Six of a Kind – Principal Spillway Conduit Sliplining of the Beautiful Run Watershed Dams

The flood control dams of the Beautiful Run Watershed were constructed during the 1960’s by the National Resources Conservation Service (NRCS) in Madison County, Virginia.  The dams are sponsored by the Culpeper Soil and Water Conservation District (SWCD).  Six of the eight total Beautiful Run dams were originally constructed with bituminous coated corrugated metal pipe (BCCMP) principal spillway conduits.  Apparently, these are the only NRCS dams constructed in the Commonwealth of Virginia with BCCMP principal spillway conduits.

In 2018, closed-circuit television (CCTV) inspections of the interiors of the principal spillway conduits and riser structures were performed for the eight Beautiful Run dams, as well as three other dams in neighboring Culpeper County.  The results of these inspections led SWCD to prioritize the repair of the dams with BCCMP principal spillway conduits based on the condition and age of the pipes.  The SWCD realized both budgetary and schedule efficiencies by electing to package the design and construction associated with the six dams into contracts to a single engineer and contractor, respectively.

The design of conduit sliplining included evaluating impacts to the hydraulic capacity of the conduits as well as identifying the appropriate carrier pipes capable of supporting/withstanding external soil and hydrostatic loads along with loads imposed during the grouting of the annular space.  Full time quality assurance observation was provided to ensure proper installation.  As such, the project design team was able to provide assistance to the sponsor and contractor to address challenges encountered during the installation process.

Lessons learned during the process of sliplining the conduits for these dams, as well as insightful considerations for the approach, design, and implementation of similar projects, will be useful to dam owners, design engineers, and contractors.  Given the condition of aging infrastructure throughout the nation, as well as improvements in construction materials and methods over the past half-century, the repairs to the principal spillway conduits for the Beautiful Run dams provide a timely example of adding extended value to structures of continuing importance.