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FLOOD PLAIN INFORMATION TALKEETNA RIVER - SUSITNA RIVER - CHULITNA RIVER
F GB 1227 .U55 T3 1972
TALKEETNA I ALASKA
coR THE MATANUSKA-SUSITNA BOROUGH BY THE DEPT. OF THF ARMY,
1SKA DISTRICT, CORPS OF ENGINEERS, ANCHORAGE~~A.
Alaska Resources J u N E 19 7 2 Library & Information Services
Apr' orage,fUaska
FLOODS • 1n TALKEETNA
This folder is an announcement of and sup
plement to the "Flood Plain Information (FPI)
Report, Talkeetna River, Susitna River and Chu
litna River, Talkeetna, Alaska." The purpose of
the report is to present the facts on flood poten
tial and flood hazards which will provide a
sound basis for land use planning and for
management decisions concerning flood plain
utilization.
Although Talkeetna has suffered damage
from major floods in the past, studies indicate
that even larger floods can occur in the future.
Emphasis is given to future floods in the FPI
Report. Maps, profiles, and cross sections have
been included to illustrate the possible extent
and severity of future floods.
Included in this folder are photographs
showing future flood heights at selected loca
tions. The flood height shown for a large flood,
the Intermediate Regional Flood (IRF), will be
equalled or exceeded once in 1 QO years on the
average, although this flood could occur in any
year. Also indicated is the flood height that
would be reached if a very large flood, the
Standard Project Flood (SPF), should occur.
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August 1971 flood at Talkeetna above the Alaska Railroad bridge.
Inside this folder are sketches illustrating the
horizontal and vertical relationship of flooded
areas and also a flooded area map from the
report showing the extent of both a large flood
(IRF) and very large flood (SPF).
Future flood heights at the Talkeetna Motel and Res tau rant
~CTION is needed Although the flood plain is only partially
developed at Talkeetna, expansion and develop
ment of tourist-oriented businesses can be ex
pected in the future. With new development,
the damage caused by floods will continue to
increase unless action is taken.
Effective regulatory measures such as zon
ing ordinances and building codes can be de
signed to prevent increased flood damages.
Flood proofing can reduce potential damages to
properties already subject to flooding and ad
ditional works to modify flooding can also be
a part of the long-run solution. A local flood
control project has already provided partial pro
tection from erosion due to flooding.
Talkeetna is not the only community with
flooding problems. Flood plain information has
already been provided for many of several
thousand flood-plagued communities. Nearly
400 of those having FPI Reports by mid-1971
have adopted or strengthened regulations, while
700 others have them under study. An addi
tional 600 communities have used the FPI Re
ports to establish interim land use controls.
This folder has been prepared for the Matanuska
Susitna Borough by the U.S. Army Corps of Engin
eers from data in the report "Flood Plain Informa
tion, Talkeetna River, Susitna River and Chulitna
River, Talkeetna, Alaska." Copies of the report and
this folder are available upon request from the
Matanuska-Susitna Borough Planning Department,
133 West Evergreen, Palmer, Alaska 99645.
Possible future flood height at FSS next to State Airfield
Clean up activity after a recent flood in on Alaskan community
FLOODS in TALKEETNA
ALASKA TALKEETNA RIVER
SUSITNA RIVER CHULITNA RIVER
BUilDING ~
in t.he LOOD PLAIN can· make FLOODS WIDER
and DEEPER
natural stream
bank-full natural stream
flooded
same flood with development
and encroachment
this ENCROACHMEN.
can change a
Small: Floo i·nto a
MAJOR FLOOD
TOOLS of FLOOD PLAIN MANAGEMENT forth~ reduction of Fiood Damage and H·uman. Suffering
MEASURES TO MODIFY FLOODS are often required to alleviate existing problems and sometimes to forestall future problems · · ·
~--..
~ .. ~. .. .... .... ...... ~-. -. . ..__,
DAMS a RESERVOIRS
HIGH FLOW DIVERSION
"' .
CHANNEL ENLARGEMENT
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OTHER MEASURES
aid the Flood Plain occupant in coping with floods · · ·
Tax Adjustments
Flood Insurance
Warning 8 Emergency
Plans CODES, URBAN RENEWAL, SUBDIVISION
FLOOD PROOFING • RELOCATIONS
FLOOD PATTERNS FOR TALKEETNA, ALASKA
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LEGEND approx1mate limits of overflow
I NORMAL STREAM
I I NTERMEOlATE REGIONAL FLOOD (IRF)
STANDARD PROJEC1 FLOOD (SPFl
PROFILES in the Flood Plain Information Report
show elevations of these floods for the entire study area
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CONTENTS
PREFACE
Settlement The Stream and Its Valley Developments in the Flood Plain
FLOOD SITUATION
Sources of Data and Records Flood Season and Flood Characteristics Factors Affecting Flooding and Their Impact
Obstructions to Floodflows Flood Damage Reduction Measures Other Factors and Their Impacts
Flood Warning and Forecasting Flood Fighting and Emergency Evacuation Plans Material Storage on the Flood Plain
PAST FLOODS
Summary of Historical Floods Flood Records Flood Descriptions
FUTURE FLOODS
Intermediate Regional Flood Standard Project Flood Frequency Hazards of Large Floods
Flooded Areas and Flood Damages Obstructions
GLOSSARY
Velocities of Flow Rates of Rise and Duration of Flooding Photographs, Future Flood Heights
ARLIS Alaska Resources
· ~ ;;/.;~' .·; -,. ~:y'>.::,ibn1ry & Information Services . ;:_
1·\:·- " · ' ·. ·\. r r ·. - Anchorage, Alaska
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SCALE IN MILES
DEPARTMENT OF THE ARMY
ALASKA DISTRICT, CORPS OF ENGINEERS
ANCHORAGE I ALASKA
FLOOD PLAIN IN FORMATION
TALKEETNA ALASKA
GENERAL MAP JUNE 1972
PLATE
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PREFACE
The portion of Talkeetna covered by this report is
subject to flooding from the Talkeetna, Susitna and Chulitna
Rivers. The properties along these streams are primarily
residential and commercial, and were severely damaged bythe
flood of 1942. The open spaces in the flood plain which may
come under pressure for future development are extensive.
Although large floods have occurred in the past, studies indicate
that even larger floods are possible~
This report has been prepared because a kn owl edge of
flood potential and flood hazards is important in land use planning
and for management decisions concerning flood pla:in· utilization.
It includes a history of flooding in Talkeetna and identifies those
areas that are subject to possible future floods. Special
emphasis is given to these floods through maps, photographs,
profiles, and cross sections. The report does not provide
solutions to flood problems; however, it does furnish a suitable
basis for the adoption of land use controls to guide flood plain
development and thereby prevent intensification of loss and
damage. It will also aid in the identification of other flood
damage reduction techniques such as works to modify flooding
and adjustments, including flood proofing, which might be
embodied in an overall Flood Plain Management (FPM) program,
Other FPM program studies--those of environmental attributes
and the current and future land use role of the flood plain as
part of its surroundings- -would also profiffrom this information.
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At the request of the Matanuska-Susitna Borough, and
endorsement of t h. e State of Alaska, Department 0f Natural
Resources, this report was prepared by the Alaska District,
Corps of Engineers, under continuing authority provided in
Section 206 of the 1960 Flood Control Act, as amended.
Assistance and cooperation of the Alaska Railroad, Federal
Aviation Agency, Alakka Department of Highways, National
Weather Service, Matanwska-Susitna Borough, and private
citizens, in supplying us e f u 1 data and photographs for the
preparation of this report are appreciated.
Additional copies of this report can be obtained from the
Matanuska-Susitna Borough. The Alaska District, C or p s of
Engineers, upon request, will p r ovid e technical assistance to
planning agencies in the interpretation and use of the data
presented as well as planning guidance and furtherassistan ce,
including the development of additional technical information.
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BACKGROUND INFORMATION
Settlement
Talkeetna~ which is an Indian n arne meaning river· of
plenty~ was established early in the Twentieth Century just
below the confluence of the Susitna~ Talkeetna.and Chulitna
Rivers. The village served as a supply and trade center for
miners operating in the foothills of the Alaska Range and
Talkeetna Mountains. Reportedly~ Talkeetna was originally
the site of a Tanaina Indian Village although there are presently
only two Indian families living in Talkeetna.
Talkeetna was the terminus of river boat traffic· from
Cook Inlet up the Susitna River. It developed as a major camp
and distribution center when the railroad was built. The rail
road station was established in 1915 and a Post Office in 1916.
During World War II many of the gold mines were shut
down as a result of war time wage and cost controls. After the
war~ mining remained unprofitable, as it is today, and most of
the mines remained c 1 o sed. However, lenient homestead
regulations brought many veterans into the area taking up some
of the population loss from unemployed miners.
Population figures for the unincorporated village of
Talkeetna are as follows: 1920-70; 1930-89; 1939-136; 1950-106;
1960-76; and 1970-182.
The Stream and Its Valley
The Talkeetna River and the Chulitna River are major
tributaries of the Susitna River. Talkeetna River~ with a total
drainage area of 2015 square miles, has its origin at Talkeetna
Giacier in the Talkeetna Mountains. FrO:m this rugged terrain
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the river flows northwest 40 miles and then southwest 40 miles
to its junction with the Susitna River at the villlage of Talkeetna.
The are as above Talkeetna., drained bythe three rivers.,
range from 350 to over 6., 000 feet in elevation and all have
portions of their higher elevations glacier covered. D rainage
areas contributing to runoff at 1 o c at ions in or near the study
areas are shown in Table I.
TABLE I
DRAINAGE AREAS
Location
Talkeetna River at Mouth Chulitna River at Mouth Susitna River at Talkeetna Susitna River Above Mouth
Of Chulitna River
River Length Miles
80 80
200
200
Drainage Area sq. mi.
2., 015 2.,630
1 1., 035
The climate of the area is characterized by moderately warm
summers and cold winters with temperature extremes ranging
from p 1 us 91 degrees F. to 48 degrees be 1 ow zero .. Annual
precipitation averages 28.8 inches and annual snowfallll4 inches.
Rainfall is generally the heaviest in July., August and September
with monthly precipitation amounts about equal for the rest ofthe
year.
Developments in the Flood Plain
The flood plain of the Talkeetna River at the village of
Talkeetna is wide and developed only on the south side at the
mouth of the river. The only bridge in the study area is the
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Alaska Railroad Bridge which crosses just upstream from the
mouth of the Talkeetna River.
The flood plain within the village of Talkeetna is occupied
by residential and commercial developments. The railroad,
highway. streets and utility 1 in e s. in addition to homes and . J '
businesses, would be· subject to flooding. This flood plain is
only partially developed and f u t u r e development .· ·.is likely,
especially with the increase in tourist traffic because of the
opening of the new Anchorage-Fairbanks highway.
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ALASKA RAILROAD BRIDGE,LOOKING UPSTREAM FROM NORTH BANK OF TALKEETNA RIVER FIGURE 1
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FLOOD SITUATION
Sources of Data and Records
The U. S. Geological Survey has maintained stream gages
at the following locations upstream from Talkeetna forth~ period .
indicated:
Location
Susitna River at Gold Creek
Chulitna River near Talkeetna
Period of Record
August 1 9 49 to present
February 1 9 58 to present
Talkeetna River above Talkeetna June 1 9 64 to present
The gage location on the Talkeetna River is shown on the
general map. The others are not within the area covered h y
this map.
To supplement the records of the gaging stations' and those
of snow surveys, newspaper files.. historical documents and
records were searched for information concerning past. floods.-
These records have helped to develop a knowledge of floods
which have occurred on these rivers and have also shown that
the floods on the three rivers do not peak concurrently.
Maps prepared for this report were based on the U. S .
Geological Survey quadrangle sheet Talkeetna B-1. River cross
sections and structural data on the bridge and culverts were
obtained by field surveys performed by Alaska District.. Corps
of Engineers, personnel.
Flood Season and Flood Characteristics
Major floods have occurred in the study area during the
spring, summer and fall seasons with the greatest recorded
flood occurring in September 1942. Floodflow stages can rise
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from normal flow to extreme flood peaks in a relatively short
period of time with high velocities in the main channels of the
rivers.
The flood of September 1942 resulted from a combination of
48 hours of heavy rains and melting snows which had recently
fallen in the mountains. In addition to floods caused by runoff,
Talkeetna is susceptible to floods caused by sudden releases of
water that have been impounded by ice jams.
Factors Affecting Flooding and Their Impact
Obstructions to Floodflows - Natural obstructions to flood
flows include trees, brush and other vegetation growing along
the stream banks in flood plain areas. Man-made encroachments
on 'or over the rivers, such as the railroad bridge, can also i
create more extensive flooding than would otherwise occur.
During floods, trees, brush and other vegetation growing in
flood plains impede floodflows, thus creating backwater and
increased flood heights. Trees and other debris may be washed
away and carried downstream to collect on the bridge or other
obstructions. As floodflows increase, masses of debris could
break loose and a wall of water and debris would surge down
stream until another obstruction is encountered. Debris could
collect against the bridge until the load exceeds its structura:l
capacity and the bridge is destroyed.
In general, obstructions restrict floodflows and result in
overbank flows and unpredictable a r e as of flooding,pos sible
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destruction of bridges and culverts and an increased velo c ity
of flow immediately downstream. It is impossible to predict
the degree or location of the accumulation of debris; t her efo re,
for the purposes of this report, it was necessary to assume that ;
there would be no accumulation of debris at the bridge 0 r any
clogging of culvert openings in the development of the flood
profiles.
Flood Damage Reduction Measures - In 19 51 the Corps of
Engineers completed an emergency bank protection project
at Talkeetna, Alaska, under Section 14 of the 1946 Flood Control
Act. The project, located on the left bank of the Talkeetna River
below the Alaska Railroad Bridge, consists of a brush and
timber fascine 1, 000 feet long which was constructed to arrest
erosion. Subsequent to construction of the emergency work, a
flood control project was authorized which called for a stone
revetment approximately 1, 500 feet long downstream from the
railroad bridge. In 1960 this authorized project was placed in
an inactive category as the emergencyti:intier faspi.j):e constr~cted
in 1951 was performing satisfactorily. Recently, the river has
cut a small channel through the fascine structure and the village
is again threatened by erosion. A restudy by the Corps of
Engineers of the authorized project to determine feasibility,
justification and local cooperation requirements under existing
conditions in the area will probably be undertaken in Fiscal Year
1973.
In an effort to control erosion arid protect its bridge, the
Alaska Railroad, in 1949, made a channel change immediately
upstream from the bridge. This realignment cuf off a
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meander of the river and allowed .the river to flow at right angles
to the bridge. Figures 2 an d.c _ 3 illustrate the before and after
conditions.
There are no existing Borough zoning ordinances, building
codes, or other regulatory measures specifically for the re
duction of flood damage. The village of Talkeetna is not
incorporated and therefore does not have any zoning powers.
This study has been requested so that it may be used as a basis
for t h e development of Flood P lad n Management planning
measures by the Matanuska-Susitna Borough.
Other Factors and Their Impact- The majority of the
inundated area at Talkeetna has been along the banks of
the Talkeetna River near its confluence with the Susitna River.
This is due largely- to the compounded backwater influence
of the Sus itna at high stages. When high runoff from the
tributaries has occurred during these periods of high stages on
the Susitna, it has aggravated the flooding by increasing the
height and duration of the river's backwater effects. Flooding
and threats of flooding promote action by local officials in flood
warning and flood fighting activities. Due to the size and nature
of the village, there is no significant problem with floatable
materials being stored in the flood plain whieh nitght cause
additional damage.
Flood Warning and Forecasting - The National Weather
Service, Alaska River Forecast Center (RFC) located in
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Anchorage, issues flood warnings for the Talkeetna area to radio
and television stations and the 1 o cal media for further
dissemination to residents of the area. In addition, the Center
maintains records of daily river stages on the Susitna River at
Gold Creek.. at the Alaska Railroad Bridge and at the Highway
Bridge at Sunshine. The National Weather Service also issues
regular weather forecasts and hazardous weather warnings for
the area.
Flood Fighting and Emergency Evacuation Plans- Although
there are no formal flood fighting or emergency evacuation plans
for the Talkeetna area, provisions for alerting area residents in
time of emergency are accomplished by the Alaska Disaster
Office through the Matanuska-Susitna Borough. This office
maintains communication with the National Weather Service
at its control center, establishing a "flood watch" during_the early
stages of flood threat. Residents along the river are warned by
radio and telephone of approaching flood conditions and advised
to evacuate the area. Subsequent flood fighting, evacuation and
rescue activities are coordinated on a Borough-wide basis with
Borough officials.
Material Storage On The Flood Plain-As previously stated,
due to the size and nature of the community, there are no
significant quantities of floatable materials stored in the flood
plain at Talkeetna. If they were present they could be carried
away by flood flows, causing serious damage to any structures
downstream.
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AERIAL VIEW OF TALKEETNA RIVER, LOOKING UPSTREAM, SHOWING NATURAL CONDITIONS OF THE RIVER IN AUGUST, 1949
FIGURE 2
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AERIAL VIEW OF TALKEETNA RIVER, AUGUST 1950, SHCWING THE CHANNEL CHANGE CONSTRUCTED BY THE ALASKA RAILROAD
FIGURE 3
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VIEW OF FASCINE FROM UPSTREAM END AS IT APPEARED IN MAY, 1951 FIGURE 4
FASCINE AS IT APPEARS TODAY FIGURE 5
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PAST FLOODS
Summary of Historical Floods
Very little information is _ available concerning historical
floods at Talkeetna. Records indicate that an ice jam
occurred on the Susitna River at Gold Creek in 1919. bu-t they
did not indicate whether or not Talkeetna was flooded. F 1 oods
have also occurred in September 1942 and August of 1971. The
1942 flood is the highest of record and is the only one that caused
any significant damage. The 1971 flood had a peak which lasted
only a few hours and only flooded the lower, abandoned, parts
of the village.
Flood Records
Information on historical floods in the Talkeetna area was
obtained from the stream gaging stations maintained by t he
U. S. Geological Survey at a number of locations within the
Susitna Watershed near Talkeetna. Additional information on
past floods was obtained from interviews with residents along
the Talkeetna River. newspaper files and historical documents.
Flood Descriptions
The following a r e descriptions of the flood of record that
occurred at Talkeetna, Alaska in September 1942:
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EXCERPTS FROM THE ANCHORAGE TIMES, 23 AND 26 SEPTEMBER 1942 (a)
WORST rLOODS rORCE RESIDENTS TO -FLEE -
Talkeetna Under · Water Use Rowboats
Nag ley Store, Trading Post, DeVault RoadHouse Are . Damaged
Returning travelers who knew Talkeetna " Before and after '' today are recounting the ravages of Monday•s flood when the Talkeetna, Chulitna and Big Susitna rivers rose far above their confining banks and partially inundated Talkeetna village.
The river rise was estimated by several as more than six feet, one cabin on the Talkeetna river was torn away and floated downstream to crack up against a mass of debris, the DeVault Roadhouse and the Talkeetna Trading Post were flooded, the old pier and boathouses on the Talkeetna are gone, and the township itself is covered with mud and glacier si 1 t.
Stacks of stove wood, cut during the summer for use this winter, were drifted away, according to those returning to Anchorage~
Women and children, sent hurriedly to Sunshine Tuesday out of danger's way, have been returned to the i r homes, it was said.
Real danger, one Anchorage man reports, was seen Monday might when the flood waters reached within eight inches of the dike. It was at that time, he said today, that the entire town was threatened for had the dike not held against the great rush of water Talkeetna would have been wiped out.
Travelers told too of the swollen creeks, some of which widened to half a mile from their normal few yards.
Work crews, for which every available able-bodiedman was recruited, are still working against odds to repair damaged structures.
-~~--------------(a) Simulated from microfilm copy
14.
Say River Rose Six Feet To Flood Homes and Stores
In one of the worst floods in memory of sourdougD _residents, rowboats are being used as a means of-transportation in Talkeetna, women and children have been evacuated to safety, and the Big Susitna, the Chulitna rampaging over the i r banks.
The three great rivers,. swollen by qs hours of heavy rains and new snows running from the mountains after warm winds, flooded their banks Monday and sent a rush of water into homes, stores and streets of the township.
While details of the damage were not immediately available, an indication is given by the report that between two and three feet of water stood in the H.w. Magley store which occupies one of the highest spots in .Talkeetna and which, during the height of the flood, was isolated as an island.
The Talkeetna Trading Post, operated by Belle McDonald near the banks of the Big Susitna, the DeVault Roadhouse, just across the road, and the Fairview Inn were probably the most seriously damaged, according to unofficial reports.
Work crews were rushed to Talkeetna to repair damaged structures weakened by flood. waters and Col, Q.F. Ohlson was there today supervising the work.
As flood water rose to an alarming height Monday, women and children were crowded on speeders and run to Sunshine and housed in the section house. It is believed between 20 and 30 were sent to temporary quarters to avoid mishap in the flood area and to provide warm and dry housing for the women and children. No accidents have been reported in meager deta i 1 s brought to Anchorage. It is believed that stores and trading posts had not as yet stocked their complete winter supplies but that damage by water to merchandise will amount to a considerable loss.
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FUTURE FLOODS
Floods of the same or larger magnitude as those that have
occurred in the past will occur in the future. Larger floods
have been e~gerienced in the gaston streams with similar
geographical and physiographical characteristics as those
found in the study area. Similar combinations of rainfall and
runoff · which caused these floods could occur in the Talkeetna
area. Therefore~ to determine t h e flooding potential of the
study area~ it was necessary to consider storms and floods that
have occurred in regions of like topography~ watershed cover
and physical characteristics. Discussion of the future floods
in this report is limited to those that have been desigl'l.ated as
the Intermediate Regional Flood and the Standard Project
Flood. The Standard Project Flood represents a reasonable
upper limit of expected flooding in the study area. The Inter
mediate Regional Flood may reasonably be expected to occur
more frequently a 1 thou g h it will not be as severe as the
infrequent Standard Project Flood.
Intermediate Regional Flood
The Intermediate Regional Flood (IRF) is defined as one
that will occur once in 1 00 years on the average~ although it
could occur in any year. The peak flow of this flood w as
developed from statistical analysis of streamflow and precipi
tation records and basin runoff characteristics for the stream
under study. In determining the Intermediate Regional Flood
for the Talkeetna and Susitna Rivers~ statistical studies were
made using the records of flood data from the U. S. Geological
Survey gaging stations throughout the vicinity of Talkeetna~
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Alaska. Peak flows thus developed for the Intermediate llegional
Floods at selected locations in the study ar~a are shown in
Table 2.
Standard Project Flood
The Standard Project Flood is defined as a major flood that
can b e expected to o ccur f r om a severe combination of
meteorological and hydrological conditions that is considered
reasonably characteristic of the geographical area in which the
study area is located, excluding extremely rare combinations.
The Corps of Engineers, in cooperation with the NOAA Weather
Service, has made comprehensive studies and in ves tigations
based on the past records of experienced storms andfloods and
has developed generalized procedures for estimating the flood
potential of streams.· Peak.discharges for the Standard Project
Flood at Talkeetna are shown in Table 2. Discharge hydrographs
for the Talkeetna SPF and the Susitna River SPF at Talkeetna
are shown on Plates 9 and 10, respectively.
Location
Susi tna River at Talkeetna
Talkeetna River at mouth
TABLE 2
PEAK FLOWS FOR INTERMEDIATE REGIONAL AND STANDARD PROJECT FLOODS
Drainage Intermediate Area Regional_Flood
sq. mi. Discharge cfs
11,035 268,000
2,015 97,000
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Standard Project Flood
Discharge cfs
315,000
121,000
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TABLE 3
FLOOD ELEVATIONS
Talkeetna River at Alaska Railroad Bridge
Flood Elevation (a)
Standard Project
Intermediate Regional
August 1971
(a) Feet, mean sea level
Frequency
354.4
351.8
346.9
A frequency curve of peak flows was constructed on the basis
of available information and computed flows of floods u. p to
the magnitude of the Standard Project Flood. The frequency·curve
thus derived~ which is available upon request, ref 1 e c t s t he
judgment of the engineers who have studied the area and are
familiar with the region; however~ it must be regarded as
approximate and should be used with caution in connection
with any planning of flood plain use. Floods larger than t he
Standard Project Flood are possible but the combination of factors
necessary to produce such large floods would be extremely rare.
Hazards of Large Floods
The extent of damage caused by any flooddepends on
the topography of the area flooded, depth and duration of flooding,
velocity of flow. r at e of r i s e • and developments in the flood
plain. An Intermediate Regional or Standard Project F lao d
on the Talkeetna and Susitna Rivers or on the Talkeetna River,
itself, will result in inundation of residential and c om)TI.erc ial
areas in the village of Talkeetna. The same . ·nood situation
on the Susitna River alone would result in only the lower end of
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the village, adjacent to the Susitna, being flooded •. Deep flood
water, flowing at high velocity and carrying floating debris, will
create conditions hazardous to persons.and vehicles attempting
to cross flooded areas. In general, .floodwater 3 or more feet
deep and flowing at a velocity of 3 or more feet per second could
easily sweep an adult person off his feet, thus creating definite
danger of injury or drowning.
Flooded Areas and Flood Damages - The areas in the village
of Talkeetna that are subject to flooding by the Intermediate
Regional and Standard Project Floods are shown on Plates 2 and
3. The actual limits of these overflow areas mayvary somewhat
from those shown on the maps because the 50 foot contour
interval and scale of the maps do not permit precise plotting
of the flooded area boundaries. As may be seen from these
plates, floodflows from the Susitna and Talkeetna Rivers
cover essentially all of the village. The highest stages of
flooding throughout the· study area occur when the. floodwaters
from the Talkeetna me e t with the high stages of the S usitna
River. Areas that will be flooded by the Intermediate Regional
or Standard Project Floods include commercial and res
idential sections along with t he associated roads and private
utilities. Considerable damage to these facilities would occur
during an Intermediate Regional Flood. The maj()rity of homes
in Talkeetna would be damaged by this flood. Heavily laden flood
waters would deposit their silt load throughout the village
due to the lower velocities of overbank flow in this are a.
Utilities and transportation facilities would be damaged in addi
tion to an interruption of communications. Most of the water wells
are not completely sealed, therefore the flooding and subsequent
19
0
J ],:)
J 0 0 D
0 D J 0 Q
u 0 D :o~~ ~
J~ J
pollution of the wells would create a serious health hazard.
Both air f i e 1 d s would be damaged and their us e limited.
Evacuation of people from the village would not be a major
problem though, due to the fact that highway access to Talkeetna
would not be affected. Floodwaters will flow over the highway
and railroad just south of Talkeetna, closing access into the
community and disrupting rail traffic between Anchorage and
Fairbanks.
Damage would b e even more severe during a Standard
Project Flood due to. the wider extent and greater depths o f
flooding, higher velocity flow and longer duration of flooding.
Plates 4, 5 and 6 show water surface profiles of the IRF and SPF.
Depth of flow in the channel can be estimated from these
illustrations. Typical crQSS sections of the flood plain at
selected locations, together with the water surface elevation
and extent of the IRF and SPF, are shown on plates 7 and 8.
Obstructions - During floods, debris c o 11 e c tin g o n the
bridge and culverts could decrease their carrying capacity and
cause greater water depths (backwater effect) upstream of
these structures. Since the occurrence and amount of debris
are indeterminate factors, only the physical characteristic of
the structure we r e considered in preparing profiles of t h e
Intermediate Regional and Standard Project Floods. Similarly,
the map s of flooded areas show the backwater effect of the
bridge but do not reflect the increased water surface elevation
that could be caused by debris collecting against the structure.
The bridge is high enough not to be inundated by floodflows.
20
However, even without considering an accumulation of debris on
the structure. it still causes a substantial backwater effect. This
backwater causes a considerable portion of the area east ofthe
Alaska Railroad to be inundated by water during major floods
which approach the IRF in magnitude. With the exception of
The Federal Aviation Administration (FAA) facilities, there is.
at present. a minimum of development in this area. Damage
to the FAA facilities would be relatively minor considering the
first floo:r elevations of these structures. Water will flow over
the railroad embankment and down into the village. The flood
waters will also flow over the railroad and highway just south of
the vi 11 age . Depths and quantity of flow cannot be accurately
determined, although both are anticipated to be minor. Overall
depths of flooding e as t of the railroad line will range up to 6
feet with the deepest area adjacent to the railroad embankment
south of the FAA airfield.
Velocities of Flow - Water velocities during floods depend
largely on the size and shape of the cross sections. conditions
oft he stream and the bed slope, all of which vary on .different
rivers and at different locations on the same river. During the
Intermediate Regional and Standard Project F 1 o o d s. average
velocities of main channel flow would range from 5 to 7 feet per
second on the Talkeetna River except at the railroad bridge
where. they would range from 14 to 17 feet per second. water
flowing above 8 feet per second is capable of causing severe
erosion to streambanks and transporting large objects. Over
bank flow in the· Talkeetna area would average 1 to 2. 5 feet per
21
()
J [):J
J
R !:::1
0 J 0 0 0 0 D
J 0
D
J:_j J
second. At these velocities. deposits of silt and other debris
can be expected.
Rates- of Rise an-d Duration of Flooding - Floods on the
Talkeetna and Susitna Rivers generally have a gradual rise
until the ground becomes saturated, then they ex pe rienc e a
constant. rapid rise of one to three days duration until the peak
is reached. Generally, the duration of the extremely high flows
does not exceed one or two days and then the flood waters drop
quickly. For the Intermediate Regional and Standard Project
Floods. Table 4 gives the maximum rates of rise. height of
rise (from critical ~tage level to maximum floodfl.ow level ) •
time of rise (time period corresponding to height of rise ).and
duration of critical stage (period of time flooding is above
critical stage level).
TABLE 4
RATES OF RISE AND DURATION (Talkeetna River at Alaska Railroad Bridge)
Maximum Height Time FLOOD Rate of of of
Rise Rise Rise ft7hr ft hrs
Intermediate Regional Flood .7 8.3 l9
Standard Project Flood .8 l0.9 26
Duration of
Critical Stage hrs
60
82
Photographs. Future Flood Heights - The levels that the
Intermediate Regional and Standard Project Floods are expected
to reach at various locations in t h e village of Talkeetna .are
indicated on the following photographs.
22
,
FUTURE FLOOD HEIGHTS AT THE ROADHOUSE ON THE MAIN STREET OF TALKEETNA FIGURE 7
FUTURE FLOOD HEIGHTS AT THE TALKEETNA MOTEL AND RESTAURANT FIGURE 8
23
FUTURE FLOOD HEIGHTS AT THE B & K TRADING CO. - MAIN STREET, TALKEETNA. U. S. POST OFFICE TO THE RIGHT
FI GURE 10
24
J
FIGURE 11 - FUWRE FLOOD HEIGHTS AT l I
I
THE FAA HOUSING SI TE
1 ~----------~--------~------~
25
J
1 d
0 D
0 D
0 D
0 0 J n J
0 J:,)
J
GLOSSARY
Backwater. The resulting high water surface in a given
stream due to a downstream obstruction or high stages in an
intersecting stream.
Flood. An overflow of lands not normally covered by water
that are used or usable by man. Floods have two essential
characteristics: The inundation of land is temporary; and the
land is adjacent to and inundated by overflow from a river,
stream, ocean, lake, or other body of standing water.
Normally a "flood" is considered as any temporary rise in
streamflow or stage, but not the ponding of surface water, that
results in significant adverse effects in the vicinity. Adverse
effects may include damages from overflow of 1 and areas,
temporary backwa~er effects in sewers and local drainage
channels, creation of unsanitary conditions or other unfavorable
situations by deposition of materials in stream channels during
flood recessions, rise of ground water coincident with increased
streamflow, and other problems.
Flood Crest. The maximum stage or elevation reached by
the waters of a flood at a given location.
Flood Peak. The maximum instantaneous discharge of a
flood at a given location . It usually occurs at or near the time
of the flood crest.
Flood Plain. The areas adjoining a river, stream, water
course, ocean, lake, or other body of standing water that have
been or may be covered by floodwater.
26
Flood Profile. A graph showing the relationship of water
surface elevation to location, the latter generally expressed as
distance above mouth for a stream. of water flowing in an open
channel. It is generally drawn to show surface elevation for the
crest of a specific flood., but may be prepared for conditions at
a given time or stage.
Flood Stage. The stage or elevation at which overflow of
the natural banks of a s tream. or body of water begins in the
reach or area in which the elevation is measured.
Head Loss. The effect of obstructions such as narrow
bridge openings or buildings that limit the are_a through whfcli
water must flow, raising the surface of the water upstream from
the obstruction.
Hydrograph. A graph showing flow values against time at
a given point., usually measured in cubic feet per second. The
area under the curve indicates total volume of flow.
Intermediate Regional Flood. A flood having an. average
frequency of occurrence in the order of -one e in_ 10 0 years
although the flood may occur in any year . It is·based on
statistical analyses of streamflow records available for t h e
watershed and analyses of rainfall and runoff characteristicS
in the general region of the watershed.
Left Bank. The bank on the left side of a river, stream or
watercourse, looking downstream.
Right Bank. The bank on the right side of a river, stream.,
or watercourse, looking downstream..
Standard Project Flood. The flood that may be expected
from the most severe combination of meteorological and
27
J
1 d
0 0 0 J J 0 0 J J D [j
],-\ \._ .. )
J
hydrological conditions that are considered reasonably char
acteristic ·of- the geographical a r e a in w hi c h the drainage
bas-in is- leea-ted-., e~elucl-ing e:x:tremely ra-re eem-bin-atiens-. Peak.
discharges for these floods are generally about 40-60 percent
of the Probable Maximum Floods for the same basihs, ~As
used by the Corps of Engineers, Standard Project _Floods are
intended as practicable expressions of the degree of protection
that should be sought in the design of flood control works, the
failure of which might be disastrous.
Underclearance Elevation. The lowest point of a bridge or
other structure over or across a river, stream, or watercourse
that limits the operting through which water flow:s. This is
referred to as "low steel" in some regions.
28
c.bin • LEGEND
OVERFLOW L1 MJTS
========~I;NT~E~R~M~E~OI~AT~E~ ~ANOAAD
:-:=r:"~:~:~:~:L::.:_~_::E_=.gl_=.8o::_NA_L _ _ ) ~~g~c T
MILES ABOVE MOUTH
I T - 3 I CROSS SECTION
-250"V- GROUND ELEVATION IN FEET SEA LEVEL OATUM
LOCATION OF SUPPLEMENTAL PROFILE
NOTES
f. MAP BASED ON U.S.G.S. QUADRANGLE SHEET TALKEETNA B- 1. MINOR ADDITIONS AN D ADJUSTMENTS MADE BY CORPS OF ENGINEERS.
Z. L IMITS OF OVERFLOW SHOWN MAY VARY FROM ACTUAL LOCATION ON GROUND AS EXPLAINED IN THE REPORT.
3. AREAS OUTSIDE THE FLOOD PL AIN MAY IE SUBJECT TO FLOODING FROM LOCAL RUNOFF.
4 . MINIMUM CONTOUR INTERVAL IS 50 F T.
0
SC A LE IN FEE T
2000 --- -1" • 2100'
4000
FLOODED AREA MAP
FLOOD PLAIN INFORMATION
TALKEETNA, ALASKA
PREPAR ED BY THE
DEPARTMENT OF THE ARMY DISTRICT, CORPS OF ENGINEERS ANCHORAGE, ALASKA
JU NE 1972
PLATE 2.
LEGEND
OVERFLOW LIMITS
====~I;;N~TE~R;;M;;;E:;;D~IA;TE~l STANDARD
=-=gn'=HAN=E=~=~=L::_P_f_8_~D-N-AL __ ) ~~g~~CT
NOTES I. MAP BASED ON B.L.M. AERIAL PHOTO·
GRAPHS FLOWN AT 1500' IN 1971.
2. LIMITS OF OVERFLOW SHOWN MAY VARY FROM ACTUAL LOCATION ON GROUND AS EXPLAINED IN THE REPORT.
3. AREAS OUTSIDE THE FLOOD PLAIN MAY BE SUBJECT TO FLOODING FROM LOCAL RUNOFF.
APPROXIMATE SCALE IN FEET
0 zoo 400 -----
FLOODED AREA MAP
FLOOD PLAIN INFORMATION
TALKEETNA, ALASKA
PREPARED BY THE
DEPARTMENT OF THE ARMY
ALASKA DISTRICT, CORPS OF ENGINEERS
ANCHORAGE, ALASKA
JUNE 1972
PLATE 3
z cl
5110
375
370
365
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335
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10,000 12,000 14,0001 16,000
LEGEND - -- STANDARO PROJECT FlOOO
- - - INTERMEDIATE REGIONAL FLOOD
• • • • • AUGUST 1971 FLOOO
~ STREAM BED
ls-2J CROSS SECTION
DEPARTMENT OF THE ARMY
ALASKA DISTRICT, CORPS OF ENGINEERS
ANCHORAGE, ALASKA
FLOOD PLAIN INFORMATION TALKEETNA, ALASKA
HIGH WATER PROFILES TALKEETNA RIVER
JUNE 1912
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LEGEND
-.-.-- STANDARD PROJECT FLOOD
--- INTERMEDIATE REGIONAL FLOOD
••••• AUGUST 1971 FLOOD
Is- 2l
STREAM BED
CROSS SECTION
DEPARTMENT OF THE ARMY
ALASKA DISTRICT, CORPS OF ENGINEERS
ANCHORAGE, ALASKA
FLOOD PLAIN INFORMATION
TALKEETNA, ALASKA
HIGH WATER PROFILES
SUSITNA RIVER
JUNE 1972
PLATE 5
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0 0 0 0 0 0
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ALASKA DISTRICT, CORP~ O,F ENGINEERS ANCHORA.E, ALA~KA
I
FLOOD PLAIN· IN~ORMATION . TALKEETN~, ALASKA
SUPPLEMENTAL HI1GH WATER PROFILE
TALKEETNA RIVER: OVERFLOW I
JUNg 1972 I
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. DISTANCE IN FEET
ALASKA RAILROAD BRIDGE
360· . ..,.. .. . ~-'-t-H- __ r-=::::±. .........~-t-~ -~.....i=- ----~----··......;-:-f:i+:+j-;-+-·+ .. ::~.;::,._.. . .L....~-+-! +-~ L...LL T.;..~, ;...........,. • · __ L, ' · -~-.1-L J. · • ' · · · I I I · • 355 ·~ .. ·--,--;- ' ' I ' . i 1 j :·· ' . ~' ' ' : i ' ..
~~-+-t-t'.f·:H-: ~ '' : I II I ~-~"t: ' : I~~ • t..;...l .. L -~-r+t , ++- --'·-+-+-' ...........-t-r 4 ·-t-t--' +1--'--: I I ~ • : ; ' • t-t-~4'. ' I ' : -+ '
350 ~~~;m~m~~~~~~~~~~->-. . ~ ' <t-4' a: .......43::t!7 - Jl 0::
345. ' .}3-++ .; .. 1 .L "<1:
EE1~~Ei~~§1§~E~~-~f]· jQ:: l" "- ----t-·. ' ' 1- . ' en 1 · • . I I , ~=- -:-f+, I _j_ ; ~ II <1: ~; r-:· :::-_?~-~~-:.: 4 ~-..J
340•, ' I . . • ' • . • <t
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
N ~ V 10 ~
DISTANCE IN FEET
EAST OF ALASKA R.R. BETWEEN TALKEETNA RIVER 8 F.A.A.
c::J CC:rJ L.:.J] [2_.::IJ ~
()
LEGEND
--- Standard Project Flood --- Intermediate Regional Flood • • • • • August 1971 Flood
NOTE:
Sections taken looking downstream. Additional section$ not shown but available at Oistr:ict Office.
DEPARTMENT OF THE ARMY ALASKA DISTRICT, CORPS OF ENGINEERS
ANCHORAGE, ALASKA
FLOOD PLAIN INFORMATION TALKEETNA, ALASKA SELECTED CROSS SECTIONS
TALKEE:TNA RIVER JUN1E 1972
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wi~;~llu · lwif~ I ~~ ~r. ~lllllm~-m-mNmfm~wl 335ffFTP:!'•I I!·• IYI[jf- f llllllli]Tl - I
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I -II !j t ! I I -~ ........ : I •• I I •• ' ' I ' •• - 1 • I + ~ t i I I j I t ~ L I - ! .. -· t !--"' ... : .... :""I":' ... ;1::!\ II• ''tl· Ill I•L II! flit! .. ! I i i en 3 2 Q __ .........__. _ __;__ ~--~~~ .__ . ..........._;_;__,__ w~;_w_ ___ -- .. W-L -l- ..!_j__ .).. _,_. _ _,__ ~-L...W..-W- . .
~ 0 0 0 0 0 0 0 0 0 0 0 ~ 0 0 0 0 0 0 0 0 0 0 0 ~ 0 0 0 0 0 0 0 0 0 0 0 - N ~ V ~ ~ ~ 00 m 0 - N ~ - - -z DISTANCE IN FEET
; SUSITNA RIVER AT TALKEETNA
2 ~ ~ -' w
• I r t 1 1 t t ; 1 n·t·t 1 1-1·-tJ t.1::.: .u t·t·j ' '1 ,., ,., ·: ' : _, __ ,_, ··-·--~---·-
355rrc]~i< T . m~~'l + :liltllfi'f H--1-t--1- - .. : 350~- ~t . _ . _ tn : •. 1. ___ .. ·ri--.... __ . .r rr:r..t~-tt ____ :tttt .t+: ----- ~- --·· ·· 't- --- --- .... · ... -- - '- 1-'----i--'··1·--•t·'-H---· -- ·-----'·
- .. . t- -TT . IIi ... - -H T• t... n . - - -.. . - i -1-. -- . ~J:-!J ! -~ It jt__[J.r-. -~ I+ ': ,:f"-JlJ. -~ -=---- ---- :_:-___ :r:~-~ - Ff - - f+- : -~-+ -+· t-~tlf-"-f! 345 H: -Jr- , -j! - , - . - - . - - -I : . ,_ ,_, - + t 3 40 Ill
1
- :.1:_\- ·: -: ~- :: .... ~- :~ = : .. t. - _ ·: ~ -~ . · _ .• _- -~ ~ =T:~ :- .. : ·_ -_ ::1_ ~- ~ •: -~ -~ ~- .. ~ : .. ~- :: _ - : ~ •. -·: . r :I\
: .· - .... 1' . . . .. ·--+-\ .. -~-- .... -- - -- ___ ,_j_ I .. .. f .. - . .. - .... - .. - - - II
3351 \ --n . - - l- \ . II . - -- I - -1-1 . . - - ·I - . -1'1'1 I ' ..... -- . . I ... - .. -- ·II --. -- -i ..... +-. .. . .... I
. I I ' I ' I 'I I I I - - t . -1 I I 1 I -- ·- ···l t -l .. 1• -! ...
330 I I ' II . II ' I ill ' ' I I ' I I II ' I I ' I I ' J ' L l' I I I II ' ' 4000 5000 6000 7000
DISTANCE IN FEET
TALKEETNA RIVER 1500' ABOVE ALASKA R.R. BRIDGE
u::.J rr'''"''"~'' u.....J..U ": ... ·r')
LEGEND -.-
[L.:J} L~
(j
--- Standard.ProjectFiood --- Intermediate Re9ional Flood • • • • • AutiJust 1971 Flood
N-OTE:
Sections taken loo•ting downstream. Additional. sections not shown but available at Distl'ict Office.
DEPARTMENT OF THE ARMY ALASKA DISTRICT, CORPS OF ENGINEERS
ANCHORAGE, ALASKA
FLOOD PLAIN INFORMATION TALKEETNA, A LA.SKA SELECTED CROSS SECTIONS
TALKEETNA 8.1 SUSITNA RIVERS JUNE 1972
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c.....J c:..J [C~ l L.3l L..:] c __J t__j
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16 18 20
DEPARTMENT OF THE ARMY ALASKA DISTRICT, C:ORPS OF ENGINEERS
ANCHORAGE, AtASKA
FLOOD PLAIN INFORMATION TALKEETNA, ALASKA
SUSITNA RIVER AT TALKEETNA STANDARD PROJECT FLOOD
HYDROGRAPH JUNE: 1972
