Red Rock Project, IA – Complete Application Received

November 11, 2021: The Low Impact Hydropower Institute has received a complete application for Low Impact Certification of the Red Rock Project. LIHI is seeking public comment on this application. Specifically, we are interested in knowing whether you think the Project meets the LIHI Low Impact Certification Criteria, as revised in the 2nd Edition Handbook. Please review the program and criteria in LIHI’s revised Handbook and then review the Project’s application materials below.

Comments that are directly tied to specific LIHI criteria (flows, water quality, fish passage, etc.) will be most helpful, but all comments will be considered. Comments may be submitted to the Institute by e-mail at with “Red Rock Project Comments” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, 1167 Massachusetts Avenue, Arlington, MA 02476. Comments must be received on or before 5 pm Eastern time on January 10, 2022 to be considered. All comments will be posted to the web site and the applicant will have an opportunity to respond. Any response will also be posted.

The Red Rock Hydroelectric Project (RRHP) is located at the Red Rock Dam on the Des Moines River, approximately 3.8 miles southwest of the Pella, IA in Marion County Iowa, approximately 45 miles southeast of Des Moines, Iowa, and approximately 143 miles above the confluence of the Des Moines River with the Mississippi River.

The U.S. Army Corps of Engineers (USACE) constructed Red Rock Dam between 1960 and 1969 to impound Lake Red Rock for flood control, recreational, and fish and wildlife purposes. The dam, reservoir, and adjacent land are federally owned and operated by the Rock Island District of the USACE. The RRHP has been constructed immediately adjacent to the left (northeast) side of the dam’s existing concrete spillway.

Red Rock Dam is a composite earthfill and concrete gravity dam with an overall length of 6,260 ft, an embankment base width of about 655 ft, and a height of 110 ft. The dam’s center section is comprised of a concrete ogee spillway with five Tainter gates and fourteen bottom outlet conduits. Marion County Highway T15 (Highway T15) traverses the length of the dam along the crest.

The dam consists of two earthfill segments with a combined length of 5,676 ft, which are linked by a concrete gravity section that contains the dam’s outlet works and spillway. On each side of the spillway is a non-overflow concrete gravity section that extends into the adjoining embankment. Large concrete gravity sections are located on each side of the spillway structure. The concrete gravity section on the northeast side, where the hydro project is located, consists of three non-overflow monoliths and one spillway transition monolith.

The concrete ogee spillway is 241 feet long and fitted with five Tainter crest gates. Fourteen bottom outlet conduits are located within the spillway structure. Each outlet discharges below minimum tailwater to a hydraulic jump-type stilling basin measuring 241 feet wide and 213.5 feet long. Baffle blocks in the stilling basin are in two rows (staggered), each 12 feet high, 16 feet long, 8 feet wide, and spaced 10 feet apart in each row.

RRHP consists of a concrete intake structure, two penstocks, a concrete powerhouse, 69 kV substation, transmission line, and utilities. The concrete intake structure used to bring water into the project, is founded on concrete pilings and consists of trash racks, emergency closure gates, stoplogs for maintenance purposes, and associated equipment. The emergency closure gates are designed to fail closed under all conditions, including loss of power to the intake structure.

Project Name Red Rock
LIHI Certificate No. N/A
LIHI Certificate Term N/A
Owner Western Minnesota Municipal Power Agency
State Iowa
Location River Mile 142.2 on the Des Moines River
Installed Capacity 55 MW
Average Annual Generation 178,800 MWh
Facility Type Run-of-release as directed by the US Army Corps of Engineers

FERC No. P-12576, issued April 18, 2011, expires on March 31, 2061

Two penstocks route water from the intake structure through the dam to the powerhouse. Each penstock is entirely buried underground and penetrates two of the concrete monoliths of the original dam. Each penstock incudes a vent shaft located near the intake structure, otherwise access to the penstocks can only be achieved through the powerhouse.

The concrete powerhouse is founded on bedrock and contains two vertical Kaplan turbine generators and associated equipment. The multi-level building includes all equipment necessary to transfer energy from flowing water to electrical energy. Plant and Unit Control systems are located in the powerhouse and control all aspects of water flow through the project and power generation.

Operation of RRHP is coordinated with the USACE to ensure compliance with the Federal Energy Regulatory Commission (FERC) issued license and related project plans. The USACE controls the timing and quantity of water released through Red Rock Dam and coordinates those releases with project staff located in Sioux Falls, SD. Water can be released through the project, and/or through existing dam infrastructure controlled by the USACE.