Revised_RiverS_APP_D.pdf

APPENDIX C

Proposed Bridge/Riprap Layout

L A

K E R

IV

E R

CITY OF RIDGEFIELD RIVER 'S'

RIDGEFIELD NWR

N

B N

S F

CUYD

EXC.

CUYD

EMB.

17+0015+0013+0011+00 9+00 7+00 5+00

0 0

40 40

80 80

120 120

160 160

200 120

STATE PROJECT

NUMBER

SHEET

P

M

A p r il

U

S S u r

D c m y fi le s p w p r o d u c ti o n d R

R P

P .d g n

C h e c k e d b y

D e s ig n e d b y

(Design TBD) Rock buttress

(Design TBD) Toe of 1:3 fill slope

(Design TBD) MSE wall

(Design TBD) Rock buttress

T

16886

UP

24" CEDAR 118° 28.15 FT

9" CEDAR 008° 43.84 FT

14" CEDAR 340° 47.82 FT

075° 10.88 FT

ELEV 20.98

24" CONCRETE OUTLET

ELEV

44.12

24" CMP INLET

ELEV 86.53

ELEV 83.29

E L E

V

E L E

V

S P

E E

D L I

M I T

NWR AREA CLOSE

RR CROSSING

F E E I

N F

O

AUTHORIZED VEHICLES ONLY

24" COTTONWOOD

32" COTTONWOOD

32" COTTONWOOD

24" COTTONWOOD

18" COTTONWOOD

18" COTTONWOOD

14" COTTONWOOD14" COTTONWOOD

16" COTTONWOOD

32" COTTONWOOD

24" MAPLE

14" ALDER40" FIR

12" MAPLE

42" FIR

42" FIR

30" MAPLE SNAG

18" CEDAR

14" MAPLE48" FIR

14" CEDAR

20" MAPLE

24" MAPLE

22" MAPLE22" MAPLE

14" MAPLE

36" CEDAR16" FIR

18" CMP

S

T E E L

T O M

IN

IM

IZ

E D

IS

T U

R B

A N

C E

S T

A Y I

N C

A R

CP

12107

SET H&T

CP

12108

SET H&T

CP

22103

IR

1/2" IR NO CAP

CP

13552

CP

22103

CP

13551

OHWL

Elev 14.58

OLWL

Elev 0.98

10+02.77 10+58.37

@time of survey Elev 7.10

Btm Exist. Bridge Elev 39.10

.2

T r a c k C

L

R t

66.67 Top of west cantilever signal

70.33 Top of west cantilever signal support

78.98 Top of west signal gate arm

12+94.32 Elev 47.00 (Track high PT, 16' Lt)

CL of closest track 25' Min. clearance to

47.00' (Base Elev. used for determining min. vert. clearance)

Exist ground, 16' Lt

Exist ground, CL

Exist ground, 16' Rt

71.00 Bottom of girder

77.00 Top of Deck @CL (assumes 6' structure depth)

13+40.00

6 7 8

11 12 13 14

16 17

.2

B

N S

F R

O W

C L

.2

B

N S

F R

O W

C L

.0

F a c e o f

M S

E w a ll

.0

C

L o f d r il le d s h a ft

.6

B a c k p a v e m e n t s e a t

12.71'

1:1.5

.4

+8.0000%

104' VC

.5

+8.0000%

60' VC

.5

+0.0000%

60' VC

.7

-8.0000% +14.34

83%

250' VC

.0

D r ii le d s h a ft l o c a ti o n

.0

D r ii le d s h a ft l o c a ti o n

.0

D r ii le d s h a ft l o c a ti o n

D r ii le d s h a ft l o c a ti o n

.0

B o r in g L o c a ti o n

APPENDIX D

Scour Analysis

Riprap Analysis

Velocity Calculations (FHWA, Hydraulic Toolbox Results)

Water Surface Elevations (Flood Profiles, 16P, Flood Insurance Study 53011CV001A)

Scour Analysis

SCOUR ESTIMATE

Project: Design for River S Bridge Replacement, WA RRP RIDG 100(2) File:

Desc: Lake River Date:

Units: ENG By:

Location Description

Check abutment scour along wingwall first. If undermined, wingwall and pipe pile will perform as pier and pier scour will control maximum scour depth.

-Y

E A

R

-Y

E A

R

-Y

E A

R

-Y

E A

R

CONSTANTS

UNITS SI or ENG ENG ENG ENG ENG g ACCELERATION OF GRAVITY, 9.81 m/s2, 32.2 ft/s2 32.20 32.20 32.20 32.20

Du D UNIT CONVERSION, 0.001 SI, 0.00328 English 0.00328 0.00328 0.00328 0.00328

LIVE-BED OR CLEAR-WATER DETERMINATION

y AVERAGE FLOW DEPTH, m, ft 27.0 29.5 27.0 29.5

D50 DIAMETER 50% FINER BED PARTICLES, mm 10 10 10 10

V AVERAGE VELOCITY, m/s, ft/s 1.5 1.6 1.5 1.6

Ku UNIT COEFFICIENT, 6.19 SI, 11.17 English 11.170 11.170 11.170 11.170

Vc (5.1) CRITICAL VELOCITY, m/s, ft/s 6.20 6.29 6.20 6.29

LB / CW LIVE BED or CLEAR WATER CW CW CW CW

LIVE-BED CONTRACTION SCOUR

y1 AVERAGE U/S DEPTH, MAIN CHANNEL, m, ft 8.0 12.5 27.0 29.5 y0 AVERAGE CONTRACTED DEPTH BEFORE SCOUR, m, ft 8.0 12.5 27.0 29.5

Q1 FLOW IN UPSTREAM CHANNEL, m3/s, ft3/S 3878.0 6372.0 9990.0 10915.0

Q2 FLOW IN CONTRACTED CHANNEL, m3/s, ft3/S 500.0 500.0 9990.0 10915.0

W1 WIDTH OF THE UPSTREAM CHANNEL, m, ft 379.0 379.0 300.0 300.0

W2 WIDTH OF THE CONTRACTED SECTION, m, ft 55.0 55.0 300.0 300.0

S1 ENERGY SLOPE OF MAIN CHANNEL, m/m, ft/ft 0.0001 0.0001 0.0001 0.0001 w (Fig 6.8) D50 FALL VELOCITY, m/s 0.500 0.500 0.500 0.500

UNIT COEFFICIENT, 1.0 SI, 3.28 English 3.28 3.28 3.28 3.28

D50 FALL VELOCITY, m/s, ft/s 1.640 1.640 1.640 1.640 k1 (p5.11) TRANSPORT COEFFICIENT 0.59 0.59 0.59 0.59

BED MATERIAL TRANSPORT MODE BL BL BL BL

V* SHEAR VELOCITY, m/s, ft/s 0.16 0.20 0.29 0.31 y2 (5.2) AVERAGE DEPTH, CONTRACTED SECTION, m, ft 4.32 4.41 27.00 29.50 yS (5.3) AVERAGE SCOUR DEPTH, m, ft 0.00 0.00 0.00 0.00

As AVERAGE SCOUR AREA, m2, ft2 0.00 0.00 0.00 0.00 scour18-4-1.xls

4/15/2014

M. Frye

Left Overbank Main Channel

CLEAR-WATER CONTRACTION SCOUR

y0 AVERAGE CONTRACTED DEPTH BEFORE SCOUR, m, ft 8.0 12.5 27.0 29.5

D50 MEDIAN DIAMETER BED MATERIAL, mm 10 10 10 10

Q DISCHARGE THROUGH THE BRIDGE, m3/s, ft3/s 500.0 500.0 9990.0 10915.0

W BOTTOM WIDTH OF THE CONTRACTED SECTION, m, ft 240.0 240.0 370.0 370.0

Ku UNIT COEFFICIENT, 0.025 SI, 0.0077 English 0.0077 0.0077 0.0077 0.0077

Dm DIA. SMALLEST NONTRANSPORT PARTICLE, m, ft 0.0410 0.0410 0.0410 0.0410 y2 (5.4) AVERAGE DEPTH, CONTRACTED SECTION, m, ft 0.58 0.58 5.22 5.63 yS (5.5) AVERAGE SCOUR DEPTH, m, ft 0.00 0.00 0.00 0.00

As AVERAGE SCOUR AREA, m2, ft2 0.00 0.00 0.00 0.00

PRESSURE FLOW CONTRACTION SCOUR

Hb DISTANCE LOW CHORD TO STREAM BED, m, ft y1 FLOW DEPTH UPSTREAM FACE OF BRIDGE, m, ft

D50 D50 OF BED MATERIAL IN OPENING, mm

Va AVERAGE VELOCITY THROUGH OPENING, m/s, ft/s

Ku UNIT COEFFICIENT, 6.19 SI, 11.17 English 11.170 11.170 11.170 11.170

Vc (5.1) CRITICAL VELOCITY, m/s, ft/s 0.00 0.00 0.00 0.00 ys VERTICAL SCOUR DEPTH, m, ft #DIV/0! #DIV/0! #DIV/0! #DIV/0!

PIER SCOUR

y1 FLOW DEPTH U/S OF THE PIER, m, ft 27.0 29.5

V1 APPROACH VELOCITY, m/s, ft/s 1.5 1.6 a PIER WIDTH, m, ft 3 3

L PIER LENGTH, m, ft 3 3

FA FLOW ANGLE, degrees 0 0

K1 (Tbl 6.1) CORRECTION FOR PIER SHAPE (0.9 to 1.1, >5deg, 1) 0.9 0.9

K3 (Tbl 6.3) CORRECTION FOR BED FORM (1.1 to 1.3) 1.1 1.1

K4, BED ARMORING, D50 > 2 mm and D95 > 20 mm

D50 DIAMETER 50% FINER BED PARTICLES, mm 10 10

D95 DIAMETER 95% FINER BED PARTICLES, mm 3.0 3.0

Ku UNIT COEFFICIENT, 6.19 SI, 11.17 English 11.17 11.17 11.17 11.17

Vc50 (6.8) CRITICAL VELOCITY D50, m/s, ft/s 0.00 0.00 6.19 6.29

Vc95 CRITICAL VELOCITY D95, m/s, ft/s 0.00 0.00 4.15 4.21

Vic50 (6.7) INCIPIENT VELOCITY NEAR PIER D50, m/s, ft/s 0.00 0.00 3.14 3.19

Vic95 INCIPIENT VELOCITY NEAR PIER D95, m/s, ft/s 0.00 0.00 1.98 2.01

Vr (6.6) VELOCITY RATIO 0.00 0.00 0.00 0.00

K4 (6.5) CORRECTION FOR ARMORED BED (>0.4) 0.00 0.00 1.00 1.00

K2 (6.4) CORRECTION FOR FLOW ANGLE (1 to 5) 0.00 0.00 1.00 1.00 yS (6.3) SCOUR DEPTH, m, ft 0.00 0.00 3.61 3.74

L/a PIER LENGTH/WIDTH RATIO (MAX. L/a = 12)) 0.00 0.00 1.00 1.00

Fr FROUDE RATIO 0.00 0.00 0.05 0.05

ABUTMENT SCOUR

L' LENGTH OF OBSTRUCTION, m, ft 0.0 0

Ae AREA OF OBSTRUCTED FLOW, m2, ft2 0.0 0

Qe OBSTRUCTED FLOW, m3/s, ft3/s 0.0 0.00

K1 (Tbl 7.1) CORRECTION FOR ABUTMENT SHAPE (0.55, 0.82, 1.0) 1.00 1

Theta EMBANKMENT ANGLE, deg (ds theta<90, us theta>90) 90 90

K2 (7.1) CORRECTION FOR FLOW ANGLE 0.00 0.00 1.00 1.00

ya (7.1) AVERAGE FLOODPLAIN DEPTH, m, ft 0.00 0.00 0.00 0.00

Ve (7.1) OBSTRUCTED VELOCITY, m/s, f/s 0.00 0.00 0.00 0.00

Fr (7.1) FROUDE RATIO 0.00 0.00 0.00 0.00 yS (7.1) SCOUR DEPTH, m, ft 0.00 0.00 0.00 0.00

TOTAL SCOUR

Base Elevation 14.5 14.5 0.0 0.0

Contraction Scour

Live Bed 0.0 0.0 0.0 0.0

Clear Water 0.0 0.0 0.0 0.0

Pressure Flow (assumes clear water) 0.0 0.0 0.0 0.0

Contraction + Pier (without Pressure Flow Scour)

Pier 0.0 0.0 3.6 3.7

Total Live Bed 0.0 0.0 3.6 3.7

Live Bed Scour Elevation 14.5 14.5 -3.6 -3.7

Total Clear Water 0.0 0.0 3.6 3.7

Clear Water Scour Elevation 14.5 14.5 -3.6 -3.7

Contraction + Pier (with Pressure Flow Scour)

Pier 0.0 0.0 0.0 0.0

Total Live Bed 0.0 0.0 0.0 0.0

Live Bed Scour Elevation 14.5 14.5 0.0 0.0

Total Clear Water 0.0 0.0 0.0 0.0

Clear Water Scour Elevation 14.5 14.5 0.0 0.0

Contraction + Abutment

Abutment 0.0 0.0 0.0 0.0

Total Live Bed 0.0 0.0 0.0 0.0

Live Bed Scour Elevation 14.5 14.5 0.0 0.0

Total Clear Water 0.0 0.0 0.0 0.0

Clear Water Scour Elevation 14.5 14.5 0.0 0.0

Note:

HEC 18, 4th ED. 5/2001 (EQUATIONS SHOWN IN PARENTHESIS)

Qe (Obstructed Flow) = ( design flow / top width of upstream channel ) * length of obstruction

Riprap Analysis

Project:

Desc: Date:

FOR ENGLISH OUTPUT, SET g = 32.2 FT/SEC2 g = 32.2 FOR METRIC OUTPUT, SET g = 9.81 M/SEC2

Riprap D65 Class Qdes Yo V VCF Dm SS SL Ss VB SFS SFB Sm Vr Vs

2 50 26.0 1.5 1.50 42 0.99 1.25 0.001 2.65 2.26 1.12 89.03 1.13 1.33 0.0101 0.0146 0.95

2 50 26.0 1.5 1.50 42 0.99 1.50 0.001 2.65 2.26 1.34 89.03 1.35 1.33 0.0101 0.0164 0.95

2 50 26.0 1.5 1.50 42 0.99 1.75 0.001 2.65 2.26 1.56 89.03 1.58 1.33 0.0101 0.0184 0.95 2 50 26.0 1.5 1.50 42 0.99 2.00 0.001 2.65 2.26 1.78 89.03 1.80 1.33 0.0101 0.0204 0.95

3 50 26.0 1.5 1.50 42 1.33 1.25 0.001 2.65 2.26 1.12 105.45 1.13 1.40 0.0084 0.0121 1.00

3 50 26.0 1.5 1.50 42 1.33 1.50 0.001 2.65 2.26 1.34 105.45 1.35 1.40 0.0084 0.0136 1.00

3 50 26.0 1.5 1.50 42 1.33 1.75 0.001 2.65 2.26 1.56 105.45 1.58 1.40 0.0084 0.0152 1.00 3 50 26.0 1.5 1.50 42 1.33 2.00 0.001 2.65 2.26 1.79 105.45 1.80 1.40 0.0084 0.0169 1.00

4 50 26.0 1.5 1.50 42 1.67 1.25 0.001 2.65 2.26 1.12 119.45 1.13 1.46 0.0073 0.0105 1.05

4 50 26.0 1.5 1.50 42 1.67 1.50 0.001 2.65 2.26 1.34 119.45 1.35 1.46 0.0073 0.0118 1.05

4 50 26.0 1.5 1.50 42 1.67 1.75 0.001 2.65 2.26 1.57 119.45 1.58 1.46 0.0073 0.0132 1.05

4 50 26.0 1.5 1.50 42 1.67 2.00 0.001 2.65 2.26 1.79 119.45 1.80 1.46 0.0073 0.0146 1.05

SAFETY FACTOR FOR RIPRAP PLACED ALONG A STREAM CHANNEL, (EQUATIONS 6.3, 6.9, 6.10, 6.11, 6.12, 6.16 AND 6.22) Yo = NORMAL FLOW DEPTH FOR DESIGN DISCHARGE WITHIN THE CHANNEL IN FEET OR METERS, CHECK SAFETY FACTORS FOR Yo = THE TOTAL DEPTH AND Yo = 0.4 OF THE TOTAL DEPTH

V = LOCAL AVERAGE VELOCITY (FT/SEC) OR (M/SEC), USE AVERAGE CHANNEL VELOCITY FOR BENDS

VCF = VELOCITY CORRECTION FACTOR FOR BENDS (1.0 FOR STRAIGHT CHANNELS

TO 2.0 FOR SEVERE CURVATURE ; RECOMMEND 1.5 FOR MOST NATURAL BENDS)

VB = LOCAL AVERAGE VELOCITY IN A BEND OR IN A STRAIGHT CHANNEL (FT/SEC) OR (M/SEC)

= ANGLE OF REPOSE FOR RIPRAP IN DEGREES

Dm = REPRESENTATIVE RIPRAP SIZE IN FEET OR METER

(NORMALLY THE SIZE THAT 65% OF THE RIPRAP IS FINER BY WEIGHT, D65, or APPROXIMATELY 1.25D50 )

SS = HORIZONTIAL UNITS PER UNIT VERTICAL(I.E. 2 HOR. : 1 VER. , SS = 2)

Abutment

River Engineering for Highway Encroachments, Highways in the River Environment, HDS NO. 6, DECEMBER 2001, River Stabilization and Bank Protection, Riprap Design and Placement, Chapter 6, FHWA

Location

DESIGN

RIPRAP DESIGN - FHWA

Design for River S Bridge Replacement, WA RRP RIDG 100(2)

Abutment Riprap 04/30/14

Riprap Channel Safety FactorsOutput

SL = LONGITUDINAL CHANNEL SLOPE IN FEET/FEET OR METER/METER

Ss = SPECIFIC GRAVITY OF THE RIPRAP

SFS = SAFETY FACTOR FOR SIDE SLOPES; RECOMMEND SFS = 1.5

SFB = SAFETY FACTOR FOR CHANNEL BED; RECOMMEND SFB = 1.5

Sm = RATIO OF TANGENTS OF FRICTION ANGLE TO SIDE SLOPE ANGLE

Vr = REFERENCE VELOCITY, FEET PER SECOND OR METER PER SECOND

= STABILITY NUMBER FOR RIPRAP ON A PLANE BED

= Sm * * SECANT(SIDE SLOPE ANGLE)

Vs = VELOCITY AGAINST THE STONE, FEET PER SECOND OR METER PER SECOND

Hydraulic Toolbox Results

Hydraulic Analysis Report

Project Data

Project Title: Design for River S Bridge Replacement

Designer: M. Frye

Project Date: Sunday, May 11, 2014

Project Units: U.S. Customary Units

Notes: Lake River

Channel Analysis: Q10

Notes:

Input Parameters

Channel Type: Custom Cross Section

Cross Section Data Station ft Elevation ft Manning's n

0.00 28.87 0.0800

40.00 25.85 0.0800

80.00 18.49 0.0800

120.00 17.68 0.0800

160.00 17.12 0.0800

200.00 17.77 0.0800

240.00 17.96 0.0800

280.00 18.89 0.0800

320.00 20.41 0.0800

360.00 14.51 0.0800

400.00 5.65 0.0600

440.00 -1.50 0.0600

480.00 1.23 0.0600

520.00 0.03 0.0600

560.00 0.00 0.0600

600.00 2.08 0.0600

640.00 8.61 0.0600

680.00 23.76 0.0800

720.00 33.32 0.0800

760.00 39.08 0.0800

800.00 43.53 -----

Longitudinal Slope: 0.0001 ft/ft

Depth: 22.0000 ft

Result Parameters

Flow: 8321.5243 cfs

Area of Flow: 5862.9047 ft^2

Wetted Perimeter: 607.4604 ft

Average Velocity: 1.4194 ft/s

Top Width: 602.3119 ft

Froude Number: 0.0802

Critical Depth: 5.9395 ft

Critical Velocity: 10.8863 ft/s

Critical Slope: 0.0342 ft/ft

Critical Top Width: 207.6901 ft

Calculated Max Shear Stress: 0.1373 lb/ft^2

Calculated Avg Shear Stress: 0.0602 lb/ft^2

Composite Manning's n Equation: Lotter method

Manning's n: 0.0475

Channel Analysis: Q50

Notes:

0.00 28.87 0.0800

40.00 25.85 0.0800

80.00 18.49 0.0800

120.00 17.68 0.0800

160.00 17.12 0.0800

200.00 17.77 0.0800

240.00 17.96 0.0800

280.00 18.89 0.0800

320.00 20.41 0.0800

360.00 14.51 0.0800

400.00 5.65 0.0600

440.00 -1.50 0.0600

480.00 1.23 0.0600

520.00 0.03 0.0600

560.00 0.00 0.0600

600.00 2.08 0.0600

640.00 8.61 0.0600

680.00 23.76 0.0800

720.00 33.32 0.0800

Depth: 26.0000 ft

Result Parameters

Flow: 12584.0378 cfs

Area of Flow: 8337.1723 ft^2

Wetted Perimeter: 641.9496 ft

Average Velocity: 1.5094 ft/s

Top Width: 635.7522 ft

Froude Number: 0.0735

Critical Depth: 7.1749 ft

Critical Velocity: 12.2185 ft/s

Critical Slope: 0.0317 ft/ft

Critical Top Width: 222.1361 ft

Calculated Max Shear Stress: 0.1622 lb/ft^2

Calculated Avg Shear Stress: 0.0810 lb/ft^2

Manning's n: 0.0544

Channel Analysis: Q100

0.00 28.87 0.0800

40.00 25.85 0.0800

80.00 18.49 0.0800

120.00 17.68 0.0800

160.00 17.12 0.0800

200.00 17.77 0.0800

240.00 17.96 0.0800

280.00 18.89 0.0800

320.00 20.41 0.0800

360.00 14.51 0.0800

400.00 5.65 0.0600

440.00 -1.50 0.0600

480.00 1.23 0.0600

520.00 0.03 0.0600

560.00 0.00 0.0600

600.00 2.08 0.0600

640.00 8.61 0.0600

680.00 23.76 0.0800

720.00 33.32 0.0800

Depth: 27.0000 ft

Result Parameters

Flow: 13867.2634 cfs

Area of Flow: 8977.7349 ft^2

Wetted Perimeter: 651.7793 ft

Average Velocity: 1.5446 ft/s

Top Width: 645.3728 ft

Froude Number: 0.0730

Critical Depth: 7.5085 ft

Critical Velocity: 12.5540 ft/s

Critical Slope: 0.0309 ft/ft

Critical Top Width: 225.6846 ft

Calculated Max Shear Stress: 0.1685 lb/ft^2

Calculated Avg Shear Stress: 0.0860 lb/ft^2

Manning's n: 0.0553

Channel Analysis: Q500

0.00 28.87 0.0800

40.00 25.85 0.0800

80.00 18.49 0.0800

120.00 17.68 0.0800

160.00 17.12 0.0800

200.00 17.77 0.0800

240.00 17.96 0.0800

280.00 18.89 0.0800

320.00 20.41 0.0800

360.00 14.51 0.0800

400.00 5.65 0.0600

440.00 -1.50 0.0600

480.00 1.23 0.0600

520.00 0.03 0.0600

560.00 0.00 0.0600

600.00 2.08 0.0600

640.00 8.61 0.0600

680.00 23.76 0.0800

720.00 33.32 0.0800

Depth: 29.5000 ft

Result Parameters

Flow: 17286.1178 cfs

Area of Flow: 10639.3336 ft^2

Wetted Perimeter: 693.0775 ft

Average Velocity: 1.6247 ft/s

Top Width: 686.2637 ft

Froude Number: 0.0727

Critical Depth: 8.3399 ft

Critical Velocity: 13.3389 ft/s

Critical Slope: 0.0292 ft/ft

Critical Top Width: 234.5282 ft

Calculated Max Shear Stress: 0.1841 lb/ft^2

Calculated Avg Shear Stress: 0.0958 lb/ft^2

Manning's n: 0.0565 megan.frye Line megan.frye Line megan.frye Line megan.frye Line megan.frye Line

APPENDIX E

Flood Insurance Study for Clark County (FIS No. 53011CV001A, 9/5/2012)

Water Quality Report (Megan Frye, WFLHD 2014)

VOLUME 2 OF 2

CLARK COUNTY,

WASHINGTON

AND INCORPORATED AREAS

COMMUNITY NAME COMMUNITY NUMBER

BATTLE GROUND, CITY OF 530025

CAMAS, CITY OF 530026

CLARK COUNTY

(UNINCORPORATED AREAS) 530024

LA CENTER, CITY OF 530248

RIDGEFIELD, CITY OF 530298

VANCOUVER, CITY OF 530027

WASHOUGAL, CITY OF 530028

YACOLT, TOWN OF 530269

FLOOD INSURANCE STUDY NUMBER

53011CV002A

CLARK COUNTY

EFFECTIVE DATE: SEPTEMBER 5, 2012

http://www.google.com/imgres?q=clark+county+washington+map&um=1&hl=en&sa=N&rls=com.microsoft:en-us:IE-SearchBox&biw=1179&bih=774&tbm=isch&tbnid=h8YBkQo0DumDiM:&imgrefurl=http://en.wikipedia.org/wiki/File:Map_of_Washington_highlighting_Clark_County.svg&docid=YJnayiMdd97vkM&imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Map_of_Washington_highlighting_Clark_County.svg/800px-Map_of_Washington_highlighting_Clark_County.svg.png&w=800&h=521&ei=6Yb8TvzXMpKTtweqyZWlDg&zoom=1�

NOTICE TO

FLOOD INSURANCE STUDY USERS

Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood

Insurance Study (FIS) report may not contain all data available within the Community Map

Repository. Please contact the Community Map Repository for any additional data.

Selected Flood Insurance Rate Map (FIRM) panels for this community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map

(FBFM) panels (e.g., floodways, cross sections). In addition, former flood hazard zone designations have been changed as follows:

Old Zone(s) New Zone

Al through A30 AE

Vl through V30 VE

B X

C X

Part or all of this Flood Insurance Study may be revised and republished at any time. In addition, part of this Flood Insurance Study may be revised by the Letter of Map Revision process, which does not involve republication or redistribution of the Flood Insurance Study. It is, therefore, the responsibility of the user to consult with community officials and to check the community repository to obtain the most current Flood Insurance Study components.

FIS Effective Date: September 5, 2012 i

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Purpose of Study

1.2 Authority and Acknowledgments

1.3 Coordination

2.0 AREA STUDIED

2.1 Scope of Study

2.2 Community Description

2.3 Principal Flood Problems

2.4 Flood Protection Measures

3.0 ENGINEERING METHODS

3.1 Hydrologic Analyses

3.2 Hydraulic Analyses

3.3 Vertical Datum

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS

4.1 Floodplain Boundaries

4.2 Floodways

5.0 INSURANCE APPLICATIONS

6.0 FLOOD INSURANCE RATE MAP

7.0 OTHER STUDIES

8.0 LOCATION OF DATA

9.0 BIBLIOGRAPHY AND REFERENCES

ii

FIGURES

Figure 1 – Floodway Schematic

TABLES

Table 1 – Initial and Final CCO Meeting Dates Table 2 – Letters of Map Change (LOMCs) Table 3 – Comparison of Major Columbia River Floods Table 4 – Summary of Discharges Table 5 – Manning’s “n” Values Table 6 – Floodway Data Table 7 – Community Map History

Exhibit 1 - Flood Profiles

EXHIBITS

Burnt Bridge Creek Panels 01P-12P China Ditch Panels 13P-15P Columbia River Panels 16P-24P Curtin Creek Panels 25P-28P East Fork Lewis River Panels 29P-40P

VOLUME 2

East Fork Lewis River Lower Split Panels 41P East Fork Lewis River Path 2 Panels 42P East Fork Lewis River Path 3 Panels 43P Fifth Plain Creek Panels 44P-47P Gee Creek Panels 48P-55P Lacamas Creek Panels 56P-65P Lewis River Panels 66P-80P Mill Creek Panels 81P-86P Packard Creek Panels 87P-92P Padden Creek Panel 93P Salmon Creek Panels 94P-111P Spring Branch Creek Panel 112P Unnamed Tributary to Gee Creek Panel 113P Washougal River Panels 114P-118P Weaver Creek Panels 119P-123P Whipple Creek Panels 124P-130P

PUBLISHED SEPARATELY:

Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Map

VOLUME 1 OF 2

CLARK COUNTY,

WASHINGTON

AND INCORPORATED AREAS

COMMUNITY NAME COMMUNITY NUMBER

BATTLE GROUND, CITY OF 530025

CAMAS, CITY OF 530026

CLARK COUNTY

(UNINCORPORATED AREAS) 530024

LA CENTER, CITY OF 530248

RIDGEFIELD, CITY OF 530298

VANCOUVER, CITY OF 530027

WASHOUGAL, CITY OF 530028

YACOLT, TOWN OF 530269

FLOOD INSURANCE STUDY NUMBER

53011CV001A

CLARK COUNTY

EFFECTIVE DATE: SEPTEMBER 5, 2012

http://www.google.com/imgres?q=clark+county+washington+map&um=1&hl=en&sa=N&rls=com.microsoft:en-us:IE-SearchBox&biw=1179&bih=774&tbm=isch&tbnid=h8YBkQo0DumDiM:&imgrefurl=http://en.wikipedia.org/wiki/File:Map_of_Washington_highlighting_Clark_County.svg&docid=YJnayiMdd97vkM&imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Map_of_Washington_highlighting_Clark_County.svg/800px-Map_of_Washington_highlighting_Clark_County.svg.png&w=800&h=521&ei=6Yb8TvzXMpKTtweqyZWlDg&zoom=1

NOTICE TO

FLOOD INSURANCE STUDY USERS

Communities participating in the National Flood Insurance Program have established repositories of flood hazard data for floodplain management and flood insurance purposes. This Flood

Insurance Study (FIS) report may not contain all data available within the Community Map

Repository. Please contact the Community Map Repository for any additional data.

Selected Flood Insurance Rate Map (FIRM) panels for this community contain information that was previously shown separately on the corresponding Flood Boundary and Floodway Map

(FBFM) panels (e.g., floodways, cross sections). In addition, former flood hazard zone designations have been changed as follows:

Old Zone(s) New Zone

Al through A30 AE

Vl through V30 VE

B X

C X

Part or all of this Flood Insurance Study may be revised and republished at any time. In addition, part of this Flood Insurance Study may be revised by the Letter of Map Revision process, which does not involve republication or redistribution of the Flood Insurance Study. It is, therefore, the responsibility of the user to consult with community officials and to check the community repository to obtain the most current Flood Insurance Study components.

FIS Effective Date: September 5, 2012 http://www.google.com/imgres?q=clark+county+washington+map&um=1&hl=en&sa=N&rls=com.microsoft:en-us:IE-SearchBox&biw=1179&bih=774&tbm=isch&tbnid=h8YBkQo0DumDiM:&imgrefurl=http://en.wikipedia.org/wiki/File:Map_of_Washington_highlighting_Clark_County.svg&docid=YJnayiMdd97vkM&imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Map_of_Washington_highlighting_Clark_County.svg/800px-Map_of_Washington_highlighting_Clark_County.svg.png&w=800&h=521&ei=6Yb8TvzXMpKTtweqyZWlDg&zoom=1� i

1.0 INTRODUCTION

1.1 Purpose of Study

1.2 Authority and Acknowledgments

1.3 Coordination

2.0 AREA STUDIED

2.1 Scope of Study

2.2 Community Description

2.3 Principal Flood Problems

2.4 Flood Protection Measures

3.0 ENGINEERING METHODS

3.1 Hydrologic Analyses

3.2 Hydraulic Analyses

3.3 Vertical Datum

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS

4.1 Floodplain Boundaries

4.2 Floodways

5.0 INSURANCE APPLICATIONS

6.0 FLOOD INSURANCE RATE MAP

7.0 OTHER STUDIES

8.0 LOCATION OF DATA

9.0 BIBLIOGRAPHY AND REFERENCES

FIGURES

Figure 1 – Floodway Schematic

TABLES

Table 1 – Initial and Final CCO Meeting Dates Table 2 – Letters of Map Change (LOMCs) Table 3 – Comparison of Major Columbia River Floods Table 4 – Summary of Discharges Table 5 – Manning’s “n” Values Table 6 – Floodway Data Table 7 – Community Map History

Exhibit 1 - Flood Profiles

Burnt Bridge Creek Panels 01P-12P China Ditch Panels 13P-15P Columbia River Panels 16P-24P Curtin Creek Panels 25P-28P East Fork Lewis River Panels 29P-40P

VOLUME 2

East Fork Lewis River Lower Split Panels 41P East Fork Lewis River Path 2 Panels 42P East Fork Lewis River Path 3 Panels 43P Fifth Plain Creek Panels 44P-47P Gee Creek Panels 48P-55P Lacamas Creek Panels 56P-65P Lewis River Panels 66P-80P Mill Creek Panels 81P-86P Packard Creek Panels 87P-92P Padden Creek Panel 93P Salmon Creek Panels 94P-111P Spring Branch Creek Panel 112P Unnamed Tributary to Gee Creek Panel 113P Washougal River Panels 114P-118P Weaver Creek Panels 119P-123P Whipple Creek Panels 124P-130P

PUBLISHED SEPARATELY:

Exhibit 2 - Flood Insurance Rate Map Index Flood Insurance Rate Map

FLOOD INSURANCE STUDY

CLARK COUNTY, WASHINGTON AND INCORPORATED AREAS

1.0

1.1 Purpose of Study

INTRODUCTION

This Flood Insurance Study (FIS) revises and updates information on the existence and severity of flood hazards in the geographic area of Clark County, including the Cities of Battle Ground, Camas, La Center, Ridgefield, Vancouver, and Washougal; and the Town of Yacolt; and the unincorporated areas of Clark County (referred to collectively herein as Clark County), and aids in the administration of the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. This study has developed flood risk data for various areas of the community that will be used to establish actuarial flood insurance rates and to assist the community in its efforts to promote sound floodplain management. Minimum floodplain management requirements for participation in the National Flood Insurance Program (NFIP) are set forth in the Code of Federal Regulations at 44 CFR, 60.3.

Please note that the City of Woodland is geographically located in Cowlitz and Clark Counties. The City of Woodland is not included in this FIS report.

In some States or communities, floodplain management criteria or regulations may exist that are more restrictive or comprehensive than the minimum Federal requirements. In such cases, the more restrictive criteria take precedence, and the State (or other jurisdictional agency) will be able to explain them.

1.2 Authority and Acknowledgments

The sources of authority for this FIS report are the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973.

The original hydrologic and hydraulic analyses for Burnt Bridge Creek, the Columbia River, the East Fork Lewis River, Gee Creek, Lacamas Creek, the Lewis River, Mill Creek, Salmon Creek, an Unnamed Tributary to Gee Creek, the Washougal River, and Weaver Creek were performed by the U.S. Army Corps of Engineers (USACE), Portland District, for the Federal Emergency Management Agency (FEMA), under Interagency Agreement No. IAA-H-l0-77, Project Order No. 15; Interagency Agreement No. IAA-H-7-76, Project Order No. 1; Interagency Agreement No. IAA-H-16-75, Project Order No. 10, 16, and 19; Interagency Agreement No. IAA-H-20-74, Project Order No. 17. This work was completed in November 1979.

The hydrologic and hydraulic analyses for this study were performed by WEST Consultants Inc., for FEMA, under Contract No. EMS-2001-CO-0068. This study was completed in August 2005. Gee Creek, Lacamas Creek, Mill Creek, Salmon Creek, and Weaver Creek were restudied entirely. A Portion of Burnt Bridge Creek was restudied.

China Ditch, Curtin Creek, Fifth Plain Creek, Packard Creek, Padden Creek, Spring Branch Creek, and Whipple Creek were studied by detailed methods.

Little Matney Creek, Matney Creek, Morgan Creek, Mud Creek, and Shanghai Creek were studied by approximate methods.

1.3 Coordination

The initial Consultation Coordination Officer (CCO) meetings were held with representatives from FEMA, the communities, and the study contractors, to explain the nature and purpose of an FIS, and to identify the streams to be studied or restudied. All affected communities were requested to provide any data pertinent to the study. The final CCO meetings were held with representatives from FEMA, the communities, and the study contractor to review the results of the study.

The initial and final meeting dates for previous FIS reports for Clark County and its communities are listed on Table 1, “Initial and Final CCO Meeting Dates”.

For this countywide study, the final CCO meeting held on September 15, 2010, and attended by representatives of FEMA, Michael Baker Jr. Inc., the WA Department of Ecology, the Port of Camas-Washougal, and the local communities of the Cities of Camas, Ridgefield, Vancouver, and Washougal; and Clark County. All problems raised at that meeting have been addressed.

2.0

2.1 Scope of Study

AREA STUDIED

This FIS report covers the geographic area of Clark County, Washington, including the incorporated communities listed in Section 1.1.

For this countywide FIS, the FIS report and FIRM were converted to countywide format, and the flooding information for the entire county, including both incorporated and unincorporated areas, is shown. Also, the vertical datum was converted from the National Geodetic Vertical Datum of 1929 (NGVD29) to the North American Vertical Datum of 1988 (NAVD88). In addition, the Transverse Mercator, State Plane coordinates, previously referenced to the North American Datum of 1927 (NAD27), are now referenced to the North American Datum of 1983 (NAD83).

Table 1 – Initial and Final CCO Meeting Dates

Community Initial CCO Date

Final CCO Date

Battle Ground, City of November 16, 1976 March 4, 1980 Camas, City of * March 5, 1980 Clark County * September 1, 1981 (Unincorporated Areas)

La Center, City of * September 26, 1986 Ridgefield, City of November 16, 1976 June 10, 1980 Vancouver, City of May 22, 1975 June 10, 1980 Washougal, City of March 30, 1979 November 18, 1979 Yacolt, Town of * *

* Data not available

The areas studied by detailed methods were selected with priority given to all known flood hazards and areas of projected development.

The November 1979 study performed by USACE provided a detailed study along Burnt Bridge Creek from City of Vancouver corporate limits to approximately 0.22 mile upstream of Northeast 152nd Avenue. The Columbia River was studied by detailed method from Clark-Cowlitz County boundary to Clark-Skamania County boundary. The East Fork Lewis River was studied by detailed method from its confluence with the Lewis River to upstream of Boy Scout Camp. The Lewis River was studied by detailed method from its confluence with the Columbia River to approximately 500 feet downstream of Merwin Dam. Unnamed Tributary to Gee Creek was studied by detailed method from its confluence with Gee Creek to approximately 500 feet upstream of Northwest 54th Avenue.

The Washougal River was studied by detailed method from its confluence with the Columbia River to approximately 0.86 miles upstream of City of Washougal corporate limits. In addition, approximate methods were used to continue the East Fork Lewis River and Lewis River studies to Big Tree Creek and the Clark-Skamania County boundary, respectively. Cedar Creek, Chelatchie Creek, and Unnamed Tributary to Chelatchie Creek were studied by approximate method.

The August 2005 study performed by West Consultants Inc provided new detailed information for Burnt Bridge Creek from the downstream face of the Interstate 205 culvert to approximately 1 mile upstream of Northeast 137th Avenue. Gee Creek, Lacamas Creek, Mill Creek, Salmon Creek, and Weaver Creek were restudied entirely. China Ditch, Curtin Creek, Fifth Plain Creek, Packard Creek, Padden Creek, Spring Branch Creek, and Whipple Creek were studied entirely by detail method. The study also provided approximate study for Little Matney Creek, Matney Creek, Morgan Creek, Mud Creek, and Shanghai Creek.

Approximate analyses were used to study those areas having a low development potential or minimal flood hazards. The scope and methods of study were proposed to, and agreed upon, by FEMA and Clark County.

This countywide FIS incorporates the determinations of Letter of Map Revisions (LOMRs) issued by FEMA, for the projects listed by community in Table 2, “Letters of Map Change (LOMCs)”.

Table 2 – Letters of Map Change (LOMCs)

Community Case Number Stream(s) / Project Identifier Clark County

(Unincorporated Areas)

Date Issued 94-10-039P The 1-percent-annual-chance flood for

Unnamed Tributary to Curtin Creek is contained in a channel and culvert west of Northeast Meadows Drive

June 21, 1994

Clark County (Unincorporated Areas)

04-10-0710P Cold Creek from approximately 750 feet downstream to approximately 600 feet upstream of Northeast 58th Avenue

June 6, 2005

2.2 Community Description

Clark County is in southwestern Washington. Adjacent counties are Cowlitz on the north;

Skamania on the east; and Multnomah and Columbia Counties, Oregon, on the south and west, respectively. Vancouver, the County seat, is in the southwestern corner of Clark County, and is linked to Portland, Oregon, by the Interstate Highway 5 Bridge over the Columbia River.

Clark County occupies an area of 627 square miles between the Pacific Coast Range on the west and the Cascade Range on the east. The western and southern areas are primarily agricultural lands. The eastern and northern areas of the county are steep, forested foothills and mountains of the Cascade Range. The soils of the northern and eastern areas are well drained, while those of the western and southern areas are poorly to moderately drained (Reference l). Most of the development in the county is along the Columbia River.

However, there are small areas of development throughout the County. The population of the unincorporated areas of Clark County rose from 238,053 in 1990 to 345,238 in 2000 (Reference 2).

Vancouver, a fast-growing suburb of Portland, Oregon, is the largest incorporated City in Clark County, with a population of approximately 143,560 in 2000. The total population of the incorporated areas of Clark County was 178,959 in 2000 (Reference 2).

Economic activity centers on industrial products, which include, in order of amount produced, lumber, pulp, paper, aluminum, carborundum, and chemicals. Agriculture is also an important industry, the major products being dairy products, livestock, poultry, vegetables, berries, and orchard fruit. In 1970, 25 percent of the Clark County work force was employed in Oregon (Reference 3).

The Columbia River, which forms the southern and western boundaries of the county, is the major inland waterway in the northwestern United States. It drains an area of approximately 241,000 square miles of southwestern Canada and northwestern United States upstream of Vancouver, Washington.

From its source on the northwestern slopes of Mount Adams, the Lewis River flows southwesterly along the northern boundary of Clark County. It drains 1,046 square miles of rugged, heavily timbered land before joining the Columbia River near Ridgefield. The East Fork Lewis River, with headwaters in the Gifford Pinchot National Forest of Skamania County, drains 212 square miles of mountainous timber land and flows westerly before entering the Lewis River near the City of La Center.

As it flows westerly and southerly into the Columbia River at Camas, the Washougal River drains 168 square miles of steep, forested land. Salmon Creek, a tributary of the Lake River, drains 92 square miles of moderately sloping agricultural land in western Clark County.

Many of the small streams of Clark County flow southerly or westerly from sources in steep timberland, pass through lower reaches of gently sloping agricultural land or residential areas, and finally enter the Columbia River.

Clark County has a temperate marine climate typical of western Washington. Summers are dry with mild temperatures, and winters are rainy with occasional snow. At Vancouver, average annual temperatures range from a mean daily minimum of 33 degrees Fahrenheit

(°F) in January to a mean daily maximum of 80°F in July (Reference 4). Average annual precipitation varies from 39 inches at Vancouver to 75 inches at Yacolt in north central Clark County. More than 65 percent of the annual precipitation occurs from November through March (Reference 5).

2.3 Principal Flood Problems

Although many large Columbia River floods have occurred in Clark County, existing flood control storage will reduce the severity of future floods. The June 1948 and June 1956 floods were typical spring-summer floods caused by snowmelt runoff. Although less significant than the aforementioned floods, the December 1964 flood is noteworthy because it was an unusually large winter flood resulting primarily from rainfall.

Peak discharges at the U.S. Geological Survey (USGS) gage at The Dalles, Oregon, for the June 1948 and June 1956 floods were 1,010,000 and 823,000 cubic feet per second (cfs), respectively. Discharges are given for The Dalles (approximately 55 miles upstream of Vancouver) rather than at Clark County because The Dalles is the first gage upstream of the mouth of the Columbia River with a reliable stage- discharge relationship. The discharge of the December 1964 flood is not comparable to the floods of 1948 and 1956 because large inflows occurred downstream of The Dalles. The estimated return periods for the 1948 and 1956 floods were 48 years and 18 years, respectively. The Columbia River floods of 1948 and 1956 caused light damage to residential areas of Clark County. Most of the damage in the unincorporated areas occurred in low lying farm and industrial areas. Emergency flood fighting measures along the Columbia River and temporary evacuation reduced damage.

The largest flood of record on the Lewis River occurred in December 1933. At the USGS gage at Ariel (station no. 14220500), the discharge was 129,000 cfs.

The historical patterns of flooding along Salmon Creek, the East Fork Lewis River, the Washougal River, Burnt Bridge Creek, and Mill Creek are similar. Overbank flooding has been minor on the upper reaches; however, near the confluence with a larger stream, backwater effects produce more frequent overbank flooding.

A combination of intense rainfall and snowmelt caused major East Fork Lewis River floods in January 1972 and December 1977. At the gage near Heisson (River Mile (RM) 20.2), the discharge for both floods was 19,200 cfs with an approximate return interval of the 1-percent-annual-chance flood. These two floods caused minor damage in Clark County.

The largest flood during the 35 years of gaging record on Salmon Creek occurred in December 1977, with a discharge of 2,600 cfs at the gage below Rock Creek at RM 22.1.

January 1954 and December 1964 were also major floods on Salmon Creek, with discharges of 1,500 and 1,460 cfs, respectively. Those floods caused only minor damage.

The only major floods on Burnt Bridge Creek have been caused by Columbia River backwater. Although it is not large for the size of the area drained, the highest flow observed on Burnt Bridge Creek was 176 cfs in December 1955. Minor flood damage was observed in adjacent unincorporated areas.

The largest flood along the Washougal River, since a USGS stream gage was established in 1944, 6 miles upstream of the City of Washougal, occurred in December 1977. The flood was an extremely rare event, greater than a 0.2-percent-annual-chance flood at the gage site, and had an estimated peak discharge of 40,400 cfs at the gage. Because there was little overbank flooding and limited development outside of the Cities of Camas and

Washougal along the river, only minor damage occurred. Other large floods along the Washougal River occurred in January 1972 and December 1964, with return periods of 18 years and 9 years and peak discharges of 27,700 cfs and 25,100 cfs, respectively.

Records of past floods on the remaining flooding sources in Clark County are not well documented, but past floods have caused only minor damage.

2.4 Flood Protection Measures

The Columbia River Basin includes more than 50 storage projects with a total flood control storage volume of approximately 40 million acre-feet (Reference 6). Significant reductions in flood elevations have been achieved through the use of that flood storage. Table 3 (Reference 7) compares Columbia River flood levels at Vancouver, Washington, with and without regulation, to demonstrate the effect of existing flood control storage.

Table 3 – Comparison of Major Columbia River Floods

June 1894 June 1948 June 1956

December 1964

Flood Crest Stages1

Vancouver Gage Unregulated 34.4 31.0 30.0 32.5 Regulated2 22.3 21.5 17.0 26.7

Days Duration Above Flood Stage3 Bankfull 74 51 70 9 Major Flood 38 26 12 2

1 National Weather Service Gage heights in feet (Zero of Vancouver Gage is +5.32 feet NAVD88) 2 Based on present level of irrigation and reservoir development 3 Flood or bankfull stage for Columbia River is 16 feet at the Vancouver Gage.

A flood of 26 feet or higher results in extensive damage and is considered a major flood.

The duration shown is based on the unregulated flood hydrograph.

The drainage districts along the Columbia River in Clark County have levees of varying flood protection capacities. Thus, safe water levels have been established by the USACE (Reference 8). The safe water level is the highest flood elevation, considering surveillance and minor remedial work, for which reasonable assurance can be given that a levee system will not fail. The determination of the levee safe water level was based on need for freeboard, structural deficiencies observed in the field, knowledge of levee and foundation materials, and flood fighting records. Although the perimeter levee of a particular drainage district may be capable of withstanding large floods, major rainstorms could cause extensive interior ponding in low areas if runoff exceeds the capacity of the dewatering-drainage pumps.

In the vicinity of Vancouver, some protection from Columbia River flooding is provided by levees along the Lower River Road and at Fruit Valley. However, certain known deficiencies in their design and maintenance limit the degree of protection to below the

1-percent-annual-chance flood level for the Lower River Road area and below the 0.2-percent-annual-chance flood level for the Fruit Valley area.

Southwest of Ridgefield at Lake River Delta and Bachelor Island are two projects that include levees, pumping stations, tide boxes, and interior drainage canals. However, certain known deficiencies in their design and maintenance limit the degree of protection to well below 1-percent-annual-chance flood levels.

The criteria used to evaluate whether a levee provides protection against the 1-percent-annual-chance flood are (1) adequate design, including freeboard, (2) structural stability, and (3) proper operation and maintenance. Levees that do not protect against the 1-percent-annual-chance flood are not considered in the hydraulic analysis of the 1-percent-annual-chance floodplain.

The Washougal Area Drainage District, constructed by the USACE in 1965 and 1966, extends 5.5 miles along the Columbia River from Lawton Creek west to Camas and includes levee embankment, revetment, tide box, and freshwater inlets, and a pumping plant with interior drainage canals.

There are three major storage projects along the Lewis River that have an effect on flood peaks. All three projects, Swift Reservoir, Yale Reservoir, and Lake Merwin, are operated by PP&L. Under the present Federal Energy Regulatory Commission license, PP&L is not required to reserve storage space for flood protection.

On August 18, 1983, FEMA and PP&L agreed to make approximately 70,000 acre-feet available for flood control storage on the Lewis River System at Merwin Dam, thus reducing the 1-percent-annual-chance discharge at Woodland from 128,000 cfs to 102,000 cfs.

Clark County follows FEMA guidelines for controlling development within the floodplain.

The county has established an ordinance intended to reduce future flood losses through control of buildings and other land uses within floodplains. The Flood Plain Combining Zone Ordinance establishes two new zoning classifications called the Floodway District and the Floodway Fringe District (Reference 9). Clark County requires building permits for all proposed construction and reviews those permits to assure that sites are reasonably free from flooding.

3.0

For the flooding sources studied by detailed methods in the county, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study.

Flood events of a magnitude that are expected to be equaled or exceeded once on the average during any 10-, 50-, 100-, or 500-year period (recurrence interval) have been selected as having special significance for floodplain management and for flood insurance rates. These events, commonly termed the 10-, 50-, 100-, and 500-year floods, have a 10-, 2-, 1-, and 0.2-percent-annual-chance, respectively, of being equaled or exceeded during any year. Although the recurrence interval represents the long-term, average period between floods of a specific magnitude, rare floods could occur at short intervals or even within the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a flood that equals or exceeds the 1-percent-annual-chance (100-year) flood in any 50-year period is approximately 40 percent (4 in 10); for any 90-year period, the risk increases

ENGINEERING METHODS

to approximately 60 percent (6 in 10). The analyses reported herein reflect flooding potentials based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes.

3.1 Hydrologic Analyses

Hydrologic analyses were carried out to establish the peak discharge frequency relationships affecting the community for each flooding source studied in detail, except the Columbia River.

The stage discharge relationship on the Columbia River is influenced by ocean tides and Willamette River backwater; thus, flood frequencies are more reliably determined for river stages than for discharges. Stage-frequency curves for seven locations on the Columbia River between RM 50 and RM 123 were developed using existing data (References 10 and 11) for fall-winter, and spring-summer flood seasons. Those locations include USGS gage No. 14144700 on the Columbia River at Vancouver, Washington (Reference 12), and USGS gage No. 1421172 on Willamette River at the Morrison Street Bridge (Reference 13). Both gages were established in 1876 (References 14 and 15).

The fall and winter curves and spring and summer curves at each location were combined by statistical methods to obtain combined stage-frequency curves. Those stage-frequency curves are the basis for the Columbia River flood profiles presented in this study.

The discharges used in floodway computations for the Columbia River were correlated, based on data at USGS gage No. 14105700 (established in 1857) at The Dalles, Washington (Reference 16), to yield water-surface profiles similar to those prepared using the combined stage-frequency curves.

The Lewis River stream gage records were statistically analyzed using the standard Log-Pearson Type III distribution, as outlined by the U.S. Water Resources Council (Reference 17). Natural and regulated discharge-frequency curves were developed for the USGS gages at Ariel and Amboy, using data from 1912 to 1978. Peak annual flows used in deriving the natural discharge-frequency curve were calculated by combining observed flows at the gage and by correlating with flow information for adjacent gaging stations in the Lewis River basin and working downstream to Merwin Dam. The regulated discharge-frequency relationship was developed by comparison of natural versus regulated discharges for six flood events in the basin. The regulated discharges for these floods were based on the PP&L plan of flood control operation, considering 70,000 acre-feet of flood control storage at Merwin Dam.

The following streams and respective periods of USGS gaging records were analyzed in the same manner as the Lewis River, the Washougal River, from 1944 to 1978; and the East Fork Lewis River, from 1929 to 1974.

Lake River and Vancouver Lake are submerged by the Columbia River during large floods;

therefore, the hydrologic analysis of the Columbia River includes the Lake River and Vancouver Lake.

Stream gage records were not available for the Gee Creek basin (Gee Creek and Unnamed Tributary to Gee Creek). Rain gage recordings were used to estimate precipitation frequencies for selected recurrence intervals used in this study. The USACE HEC-l flood hydrograph computer program (Reference 18) was then used to develop peak discharges.

Burnt Bridge Creek discharge-frequency data were based on records from the USGS crest stage gage at RM 2.9 and on an analysis of rainfall and runoff characteristics of Burnt Bridge Creek basin and the general region.

A discharge-frequency curve was developed for Cedar Creek basin using 21 years of recorded data at the USGS gage on Cedar Creek near Ariel and discharges obtained using the regional method presented in Procedure for Determination of Maximum Annual Flood Peak and Volume Frequencies for Portland District

(Reference 29). That report utilizes multiple regression analysis to determine discharges of an ungaged basin for selected recurrence intervals using the drainage area and normal annual precipitation. Cedar Creek basin includes Cedar Creek, Chelatchie Creek, and Unnamed Tributary to Chelatchie Creek.

Flood flow frequencies for Salmon Creek, Curtin Creek, Mill Creek, Weaver Creek and Morgan Creek were based on a statistical analysis of the results of a long-term simulation using the Hydrological Simulation Program Fortran (HSPF) computer program. The HSPF program is a continuous rainfall-runoff watershed model. Continuous simulation of multiple years to several decades allows the watershed to be evaluated under a variety of flow conditions ranging from low summer base flows to periods of winter flooding. In particular, continuous modeling allows simulation of floods in response to a wide variety of individual storm characteristics and sequence of storm events. The development of the HSPF model for the Salmon Creek watershed is documented in Hydrologic Analysis of Salmon Creek Watershed using the HSPF Model

(Reference 20). The model results at various locations within the watershed were analyzed in accordance with criteria outlined in Bulletin 17B (Interagency Advisory Committee on Water Data, 1982). Discharge-frequency data were computed using the HEC-FFA computer program (HEC 1992) developed by the Hydrologic Engineering Center of the USACE, using a systematic record of 61 years.

A discharge-frequency curve was developed for Spring Branch Creek, Mud Creek, Whipple Creek, and China Ditch using the regional method presented in Magnitude and Frequency Flood in Washington

(Reference 21). That report utilizes multiple regression analyses to determine discharges of an ungaged basin for selected recurrence intervals using drainage area and normal annual precipitation data.

The discharge-frequency data for the Little Washougal River, Fifth Plain Creek, and Lacamas Creek and Lake were also determined using the regional method described in Reference 19.

Peak discharge-drainage area relationships for the streams studied by detailed methods in Clark County are shown in Table 4, “Summary of Discharges”.

Table 4 – Summary of Discharges

PEAK DISCHARGES (cfs)

FLOODING SOURCE

DRAINAGE

AREA

AND LOCATION

10%-

ANNUAL-

(SQ. MILES)

2%-

ANNUAL-

CHANCE

1%-

ANNUAL-

CHANCE

0.2%-

ANNUAL-

CHANCE

Burnt Bridge Creek At mouth 22.5 115 220 255 330 At USGS Gage 19.8 120 230 270 340 At N.E. 112th Avenue 5.0 55 110 135 180

China Ditch At mouth 8.9 495 665 740 915

Curtin Creek At mouth 11.0 335 460 520 670 At NE 109th Street 4.5 225 360 405 530 At NE 83rd Street 1.0 60 85 95 130

East Fork Lewis River

At mouth 212.0 19,200 24,400 26,900 32,000 Upstream of confluence with Lockwood Creek 185.0 17,000 21,700 23,800 28,300

Approximately 17,000 feet downstream of Daybreak Road 165.0 20,650 28,630 32,200 40,900

At Daybreak Road 152.0 18,600 26,050 29,300 37,210 At Lewisville Park 150.0 15,300 19,400 21,400 25,400

Fifth Plain Creek

At mouth 20.2 1,280 1,750 1,960 2,460 Upstream of China

Ditch 9.0 650 895 1,000 1,260 Upstream of

Shanghai Creek 4.6 360 495 555 700 At 119th Street 2.6 225 315 350 445

Gee Creek

At Burlington Northern Railroad 13 850 1,010 1,080 1,260

At County Road 9 580 695 745 870

Lacamas Creek At Goodwin Road 52.8 4,170 5,740…