Reports
Sediment Accumulation and Characterization of the Bloede Dam Impoundment
2012, Ortt, R.A., Jr., and Sylvia, E.R.
File Reports, Coastal and Estuarine Geology, File Report 2012-01
Abstract
In response to a request by American Rivers, Maryland Geological Survey (MGS) was contracted to study the sub-surface geological conditions and sediment properties within the Bloede Dam impoundment located in Howard and Baltimore Counties in the State of Maryland. Sub-surface data was collected within the impoundment using ground penetrating radar and acoustic seismic equipment. Records were analyzed to determine the underlying geology. Cores were collected at eleven locations to quantify the physical and chemical properties of the sediment, and to test for the presence of specified pollutants. The fieldwork for this study occurred between November 2011 and February 2012.
Sub-surface data collection on the floodplain adjacent to the Bloede impoundment was collected, but the results were inconclusive. Ground-penetrating radar was used for the collection, and the environmental conditions degraded the ability of the equipment to penetrate deeply into the soils.
Sub-bottom seismic data was collected within the river, and the underlying geology of the river was defined along sixteen transects. These transects show a historic river channel at 25 meters depth just upstream of the dam. Further upstream, the historic river channel broadens into a basin ranging from 10 to 30 meters in depth across the valley. This historic basin is north of the current river thalweg in the vicinity of the dam, and it is west of the current river thalweg near the pedestrian swinging bridge.
The sediments deposited behind Bloede Dam within the river are very homogenous, and consist of sand and gravel with less than 2 percent of mud. The soils on the floodplain adjacent to the Bloede impoundment vary both spatially and with depth; however, they generally are muddy sands ranging to sandy muds at depth.
Based on the elements and pollutants analyzed in this report, the sediments located within the Bloede Dam impoundment and the adjacent floodplain do not have any pollutant levels above the expected levels of the regional geology.
