News letter Dam edition

Ingeokring Newsletter
Dams in the Western USA
Erik Schoute, Royal Boskalis Westminster nv
Introduction
While working in the United States, I spent some time vacationing
in the Southwest of the USA in the summer of 2003
and in the Northwest of the USA/Southwest of Canada in
the fall of 2004. During these two road trips, on which occasions
we clocked 6 000 and 10 000 kilometres on the car’s
odometer, we came across some very interesting hydropower
projects. As I was travelling with a friend who graduated
at TU Delft as a Civil Engineer, we certainly could not
just drive by without getting a closer look into some of these
projects. In this article, some of my own impressions about
the dams will be presented together with background information
collected while on the road and from the internet.
area in a period from 1946 to 1948. The site met several criteria:
the area forming the basin could contain an immense
amount of water, the canyon walls and bedrock foundation
were strong and stable enough to safely support the high
dam and a large source of good rock and sand was available
at nearby Wahweap Creek.
2003 Road Trip: Glen Canyon Dam and Hoover Dam
During the trip in the summer of 2003 which started and
ended in Las Vegas, the route went clockwise through Nevada,
Utah, Colorado, New Mexico, Arizona, California and
back into Nevada. The magnificent scenery, good roads and
road side services make the Southwest of the USA a particularly
great region to travel around. In this area of the USA, a
vast amount of National Parks can be found (to name just a
few that were visited: Zion, Bryce Canyon, Capitol Reef, Glen
Canyon, Canyon de Chelly, Grand Canyon, Lake Mead and
Death Valley). Two of these National Parks are also home or
close to some of the most spectacular hydropower projects
in the world: Glen Canyon Dam and Hoover Dam.
Glen Canyon Dam
Glen Canyon Dam is part of the Glen Canyon National Recreation
Area, which covers over 5 000 km 2 in Arizona and
Utah. The dam is situated in the Colorado River near Page,
Arizona.
Glen Canyon Dam is a concrete thick gravity arch dam
(’thick’ meaning with a base thickness to structural height
ratio of 0.3 or greater) with a height of 216 m and a crest
length of 475 m. Width of the dam is 7.5 m at the crest and
91 m at the base. See Figure 1 for an impression of Glen
Canyon Dam and Bridge.
Fig. 1 Looking south, with Lake Powell at the bottom of the photo, then
Glen Canyon Dam and Glen Canyon Bridge (source: en.wikipedia.org/
wiki/Glen_Canyon_Dam).
Glen Canyon was carved by differential erosion from the
Colorado River over an estimated 5 million years. The Colorado
Plateau, through which the canyon cuts, arose some 11
million years ago. Within that plateau, there are layers of
rock from over 300 million years old to the relatively recent
volcanic activity. Navajo Sandstone, the result of compressed
sand dunes, forms the canyon walls at the dam site
and throughout most of Lake Powell. The sandstone is remarkably
uniform and homogeneous over wide areas and
nearly identical samples can be obtained from areas separated
by many kilometres. Navajo Sandstone is buff to reddish,
fine to medium grained, and soft to moderately hard. It
is massive with pronounced cross-bedding and commonly
indistinct horizontal bedding. The sandstone is moderately
porous and highly absorptive, owing to the high capillarity
created by the small size of intergrain pore spaces.
The remote location in a part of the Colorado River valley
called Marble Canyon was selected by a group of Bureau of
Reclamation engineers and geologists, who explored the
Dam edition | Double Issue 2007/2008 | 53