Reports

Bathymetry and sediment accumulation of Little Seneca Lake

2011, Ortt, R.A., Jr., Wells, D.V., and Van Ryswick, S.

File Reports, Coastal and Estuarine Geology, File Report 2011-03

Executive Summary

In response to a request by the Washington Suburban Sanitary Commission, Maryland Geological Survey (MGS) was contracted to study the bathymetry and sedimentation of Little Seneca Lake located in Montgomery county in the State of Maryland. Bathymetric data were collected for the reservoir, current storage capacity and a drawdown curve were determined, and the volume of sediment accumulation for the reservoir was calculated. The collection, analysis, and presentation of this report were made to be consistent with the most recent bathymetric and sedimentation reports from Triadelphia and Rocky Gorge Reservoirs (Ortt et al, 2007), Loch Raven and Prettyboy Reservoirs (Ortt et al, 2000), and Liberty Reservoir (Ortt and Wells, 2003) located within the State of Maryland.

Bathymetric data for the reservoir was collected in July and August of 2010. This data was collected using differential global positioning service (DGPS) techniques and digital echosounding equipment. Over two hundred thousand discrete soundings were collected and used to generate a current bathymetric model of Little Seneca Lake. Several methods of analysis were used to generate the models. The bathymetric models indicate a current storage capacity of 3.92 billion gallons [14.846 million cubic meters] with a surface area of 473 acres [1.91 million square meters].

Analysis was performed on the pre-dam construction topography and the bathymetric survey of 1996. The current capacity of the reservoir is more than the calculated capacity from the 1996 survey. A greater density of data in the 2010 survey is the most likely reason for this difference. The total storage volume loss calculated from the pre-construction topography to the current bathymetry is 337 acre-feet [0.416 million cubic meters]. The average annual loss rate is 12.5 acre-feet per year [0.015 million cubic meters] or 0.1% of the original volume.

Downloads and Data

File Report 2011-03 (pdf, 2.6 MB)
File Report 2011-03, plate 1 (pdf, 8.6 MB)
File Report 2011-03, plate 2 (pdf, 5.9 MB)
Reservoir Bathymetry Data