Southeastern Geographer

abstract:

Ozarks watersheds have responded to land clearing and settlement disturbances by transporting large amounts of gravel and sediment to main valleys of medium-large river systems. Historical gravel and sediment accumulate in disturbance zones, which are areas of excessive channel activity that can be detected over time using historical aerial photographs. This project uses a series of aerial photos from 1937–2018 to identify disturbance zones in the Big River of southeast Missouri, which has a history of lead mining and ore processing that has caused widespread contamination of the channel and floodplain deposits. Variations in active areas of the historical meander belt show that disturbance zones account for 24 percent of the channel length at an interval of one per 2.5 km of channel. Megabars and extensions are the most prominent types of disturbance zones, but translations and cutoffs are larger with higher potential for sediment storage. From 1937 to 1976, areas of channel activity have cycled between expansion and contraction. However, after a period of recovery prior to 1976, disturbance zone areas have been expanding over the last 40 years likely in response to an increase in flood magnitude and frequency from more high intensity rainfall events since 1973.