentation rates of >4 m/ka have been documented on the levees. Early Archaic sites on levees indicate that the lower Kanawha River has been relatively stable and its meanders have not migrated significantly during the last 8,000 years.