HEADER HERE CONTRIBUTIONS PROFESSIONAL were dislodged by flood flows. Seepage was observed between stone blocks at several locations of both sidewalls. Capping stones on the overflow sections (crest/apron) were missing or misaligned. Seepage also occurred from a round arch conduit outlet (flow of 10 gallons/minute). The right exit stream bank/overflow section was extensively eroded up to 250 feet downstream (Pictures 2a, 2b and 3).
Phase I Inspection by the US Army Corps of Engineers (USACE) The Phase I inspection was performed pursuant to authority granted by The National Dam Inspection Act, Public Law 92367, to the Secretary of the Army, through USACE, to conduct inspections of dams throughout the United States. The purpose was to evaluate if the dam constitutes a hazard to human life or property. Site visits were conducted in March 1979 (pre-Tropical Storm David) and September 1979 (post-Tropical Storm David).
Figure 3a. Cross-section of Lake Roland Dam
Damage by Tropical Storms
The USACE Assessment Included the Following Observations
Tropical storms Agnes (June 1972), and David (September 1979) caused flooding and eroding of the earth and rubble fill on the downstream side of the abutments and non-overflow sections of the dam. During Agnes, flood runoff overtopped the non-overflow section by 3 feet (9 feet over the overflow spillway). Hurricane Connie (1955) caused an estimated discharge through the overflow section of 5,500 cubic feet/second (cfs), which was the maximum discharge capacity. This severely eroded backfill from the downstream non-overflow section slopes, exposing the stone block walls. Some capping stones
Dam classified as an “intermediate size,” “high hazard” with a recommended spillway design flood of 100% Probable Maximum Flood (PMF). Non-overtopping flood discharge capacity was only 10% PMF. Predicted failure of dam at discharge of 35% of PMF! At one-half and full PMF, the dam will be overtopped by 7 feet and 12 feet with flow durations of 9 and 10.5 hours, respectively. PMF inflow design flood is 61,500 cfs. Substantial property damage and loss of life will occur in the Jones Falls floodplain – Bare Hills, Mount Washington, Hampden, Woodberry, and Baltimore City. Inoperable reservoir drain slide
Picture 2a. Damage to left over-flow section of lake 26
AEG NEWS 64(2)
Spring 2021
