Halcrow was commissioned by Traylor Bros to undertake a tender design for the Elm Rd Generating Station (ERGS) Cooling Water Intake Tunnel. The tunnel was part of a $2bn project to construct a new ERGS power station at Oak Creek, Wisconsin.

The aim of the design/build contract was to construct a system capable of delivering 820,000gpm to the existing Oak Creek Power Plant (OCPP), to replace the existing shoreline intake, and 740,000gpm to the new ERGS forebay.

key factors:

	preliminary design of system hydraulics
	8,500ft long, 25ft ID TBM driven rock tunnel
	370ft long, 26.5ft diameter drill and blast launch chamber
	30ft and 24ft ID shafts through soft ground and rock
	4No. steel lined offshore riser shafts
	lake bed intake consisting of wedge wire screens and manifold pipe
	RC dike wall structure with hydraulic gates
	booster pumping station for 840,000gpm

The system consisted of an intake structure located 8,000ft out in Lake Michigan in 40ft of water, an offshore tunnel connecting to the existing OCPP forebay via a drop shaft located in the Oak Creek inlet channel; a 1,300ft long onshore tunnel, with a further drop shaft linking with the ERGS forebay. In addition, the contract required construction of a watertight "dike wall' to seal off the Oak Creek channel and a pumping station to enable the flow level into the existing OCPP intake to be controlled.

Halcrow's initial task was the preliminary design of the hydraulics, in order to size tunnels and shafts, and estimate head loss to ensure that the required water levels were provided in the ERGS and OCPP forebays. The hydraulic design also allowed for potential infestation with zebra mussels, which would increase head losses.

In addition to the client's base design, Halcrow also designed alternatives to suit the contractor's construction methodology and reduce cost. These included an alternative layout for the lake bed intake structure, an improved layout for the OCCP forebay and booster pumping station, and a redesigned ERGS forebay structure consisting of a 160ft ID slurry walled shaft, instead of a rectangular structure requiring tie-backs for support.