September/October 2021 - 16

COVER
STORY
2021 OPA Winner: Hydroelectric Dam Conversion
With Diaphragm Walls, Retention Systems
Completed upstream diaphragm wall, intake structure (left) near existing structures
Converting Red Rock Dam in Iowa to produce hydroelectric
power required extensive water- and earth-retention
systems to maintain the integrity of the existing flood control
dam. Construction challenges included excavations up to 70 ft
(21 m) deep on the upstream and downstream sides of the
existing dam and modifications to convey water from the
reservoir to a new powerhouse, which ultimately amounted
to " putting holes in a perfectly good dam. " The extensive
retention systems for the Red Rock Hydroelectric Project that
received DFI's Outstanding Project Award (OPA) for 2021
included an unusually high cantilevered diaphragm wall to
retain a permanent cut through the embankment dam.
Project Elements
The U.S. Army Corps of Engineers (USACE) constructed Red
Rock Dam on the Des Moines River near Pella, Iowa, in the
1960s - creating Lake Red Rock, the largest reservoir in Iowa.
The USACE dam is an earthfill structure with a chimney filter
and blanket drain. It features a central concrete control
structure consisting of 13 adjoining monolithic segments that
house 14 sluice gates and 5 radial tainter gates. The dam has an
overall length of 6,260 ft (1,908 m) and a height of 110 ft (34 m).
A county highway traverses the length of the dam along the
crest. Western Minnesota Municipal Power Agency and
Missouri River Energy Services developed the hydroelectric
project to diversify their electric generation portfolio. The main
project elements are:
* A cantilevered concrete diaphragm wall that retains the
integrity of the embankment dam along the side of a new
intake channel for water entering the hydroelectric plant.
The 69 ft (21 m) high diaphragm wall is one of the tallest of
its type in the world.
* A second concrete diaphragm wall, which serves as a
cutoff wall along the axis of the embankment dam.
* The new intake structure, which has emergency-closure
gates and is founded on drilled shafts.
* Two 21 ft (6.4 m) diameter steel-lined penstocks (pressure
conduits) that convey water through the dam to a
powerhouse.
* Two vertical Kaplan turbine-generator units, located in
the powerhouse.
* A substation on the upstream side of the powerhouse
connecting to a buried transmission line.
The intake, penstocks and powerhouse were constructed next
to the existing dam's spillway, where the embankment fill
wraps around the end of the concrete gravity section.
16 * DEEP FOUNDATIONS * SEPT/OCT 2021
AUTHORS Thomas G. Andrews, P.E., and Rachael V. Bisnett, P.E., Stantec Power & Dams

September/October 2021

Table of Contents for the Digital Edition of September/October 2021

Table of Contents
September/October 2021 - Intro
September/October 2021 - 1
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September/October 2021 - Table of Contents
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