Tuesday, October 2, 2007

Sediment Fills the Port Tobacco River

The most common reasons given for the decline of Port Tobacco include:
1. Sediment filled the river, pushing the port southward
2. The burning of the courthouse which facilitated removal of the county seat to La Plata

Today we will look at the first reason, using data from the following reference:
Defries, Ruth (1986) Effects of Land-Use History on Sedimentation in the Potomac Estuary, Maryland: A Water Quality Study of the Tidal Potomac River and Estuary. United States Geological Society. This paper is available on-line from the USGS.

Port Tobacco is in the middle of the Potomac Estuary. An estuary is a river valley that has been drowned by rising sea levels. Estuaries are not geologically permanent and are prone to filling in with sediment. The rate of sedimentation was studied by Defries using pollen cores taken from various points in the Port Tobacco River.

The sedimentation rate of the river near the town of Port Tobacco was estimated at greater than 1.14 centimeters per year between 1840 and 1978. The 1.14 centimeters over 138 years adds up to 157.32 centimeters of soil development! That is 5.16 feet of soil. Such rapid sedimentation is often linked to the clearing of land for agriculture and other development that loosens the soil, removes plant roots, and increases runoff.

Defries believes the rate of sedimentation near Port Tobacco was highest between the years of 1840 and 1860. Archaeological and archival studies of Port Tobacco should tell us why this might be. Was Port Tobacco expanding in the mid-1800s? Or did some catastrophic event, such as a hurricane, hit the town?


P.S. For more information on the Port Tobacco River, visit the Port Tobacco River Conservancy, Inc.

No comments: