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54 JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
Denver’s Forgotten Flood
The Geomorphologic Impacts
of the 1933 Castlewood Dam Failure
Kaelin M. Groom and Casey D. Allen
IN 1933, AFTER FORTY-THREE years of controversy
and disquiet, the 1890s Castlewood Dam collapsed,
causing one of the worst floods ever reported on Cherry
Creek in Denver, Colorado. However, despite the colos-
sal damages and resultant economic woes, the flood and
its profound impacts have remained widely under-
researched, and, for many, forgotten. Historic reports
outline the implications in the city and several engineer-
ing reports expose the cause but nothing of the dramatic
changes in canyon or the people. How did this event alter
the canyon? Not only the channel shape and scoured
walls but also, and more profoundly, the geomorphology.
In what capacity did the 1933 Castlewood Dam failure
impact the natural progression of erosion, deposition,
and geomorphology in Castlewood Canyon?
Through a compilation of existing data, collection of
new field data, and technical analyses, this study seeks a
greater understanding of the overall geomorphological
implications of the great 1933 flood. There are two major
components: tracking the erosion and deposition of ma-
jor masonry flood debris (i.e., structural clasts or blocks
from the dam itself) and estimating the total sediment
displacement via GPS and Laser Rangefinder-generated
cross sections and geologic comparisons. The objective
rests in producing an idea of just how this event resulted
in rapid, but long-term changes in the landscape.
Castlewood Dam History
Castlewood Dam was built in 1890 by the Denver Water
Storage Company partnered with the Denver Land and
Water Company, a committee of landowners who were
trying to sell large portions of the surrounding farmland.
The purpose was to provide a reliable water source to
entice settlers and increase property value, as the soil is
fertile but there wasn’t enough natural water for irriga-
tion farming.1The dam was a rock fill design composed
of two separate walls, a straight wall on the reservoir side
and an angled stepped wall on the downstream side, with
gravel (i.e., rock fill) and concrete poured in between.2
Without the aid of modern technology, the dam, com-
pleted in only eleven months, was built entirely by hand
and mule with Mr. A. M. Welles as designer and chief
engineer. For such a rapid construction, the dam was
impressive: over 183 meters across, 21 meters tall, and
15 meters deep at its base. Masonry stones were quarried
from nearby cliffs and were primarily Castlerock
Conglomerate. The reservoir had a maximum capacity of
6.4 million cubic meters, however, by the time the dam
failed, reports claim it had silted in by nearly 50 percent.3
From the moment the dam began impounding any sig-
nificant amount of water, it began to leak (Figure 1).
Countless reports were filed by a number of government
and private agencies ensuring the dam’s safety but the
dam’s stability was publicly debated continuously until
the day it failed. Local newspaper headlines ranged from
“Castlewood Is Safe” (Rocky Mountain News–1896) to
“Castlewood Dam Not Over-Strong: Engineer Ryan
Doubts That It Can Withstand a Flood” (The Denver
Republican — 1900) and other such contradictions were
released nearly annually. Eventually, in 1900, A. M.
Welles wrote a letter to The Denver Post newspaper de-
fending his work:
“The Castlewood dam will never, in the life of any
person now living, or in generations to come, break
to an extent that will do any great damage either to
itself or others from the volume of water impound-
ed, and never in all time to the city of Denver.”4
Persistent controversy, along with various financial
complications, spurred ownership of the Castlewood
Dam to change eight times during its lifetime.5Each new
owner would hire inspectors, release new reports, and
continue advertising the surrounding irrigated farmland,
all the while the safety concerns were neglected and the
dam fell into disrepair.5Between 1912 and 1933 spikes
in reservoir levels indicate twelve separate events that
could have flooded the valley had the creek been left
uncontrolled. Over time the weakened dam, led to a myr-
iad of quick fixes and modifications. In May 1897, high
lake waters and foundation settling caused multiple
55
JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
horizontal cracks 5–10 cm deep,
requiring the reservoir to be com-
pletely drained for repairs.6Then, in
1899, massive amounts of earth were
placed against the upstream face of
the dam, in hopes of reinforcing the
structure and sealing the infamous
leak.7Unfortunately, the attempt was
unsuccessful and the dam continued
to seep for the next three decades.
Then, on the night of August 3,
1933, the Castlewood Dam gave cre-
dence to the “sensationalist prattle”
Welles had so vocally detested in his
1900s letter. After several days of
steady rain, a cloudburst over the
Cherry Creek drainage basin pum-
meled parts of the 450 square km
region with 8–23 cm of rain within a
matter of hours and massive amounts
of water flowed into the Castlewood
Reservoir. Later reports estimate the
peak inflow of 100 cubic meters per
second (m3/s) into the reservoir.8In
an interview with Colorado State En-
gineer M. C. Hinderlider, the care-
taker who lived near the dam, Hugh
E. Paine, recounts the unprecedented
inflow: “At 11:15 o’clock the water
was [1.8 m] below the spillway. . . .
By midnight the water had raised to
the top of the dam [and] by 12:15, a
torrent of water was pouring over
and through the dam. . . .” Later in
the same report, Hinderlider extra-
polated the startling discharge over-
topping the dam: “The dam was
overtopped the full length thereof to
a depth of [0.3 m], which caused a
discharge thru the spillway of a
depth of [1.5 m], estimated to have
been [85 m3/s]. At the same time the
discharge of the remainder of the
crest approximated [70 to 85 m3/s]
making the total flow from [155 to
170 m3/s] over the dam.9The de-
crepit dam could not withstand the
pressure and within 45 minutes the
center gave way, sending an estimat-
ed 6.4 million cubic meters of water
crashing downstream.10 According to
a 1933 report filed with the United
States Department of the Interior,
peak discharges were as high as
3,600 m3/s at the dam, though this
Figure 1. Dating 1890–1910, these images show the Castlewood Dam’s infamous
leak with several men for scale. The dam seeped for the entire 43 years it was in use
and was a great concern to those residing downstream. Photos from the Colorado
Historic Society and Castlewood Canyon State Park.
Figure 2. These images show the various impacts of the 1933 Castlewood Dam
failure. Photo A, from the Colorado Historic Society, shows an aerial shot of Denver’s
famous Union Station completely inundated. A little closer to the ground, photo B
from the Denver Historical Society displays the flooded train yard. Photo C, from the
Colorado Historic Society, is the breached dam the day after the flood and photo D is
the dam ruins today by Kaelin M. Groom.
56 JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
figure is contested,11 960 m3/s at the
Kenwood Dam site 37 km down-
stream, and by the time the flood
waters reached Denver, 50 km down-
stream, it was still greater than 450
m3/s, nearly double any subsequent
flood on Cherry Creek at Denver.12
The sustained damages were ex-
tensive totaling $1.7 million in 1933
currency, nearly $30 million today.13
Union Station, situated downtown,
was beneath a meter of water, with
the basement and baggage subways
entirely inundated (figure 2). Several
bridges were destroyed and 15th
Street was inundated with 0.6 m of
water.14 Of the estimated losses,
nearly $960,000 was suffered in the
farmlands upstream of Denver and
additional economic damages came
from the loss of water supply to over
12 square km of the surrounding
area.15
Multiple prior studies have been
conducted at the dam site to deter-
mine to cause for the breach. Some
claim there was a natural spring un-
der the dam that weakened the foun-
dation while others say the entire
structure actually dislodged and
shifted downstream 0.6 m before it
failed.16 The official cause, as re-
ported by Colorado State Engineer
H. C. Hinderlider, attributed the
cause to “foundation percolation
coupled with intense overtopping.”17
Despite being the largest recorded
flood on the Cherry Creek and one of
the most expensive in Denver his-
tory, little research, past or present,
has addressed its lasting repercus-
sions or geomorphologic impacts on
the canyon itself. This study is the
first to address such questions.
Physical Geography
of Castlewood Canyon
Basic geologic structure. There
are three primary geologic forma-
tions exposed in Castlewood Can-
yon. The oldest is the tuff-colored
Dawson Arkose Sandstone (55 mya)
often separated into the Upper and
Lower Dawsons. This friable layer is
mostly exposed downstream of the
Castlewood Dam.18 Above the Daw-
son there is the Wall Mountain Tuff,
37 mya. This rhyolite stratum varies
in color from blues to pinks to grey-
ish purples and can be found
throughout the canyon, particularly
as large clasts in the next geologic
formation and caprock: the Castle-
rock Conglomerate (34 mya), lithi-
fied components of alluvial fans
from the ancestral Rocky Moun-
tains.19
Climate. As mid-latitude steppe
(BSk Köppen classification), central
Colorado enjoys a dry moderate
climate. Throughout the year hu-
midity remains relatively low with
average annual precipitation of 43
cm and average annual snowfall of
148 cm. Temperatures range from an
average of 30?C in July to -8?C in
January.20
Slope. The stream gradient varies
greatly throughout the canyon with
an overall average is 0.0067 m/m.
The area once covered by the old
Castlewood Reservoir has a lower
slope of 0.0037 m/m where the deep-
er canyon at and below The Falls is a
greater 0.0134 m/m as derived from
high-resolution 1.5 m interval hyp-
sometric maps.
Vegetation. Within the northern
most extent of the Palmer Divide,
Castlewood Canyon is a hub of vari-
ous biomes: Ponderosa pine savanna
and Douglas fir woodland through-
out the canyon, mixed foothill shrub-
lands on the drier slopes, mixed and
short grass prairies in the old reser-
voir, and wetlands along the creek.
The most common species found
within the study area are ponderosa
pine, chokecherry and Gambel’s
oak.21
Paleoflood Investigations
The absence of pre-1933 channel
geometry data limited the validity of
before and after comparison so con-
ventional paleoflood techniques
were utilized. Though paleoflood
hydrology and research usually
focuses on prehistoric floods, its
methods are also applicable toward
historic floods,22 as is the case with
Castlewood Canyon. Spatial analysis
of large debris deposition, and cross
sections of flood terraces and gravel
bars were conducted to gain greater
understanding of the 1933 flood’s
behavior and erosive power. In the
following sections both components
will be expounded followed by
analysis and discussions.
Site Selection
For the purpose of maintaining a rel-
ative consistency in variables (chan-
nel width, canyon dynamics, ex-
posed geology, etc.), the scope of
this study concentrated on the chan-
nel length (or reach) from at the
Castlewood Dam ruins to the open-
ing of the canyon, approximately 2.7
km downstream (figure 3). Once the
flood reached the plains its behavior
would have changed and previous
methodology would no longer apply
and any paleoflood evidence found
upstream of the reservoir site would
only pertain to natural floods and
mute to the study of the dam failure.
The area known as The Falls, rough-
ly 0.8 km downstream of the dam,
marks a significant change in the
canyon. At this point there is evi-
dence of turbulence and the down-
stream canyon becomes a deep ra-
vine with little to no vegetation,
large exposures of the Dawson Ar-
kose Formation, and very distinct
flood terraces with a number of large
gravel bars. This becomes an impor-
tant location for both debris distribu-
tion at and around The Falls and
along the cross sectional portions of
the terraces directly downstream.
Field Techniques
As this is exploratory research, no
remotely-sensed data were available,
so a number of field techniques were
applied. The positions of debris and
cross sections were recorded with a
Trimble™Juno SB®GPS unit with
+/- 3 m accuracy and cross section
57
JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
Figure 3. Map of the study area showing Castlewood Canyon State Park’s location within the state of Colorado and the sites
relevant to this research. Kaelin M. Groom 2012.
58 JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
geometry was measured with a Laser
Technology Inc.™True Pulse 360R®
laser rangefinder in conjunction with
the GPS unit with +/- 1 ft accuracy.
Once mapped, these data reveal an
intriguing relationship.
Dam-cut blocks. Large and high-
event floods, principally on higher
gradient streams (0.003 m/m (0.17
degrees) or more), often transport
large amounts of sediment and
other debris causing the majority of
damages sustained. In the case of
Castlewood Canyon, the masonry
blocks, or dressed stone, from the
breached dam acted as powerful
scouring tools as they were sent
crashing through the canyon.
Studying certain elements of these
blocks by calculating how many
were removed from the dam struc-
ture and analyzing spatial patterns of
deposition can provide a greater
understanding of the
flood’s behavior and its
geomorphologic impacts.
In the history of this can-
yon, this is the first study
to address the debris of the
flood, specifically the mas-
onry blocks.
To study the boulders
outside of the dam struc-
ture they must first be
identified. Because they
were extracted from local
cliffs, geology alone is not
enough, nor size and
shape. Although the
majority of hand-cut
blocks are roughly 60 cm
x50 cm x120 cm they were
not symmetri-cal and lin-
ear bedding planes caused
many of
the boulders in the area
to decay angularly. This
creates some confusion
as many preexisting boul-
ders have the correct size
and shape but have no
other signs of identifica-
tion and could possibly be
naturally formed. For
these reasons, all blocks
Figure 4: The identification of the masonry blocks through drill/blast marks and his-
toric mortar. Many of the boulders near the ruined dam have both but further down-
stream the constant battery of the floodwaters detached the mortar and the drill
marks become the more consistent indicator. Photo by Kaelin M. Groom.
Figure 5: Map of the cross sections recorded directly downstream of the Falls shown with rela-
tive location to the Falls Boulder Field. Kaelin M. Groom 2012.
59
JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
were identified in this study by iso-
lating anthropogenic stone-dressing;
specifically drill marks and historic
mortar.
One method was locating blocks
with drill scars, indicating that they
were quarried. These drillholes are 4
cm wide half cylindrical marks cut
from the edges of the stone into the
center. They can be anywhere from 8
cm to 60 cm long and can be found
on all sides of the block. These were
verified by finding marks on clasts
still part of the ruined dam as well as
others downstream. However, due to
the magnitude and debris contained
in the flood, this method of identifi-
cation becomes increasingly difficult
farther downstream, as many sus-
pected drill marks are battered and
eroded beyond conclusive identifica-
tion. Several boulders found over 3
km downstream have the right size,
shape, and geology, but the edges
have been so rounded any evidence
of quarrying is negligible.
Another form of identification
was the presence of historic mortar
still attached to the boulders. Very
distinct from the local geology, thin
slabs of mortar are easily recog-
nized. Unfortunately, much like the
drill marks, this characteristic is only
valid for a certain distance down-
stream before the erosive power of
the flood debris detached the cement
from the blocks. Many clasts close to
the dam have both drill marks and
attached mortar, verifying the me-
thod of identification, but down-
stream the drill marks are more reli-
able (figure 4).
Sediment displacement. Lack of
high-resolution pre-flood channel
geometry downstream from the
Castlewood Dam necessitated GPS-
generated cross sections. This is
speculative, however conventional,
and is only meant to derive esti-
mated but valuable sums. The cross
section element is primarily focused
on the canyon directly below The
Falls where flood terraces are most
clearly seen. Volumes of sediment
displaced per cross section were esti-
mated and then averages were
applied to the entire downstream
canyon reach.
Distinct flood terraces, 1933 pale-
oflood debris deposits, and well-
defined previously buried soil pro-
files made the lower canyon a unique
study reach for obtaining cross sec-
tions. Three specific terraces can be
identified: (i) the speculated original
stream elevation, (ii) material dis-
placed during the 1933 flood, and
(iii) all subsequent erosion. Historic
photographs and topographic maps
support this assumption. Four cross
sections were recorded roughly 15
meters apart to define the 60-meter
study area (figure 5). Using the three
levels, polygons were created to
extrapolate the volume of displaced
material coinciding with each ero-
sional era: the pre-1933 flood and
post-1933 geometry (figure 6).
Analysis
Dam Cut Block Spatial Analysis
Through the analyses of historic
photographs (estimating number of
Figure 6: Image of the
three terraces down-
stream of the dam.
Note the slight under-
cutting at the base of
the 1933 flood terrace
denoting the vertical
limit of subsequent
floods. The distinct
contrasts of tree sizes
within and without the
flood zone also serves
as a high water mark.
Photo by Kaelin M.
Groom.
60 JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
cut blocks per row) and geometrical-
ly reverse engineering original blue
prints it is extrapolated that the flood
displaced approximately 7,900 boul-
ders. This is roughly 60 percent of
the entire dam structure and nearly
the entire loose rock fill core. Aver-
aging around 723 kg each (found
through density analysis of smaller
samples of the same material then
applied to the masonry blocks), this
means over 5.7 million kg of debris
was moved during a single event, not
counting massive quantities of the
sediment built up behind the dam
and in situ boulders downstream in
the canyon. Because it is speculated
that the dam failed nearly instanta-
neously, a hypothesis supported by
large still-mortared sections (rough-
ly 1.5 m x 1.2 m x 1.8 m) of the
structure found immediately down-
stream, this is a tremendous mass to
move at once and several masonry
boulders have been discovered near-
ly 3.2 km downstream. To maintain
that kind of carrying capacity for so
long the flood demonstrated an
incredible estimated energy of over
236,000 Watts at the dam (derived
from the standard equation ˆ=QpS/w
where ˆ = stream power, Q = dis-
charge, p = density, S = slope, and w
= stream width) and 420 million
Joules (E = Pt, where E = Energy in
Joules, P = Power in Watts, and t =
time in seconds) for the 1.5 hours it
took to drain the reservoir. It is com-
monly reported the peak discharge at
the dam during the flood was a
colossal 3,600 m3/s, and still 850 to
1,250 m3/s only 3.2 km further
downstream,23 but the knowledge
that water was also transporting over
5.7 million kg of masonry boulders
those numbers gain new meaning.
Besides estimating how many
masonry boulders were displaced,
Figure 7: Map of flood debris and deposition in and around the Falls area. Kaelin M.Groom 2012.
61
JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
another clue into the flood’s behav-
ior is examining where they were
deposited. With basic GPS technol-
ogy and identification methods ex-
plained above, spatial patterns of de-
position could be mapped and ana-
lyzed. Of the 7,900 estimated boul-
ders displaced, only 108 (roughly 2
percent) were located and identified.
The disparity could be due to loss of
identifying marks, thick vegetation,
and the very realistic possibility of
being buried beneath the massive
quantities of finer sediments moved
during the flood, especially since
during high water events, it is typi-
cally the finer particles that are the
last to settle and accumulate. As ex-
pected, the majority of the deposi-
tion patterns followed basic fluvial
principles such as settling on the in-
ner point bars with fewer in the outer
cut banks, dropping in clusters
where the flood lessened in carrying
capacity (e.g., reduced flow compe-
tence), and so on, except for The
Falls, the only known water-
falls on Cherry Creek (figure
7).
In this section of the study
area, approximately 0.8 km
downstream from the dam,
the canyon walls naturally
narrow and the stream gradi-
ent increases from 0.0037
m/m to 0.0134 m/m. Conse-
quently, due to the channel
contraction and increase in
channel gradient, the stream
velocity and flow competence
increase. In this situation,
widely used fluvial methods
indicate that little deposition
will be located in the channel
margins, while here there are
several clusters of boulders
dropped in the center of the
main flow path. What makes
this possible is the presence
of massive motorhome-sized
boulders (roughly 3 m x 4 m
x 6 m) funneled by the nar-
rowing canyon during the
flood. The original positions
of these boulders are un-
known, though multiple hypotheses
exist. One is that they were buried in
the soft bedrock and as the flood
eroded the area, they settled on the
streambed. Another was that they
fell from adjacent cliffs from chan-
nel wall scouring and undermining,
though the shallow slopes discour-
age this thought. Yet another possi-
bility is that they dislodged from the
steeper, rockier cliffs upstream clos-
er to the dam and the flood rolled
them down to where they clustered
at the falls and at the canyon mouth
(near the USGS Franktown gage). In
any case, there is evidence that these
colossal boulders were moving
during the flood, such as smaller
masonry, flimsy pieces of historic
sheet metal, and trees lodged
beneath the boulders.
These massive boulders impeded
the flood flow and a number of mas-
onry boulders became wedged and
trapped in the ensuing rapids. His-
toric topographic maps from the
USGS and the lack of historic photo-
graphs suggest Cherry Creek was a
graded stream with no existent knick
points or falls directly prior to the
1933 flood. Also supporting this hy-
pothesis is the presence of a gravel
bar, a well-established maximum
water-level marker and paleostage
indicator (Jarrett and England,
2002),24 level with the tops of the
massive boulders but several meters
higher than the falls. A number of
dressed stones can be found on this
particular gravel bar, which would
normally raise questions: How were
these transported here and how can
they be so much higher than The
Falls? But in this instance, their
existence suggests that they were
deposited during the beginning
stages of the flood, before the
falls were carved, and it wasn’t un-
til the flood became channeled as
the falls deepened that the upper
level became a gravel bar and high-
water mark (figure 8). Whether
Figure 8: Image of the Falls and congested boulder field looking upstream. Note the two men
near the falls for scale. Though not clearly visible from this angle due to vegetation, a large
gravel bar extends well past the Falls. Photo by Kaelin M. Groom.
62 JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
through irregular deposition pat-
terns or the hypothetical genesis of
the falls as they now are, the spatial
analysis of the dam cut blocks begin
to elaborate the enormity of this
flood and its consequences. But what
of the canyon itself?
Sediment
Displacement Analyses
Results show that along the 60 m
study reach alone almost 10 thou-
sand cubic meters of material was
displaced during the 1933 flood
event and 1.3 thousand cubic me-
ters from 1933 to 2012 (Table 1).
When the averages were applied to
the entire 3.2 km downstream
canyon it is estimated that nearly
560 thousand cubic meters total
was removed in the flood event and
another 70 thousand cubic meters
post-1933.
The nature and magnitude of the
erosion that was attained during this
event is both a cause and effect of the
local geology. The majority of
Castlewood Canyon is composed of
the porous yet resilient Castlerock
Conglomerate Formation. The dam
itself was constructed with cut
blocks of the tough conglomerate.25
However, further downstream the
loosely consolidated, and highly ero-
sive, Dawson Arkose Sandstone is
exposed. This is where the 1933
flood becomes so instrumental. The
only visible outcrop of the Dawson
formation runs from the old reservoir
and to approximately 2.4 kilometers
downstream from the dam. One pos-
sible hypothesis for this suggests the
upstream canyon has not experi-
enced floods of sufficient magnitude
and associated stream power to
erode the resilient Castlerock Forma-
tion to expose the Arkose. However,
the extraordinary nature of the 1933
dam-failure flood was enough to
cause downstream disparity. How-
ever, there is evidence in historic
photographs to suggest small por-
tions of the formation of the Arkose
were already exposed in the down-
stream canyon before 1933, but
nowhere near to the extent as to-
day. In any case, preliminary find-
ings suggest the 1933 flood’s ero-
sive power stemmed from flood
waters exponentially increasing
exposure of the weaker Arkose, dis-
placing inordinate amounts of sedi-
ment along its downstream path,
adding to the sediment supply and
overall active load.
Overall
Geomorphological Impacts
Although the immediate impacts of
the Castlewood Dam failure flood
are impressive, the lasting implica-
tions are much more profound. Not
only were massive quantities of ma-
terial removed from the canyon, but
also cut masonry boulders now lit-
ter the canyon adding a new element
to the canyon’s geomorphology.
Stream behavior and deposition pat-
terns have to adjust to the new ob-
stacles, thus altering the path of
natural meanders, no matter how
small.
Another dramatic change to the
canyon is the possible introduction
of The Falls. This one point has
changed the nature of the stream
channel, and fluvial state, as Cherry
Creek through Castlewood Canyon
is no longer a graded stream. The
Falls also add new components to
the geomorphology of the canyon
with increased turbulence and
velocity of the water, more down-
ward erosion below the falls, and
Summary of Substantial Rainfall and Flood Events in Cherry Creek Basin
Precip. Precip. Peak
Flood Name / Location Date Amount Duration Discharge
(cm) (hurs) (cfs)
Cherry Creek in Denver July 14, 1912 Appx. 5.3 2 25,000
Upper Cherry Creek in Parker June 28, 1922 2.5 – 10 2 17,000
Castlewood Dam Failure August 2–3, 1933 7.6 – 22.9 9 126,000*
Franktown-Parker August 5, 1945 5.1 – 12.7 unknown 10.700
Cherry Creek and Plum Creek Divide June 16, 1965 15.2 – 25.4 3 58,000**
* 126,000 at dam, 34,000 at Franktown, 16,000 in Denver
** Recorded and containe at Cherry Creek Reservoir, Never reached Denver
Add smaller floods from Franktown gaging station (esp. 9,170)
Table 1: Table showing the average discharges of recent floods as monitored by the Unites States Geologic Survey gaging station
number 06712000 established in 1936.
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Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
the cluster of up to massive boul-
ders impede nearly all flood debris
from continuing downstream. Many
of the park’s past bridges and
various debris washed downstream
in recent in floods (most recently
on July 2, 2006) can be found
lodged in the Fall’s upstream bould-
er field.
Additionally, the deep scouring of
the lower canyon effectively cut off
the river from the natural flood
terraces, sparking an entirely new
pattern of erosion and deposition.
Comparing pre- and post-1933
USGS quadrilateral 7.5 x 7.5 min-
ute topographic maps also reveals
a spatial pattern of erosion. The
natural meanders have been wid-
ened by an estimated average of
110 m and by as much as 150 m
in the areas with higher slopes. As
the debris-loaded waters followed
the preexisting meanders, the soft
Arkose Sandstone channel walls
eroded allowing the meanders to
widen and deepen. The irony, how-
ever, is that these exaggerations are
likely to last until the next large
flood. The 1933 flood not only
scoured the sides of the canyon by
as much as 18 m, but the flood
also deepened the canyon drastic-
ally, in many places as much as
9 m. The overwhelming dam-failure
discharge compared to smaller,
natural floods had a channeling
effect on the canyon and now all
subsequent floods must follow the
deep resultant channel incision. In
the lower canyon below the falls,
undercutting the resistant conglom-
erate suggests the limited impact
of relatively small post-1933
floods (the largest known post-
1933 flood in the canyon was 260
m3/s, see Table 1) have on the can-
yon as a whole. Because the Frank-
town gage was installed in 1940,
we do not have specific data for
particular flood events from 1934
to 1939. However, if there had been
a substantial flood, it would have
been documented by the USGS as
a “miscellaneous flood,” and no such
record exists.
Discussion and Conclusions
The significance of this research is
that it offers an introduction to the
geomorphology of Castlewood Can-
yon and lays the groundwork for
Figure 9: The ruins of the Castlewood Dam, ca. 2012, by Thomas Barrat. ID 28179822, Dreamstime.com.
64 JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
future exploration. The irregular dis-
tribution of the quarried stone from
the dam and massive gravel bars at
The Falls support a myriad of genet-
ic hypotheses and is now primed for
further analysis. Can Castlewood
Canyon serve as a case study of
waterfalls created through traumatic
flood events? The distance these
dressed or quarried stone were en-
trained and moved also reveals po-
tential research. While this study
area did not extend past the mouth of
the canyon, stone derived from the
dam were still being discovered up
to that limit and could possibly be
found well into the Franktown Val-
ley; their existence and deposition
could be mapped. The cross section
analysis can also be expanded. More
detailed measurements throughout
the entire canyon would offer a more
accurate assessment of sediment dis-
placement, where this study was
only meant to establish a base esti-
mation.
So while the greater details are
still yet to be defined the geomor-
phologic impacts of Denver’s
forgotten flood have been given new
light. In an instant the 1933 Castle-
wood Dam failure not only altered
the shape, composition, and exposed
geology in the canyon but also the
manner in which the canyon itself
changes. The once graded stream is
now riddled with turbulence, boul-
ders with no natural reason for exist-
ing scatter the exaggerated bends,
and Cherry Creek continues its lone-
ly journey through the hollowed
deep canyon.
Notes
1. Colorado State Parks. “Castle-
wood Canyon State Park: Castle-
wood Dam,” 2007, Brochure.
2. Hardesty, W. P. “The Castlewood
Rock-Fill Dam and the Canal of
the Denver Land and Water Co.”
Engineering News. XLI. no. 6
(1899): 82–84.
3. Tyrone, K. “Castlewood Ruins:
A monument to Nature’s Ca-
price.” Englewood Herald Sen-
tinel, sec. 5, June 29, 1972.
4.
Welles, A. M. “The Castlewood
Dam Controversy.” The Denver
Post, May 2, 1900.
5. Patterson, C. L. “Flood Control
on Cherry Creek above Denver,
Colorado,” Colorado Water Con-
servation Board, November 1,
1937, 8–10.
6. Hardesty, W. P. “The Castlewood
Rock-Fill Dam and the Canal of
the Denver Land and Water Co.”
Engineering News. XLI. no. 6
(1899): 82–84.
7. “Act of God Blamed for Dam
Break.” Denver Post, August 9,
1933.
8. Corps of Engineers, Department
of the Army, Omaha District,
“Flood Plain Information Cherry
Creek: Cherry Creek Lake
Through Franktown, Colorado.”
Prepared for Arapahoe County,
Douglas County, Urban Drain-
age and Flood Control District,
Colorado Water Conservation
Board, (1976).
9. “Act of God Blamed for Dam
Break.”Denver Post,August 9,
1933.
10. Colorado State Parks. “Castle-
wood Canyon State Park:
Castlewood Dam,” 2007, Bro-
chure.
11. Jarrett, R. D., 2000, Paleoflood
investigations for Cherry Creek
basin, Eastern Colorado, in
Hotchkiss, R. H., and Glade,
Michael, editors, Building Part-
nerships, Proceeding of the 2000
Joint Conference on Water Re-
sources Engineering and Water
Resources Planning and Man-
agement, July 30–August 2,
2000, Minneapolis, MN, Ameri-
can Society of Civil Engineers,
Reston, VA,. 1–10.
12. Thompson, A. H. “Bureau of
Reclamation Cherry Creek Re-
port” United States Department
of the Interior,April 1938.
13.
Follansbee, R., L. R. Sawyer,
United States Department of the
Interior (1948). “Floods in Colo-
rado.” United States Government
Printing Office, 59–67.
14. Forrest, K., and C. Albi. Den-
ver’s Railroads: The Story of
Union Station and the Rail-
roads of Denver. Denver, CO:
Colorado Railroad Museum,
1982.
15. Corps of Engineers, Department
of the Army, Omaha District,
“Flood Plain Information Cherry
Creek: Cherry Creek Lake
Through Franktown, Colorado.”
Prepared for Arapahoe County,
Douglas County, Urban Drain-
age and Flood Control District,
Colorado Water Conservation
Board (1976).
16.
Tyrone, K. “Castlewood Ruins:
A monument to Nature’s Ca-
price.” Englewood Herald Sen-
tinel, sec. 5, June 29, 1972.
17. “Act of God Blamed for Dam
Break.” Denver Post, August 9,
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18. Colorado State Parks. “Castle-
wood Canyon State Park: Geol-
ogy,” 2007, Brochure.
19. Richardson, G. B. (1913) “De-
scription of the Castle Rock
Quadrangle.” United States Geo-
logic Survey.
20. Western Regional Climate Cen-
ter. 2012 “Climate of Colorado.”
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21. Colorado Parks and Wildlife.
“Plants at Castlewood Canyon
State Park,” 2011, www.parks.
co.us/Parks/CastlewoodCanyon/
Nature/Plants.
22. Baker, V. R. (1987) Paleoflood
hydrology and extraordinary
flood events. Journal of Hydrol-
ogy, 96, 79–99.
23. Jarrett, R. D., 2000, Paleoflood
investigations for Cherry Creek
basin, Eastern Colorado, in
Hotchkiss, R. H., and Glade, Mi-
chael, editors, Building Partner-
ships, Proceeding of the 2000
Joint Conference on Water Re-
sources Engineering and Water
Resources Planning and Man-
agement, July 30–August 2,
2000, Minneapolis, MN, Ameri-
65
JOW, Spring 2014, Vol. 53, No. 2
Groom and Allen: Denver’s Forgotten Flood: The Geomorphologic Impacts of the 1933 Castlewood Dam Failure
can Society of Civil Engineers,
Reston, VA, 1–10.
24. Jarrett, R. D., and England, J. F.,
Jr., 2002, Reliability of pale-
ostage indicators for paleoflood
studies: Ancient Floods, Modern
Hazards: Principles and Appli-
cations of Paleoflood Hydrology,
AGU’s Water Science and Ap-
plication Series, vol. 5, 91–109.
25. Hardesty, W. P. “The Castlewood
Rock-Fill Dam and the Canal of
the Denver Land and Water Co.”
Engineering News. XLI. no. 6
(1899): 82–84.
A native of Colorado, KAELIN M.
GROOM is a PhD candidate in
Environmental Dynamics at the
University of Arkansas, where she
also obtained her masters in geogra-
phy. Her specialties include geomor-
phology, cartography, cultural re-
source management, and heritage
tourism. Professionally, she has also
worked as a research consultant with
domestic and international agencies
such as the U.S. National Park Ser-
vice, Grenadian National Museum,
and the Petra National Trust with ties
to UNESCO.
A champion of fieldwork and an
award-winning scholar and teacher
at the University of Colorado Denver,
Dr. Casey D. Allen works at the
human-environment interface. Allen
has conducted research around the
West and specializes in arid lands,
geomorphology, rock decay, and
environmental perception. He has
also worked with the Hopi Nation,
Petrified Forest National Park, and
Nation of Grenada (Caribbean) to
assess their rock art (petroglyphs) in terms of sustainability, and runs
twoosuccessful international field study programs for students:
Sustainability in the Caribbean and Geography by Rail®.
