How to Drain an Impoundment – Design, Repair and Replacement

The Virginia Impounding Structure Regulations (Regulations) require that low-level outlet systems in existing dams be kept operational. For dams built without low-level outlet systems, the Regulations stipulate that low-level outlet systems be retrofitted when practicable. In December 2020, the Department of Conservation and Recreation (DCR) and Virginia Soil and Water Conservation Board published a new “Guidance Document on the Design and Use of Devices to Lower the Reservoir Water Level” to describe the standard operating procedures and expectations of DCR in their administration of the Regulations regarding low level outlets.  This guidance document emphasizes that high and significant hazard potential classified dams are the current focus of the operational and retrofit requirements of the Regulations while also noting that the owner and its professional engineer have latitude in low-level outlet system design and use.

This presentation will review low-level outlet configurations, drawdown calculations, and best practices to rehabilitate, replace, or retrofit outlet works for dams. This presentation will also cover the DCR Guidance Document definition of “when practicable” as well as long-term operational considerations for dam owners.