Piano Key Weir for Enlargement of the West Fork of Eno River Reservoir

The West Fork of Eno River Reservoir Dam is located near Hillsborough, North Carolina, USA. The earthen embankment dam provides an impoundment used by the town for water supply. The project was originally completed in 2000 with forethought by the owner for an expansion, which was anticipated in the original design. Currently, the design of that expansion to raise the reservoir level for increased water supply is underway. Following a detailed analysis of viable upgrades, a piano key (PK) weir (anticipated as the first to be constructed in the USA) was selected by the owner due to its effectiveness in meeting project requirements. Presented in this paper are the site-specific characteristics of the existing auxiliary chute spillway, the proposed PK weir, and additional modifications to the chute. This paper also presents site-specific information including the existing auxiliary chute spillway, the new PK weir, and additional modifications to the auxiliary chute. The results include the comparison of four PK weir hydraulic design methods for sizing the spillway. Details and results of a CFD model are also included. Finally, additional significant design considerations are presented, which include anticipated hydraulic conditions in the downstream chute and identified existing structure deficiencies; estimated spillway design flood hydraulic force distributions taken from the CFD model; the PK key weir stability summary; and other important project aspects including embankment modifications and seepage control measures. It is anticipated that this project will be of interest to those concerned with dam safety and will further encourage the consideration of PK weirs in the USA.