The Montgomery County Council in the US state of Maryland has unanimously approved US$3.8M to fund repairs on the 41-year-old Lake Needwood dam in Derwood.
The repairs are needed as a result of storm damage from heavy rains that pounded the area during the last week of June. The rains resulted in a rapid rise of the water level in Lake Needwood. The reservoir peaked nearly 7.6m above its normal level, and on 27 June uncontrolled leakage occurred on the left downstream slope and abutment of the dam. Since such seepage can compromise an earthen dam, the county evacuated about 2200 residents downstream, mostly in Aspen Hill, in the early-morning hours. The leaks stopped and the lake itself receded three days later.
A report on the dam says that remedial action should include installation of a grout curtain in the fractured rock beneath and around the sides of the dam. The report also recommends constructing a surface filter drain on the downstream toe of the dam to collect and mitigate any additional seepage.
The Maryland Department of the Environment, which has jurisdiction over dams in Maryland, requires the implementation of remedial measures for the dam no later than 31 March. Other ongoing work related to the project includes the update and improvement of the Emergency Action Plan for both Lake Needwood and nearby Lake Frank and the installation of automated monitoring instrumentation at both lakes.