Heavy rains in Prince William County and across the region have closed numerous roads and in some cases caused substantial damage to the roadway infrastructure. Currently Prince William County is under a flood warning until 5:15 p.m. With the vast amount of rainfall, the county has received overnight and into the early morning, the waters levels at Lake Jackson Dam have risen above their normal levels. During the morning, water levels rose above the normal levels triggering a Stage 3 Dam Emergency requiring the evacuation of two residences near the Lake Jackson Dam by fire and rescue units.
There are 3 stages/levels and various phases of activity that determine the procedure for responding to an emergency at Lake Jackson Dam:
Stage 1: Flood Watch
Phase A – Rain is falling.
Action: The Public Safety Communications Center (PSCC) and the Department of Public Works (DPW) monitors weather forecasts and observes rainfall.
Phase B – Heavy rain is occurring (1inch or more in a 24-hour period). The taintor gate is not open. (Taintor Gate is a type of radial arm floodgate used in dams and canal locks to control water flow.)
Action: Monitoring equipment at the dam notifies PSCC when DPW operator is to be informed when water level is greater than 1.5 feet. In addition, after heavy rains, PSCC (nonworking hours) or the DPW (working hours) monitors the dam level at least every 2 hours and places DPW operator on call when the water level reaches 1.5 feet and rising. The DPW is responsible for monitoring the water level during the storm event and will open the gate if water level is 1.5 feet and rising. Opening the gate automatically declares a Stage 2 condition.
Stage 2: Flood Warnings
Phase A – Water is over 2 feet above spillway and rising or the taintor gate is being operated.
Action: DPW operator will monitor the water level every 2 hours. He/she operates the gate to maintain the water level between 0.5 feet and 3 feet, if possible.
Phase B – Water has reached 4.5 feet and is continuing to rise, and rain has fallen anytime in the past 24 hours.
Action: The dam operator must notify the PSCC. The Department of Fire and Rescue prepares for possible evacuation of residents in low-lying areas.
Stage 3: Dam Emergency
Phase A – The water level is 6.5 feet and rising, or there are visual indications of potential dam failure.
Action: DPW will notify PSCC of dam emergency and will update changes in the situation. The Department of Fire and Rescue will notify the Emergency Operations Center (EOC) Coordinator; all affected upstream and downstream residents must be evacuated.
In case of potential dam failure during a period of low flow, the river downstream and the lake should be kept clear of fishermen and boaters. No residents need to be evacuated.
Phase B – Dam Breach Occurs
Action: PSCC will secure the area, check the Route 234 bridge for obvious displacement, and check the area within sight of the Route 234 bridge for rescue needs. The Department of Public Works will notify the Department of Conservation and Recreation’s Division of Soil and Water Conservation Dam Safety Section and the Virginia Department of Transportation.
Currently, the water levels at the dam are receding; the situation is under constant monitoring.