NPCA-2021-008 - Virgil Dams Erosion Control Engineering Design Project

This Request for Proposal (the “RFP”) is an invitation by Niagara Peninsula Conservation Authority to qualified engineering firms to submit proposals to provide engineering services to design erosion protection on the downstream face of the Upper and Lower Virgil Dams’ earth embankments as further described in ‘Appendix D – RFP Particulars’

The Virgil Dams and Reservoirs were constructed in 1968. Owned and operated by the Niagara Peninsula Conservation Authority, these structures are located on Four Mile Creek in the Town of Niagara-on-the-Lake. The facility is comprised of the Upper Virgil Dam (located upstream of Line 3), and the Lower Virgil Dam (located upstream of Line 2). Please refer to the attached Virgil Dams Site Plan. The drainage area upstream of the reservoirs is approximately 22.6 square kilometers (8.7 square miles).

The primary purpose of the reservoirs is to provide water for irrigation. The Virgil Dams Conservation Area is also used by the public for passive recreational purposes such as hiking, fishing, and bird watching. The waters of the Reservoirs are warm and turbid, only supporting fish species that can tolerate these conditions such as carp, catfish, and perch. The Non-Provincially Significant Virgil Conservation Area Wetland Complex is found throughout the property in addition to woodlands along the shores.

Both dams are similar in design and construction. The structures consist of 125m long (approx.) earth embankments with a 17m long concrete spillway section. Timber flashboards increase the storage level in the reservoirs. Both reservoirs are only 3 to 4 feet deep (due to sediment build-up over the years) with the depth increased by an additional 3 feet with the timber flashboards installed.

A Dam Safety Audit was undertaken for this facility in 2020 by Hatch which concluded that both dams are in good condition. However, it was determined that neither the Upper nor Lower Virgil Dams were capable of safely passing the calculated Inflow Design Flood (of 136 cubic meters per second) without the earth embankments being overtopped.

As such, the NPCA is inviting qualified engineering firms to submit proposals to provide engineering services to design erosion protection on the downstream face of the Upper and Lower Virgil Dams’ earth embankments in order to prevent failure during the Inflow Design Flood.