Emergency Detection, Evaluation, and Response at Little Creek Dam

Little Creek Dam is owned and operated by Newport News Waterworks.  It is a 1,900-foot-long, High Hazard structure located in James City County, Virginia constructed in 1980.  The dam consists of an earthfill embankment with three benches along the downstream face, a concrete swale along the right abutment, a riprap swale along the left abutment, internal filter drain system with outlet features, a stormwater drain system, and a riser structure with a 72-inch concrete outlet pipe.

The dam was initially raised to the design pool in 1982, after which time seepage and erosion concerns were detected.  Since that time, observed concerns have included seepage and wet areas along the right groin, erosion along the left groin, and multiple seepage points along the toe. These issues have led to small modifications and repairs to the dam. Dam assessments performed in 2017 and 2019 included seepage, slope stability, and internal erosion evaluations. Geotechnical exploration, instrument installations, and laboratory testing were completed as part of the assessments which resulted in rehabilitation recommendations.

On February 7, 2020, prior to implementation of the 2019 recommendations, Waterworks staff reported a sand boil at the toe of Little Creek Dam near the same location where clear seepage was observed and documented during an annual inspection in April 2019.  Over the following two months, two additional sand boils developed in the tidal wetlands just beyond the toe of the dam.  Waterworks, with consultation from Stantec, referenced the Emergency Action Plan (EAP) and classified the events as a Stage 1 Emergency.  This emergency stage triggered daily monitoring and a controlled drawdown of the reservoir approximately 10 feet lower than normal pool. Monitoring observations following drawdown and frequent communication between Waterworks and Stantec eventually led to a decrease in monitoring frequency which is still ongoing.

This presentation will be co-presented by staff from Newport News Waterworks and Stantec and will discuss how the dam safety issue was detected and evaluated using the EAP, the monitoring approach, and internal and external communications. Further analyses and recommendations which resulted from this ongoing event will also be outlined. This will also serve as “Part 2” of a presentation from the 2020 VLWA conference which discussed the recommended improvements identified in the 2017 and 2019 assessments.