Shallowford Lake Dam No. 1 and Dam No. 2 Repairs – Lewisville

Shallowford Lake Homeowners Association in Lewisville, North Carolina maintains two dams located in the common area in their subdivision. This project included upgrading the spillway capacity of both dams to meet reduced High Hazard requirements and replacing the failed principal spillways with a new system. The lakes were located in the subdivision with developed properties adjacent to the dams.  One dam had a clubhouse and pool on the dam and the other had a State Road located on the downstream slope. The site restrictions did not allow construction of adjacent emergency spillways, and the design had to limit impacts to the existing structures in the dams.

An analysis of the downstream area was prepared to show that the sunny day dam failure would not damage downstream structures and that the downstream structures would be flooded if the dam was removed.  This allowed a reduction in the spillway requirements.  A large diameter riser and barrel was constructed in each dam to pass the design storm event.  The sites were graded to provide additional flood storage in the lake pool to help meet the spillway capacity requirements.  Design of the project included surveying, HEC1 Modeling to confirm spillway capacity and downstream impacts, HEC2 modeling to determine flood elevations downstream, site grading, spillway improvements, Land Quality permits for dam repairs and erosion control, NCDOT encroachments for dam/roadway construction, and Corp of Engineer permits for dam repair activities.  The project included repairs to Dam No. 1 and Dam No. 2 as follows:

Dam No. 1:    The removal of an existing CMP riser and barrel, replacing the structure with a 96-inch diameter concrete riser and 54-inch DIP barrel, replacing the excavated fill material with clean compacted soil, and additional seepage control structures and repairs to the upstream and downstream slope of the dam.

Dam No. 2:    The removal of an existing concrete spillway and CMP riser, barrel, and bottom drain, replacing the structure with a 90-inch diameter concrete riser and 48-inch DIP barrel, construction of a new connection manhole to route flow under the state road, replacing the excavated fill material with clean compacted soil, construction of a berm along the top of the dam and repairs to the upstream slope of the dam and the installation of a new catch basin and 36-inch RCP culvert beneath Wyntfield Drive.

AWCK provided the Design, Permitting, Bidding, Construction Inspection, and Contract Administration.

Project Manager: G. Wesley Webb, P.E.
Completion: 1997
Construction Cost: $335,000