POWER September 2021 - 22

TOP PLANT
Red Rock Hydroelectric Project:
Successfully Generating New
Power from a Pre-Existing Dam
Courtesy: Missouri River Energy Services
There are challenges to adding power generating capability to a dam built for
flood control, but the Red Rock Hydroelectric Project shows that the obstacles
are not insurmountable. With the right team, success is achievable.
Aaron Larson
C
onventional hydropower produced
about 7.25% of the total electricity
generation in the U.S in 2020. Yet,
only about 3% of the roughly 80,000 dams
installed in the U.S. generate electricity.
Many of the non-powered dams were constructed
for purposes such as recreation,
stock/farm ponds, flood control, water supply,
and irrigation. Many are small, and, in
most cases, it would be impractical to add
power generation to them. However, there
are exceptions. The Oak Ridge National
Laboratory conducted a study and found
that adding electricity generating capability
to the 100 largest non-powered dams
could provide 8 GW of new hydropower-
essentially, the " low-hanging fruit. "
The Red Rock Hydroelectric Project
The Red Rock Hydroelectric Project
(RRHP) on the Des Moines River, about
2.5 miles southwest of Pella, Iowa, is
one example of just such a project. The
Red Rock Dam was constructed by the
U.S. Army Corps of Engineers (USACE)
in 1969 for flood control, which remains
the dam's primary purpose today.
Missouri River Energy Services (MRES)-
a 61-member organization of municipalities
spread across Iowa, Minnesota, and North
and South Dakota-made the decision to
add power generation to the existing Red
Rock Dam based on its desire to supply
clean, reliable, cost-effective, long-term
renewable electricity to its members. The
successful project is a 2021 POWER Top
Plant award winner in the Renewable Energy
category. It now operates on a " Run
of Release " basis as directed by the USACE,
so as not to affect the flood control
22
operations for the Des Moines River.
After acquiring the Federal Energy
Regulatory Commission license from the
original project developer, MRES awarded
a design contract to Stantec in 2011. Stantec
(formerly MWH) was the Engineer of
Record for the plant (from the intake structure
to the tailrace). Other companies that
played major roles in the development and
construction of the RRHP include DGR
Engineering (Engineer of Record for the
substation,
transmission,
and
utilities),
Voith Hydro (equipment manufacturer for
the turbines [Figure 1], generators, and
balance-of-plant systems), Ames Construction
(general contractor for project
construction), and Rockwell Automation
(Allen-Bradley programmable controllers
for the plant control system). The project
was developed using a hybrid " design-bidbuild "
approach in which the engineers
completed much of the design, including
temporary structures, while leaving the detailed
design of mechanical and electrical
systems to the contractor.
A Challenging Project
" Constructing a project immediately adjacent
to an operating spillway presented
significant challenges, " Tom Andrews,
vice president of Power and Dams with
Stantec, told POWER. " Construction of
the permanent works required upstream
and downstream cofferdams, and several
excavations up to 70 feet deep into
the existing dam and its foundation,
plus penetrations through the existing
concrete gravity monolith. The intrusive
nature of the work required that steps
be taken during construciton to reduce
potential impacts to the dam's integrity
www.powermag.com
1. The Red Rock project has two verticalshaft,
single-runner, Kaplan-type hydro turbines
with adjustable runner blades and wicket
gates. Each unit has a rated turbine output of
21.6 MW while operating at the rated speed
and design net head of 62.1 ft. Courtesy: Missouri
River Energy Services
and to maintain dam safety. "
As the project engineer, Stantec prepared
designs for all the temporary works,
and construction sequence drawings
were developed to prescribe the staged
construction of the project. The sequence
defined by those drawings became part
of the design criteria for the final design of
the temporary and permanent structures,
as they outlined the loading conditions
during each phase of construction.
Excavation support systems were designed
to minimize deformations and the
potential for construction-induced cracking
of the embankment, and a concrete
diaphragm wall along the axis of the dam
was designed as a seepage cutoff. Additionally,
a rigorous surveillance inspection
and
instrumentation
monitoring
program
was implemented to evaluate
the performance of the dam, as well as
the temporary and permanent works,
during and after construction.
" Prior to the start of construction,
POWER| September 2021
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POWER September 2021

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