Scour Calculations

Scour Calculations

By: JGS 8/20/2004

Ck. By: JRJ 8/23/2004

Scour Calculations

For

State Route 2025 / Section 153

Segment 0390 / Offset 0822

Bridge Replacement Over

Garretts Run

In

Manor Township

Armstrong County, Pennsylvania

Garretts Run #3

Prepared by:

Pennsylvania Department of Transportation

Engineering District 10-0

Indiana, Pennsylvania

Controlling Storm:

There is no QRecord and no roadway overtopping, therefore, Q100 is most critical

Contraction Scour Q100

Channel: Check for live bed or Clearwater scourVc=11.17y1/6D501/3(Eq. 5.1, pg.5.2, HEC -18)

Where: y = depth of flow @ upstream section = 5.33 ft. (pg. 4)

D50 = particle size of which 50 % are smaller = 2.5in.

= 0.208 ft. (assume very coarse gravel)

Vc=11.17(5.33)1/6(0.208)1/3 = 8.75 ft/s

Channel velocity @ upstream section sta. 603.7065 = 7.38 ft/s (pg. 4)

Since Vc > V, No live bed scour exists. Clearwater contraction scour exists.

Clearwater Contraction Scour

(Eq. 5.4, pg.5.13, HEC -18)

Where:

Y2 = Average depth in the contracted section

Q = Flow through bridge in the contracted section =1722cfs(pg.4)

Dm = Particle size in mixture equal to 1.25 X D50

= 1.25 x 0.208 ft. = 0.26 ft.(See attachment A)

W = Bottom width of contracted section = 30 ft. (pg. 6)

= 5.87 ft.

Ys = Y2 Y0

Where:

Ys = Average scour depth

Y0 = Existing depth in contracted section before scour

= area channel / top width

= 262.52 / 46.45 (pg. 4)

= 5.65 ft.

Ys = Y2 Y0 = 5.87ft. 5.65 ft. = 0.22ft.Local Scour Q100

Since there is no flow obstructed by the abutments or approach embankments and no flow in the floodplain for Q100, the local scour depth is zero.Contraction Scour Q500Channel: Check for live bed or Clearwater scourVc=11.17y1/6D501/3(Eq. 5.1, pg.5.2, HEC -18)

Where: y = depth of flow @ upstream section = 6.03 ft. (pg. 5)

D50 = particle size of which 50 % are smaller = 2.5in.

= 0.208 ft. (assume very coarse gravel) (See attachment A)Vc=11.17(6.03)1/6(0.208)1/3 = 8.93 ft/s

Channel velocity @ upstream section sta. 603.7065 = 8.19 ft/s (pg. 5)

Since Vc > V, No live bed scour exists. Clearwater contraction scour exists.

Clearwater Contraction Scour

(Eq. 5.4, pg.5.13, HEC -18)

Where:

Y2 = Average depth in the contracted section

Q = Flow through bridge in the contracted section =2411cfs (pg.5)

Dm = Particle size in mixture equal to 1.25 X D50

= 1.25 x 0.208 ft. = 0.26 ft.(See attachment A)

W = Bottom width of contracted section = 30 ft. (pg. 6)

= 7.84 ft.

Ys = Y2 Y0

Where:

Ys = Average scour depth

Y0 = Existing depth in contracted section before scour

= area channel / top width

= 326.48 / 49.84 (pg. 5)

= 6.55 ft.

Ys = Y2 Y0

= 7.84 ft. 6.55 ft. = 1.29 ft.Local Scour Q500

Since there is no flow obstructed by the abutments or approach embankments and no flow in the floodplain for Q500, the local scour depth is zero.

SummaryScourAbutment 1Abutment 2

100 yearContraction (ft)0.220.22

Local (ft)00

Total (ft)0.220.22

500 yearContraction (ft)1.291.29

Local (ft)00

Total (ft)1.291.29

References:

FHWA NHI 01-001, May 2001,HEC-18, 4th Edition

PENNDOT DM-4, Chapter 7, April 2000 Edition

Plan: PROP4189A Garrett's Run Reach RS: 603.7065 Profile: Q-100

E.G. Elev (ft)835.32 ElementLeft OBChannelRight OB

Vel Head (ft)0.85 Wt. n-Val.0.05

W.S. Elev (ft)834.48 Reach Len. (ft)202020

Crit W.S. (ft)832.56 Flow Area (sq ft)233.24

E.G. Slope (ft/ft)0.007959 Area (sq ft)233.24

Q Total (cfs)1722 Flow (cfs)1722

Top Width (ft)43.76 Top Width (ft)43.76

Vel Total (ft/s)7.38 Avg. Vel. (ft/s)7.38

Max Chl Dpth (ft)6.72 Hydr. Depth (ft)5.33

Conv. Total (cfs)19301.7 Conv. (cfs)19301.7

Length Wtd. (ft)20 Wetted Per. (ft)50.2

Min Ch El (ft)827.76 Shear (lb/sq ft)2.31

Alpha1 Stream Power (lb/ft s)17.05

Frctn Loss (ft)0.17 Cum Volume (acre-ft)0.522.390.01

C & E Loss (ft)0.03 Cum SA (acres)0.390.450.01

Plan: PROP4189A Garrett's Run Reach RS: 562.31 BR U Profile: Q-100

E.G. Elev (ft)834.71 ElementLeft OBChannelRight OB

Vel Head (ft)0.67 Wt. n-Val.0.05

W.S. Elev (ft)834.04 Reach Len. (ft)27.6727.6727.67

Crit W.S. (ft)831.69 Flow Area (sq ft)262.52

E.G. Slope (ft/ft)0.005258 Area (sq ft)262.52

Q Total (cfs)1722 Flow (cfs)1722

Top Width (ft)46.45 Top Width (ft)46.45

Vel Total (ft/s)6.56 Avg. Vel. (ft/s)6.56

Max Chl Dpth (ft)7.14 Hydr. Depth (ft)5.65

Conv. Total (cfs)23748.1 Conv. (cfs)23748.1

Length Wtd. (ft)27.67 Wetted Per. (ft)49.43

Min Ch El (ft)826.9 Shear (lb/sq ft)1.74

Alpha1 Stream Power (lb/ft s)11.43

Frctn Loss (ft)0.16 Cum Volume (acre-ft)0.522.070.01

C & E Loss (ft)0.02 Cum SA (acres)0.390.390.01

Plan: PROP4189A Garrett's Run Reach RS: 603.7065 Profile: Q-500

E.G. Elev (ft)836.85 ElementLeft OBChannelRight OB

Vel Head (ft)1.04 Wt. n-Val.0.05

W.S. Elev (ft)835.81 Reach Len. (ft)202020

Crit W.S. (ft)833.59 Flow Area (sq ft)294.32

E.G. Slope (ft/ft)0.008469 Area (sq ft)294.32

Q Total (cfs)2411 Flow (cfs)2411

Top Width (ft)48.81 Top Width (ft)48.81

Vel Total (ft/s)8.19 Avg. Vel. (ft/s)8.19

Max Chl Dpth (ft)8.05 Hydr. Depth (ft)6.03

Conv. Total (cfs)26199.1 Conv. (cfs)26199.1

Length Wtd. (ft)20 Wetted Per. (ft)56.77

Min Ch El (ft)827.76 Shear (lb/sq ft)2.74

Alpha1 Stream Power (lb/ft s)22.45

Frctn Loss (ft)0.18 Cum Volume (acre-ft)1.152.910.03

C & E Loss (ft)0.04 Cum SA (acres)0.570.470.03

Plan: PROP4189A Garrett's Run Reach RS: 562.31 BR U Profile: Q-500

E.G. Elev (ft)836.19 ElementLeft OBChannelRight OB

Vel Head (ft)0.85 Wt. n-Val.0.05

W.S. Elev (ft)835.34 Reach Len. (ft)27.6727.6727.67

Crit W.S. (ft)832.65 Flow Area (sq ft)326.48

E.G. Slope (ft/ft)0.005452 Area (sq ft)326.48

Q Total (cfs)2411 Flow (cfs)2411

Top Width (ft)49.84 Top Width (ft)49.84

Vel Total (ft/s)7.38 Avg. Vel. (ft/s)7.38

Max Chl Dpth (ft)8.44 Hydr. Depth (ft)6.55

Conv. Total (cfs)32653.4 Conv. (cfs)32653.4

Length Wtd. (ft)27.67 Wetted Per. (ft)52.88

Min Ch El (ft)826.9 Shear (lb/sq ft)2.1

Alpha1 Stream Power (lb/ft s)15.52

Frctn Loss (ft)0.17 Cum Volume (acre-ft)1.152.510.03

C & E Loss (ft)0.01 Cum SA (acres)0.570.40.03

ATTACHMENT A

Table 3.7.1 Sediment grade scale

Appropriate Sieve

Mesh

Size

Openings per Inch

U.S.

Millimeters

Microns Inches

TylerStandard

Class4000-2000 . . . . . . . . . . . . . . . . . . 160-80

. . . . . . . . . . . . Very large boulders

2000-1000 . . . . . . . . . . . . . . . . . . 80-40

. . . . . . . . . . . . Large boulders

1000-500 . . . . . . . . . .

. . . . . . . . 40-20

. . . . . . . . . . . . Medium boulders

500-250 . . . . . . . . . .

. . . . . . . . 20-10

. . . . . . . . . . . . Small boulders

250-130 . . . . . . . . . .

. . . . . . . . 10-5

. . . . . . . . . . . . Large cobbles

130-64 . . . . . . . . . .

. . . . . . . . 5-2.5

. . . . . . . . . . . . Small cobbles

64-32

. . . . . . . . . .

. . . . . . . . 2.5-1.3 . . . . . . . . . . . . Very coarse gravel

III-24

32-16 . . . . . . . . . . . . . . . . . . 1.3-0.6 . . . . . . . . . . . . Coarse gravel

16-8 . . . . . . . . . . . . . . . . . . 0.6-0.3 2 . . . . . . . Medium gravel

8-4 . . . . . . . . . .

. . . . . . . . 0.3-0.16 5 5 Fine gravel

4-2 . . . . . . . . . .

. . . . . . . . 0.16-0.08 9 10 Very fine gravel

2-1 2.00-1.00 2000-1000 . . . . . . . . 16 18 Very coarse sand

1-1 1.00-0.50

1000-500 . . . . . . . . 32 35

Coarse sand

1/2-1/4 0.50-0.25 500-250 . . . . . . . . 60 60 Medium sand

1/4-1/8 0.25-0.125 250-125 . . . . . . . . 115 120 Fine sand

1/8-1/16 0.125-0.062 125-62 . . . . . . . . 250 230 Very fine sand

1/16-1/32 0.062-0.031 62-31 . . . . . . . . Coarse silt

1/32-1/64 0.031-0.016 31-16 . . . . . . . . Medium silt

1/64-1/128 0.016-0.008 16-8 . . . . . . . . Fine silt

1/128-1/256 0.008-0.004 8-4 . . . . . . . . Very fine silt

1/256-1/512 0.004-0.0020 4-2 . . . . . . . . Coarse clay

1/512-1/1024 0.0020-0.0010 2-1 . . . . . . . . Medium clay

1/1024-1/2048 0.0010-0.0005 1-0.5 . . . . . . . . Fine clay

1/2048-1/4096 0.0005-0.00024 0.5-0.24 . . . . . . . . Very fine clay (Rouse, 1950, p. 776)

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