June 03, 2020
On Site at Pump Road Dam In Honor Of National Dam Safety Awareness Day
By: Bonnie Dunkel
April and May brought plenty of rain to central Virginia, and with National Dam Safety Awareness Day having just occurred on May 31st, we wanted to spotlight a unique dam project that was recently completed in Henrico County, Virginia.
Pump Road Dam is an existing earthen Dam located along Deep Run Creek within Henrico County. I met up with Mike Claud, PE, CFM, who managed the project, to tour the site and learn more about the project.
The approximately 12-acre lake is located in the Short Pump neighborhood in the western area of the County and is used as a recreational facility for the surrounding residential properties.
In 2018, a rainfall event triggered severe flooding and caused the dam to overtop. This overtopping caused damage to the downstream section of the dam. To prevent future damage from rainfall events, renovations to the Pump Road Dam were prioritized.
Timmons Group worked with County staff to bring the dam into compliance with the Virginia Impounding Structure Regulation requirements. Our services included tasks to perform a detailed hydrologic analysis for the contributing watershed along with a hydraulic analysis of the existing outlet structure capacity and its ability to convey the required spillway design storm flow in accordance with Dam Safety regulations. Timmons Group developed a detailed dam failure analysis utilizing HEC-RAS to determine the downstream inundation area. The dam was determined to be a High Hazard structure based the amount of traffic that utilizes the road daily.
An alternatives analysis was performed to determine various renovation options for the dam that would meet the regulation requirements. Based on information from the alternatives analysis, it was determined that overtopping protection would be constructed to protect the impoundment from failure during passage of the required spillway design storm event.
The initial design considered the use of Articulated Concrete Blocks (ACB’c) for the overtopping protection. However, due to an existing sanitary sewer line that passed through the dam and issues with having to close the road for crane access to place the ACB’s, another option was proposed. Timmons Group, in conjunction with Watershed GEO, presented a new product called HydroTurf to the County. HydroTurf is an engineered revetment solution specifically designed to provide armoring of hydraulic structures against high velocity and shear stress. It offers the aesthetics of vegetation combined with better performance than traditional hard armor. It is also significantly less costly than other traditional methods. Construction of the system is rapid, low impact, and provides an impermeable geomembrane protected by engineered turf which is infilled with HydroBinder, resulting in a fiber reinforced high-strength concrete matrix.
The use of HydroTurf for overtopping protection had not been previously approved by DCR Dam Safety. Timmons Group coordinated with Watershed GEO to provide information to DCR Dam Safety to obtain their approval. Timmons Group prepared detailed design plans for installation of HydroTurf on the downstream dam slope and provided field inspection and administrative services during construction. Pump Road Dam was the first HydroTurf installation completed in the State of Virginia. This revolutionary technology looks like natural vegetation, but provides overtopping protection that is easier to install and maintain than traditional methods. Construction of the renovation work began in May 2019 and was completed in September 2019.