The Federal Energy Regulatory Commission on Sept. 23 approved an April 2009 application from Northern Illinois Hydropower LLC for an original license to construct and operate the Dresden Island Hydroelectric Project, to be located at the U.S. Army Corps of Engineers’ Dresden Island Lock and Dam on the Illinois River near the Town of Morris in Grundy County, Illinois.
The project’s authorized capacity being licensed is 10.96 MW.
In September 2014, Northern Illinois had amended its application to:
- alter the location of the proposed powerhouse at Dresden Island Dam from headgate sections 1 through 6 to sections 10 through 18;
- increase the number of proposed turbine/generator units from three to four;
- reduce the installed capacity of the proposed project from 11.7 MW to 10.96 MW;
- reduce the minimum hydraulic capacity of the proposed project from 750 to 455 cubic feet per second (cfs) and reduce the maximum hydraulic capacity from 10,560 to 9,100 cfs;
- replace its proposal for a 0.86-mile-long, 13.2-kV transmission line with a 0.60-mile-long, 34.5-kV transmission line; and
- include a proposal to cease project operation when the Corps’ flow releases through its Tainter gates fall below 1,000 cfs.
The project will be located on the Illinois River at river mile 271.5, approximately 1.5 miles downstream from its confluence with the Kankakee River. The Illinois River flows for 273 miles in a southerly and southwesterly direction to its confluence with the Mississippi River near Grafton, Illinois.
The primary role of the Dresden Island Lock and Dam is to maintain a water surface elevation within the Dresden Island Reservoir for commercial navigation. At the time of construction, hydropower was considered at the dam but was not installed. However, both dam and spillway structures (e.g., headgates) were constructed to allow for future hydropower development. Dresden Island Dam impounds the 14.5-mile-long, 1,985-acre Dresden Island Reservoir.
The project will use nine of the currently inoperable headgates at the Dresden Island Dam. A 310-foot-long by 134-foot-wide headrace channel will be excavated immediately upstream of the dam to convey water from the Dresden Island Reservoir into the headgate structure. The concrete plugs located in headgates 10 through 18 will be removed and the existing headgate openings will be fitted with coarse debris racks spaced at six inches on center. The existing headgate slots will be modified to accept new bulkhead gates to allow for the dewatering of the entire forebay.
A 152-foot-wide by 39-foot-long forebay, tapering to 125 feet wide at the downstream end, will be constructed immediately downstream of headgates 10 through 18 to direct water into four powerhouse intakes. Trashracks with 2-inch clear bar spacing will be installed upstream of the four new 27.2-foot-wide headgates. The 122-foot-wide by 134-foot-long powerhouse will contain four identical 3,880-horsepower Kaplan turbines each coupled to a new 2.74-MW generator for a combined installed capacity of 10.96 MW.
A 125-foot-wide by 100-foot-long tailrace channel will be excavated immediately downstream of the powerhouse to return flows from the powerhouse to the Illinois River.
A 0.6-mile-long, 34.5-kV transmission line will transmit power from a new 20-foot-wide by 20-foot-long switchyard to be located 50 feet northeast of the powerhouse to an interconnection point at an existing substation owned by Commonwealth Edison. The transmission line will run via conduit or existing cable trays across the dam to the downstream end of the lock, at which point, the transmission line will be supported by new poles.
The project, as licensed, will generate an average of 58,500 megawatt-hours (MWh) annually.