Appendix C-Dam Breach Technical Memorandum

7/30/2019 Appendix C-Dam Breach Technical Memorandum

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Canyon Creek Meadows Dam and Reservoir

Dam Breach Analysis - DRAFT(WEST Consultants, Inc.)

Executive SummaryThe potential flood inundation from a hypothetical dam failure of Canyon Creek Meadows Damwas assessed. The dam site is located 19 miles southeast of Canyon City in Grant County,

Oregon. A dam breach of Canyon Creek Meadows Dam is expected to flow through the canyonand into the valley downstream of the dam site. From there, the flood wave will flow parallel toHighway 395 to Canyon City. The floodwaters will continue through the City of John Day and

spread out over the floodplain of the John Day River. The cities of John Day and Canyon City

will be significantly impacted by a dam breach event at Canyon Creek Meadows Dam.

Three dam breach scenarios were evaluated. 1) an overtopping failure caused by the Local Storm

Probable Maximum Precipitation (PMP) 6-hour storm event 2) an overtopping failure caused bythe General Storm PMP 72-hour storm event, and 3) a “Sunny Day” event where the dam failure

is triggered by earthquake or internal dam erosion (piping).

A hydrologic model of the Canyon Creek Meadows Reservoir and contributing drainage basin

was developed using the Hydrologic Engineering Center Hydrologic Modeling System (HEC-

HMS). The hydrologic model was used to determine the Probable Maximum Flood (PMF) inflowhydrographs from the Local PMP and General Storm PMP precipitation estimates. An unsteady

Hydrologic Engineering Center River Analysis System (HEC-RAS) hydraulic model of Canyon

Creek was developed to simulate a dam breach of Canyon Creek Meadows Dam. The model was

constructed using geometry defined by a Digital Terrain Model and field measurements, PMFinflow hydrographs, and dam breach parameters.

The Local Storm PMF, General Storm PMF, and Sunny Day failure scenarios were run toestimate maximum water surface elevations in the study area. The results were compared to the

dam breach analysis results conducted as part of the Emergency Action Plan (EAP) for Canyon

Creek Meadows Dam (ODFW 2008).

The Local PMF dam failure event provides similar results to that of the EAP dam breach

analysis. Of the three failure scenarios evaluated, the Sunny Day failure is considered the most

probable, given the conclusion of the USACE inspection report published in 1999, but results inthe least amount of flood inundation compared to the Local and General PMF events. However,

the peak discharge in Canyon Creek resulting from the Sunny Day failure is similar to the FEMA

500-year peak discharge. According to the Flood Insurance Rate Maps for the Cities of John Dayand Canyon City (FEMA 1982, 1987), the 500-year flood event causes significant flooding along

Canyon Creek.

Of the three dam breach scenarios evaluated, the maximum flood inundation is caused by failure

during the Local PMF event. For both the General PMF and Local PMF, the existing spillway

did not have adequate capacity to prevent the dam from overtopping. As a result, if the dam wasto be rehabilitated or replaced, a larger capacity spillway and/or higher dam crest elevation would

be required in order to safely pass the PMF without overtopping.



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In the vicinity of the confluence with Wickiup Creek, the overbank flood depths for the Local and

General PMF are expected to be 19.6 feet and 13.6 feet, respectively. Approximately 2,500 feetupstream of the confluence with Vance Creek, the overbank flood depths for the Local and

General PMF are expected to be 17.8 feet and 11.0 feet, respectively. In Canyon City, the

overbank flood depths for the Local and General PMF are expected to be 11.0 feet and 6.9 feet,

respectively. In the vicinity of the Grant Union High School in John Day, the overbank flood depths for the Local and General PMF are expected to be 8.4 feet and 5.3 feet, respectively.

Further downstream, in the vicinity of the John Day fairgrounds, the overbank flood depths for the Local and General PMF are expected to be 3.6 feet and 2.1 feet, respectively. Significantflooding would occur in the communities of Canyon City and John Day for both PMF events. As

a result, it is expected that significant property damage and loss of life would occur.

IntroductionCanyon Creek Meadows Dam is classified as high hazard structure by the Oregon Water

Resources Department Dam Safety Program. Due to this classification, the appropriate designinflow flow for conducting a dam breach analysis is the Probable Maximum Flood (PMF) event.

The PMF is the flood associated with the Probable Maximum Precipitation (PMP), which is

theoretically the greatest depth of precipitation for a given duration that is physically possible

over a particular geographic location at a certain time of year.

For this study, the PMP calculations were developed using the latest methodology outlined in

Hydrometeorological Report (HMR) No. 57 (NWS, 1994). A Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) model of the Canyon Creek watershed was created to

estimate the PMF event inflow hydrograph to the reservoir formed by Canyon Creek Meadows

Dam.

Breach parameters for the dam were estimated using several regression equations appropriate to

the type and size of the involved dam and reservoir. An unsteady HEC-RAS hydraulic model of Canyon Creek was developed. The dam breach analysis of Canyon Creek extends approximately

24 miles, from Canyon Creek Meadows Dam to approximately 500 feet upstream of theconfluence with the John Day River.

Three dam failure scenarios were evaluated. Dam failure scenarios evaluated included the

General and Local PMF inflows as well as a “Sunny Day” failure. A General PMF is the

maximum flow that could result from the General PMP, which is the theoretical maximum total precipitation resulting from a 3-day storm that occurs over an area of up to 10,000 square miles.

A Local PMF is the maximum flow that results from the Local PMP, which is the theoretical

maximum precipitation resulting from a 6-hour storm that occurs over an area of less than 500square miles. A “Sunny Day” failure assumes failure of the dam by means other than a storm

induced flood event, such as a failure triggered by earthquake or internal dam erosion (piping).

Each failure scenario produced by this study was compared to the dam breach analysis results

conducted as part of the Emergency Action Plan (EAP) for Canyon Creek Meadows Dam. TheEAP was published in 2008 by the Oregon Department of Fish and Wildlife (ODFW). The dam

breach analysis developed for the EAP used “FLDWAV”, a generalized flood routing program

developed by the National Weather Service.



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Dam and Channel Characteristics

Dam and Reservoir

Canyon Creek Meadows Dam is located on Canyon Creek approximately 19 miles southeast of

Canyon City in Grant County, Oregon. The dam is situated in the Malheur National Forest and is

owned and operated by the ODFW. The purpose of the reservoir created by Canyon Creek Meadows Dam is for recreation. A location map is shown in Appendix A. The Dam was

designed and constructed by the Oregon State Game Commission, now known as the ODFW, and

was completed in November 1963.

The dam is located within Section 29, Township 15 South, Range 33 East, Willamette Meridian.

Canyon Creek is a tributary of the John Day River and the confluence is approximately 24 stream

miles below the dam location. Failure of Canyon Creek Meadows Dam could result indownstream loss of life and substantial property damage. The location of the dam is shown in

Figure 1.

The dam is a zoned rock-fill structure approximately 165 feet in length, with a maximum heightof 53 feet, and a crest width of 15 feet. Total storage volume at normal pool elevation is 271

acre-feet. The contributing basin area to Canyon Creek Meadows Dam is 6.2 square miles, based

on United States Geological Survey (USGS) Quadrangle Maps. Land cover in the basin is primarily pine forest. The watershed varies in elevation from about 5,050 ft (NGVD29) at the

reservoir site to 7,650 feet (NGVD29) along the watershed boundary.

The dam is located at the west end of the reservoir and the pool elevation is maintained by a

gated outlet. The regulating outlet is an 18-inch diameter corrugated metal pipe with a slide gate,

and is located along the centerline of the channel at the upstream toe of the dam. The spillwayconsists of an uncontrolled, gunite lined side-channel spillway with a crest elevation of 5,045 feet

(NGVD29) and a crest length of approximately 30 feet.

When the reservoir was first filled in 1964, dam leakage was observed (ODFW 2008). Typically,

the reservoir was completely drawn down by the late summer because of the dam leakage.

Subsequently, inspections revealed both the north and south abutments leaked. A grout curtain

and impermeable blanket were placed upstream of the south abutment in 1966 and 1967 but did not seem to reduce leakage. In November 1998, the U.S. Army Corps of Engineers (USACE)

inspected the dam and found the dam in an “unsatisfactory condition” (USACE, 1999).

However, in the USACE report notes there is “a risk of a relatively rapid failure” and that itshould not be left in its current condition for more than a few seasons (USACE, 1999). As a

result, the 18-inch outlet gate was locked open so the reservoir would no longer be allowed to

retain a pool for an extended period of time. During a site reconnaissance on June 18, 2009, thereservoir was observed to be dry, with the exception of minor flow in the stream channel.

Stream Channel

Downstream of Canyon Creek Meadows Dam, Canyon Creek enters a confined canyon with a

slope of approximately 3 percent. The creek is confined by the canyon for approximately 5 milesand has an average bottom width of 10-15 feet. Canyon Creek then enters a valley varying from

100 to 800 feet in width. The slope decreases to 1-percent and the average stream width is

approximately 25 feet. This reach of Canyon Creek would have been naturally unconfined and



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connected with the floodplain. However, due to past land use practices, sections of this reach

have been relocated to the toe of the valley wall and/or against the roadway embankment.



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Figure 1. Location of Canyon Creek Meadows Dam.



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The stream flows through the relatively wide and flat valley for approximately 12 miles before

entering a second canyon. The gradient increases to an average of 2-percent and stream channelvaries from 25 to 30 feet in width. The stream channel is confined by the steep canyon to the

west and US Highway 395 to the east. The stream flows through the narrow canyon for

approximately 3 miles before entering Canyon City. At this point, the gradient lessens to 1-

percent as the stream enters a somewhat wider portion of the valley where Canyon City islocated. From Canyon City to the confluence of the John Day River, the channel is entrenched

and a significant portion of the banks are protected by riprap. The stream continues through theCity of John Day and transects the John Day River floodplain until it reaches the confluence,approximately 24 stream miles below the dam.

Data Collection

Topographic Data

A 30-m seamless Digital Elevation Model (DEM) for the area along with an aerial image of the

Canyon Creek drainage basin was obtained from the USGS National Map Seamless Server

through the website at (http://seamless.usgs.gov/index.php). All digital data have a North

American Datum 1927 (NAD27) horizontal datum and Universal Transverse Mercator (UTM),Zone 11N projection. The DEM was extracted in the form of a grid and used to define the terrain

of the site.

Field Survey

A detailed survey of the lower portion of the reservoir and Canyon Creek Meadows Dam was

performed in September 2009 by John Thompson and Associates, Inc. A DTM was extracted from the survey data and used to define the reservoir and dam geometry in the hydraulic model.

Field Reconnaissance

A field reconnaissance was conducted by WEST Consultants in September, 2009. Field

observations were made of the channel and overbank of Canyon Creek, from the outlet of Canyon Creek Meadows Dam to the confluence of the John Day River. Canyon Creek was

divided into several reaches, based on stream gradient and valley width, and representative

channel geometry was approximated for each of the stream reaches. Channel and overbank roughness characteristics were also noted for each reach. Approximate dimensions of major

hydraulic structures, such as bridges and culverts, were recorded during the field reconnaissance.

Hydrologic Model Development

General Methodology

An HEC-HMS model of Canyon Creek watershed was developed to provide PMF inflowhydrographs to the reservoir. The PMP was derived using the methodology presented in National

Weather Service (NWS) HMR 57, “Probable Maximum Precipitation – Pacific NorthwestStates.” (NWS, 1994)

Development of Probable Maximum Precipitation (PMP)

HMR 57 provides a process for determining the PMP for two different conditions, the General

and Local Storm PMP. The General Storm procedure estimates the PMP for a storm duration of 3 days for areas covering up to 10,000 square miles. The Local Storm PMP estimates the PMP



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for a storm duration of 6 hours for areas covering less than 500 square miles. HEC-HMS was

used to determine the flood hydrographs for the PMF. The Soil Conservation Service (SCS)Curve Number loss method was used to estimate rainfall excess as a function of total

precipitation, soil type, land cover, land use, and antecedent moisture conditions.

The total drainage area of Canyon Creek is 116 square miles. The contributing area upstream of Canyon Creek Meadows Dam is 6.2 square miles. Both the General Storm PMP and Local

Storm PMP consider only the contributing area of the watershed upstream of Canyon Creek Meadows Dam. The drainage basin above Canyon Creek Meadows Dam is shown in Figure 4.

The all-season General Storm PMP for the basin was estimated to be 11.5 inches for the 24 hour

period of maximum rainfall. This value was obtained from the General Storm 10-mi2, 24-hour

PMP index map (Map 4-SW in HMR 57). The incremental estimates and temporal distribution

of the General Storm PMP for a 72-hour duration were determined using the methodology

outlined in HMR 57. The General Storm PMP hyetograph for all contributing basins as

presented in Figure 2 was entered as time-series rainfall data in HEC-HMS.

.

Figure 2. General Storm PMP Hyetograph for the Canyon Creek Meadows Dam Basin.

The Local Storm PMP for the basin was estimated to be 8.8 inches for the 1 hour period of

maximum rainfall. This value was obtained from Figure 15.36 in HMR 57, the 1-hour 1-mi2

local storm PMP index map. The temporal distribution of the Local Storm PMP was determined using the methodology outlined in HMR 57. The resultant Local Storm PMP hyetograph for the

Canyon Creek watershed is presented in Error! Reference source not found. and was entered astime-series data in HEC-HMS. Conservative values for input parameters such as Manning’s n

values for overland and shallow concentrated flow paths, SCS curve numbers for various



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antecedent moisture conditions, and time of concentration were used to define the PMF

hydrograph.

The General Storm PMF peak discharge to the Canyon Creek Meadows Reservoir was

determined to be 3,954 cfs, with a total hydrograph volume of 5,553 acre-ft. The Local Storm

PMP analysis produced a PMF of 25,433 cfs, with a total hydrograph volume 2,642 acre-ft.

Figure 3. Local Storm PMP Hyetograph for the Canyon Creek Meadows Dam.



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Figure 4. Canyon Creek Meadows Dam Contributing Basin.



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Hydraulic Model Development

General Methodology – Objective of the Model

HEC-RAS version 4.0 was used to conduct the dam breach analysis for Canyon Meadows Dam.

It is a one-dimensional unsteady flow routing model capable of integrating complex channels and structures under dynamic hydrologic conditions. HEC-RAS also has the capability to model dam

breach events under a wide range of scenarios. Cross sections, stream centerlines, and other

geometric features of the stream were extracted from available topographic data using HEC-GeoRAS and ArcGIS. Dam failure scenarios were analyzed for the Sunny Day and Probable

Maximum Precipitation (PMP) meteorological events. The objective of the modeling effort was

to define the potential impact of a dam breach on downstream reaches including the higher

populated areas of Canyon City and the City of John Day, which are located approximately 19miles and 21 miles downstream, respectively.

Geometry

The HEC-RAS model of the Canyon Creek study area consists of one storage area, one reach and

sixteen structures. The reservoir above the dam was modeled as storage area with a lateral inflow

from the contributing 6.2 mi2

watershed upstream of the dam. The stage-storage relationship for

the reservoir was obtained from Phase I Inspection Reports (OWRD, 1980). HEC-GeoRAS,Version 4.1.1, was used as an extension to ArcGIS to generate the Stream Centerline and cross

sections for the HEC-RAS model of Canyon Creek. A plan view of the HEC-RAS Model is

shown in Figure 5.

Cross Sections

Cross sections are used to define the shape of the stream channel, adjacent floodplain and characteristics such as roughness, flow expansion and contraction, and ineffective flow areas. A

total of 204 cross sections were used in the hydraulic model of Canyon Creek. The cross sections

were extracted from the USGS DEMs using HEC-GeoRAS and supplemented with field reconnaissance measurements for the channel geometry. The cross sections were located to

adequately describe geometric features such as hydraulic roughness changes, grade breaks, and flow expansion and contraction. The cross sections are generally oriented perpendicular to theexpected flow lines of the maximum flood wave.

Structures

Sixteen bridge/culvert structures are represented in the Canyon Creek HEC-RAS model. Onlystructures which could withstand or impede a flood wave caused by a dam breach were

represented in the hydraulic model. These structures include the four culvert and embankment

crossings in the Malheur National Forest for Forest Roads NFD 1539, NFD 15, NFD 1516, and NFD 6500-366; County Road 65 bridge located 10 miles downstream of the dam; US Highway

395 bridge located 16 miles downstream of the dam; seven bridges in Canyon City which include

crossings at Adam Road, Bridge Street, Izee Street, Main Street, Portal Street, Nugget Street and Inland Street; and three bridges in the City of Canyon City which include 2nd

Avenue, 4th

Avenue, and Main Street / US 395. The HEC-RAS geometry for the structures was derived fromfield measurements and aerial photography.

Canyon Creek Meadows Dam was defined as an in-line structure. The HEC-RAS model damgeometry is derived from field survey data, as well as data obtained from the Phase I Inspections

Report (OWRD, 1980). Data for components such as outlet works, embankment side slopes,

culvert and bridge coefficients, etc. were entered directly into the HEC-RAS model.



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Roughness Values

Manning’s n-value ranged from 0.05 to 0.07 for the main channel and 0.06 to 0.1 for overbank

areas. For the Local PMP storm event the Manning’s n-value for the main channel ranged from

0.06 to 0.07 for the main channel and 0.1 for the overbank in order to reflect the dynamic and

extreme nature of a dam breach flood wave, the heavy amount of woody debris within thechannel, and to provide numerical stability to the hydraulic model. Manning’s n-values were

based on published values for similar conditions (Chow, 1959; Barnes, 1987), on Jarrett’sRoughness Equation for steep streams (Jarrett, 1984), and on engineering judgment and experience.

External Boundary Conditions

For unsteady flow models, upstream boundary conditions are typically input as discharge

hydrographs. The input hydrographs for the Canyon Creek Meadows Dam Brach model

represent the Local PMF and General PMF flood events developed in HEC-HMS. The

downstream boundary condition was set to normal depth using a slope of 0.009 measured fromthe DEM.



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Figure 5. Plan View of Canyon Creek HEC-RAS Model Geomet



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Dam Breach Analysis

Dam Failure Scenarios

Three possible dam breach events were evaluated; 1) Sunny Day, 2) Local Storm PMF, and 3)

General Storm PMF. Both PMF events consider a storm event contributing to only the watershed upstream of Canyon Meadows Reservoir. The Sunny Day event consists of a piping failure of

the dam while the reservoir pool is approximately one foot above the spillway crest. For both the

Local Storm and General Storm PMF events, the spillway was shown to be inadequate to passthese flood events without overtopping the dam. Therefore, an overtopping failure scenario was

used.

Failure Characteristics

Because dam failure is a hypothetical event, the actual breach size, location, and timing are

unknown and must be estimated. A range of potential breach sizes and formation times were

considered. Additionally, the location of the breach and the breach initiation must be assumed.For Canyon Creek Meadows Dam, the most conservative failure scenario is an overtopping

failure located above the deepest point in the reservoir.

Determination of Breach ParametersThe parameters needed for the HEC-RAS dam breach model are breach shape, breach width,

time to failure, pool elevation at time of failure, and breach side slope. The reservoir is

impounded by an earthen dam, a trapezoidal breach growing linearly with time was assumed.Dam breach parameters were calculated for both overtopping and piping failure mechanisms.

Breach width and time to failure were calculated using the various equations and methodologies

listed in Table 1.

Table 1. Equations used for breach parameter calculations.

Reference Breach Width (m) Failure Time (hr)

Bureau of Reclamation (1982) wh B 3= Bt 011.0=

MacDonald & Langridge-Monopolis(1984)

769.0)(0261.0 wwer hV V = for Earth

fill dams

364.00179.0 er V t =

Von Thun & Gillette (1990) bw C h B += 5.2

wht 015.0=

easily erodible, based on head

)614( +=

wh Bt

Easily erodible, based on head and width

Froehlich (1995)19.032.0

1803.0 bw hKV B = 9.053.0

00254.0−

= bw hV t

Federal Energy Regulatory

Commission (FERC) (1998) 2 to 4 times the dam height

0.1 to 1.0 for engineered, compacted

Earth dams

0.1 to 0.5 for non-engineered, poor

construction Earth dams

B = average breach width (m)

t = failure time (hr)Ver = volume of embankment material eroded (m3)

hw = height of water above breach invert at time of failure (m)

Vw = volume of water stored above breach invert at time of failure (m3)

C b = offset factor, a function of reservoir volume (for reservoirs < 1.23*106, C b = 6.1 m)

K = overtopping multiplier (1.4 for overtopping failure and 1.0 for piping failure)h b = height of breach (m)



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The elevation of the reservoir pool at the time of failure for an overtopping failure can range from

0.3 to 1.5 m (1 to 5 feet) above the dam crest (Federal Energy Regulatory Commission, 1998).The FERC guidelines also state that the breach side slope for an engineered, compacted, earthen

dam can range from 0.25:1 to 1:1 (H:V). However, since there was a physical limitation to the

bottom width of the breach, the side slopes were made shallower to more closely match the

geometry of the valley side slopes, which are 1:1 along the left bank and 1.2:1 along the right bank.

Table 2 presents a summary of dam breach parameters assumed for Canyon Creek MeadowsDam. The breach parameters selected were the most conservative, yet realistic values calculated

from the available equations shown in Table 1. These parameters produced the highest expected

peak flow from the breach. A cross section of the dam which shows the breach geometry isshown in Figure 6.

Table 2. Canyon Creek Meadows Dam Breach Parameters.

Dam height (ft) 48.8

Full formation time (hours) 0.35

Side slope (H:V) left 1:1, right 1.2:1Bottom of breach width (ft) 5

Figure 6. Dam Breach Geometry

Breach

Spillway



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Dam Breach ResultsThe results of the three HEC-RAS dam breach scenarios and the EAP dam breach analysis for selected locations are summarized in Table 3. Water surface elevations from the HEC-RAS dam

breach model at cross section locations similar to that in the EAP and water depths estimated

from the EAP report are shown in Figure 7 through 11.

Table 3. Canyon Creek Meadows Dam Breach Results.

Sunny Day General PMF Local PMF EAP(ODFW 2008)

Canyon Creek Meadows Dam

Peak outflow (cfs) 14,950 20,309 38,279 101,000

Peak depth (ft) 40.3 50.2 53.9 56

EAP Section 2 – Wickiup Camp (2,000 ft upstream of Wickiup Creek confluence)

Peak flow (cfs) 7,884 17,106 31,349 ---1

Maximum channel depth (ft) 10.5 15.0 21.0 ---2

Maximum overbank depth (ft) 9.1 13.6 19.6 16.2

Time of peak (hours) 1.0 0.8 0.8 ---1

EAP Section 3 – Hot Springs (2,500 ft upstream of Vance Creek confluence)

Peak flow (cfs) 2,623 9,546 19,713 ---1




EAP Section 5 – Canyon City (southern corporate limit)

Peak flow (cfs) 2,254 8,378 16,995 ---1




EAP Section 6 – John Day at Grant Union H.S.

Peak flow (cfs) 2,155 8,064 16,542 ---1



Time of peak (hours) 5.3 4.0 3.9 2.54

EAP Section 7 - John Day fairgrounds

Peak flow (cfs) 2,020 7,790 15,268 ---1



Time of peak (hours) 5.8 4.3 4.2 3.34

1 Data not available.

2 EAP cross section did not include channel geometry.

It should be noted that the geometry used for the EAP dam breach analysis is different than the

HEC-RAS dam breach model geometry. The EAP geometry was estimated directly from USGS

Quadrangle maps on which the channel geometry is not well defined. This is apparent from the



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cross section figures shown in Section V of the EAP (ODFW, 2008). For the updated dam

breach analysis, the hydraulic cross sections were extracted from USGS 30-meter DEMs usingHEC-GeoRAS and then supplemented with observed channel geometry. Further, the HEC-RAS

geometry provides a more detailed representation of the actual stream and overbank geometry of

Canyon Creek. The updated analysis includes 204 cross sections and 16 hydraulic structures,

while the EAP FLDWAV analysis used only seven cross sections (ODFW 2008). The moreaccurate representation of the channel, floodplain, and hydraulic structures creates more

backwater and ineffective flow areas, and thus, increases the time of flood wave arrival in thecommunities of Canyon City and John Day. Since the cross section geometries of the two dam breach analyses are not directly comparable, only maximum overbank depths for the EAP

analysis are shown in Table 3.

As seen in Table 3, the EAP dam breach analysis provides similar results to that of the HEC-RAS

results for the Local PMF, even though the peak outflow for the EAP analysis (101,000 cfs) is

significantly larger than the HEC-RAS dam breach model results (38,279 cfs).

Of the three failure scenarios evaluated, the Sunny Day failure is considered the most probable,

given the conclusion of the USACE inspection report published in 1999, but causes the least

amount of flood inundation compared to the Local and General PMF events. However, floodingcaused by a Sunny Day failure is still considered significant. The Flood Insurance Study (FIS)

for the City of Canyon City (FEMA, 1987) lists flood discharges for Canyon Creek as 1,600 cfs

for the 100-year flood event and 2,000 cfs for the 500-yr flood event. As seen in Table 3, the peak discharges for the Sunny Day event are similar to the FEMA 500-year peak discharge.

According to the Flood Insurance Rate Maps for the Cities of John Day and Canyon City

(FEMA, 1982 & 1987), the 500-year flood event causes significant flooding along Canyon

Creek.

The maximum flood inundation is caused by failure during the Local PMF event which results

from a relatively large amount of precipitation over a relatively short six hour period. For both

the General PMF and Local PMF, the existing spillway did not have adequate capacity to preventthe dam from overtopping. As a result, if the dam was to be rehabilitated or replaced, a larger capacity spillway and/or higher dam crest elevation would be required in order to safely pass the

PMF without overtopping.



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500 600 700 8004300

4310

4320

4330

4340

4350

Canyon Meadows Dam Breach Plan: 1) Local PMF 10/16/2009 2) sunny 10/16/2009 3) general 10/16/2009

Station (ft)

E l e v a t i o n

( f t )

Legend

WS MaxWS - Local PMF

WS MaxWS - general

WS MaxWS - sunny

Ground

Ineff

Bank Sta

.1 .07

.1

Figure 7. HEC-RAS cross section near EAP Section 2 (Wickiup Camp).

500 600 700 8003875

3880

3885

3890

3895

3900

3905


Station (ft)

E l e v a t i o n

( f t )

Legend

WS MaxWS - Local PMF

WS MaxWS - general

WS MaxWS - sunny

Ground

Bank Sta

.1 .065 .1

Figure 8. HEC-RAS cross section near EAP Section 3 (Hot Springs).

Estimated EAP depth (16.2 ft)




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100 200 300 400 5003220

3230

3240

3250

3260

3270

3280


RS =16580.2*

Station (ft)

E l e v a t i o n (

f t )

Legend

WS Max WS - Local PMF

WS Max WS - general

WS Max WS - sunny

Ground

Bank Sta

.1 .06 .1

Figure 9. HEC-RAS cross section near EAP Section 5 (Canyon City).

200 300 400 500 600 700 800 9003140

3150

3160

3170


RS =7888

Station (ft)

E l e v a t i o n (

f t )

Legend


WS Max WS - general

WS Max WS - sunny

Ground

Bank Sta

.1 .06 .1

Figure 10. HEC-RAS cross section near EAP Section 6 (John Day at Grant Union H.S.).





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500 1000 1500 2000 2500 30003070

3075

3080

3085

3090


RS =1315

Station (ft)

E l e v a t i o n (

f t )

Legend


WS Max WS - general

WS Max WS - sunny

Ground

Bank Sta

.1 .06

.1

Figure 11. HEC-RAS cross section near EAP Section 7 (John Day Fairgrounds).




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REFERENCES

Barnes, H. H. Jr., 1987. “Roughness Characteristics of Natural Channels,” U.S. Geological

Survey Water-Supply Paper 1849.

Chow, VT, 1959. Open Channel Hydraulics, McGraw-Hill Book Company, New York, NY.

Evans, S. G., 1986. “The Maximum Discharge of Outburst Floods Caused by the Breaching of Man-Made and Natural Dams,” Canadian Geotechnical Journal, vol. 23, August 1986.

Federal Emergency Management Agency, Flood Insurance Study, City of Canyon City, Grant

County, Oregon, September 18, 1987

Federal Emergency Management Agency, Flood Insurance Study, City of John Day, Grant

County, Oregon, Revised February 23, 1982

Federal Emergency Management Agency, Flood Insurance Rate Map, Panel No. 410075 0001B,

City of Canyon City, Grant County, Oregon, September 18, 1987

Federal Emergency Management Agency, Flood Insurance Rate Map, Panel No. 410077 0001,

City of John Day, Grant County, Oregon, Revised February 23, 1982

Federal Energy Regulatory Commission, 1988. “Engineering Guidelines for the Evaluation of

Hydropower Projects,” FERC 0119-1, Office of Hydropower Licensing, July 1987, 9p,revised in 1998.

Froehlich, D. C., 1995. “Embankment Dam Breach Parameters Revisited”, in: Water Resources

Engineering, 1995 ASCE Conference, San Antonio, TX, August 14-18, 1995, p. 887-891.

Jarrett, R. D., 1984. “Hydraulics of High-Gradient Streams,” Journal of Hydraulic Engineering,

Vol. 110, No. 11.

John Thompson and Associates, Canyon Creek Meadows Dam Topography, 1-foot Contours,

September 9, 2009

MacDonald, T. C. and Langridge-Monopolis, J., 1984. “Breaching Characteristics of DamFailures,” Journal of Hydraulic Engineering, Vol. 110, No. 5, p. 567-586.

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HEC-RAS , Training Manual, 2007

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Documents

Appendix C-Dam Breach Technical Memorandum