WY_129_(1)_Final_Hydraulics_Report.pdf

Hydraulics Report

WY 129 (1)

Sand Creek Bridges

Prepared by

Veronica Ghelardi, PE

Hydraulic Engineer

Central Federal Lands

October 2014 ii

Table of Contents

BACKGROUND AND OBJECTIVES

PROJECT DATA

STANDARDS

HYDROLOGIC ANALYSIS

HYDRAULIC ANALYSIS

EXISTING CONDITIONS

Bridge 1

Bridge 2

Bridge 3

Bridge 4

Bridge 5

Bridge 6

PROPOSED CONDITIONS

Proposed Bridge 1

Proposed Bridge 2

Proposed Bridge 3

Proposed Bridge 4

Proposed Bridge 5

Proposed Bridge 6

SCOUR COUNTERMEASURES

REFERENCES

APPENDIX A

HYDROLOGY

APPENDIX B

HYDRAULIC ANALYSIS

APPENDIX C

SCOUR ANALYSIS

APPENDIX D

RIPRAP ANALYSIS

iii

Table of Figures

Figure 1. Project Location Map

Figure 2. Bridge Locations

Figure 3. Bridge 1 Existing Water Surface Elevation at Upstream Face of the Bridge

Figure 4. Bridge 2 Existing Water Surface Elevation at Upstream Face of the Bridge

Figure 5. Bridge 3 Existing Water Surface Elevation at Upstream Face of the Bridge

Figure 6. Bridge 4 Existing Water Surface Elevation at Upstream Face of Bridge

Figure 7. Bridge 5 Existing 10-yr Water Surface Elevation at Upstream Face of Bridge

Figure 8. Bridge 6 Existing 10-year Water Surface Elevation at Upstream Face of Bridge

Figure 9. Bridge 1 Proposed 25-year Water Surface Elevation

Figure 10. Bridge 2 Proposed 50–year Water Surface Elevations

Figure 11. Bridge 3 Proposed 25-year Water Surface Elevation

Figure 12. Bridge 4 Proposed 25-Year Water Surface Elevation

Figure 13. Bridge 5 Proposed 10-year Water Surface Elevation

Figure 14. Bridge 6 Proposed 10-yr Water Surface Elevation

List of Tables

Table 1. Log Pearson Type III Analysis

Table 2. Wyoming Regression Equations Summary

Table 3. Comparison of Discharges for LP III Analysis and Wyoming Regression

Table 4. Discharges for Bridges 1 and 6 calculated from the Weighted Average Peak-Flow Equation

Table 5. Existing Condition Bridge Summary

Table 6. Proposed Condition Bridge Summary

Table 7. Summary of Proposed Scour Calculations for all Six Bridges

Table 8. Calculated Riprap Class and Scour Elevation for each Bridge

Table 9. Bridge Summary of Capacity, Freeboard and Scour Depths

BACKGROUND AND OBJECTIVES

The purpose of this report is to provide hydraulic recommendations for the replacement of six (6) bridges along Sand Creek Road in Crook County, Wyoming. Crook County is located in northeastern

Wyoming near the South Dakota border (Figure 1).

Figure 1. Project Location Map

The bridge locations can be referenced by the following Latitude and Longitude coordinates:

Bridge 1: 44˚30’16.60” N, 104˚05’53.75” W

Bridge 2: 44˚30’10.14” N, 104˚05’55.65” W

Bridge 3: 44˚29’54.24” N, 104˚06’08.89” W

Bridge 4: 44˚29’44.97” N, 104˚06’28.63” W

Bridge 5: 44˚29’30.26” N, 104˚06’27.36” W

Bridge 6: 44˚29’14.41” N, 104˚07’02.83” W

Begin Project

End Project

Figure 2. Bridge Locations

Central Federal Lands in cooperation with Crook County plans to replace the six timber bridges under project WY 129 (1) with bridges having capacities that are equal to or greater than the existing capacity bridges without major adjustments to the road profile. The bridge locations are shown in Figure 2.

PROJECT DATA

Sand Creek Road is south of Beulah, WY and I-90. Sand Creek is a meandering stream that runs roughly parallel to the road and flows in a south to north direction. Because of the meandering nature of the stream, the roadway crosses the stream multiple times as it makes it way north. Six single span, existing timber bridges cross Sand Creek and make up this project. Per the FLAP application Sand Creek Road has an Average Daily Traffic (ADT) of 242 vehicles per day.

STANDARDS

The Central Federal Lands Highway Division standard design flood for new bridges is the 50-year flood event with 2 ft. of freeboard. If this standard cannot be met, a risk based approach is taken and the bridge capacity is designed to be equal to or greater than the existing bridge capacity. Given the low

ADT of 242 vehicles per day, this road is considered a low volume road by CFL standards. The Crook

County FLAP request included a cost estimate for the replacement bridges with no substantial road re-grading. Therefore the proposed bridges are based on a capacity design that is equal to or greater than the existing bridges.

HYDROLOGIC ANALYSIS

The Watershed Modeling System, WMS, v 9.1.10, was used to delineate the watersheds of bridges 1 and

6. A United States Geological Service, USGS, gaging station (#06429905) is located on Sand Creek at

Ranch A, near Beulah, WY. This gage has approximately 28 years of discontinuous record. The gage is located in the middle of the six bridges at Latitude: 44.520278 N and Longitude: -104.08333 W.

The annual peak flows were acquired from the USGS website for analysis. The Log Pearson Type III (LP III) analysis is widely used for flood analyses of peak flow gage data. A minimum of 10 years of data is required to perform a statistical analysis; the more years of data, the more reliable the results. The location of gage # 06429905 was moved once in the period of record, which resulted in a change in the stage reference elevation but the location change did not affect the discharge measurements. The LP III

Analysis can be seen in Appendix A and the results are shown in Table 1.

Return Period

Q (cfs)

2 55

5 148

10 277

25 594

50 1025

100 1737

500 5623

Table 1. Log Pearson Type III Analysis

While a LP III analysis was performed on the data, there was concern about the low annual peak data and the relatively short period of record. Therefore, the USGS regression equations were calculated to use as a comparison of the LP III analysis.

The project location is in the southeastern part of Crook County and therefore it is in the USGS Wyoming Hydrologic Region 4. (See Appendix A for equations) The resulting discharges from the regression equations are shown in Table 2.

Recurrence Interval (yrs)

Discharge (cfs)

2 140

10 680 25 1315 50 2050

100 3095 500 8015

Table 2. Wyoming Regression Equations Summary

The comparison of the results showed that the two methods produced a wide difference in return period discharges, Table 3.

Recurrence

Interval (yrs)

Discharge - LP III Analysis (cfs)

Discharge –WY regression equations

(cfs)

2 55 140 10 148 680 25 277 1315 50 594 2050

100 1025 3095 500 5623 8015

Table 3. Comparison of Discharges for LP III Analysis and Wyoming Regression

To better understand the factors influencing the flood flows in this part of Wyoming, the USGS Wyoming

Water Science Center, which maintains the gage, was contacted. According to the USGS many streams in the region of our project (Black Hills) are dominated by spring flow such that high frequency flow events with low annual peaks are more prevalent than those observed in other watersheds. Other complicating factors are annual peaks generated by different events and the skew in this region has a high degree of variability and uncertainty. It was therefore recommended that the weighted approach methodology from the USGS “Peak-Flow Characteristics of Wyoming Streams” be used to determine the peak discharges.

The weighted approach uses the “regional regression equations to improve peak-flow analyses at gaging stations. For any given frequency, a weighted average of the magnitudes determined from the regional equation plus the gaging station frequency analysis generally results in a better estimate of the peak-flow magnitude at a gaged site with a short period of record.”1 For sites in the “plains and basins of the

State, records less than about 25 years are considered short. The weighted approach equation is:

QTW = (nQTS + enQTR)/ (n+en)

Where:

Peak Flow Characteristics of Wyoming Streams, Kirk Miller, Water-Resources Investigations Report 03-4107, USGS, 2003.

QTW = weighted peak flow in cfs for recurrence interval of T years n = number of annual peaks used to compute QTS

QTS = gaging station peak flow in cfs for recurrence interval of T years, determined from gaging station peak-flow frequency analysis en = average equivalent years of record for QTR

QTR = peak flow in cfs for recurrence interval of T years from regional regression equation

The weighted approach was calculated using the LP III analysis performed on the gage data and the Wyoming regional regression equations for the Black Hills.

Once the weighted gage discharge was calculated, the discharge per square mile was determined based on the gage drainage area for each return period. Bridge discharges for bridges 1 and 6 were calculated by multiplying the discharge per square mile by the bridge drainage area. The results are shown in Table 4 below for bridges 1 and 6 with discharges rounded off to the nearest 5 cfs.

Gage Bridge #1 Bridge #1 Bridge #6 Bridge #6

Return Period

Weighted Discharge

(cfs)

Discharge /sq mi (cfs)

Drainage Area (sq mi)

Discharge (cfs)

Drainage Area (sq mi)

Discharge (cfs)

2 65 0.24 272.36 65 267 65

10 345 1.25 272.36 340 267 335

25 765 2.78 272.36 760 267 745

50 1315 4.78 272.36 1300 267 1275

100 2170 7.89 272.36 2150 267 2110

500 6545 23.80 272.36 6480 267 6355

Table 4. Discharges for Bridges 1 and 6 calculated from the Weighted Average Peak-Flow Equation.

As can be seen in Table 4, the difference in the bridge discharges for the return periods 2-year through

100-year vary at most by 40 cfs (at the 100-year return period). The 500-year varies by 125 cfs between bridges 1 and 6 . Since the other four bridges are in such close proximity to and lie between bridges #1 and #6, the discharges for the above two bridges will be used for the hydraulic analysis of all bridges, as follows: Bridges 1, 2, 3, and 4 are assigned the discharges for Bridge 1; Bridges 5and 6 use the same discharges as Bridge 6.

HYDRAULIC ANALYSIS

EXISTING CONDITIONS

Atkins consulting group was involved in the scoping trip and provided some of the information the hydraulic modeling is based on such as mile post locations, type of existing structures, and channel bed material. All six bridges are single span timber bridges.

The CFLHD survey crew provided the cross sections for the hydraulic analysis at each bridge. An existing hydraulic analysis of each bridge was performed using HEC-RAS 4.1 to determine the water surface elevations at each bridge for return periods 2-, 10-, 25-yr and, for bridge #2 the 50-yr. In addition the incipient overtopping discharge was determined for all the bridges. The models extents vary for each bridge. All bridge openings are measured from abutment face to abutment face and represent the open area for flow to pass through. When discussing right or left bank, it is assumed that we are looking downstream in all instances.

When discussing the overtopping event, it is the road that is overtopping first for bridges 2 through 6. Bridge 1 shows that overtopping occurs first on the far right side of the bridge.

Bridge 1

Bridge 1 is located at Mile Post 3.4. It is a timber bridge with an opening of 31 feet. The Scoping

Report states that the channel bed is made up of fine sands and fines with some large cobbles at the bridge. An aerial view taken from Google Earth shows that the upstream 60 ft. of channel is perpendicular to the bridge and the downstream channel is perpendicular to the bridge for approximately 100 ft.

The existing bridge low-chord has an elevation of 3664.46 ft. The hydraulic model showed that the bridge passes the 25-yr flood event (760 cfs) with 0.44 ft. of freeboard (Figure3). The overtopping event is between the 25- and 50-year flood events.

Figure 3. Bridge 1 Existing Water Surface Elevation at Upstream Face of the Bridge.

Bridge 2

Bridge 2 is located at mile post 3.5 and has an opening of approximately 26 feet. The Scoping

Report states that it is founded on a timber pile foundation. The bridge is not skewed in the hydraulic model. The channel bed material is composed of sand and gravel with some large boulders. There is a steep slope on the left, upstream embankment.

The existing bridge has a 0.5% slope. Since the low-chord follows the slope of the deck, the average low chord elevation of the bridge is 3680.7 ft. The hydraulic model shows that the bridge capacity accommodates the 25-year flood event with about 1.5 feet of freeboard (Figure 4).

-100 -50 0 50 100 150 200 250

Sand Creek Br #1 Plan: Bridge #1-existing-sens .013

Geom: Br #1 - Existing from Survey

RS = 1680

Station (ft)

E le v a ti o n ft)

Legend

WS incipient

WS 25-yr

WS 10-yr

Crit incipient

WS 2-yr

Crit 25-yr

Crit 10-yr

Crit 2-yr

0.0 ft/s

0.2 ft/s

0.4 ft/s

0.6 ft/s

0.8 ft/s

1.0 ft/s

Ground

Ineff

Bank Sta

.05 .035 .05

25-year WSEL

3664.03 ft

Figure 4. Bridge 2 Existing Water Surface Elevation at Upstream Face of the Bridge.

Bridge 3

Bridge3 is located at mile post 3.9. The bridge is set on a timber foundation and has a 24 foot opening. The bridge is not skewed in the hydraulic model. The Scoping Report states that the channel bed material is comprised of fines and large cobbles.

The bridge low chord has an elevation of 3712.54 ft. The hydraulic model based on the survey cross sections shows that the bridge capacity accommodates the 25-year flood event with 1.3 feet of freeboard,( Figure 5).

of 3679.19 ft.

Figure 5. Bridge 3 Existing Water Surface Elevation at Upstream Face of the Bridge

Bridge 4

Bridge 4 is located at mile post 4.3. This bridge is founded on concrete abutments with an unknown foundation depth. The channel bed material is composed of sand with cobbles and boulders. The existing bridge has an unskewed open area of 50 feet. The aerial view from Google Earth shows that if looking downstream, upstream of the bridge splits with some flow going around a high point with a house in the middle. The split flow rejoins the channel directly upstream of the bridge on the left bank.

The returning flow is directed at the opposite bank immediately upstream of the right abutment for all flow events. During high flow events the main channel flow is skewed 45 degrees to the bridge so the bridge was skewed 45 degrees in the hydraulic model.

The bridge low chord has an elevation of 3730.25 ft. The hydraulic model shows that the bridge capacity accommodates the 10-year flow with 2.7 feet of freeboard (Figure 6). The 25-year flood event passes through the structure but it is under pressure flow.

-100 -50 0 50 100 150

Sand Creek Br#3 Plan: Br #3 existing - .01

Geom: Br #3- existing from survey

RS = 3193

Station (ft)

E le v a ti o n ft)

Legend

WS 50-yr

WS 25-yr

WS 10-yr

WS 2-yr

2.6 ft/s

2.8 ft/s

3.0 ft/s

3.2 ft/s

3.4 ft/s

3.6 ft/s

3.8 ft/s

Ground

Ineff

Bank Sta

.045 .035 .045

25-yr WSEL

3711.26 ft.

Figure 6. Bridge 4 Existing Water Surface Elevation at Upstream Face of Bridge

Bridge 5

Bridge 5 located at mile post 4.7 is founded on timber piles and is 41 feet long. The bridge is set at a 53 degree skew to the flow with a steep, upstream right embankment. The bridge was skewed 53 degrees in the hydraulic model.

The bridge low chord has an elevation of 3754.07ft. The hydraulic model reveals that the existing bridge capacity is the 10-year flood event with 1.56 feet of freeboard, (Figure 7). The 25-yr flood event passes through the bridge but is under pressure flow with no freeboard.

-50 0 50 100 150 200

Sand Creek Br#4 Plan: Sand Creek Es Br #4_sens 012

Geom: Br#4 Existing

RS = 4495

Station (ft)

E le v a ti o n ft)

Legend

WS 25-yr

WS 10-yr

WS 2-yr

1.5 ft/s

2.0 ft/s

2.5 ft/s

3.0 ft/s

3.5 ft/s

4.0 ft/s

4.5 ft/s

Ground

Ineff

Bank Sta

.05 .

.035 .045

10-year WSEL

3727.59 ft

Figure 7. Bridge 5 Existing 10-yr Water Surface Elevation at Upstream Face of Bridge.

Bridge 6

Bridge 6 is located at mile post 5.5. The existing bridge is 36.5 ft. long and is founded on a timber foundation. Timber lagging consisting of 4” x 12” planks are placed behind the timber piles to retain fill behind the abutments. The bridge is set at a 45 degree skew to the flow. The stream bed is comprised of gravels, cobbles with a few boulders.

The bridge low chord has an elevation of 3793.30 ft. The bridge cross sections for the existing hydraulic model were skewed 45 degrees to accommodate the bridge skew. The model showed that the 10-year discharge passes the bridge with 1.7 feet of freeboard, Figure 8. The incipient overtopping flow is 615 cfs, between the 10- and 25-yr flows.

-80 -60 -40 -20 0 20 40 60 80

Sand Creek Br#5 Plan: Sand Creek Br #5 - 015

Geom: Bridge #5 Existing-skew angle used at br

RS = 5235

Station (ft)

E le v a ti o n ft)

Legend

WS incipient

WS 25-yr

WS 10-yr

WS 2-yr

2.0 ft/s

2.2 ft/s

2.4 ft/s

2.6 ft/s

2.8 ft/s

3.0 ft/s

3.2 ft/s

Ground

Ineff

Bank Sta

.045 .035 .045

10-year WSEL

3752.51 ft

Figure 8. Bridge 6 Existing 10-year Water Surface Elevation at Upstream Face of Bridge

Three of the existing six bridges pass the 25-year flood event with freeboard. The three remaining bridges pass the 10-year flood event with freeboard. Bridge 6 overtops the road for flows between the

10- and 25-year flows. Table 5 provides a summary of the existing condition for the six bridges.

0 20 40 60 80 100

Sand_Creek_Br#6 Plan: 1) exist sens 012

Geom: Br 6 existing -survey skewed 45 degrees

RS = 6314

Station (ft)

E le v a ti o n ft)

Legend

WS incipient

WS 10-yr

WS 2-yr

1.0 ft/s

1.2 ft/s

1.4 ft/s

1.6 ft/s

1.8 ft/s

2.0 ft/s

Ground

Ineff

Bank Sta

.05 .035 .05

10-Year WSEL

3791.64 ft.

Bridge

Unskewed Length (ft)

Return Period Passing

WSEL

(ft)

Velocity (ft/s)

1 37 25-yr 3664.03 3.4

2 24 25-yr 3679.17 7.09

3 26 25-yr 3711.25 6.89 4 51 10-yr 3727.59 5.75

5 37 10-yr 3752.51 4.69

6 37 10-yr 3791.64 3.88

Table 5. Existing Condition Bridge Summary

PROPOSED CONDITIONS

The intent of this project to replace the six bridges with bridges of equal or greater capacity and minimum impact to the existing road profile. Existing bridges 1,2,5, and 6 will be replaced with GRS-IBS bridges with vertical abutment walls. Bridges 3 and 4 will be replaced with bridges on deep foundations with spill-through abutments. All replacement bridge openings are measured from abutment face to abutment face and represent the opening for flow to pass through.

In all cases, the design flow is that flow with at least 1.5 feet of freeboard. 1.5 feet of freeboard was selected to encourage passage of large debris through the bridge. In some cases this means that the bridge capacity can pass the 25-yr flood but there is too little freeboard so the selected design storm is the 10-yr flood event.

Proposed Bridge 1

The proposed bridge replacement is a GRS bridge with a 38 foot opening from abutment to abutment face and a low chord elevation of 3665.74 ft. This bridge accommodates the 25-year flow with 1.8 feet of freeboard, Figure 9. The overtopping flow of 1700 cfs is greater than the 50-year discharge. Since the proposed road profile increases in grade from south to north, the overtopping would occur first on the road south of the bridge.

Figure 9. Bridge 1 Proposed 25-year Water Surface Elevation

Proposed Bridge 2

The proposed bridge replacement is a GRS bridge with a 30 foot opening from abutment to abutment face. The low chord of the bridge matches the slope of the bridge deck that is on a 0.8% slope. The average elevation of the low chord is 3681.92 ft. The bridge accommodates 50- year flood event with

2.1 ft. of freeboard, Figure 10. The incipient overtopping discharge is 1518 cfs.

-100 -50 0 50 100 150 200 250

Sand Creek Br #1 Plan: Bridge #1-proposed GRS 2-5-14

Geom: Br #1 - Proposed GRS 2-5-14

RS = 1680

Station (ft)

E le v a ti o n ft)

Legend

WS incipient

WS 50-yr

WS 25-yr

WS 10-yr

WS 2-yr

0.0 ft/s

0.2 ft/s

0.4 ft/s

0.6 ft/s

0.8 ft/s

1.0 ft/s

Ground

Ineff

Bank Sta

.05 .035 .05

3664.01 ft.

Figure 10. Bridge 2 Proposed 50–year Water Surface Elevations

Proposed Bridge 3

The proposed bridge 3 replacement is a 44 ft. long bridge set on deep foundations with spill-through abutments. The bridge opening has an unskewed length of 37 feet. The bridge low chord follows the bridge deck grade of 1% giving an average low chord elevation of 3713.08 ft. The bridge passes the 25-year flood flow with 1.5 ft. of freeboard, Figure 11. The incipient overtopping discharge is 1295 cfs.

Slightly less than the 50-yr discharge.

50-year WSEL

3679.11 ft.

Figure 11. Bridge 3 Proposed 25-year Water Surface Elevation

Proposed Bridge 4

The proposed bridge 4 is a 49 ft. long bridge set on deep foundations with spill-through abutments set at a 45 degree skew to the road. The unskewed bridge opening length is 42 feet. High flows are skewed to the bridge at a 45 degree angle so a bridge length of 29.7 ft. was used in the HEC RAS model. The bridge low chord follows the bridge deck grade of 0.8% so the average low chord is 3730.8 ft. providing

2.3 feet of freeboard for the 25-year flow, Figure 12. The incipient overtopping discharge is 1100 cfs.

-100 -50 0 50 100 150

Sand Creek Br#3 Plan: B_Prop 37 ft bridge-new road profi le

Geom: Br #3- B proposed 37 ft(2-3-14) br-Leo

RS = 3193

Station (ft)

E le v a ti o n ft)

Legend

WS 50-yr

WS incipient

WS 25-yr

WS 10-yr

WS 2-yr

2.2 ft/s

2.4 ft/s

2.6 ft/s

2.8 ft/s

3.0 ft/s

3.2 ft/s

3.4 ft/s

Ground

Ineff

Bank Sta

.045 .035 .045

3711.63 ft.

Figure 12. Bridge 4 Proposed 25-Year Water Surface Elevation

Proposed Bridge 5

The proposed bridge 5 is a GRS-IBS bridge. The road is skewed 53 degrees to the channel. The proposed unskewed bridge length is 55.67 ft. The proposed abutments are skewed 30 degrees and HEC

RAS bridge cross sections were skewed 23 degrees to reflect the remaining abutment skew in relation to the channel flow. The bridge low chord will follow the 1% grade of the bridge deck giving an average low chord elevation of 3755.07 feet. The new bridge will accommodate the 10-yr flow with 2.5 feet of freeboard, Figure 13. The 25-yr passes the bridge with 0.56 feet of freeboard. The incipient overtopping discharge is 950 cfs.

-50 0 50 100 150 200

Sand Creek Br#4 Plan: Sand Cr #4 Proposed 42' opening

Geom: Br#4 A_Proposed 42' br opening

RS = 4495

Station (ft)

E le v a ti o n ft)

Legend

WS 25-yr

WS 10-yr

WS 2-yr

1.0 ft/s

1.5 ft/s

2.0 ft/s

2.5 ft/s

3.0 ft/s

3.5 ft/s

Ground

Ineff

Bank Sta

.05 .045 .035 .045

3728.54 ft.

Figure 13. Bridge 5 Proposed 10-year Water Surface Elevation

Proposed Bridge 6

The proposed bridge 6 is a GRS IBS bridge with abutments set at 30 degrees to the road. The bridge is skewed 45 degrees to the flow with an unskewed length of 65 feet. The bridge was skewed 15 degrees in the HEC RAS model. The bridge low chord follows the -1% grade of the road so that the average low chord is 3793.73 feet. The bridge accommodates the 10-yr flood flow with 2.3 ft. of freeboard, Figure

14. The bridge passes the 25-yr flood flow with 0.4 feet of freeboard. The incipient overtopping discharge is 1230 cfs.

10-yr WSEL

3752.53 ft.

Figure 14. Bridge 6 Proposed 10-yr Water Surface Elevation

A summary of the proposed bridge information is shown in Table 6.

Unskewed Length (ft)

Return Period Passing

WSEL

(ft)

Velocity (ft/s)

1 38 25-yr 3664.01 3.39

2 38 50-yr 3679.81 10.02

3 39 25-yr 3711.63 5.98

4 42 25-yr 3728.54 8.17

5 55.7 10-yr 3752.53 3.39

6 55 10-yr 3791.4 2.90

Table 6. Proposed Condition Bridge Summary

SCOUR

A scour analysis was performed at each bridge for the incipient overtopping discharge. The analyses included evaluating abutment scour using the methods found in HEC 18 and vertical contraction (pressure) scour. The

NCHRP method was used for estimating abutment scour which includes contraction scour so no separate scour analysis was conducted. The incipient overtopping discharge is the discharge that is just about to overtop the road. This is the discharge with the most scour potential due to the fact that all the flow must pass under the bridge. Once the flow overtops the road it provides relief so that larger discharges typically do not increase the scour potential at the bridge so no check scour computations were performed.

10-yr WSEL

3791.38 ft.

The largest scour depth calculated at each bridge is shown in Table 5. The scour analysis for each bridge is shown in Appendix C. The GRS abutment footings should be a minimum of 1 ft. below the scour elevation or in this case, the top of the footing will be placed at the scour elevation.

Bridge #

Incipient Discharge

(cfs)

Abutment

Scour Depth (ft)

Pressure

Largest Scour

Scour Elevation (ft)

1 1700 0 2.4 2.4 3652.00

2 1522 4.2 2.5 4.2 3669.70

3 1295 5.5 3.9 5.5 3700.54

4 1100 7.8 8.7 8.7 3714.70

5 950 0 1.2 1.2 3747.64

6 1275 0 0 0.0 3787.66

Table 7. Summary of Proposed Scour Calculations for all Six Bridges

SCOUR COUNTERMEASURES

All bridges will have riprap installed as a countermeasure to protect the bridge abutments from scour.

Riprap sizing at the abutments was based on HEC 23 Volume 2. The riprap sizing calculations are shown in Appendix D. Table 6 shows the preliminary riprap size needed at each bridge for scour protection and the scour elevation. In some cases riprap sizes in Table 6 may be increased for cost benefit. The calculated riprap classes for each bridge are shown in Appendix D.

Calculated Rip Rap Class

Recommended Rip Rap Class

Elevation (ft)

1 2 (D50 = 9 in) 2 3752.0

2 6 (D50 = 21 in) 6 3669.70

3 5 (D50 = 18in) 6 3700.74

4 5 (D50 = 18 in) 6 3713.60

5 2 (D50 =9 in) 2 3747.75

6 1 (D50 = 9 in) 2 3787.54 Table 8. Calculated Riprap Class and Scour Elevation for each Bridge

SUMMARY

The discharges for the 2-, 10-, 25-, 50-, and 100-yr return periods were determined using the weighted approach method based on the USGS Wyoming Regression Equations and a Log-Pearson Type III analysis of the gage data.

The replacement bridges capacity will be greater than or equal to the existing bridge capacity. Bridges

1,2,5 and 6 will be GRS-IBS bridges and bridges 3 and 4 will be replaced with bridges founded on deep foundations with spill-through abutments. The top of the GRS abutment foundations will be placed at the scour elevation.

Table 7 provides a summary of the existing and proposed bridge capacities, the depth of freeboard for the design flood, and the proposed bridge scour depths.

Bridge #1 38’ opening

Bridge #2 38’ opening

Bridge #3 37’ opening

Bridge #4 42’ opening*

Bridge #5 55’ 8” opening*

Bridge #6 55’ opening*

Existing Flood event passing under the bridge

25-yr

10-yr

Proposed Flood event passing under the bridge

50-yr

Freeboard (ft)

1.8

2.1

1.5

2.3

2.5

2.3

Scour depth

2.4

4.2

5.5

9.8

1.2

Table 9. Bridge Summary of Capacity, Freeboard and Scour Depths.

* bridge opening unskewed length

REFERENCES

Aquaveo, LLC (2013) Watershed Modeling System 9.1 (www.aquaveo.com).

Federal Highway Administration (2013) Hydraulic Toolbox, (www.fhwa.dot.gov/engineering/hydraulics/index.cfm).

Federal Highway Administration (2008) “Project Development and Design Manual” Federal Lands

Highway Division. US Department of Transportation. Chpt. 7.

Federal Highway Administration (2002)” Highway Hydrology, Hydraulic Design Series No0.2, Second

Edition.

Federal Highway Administration (2009) Bridge Scour and Stream Instability Countermeasures:

Experience, Selection, and Design Guidance, Hydraulic Engineering Circular No, 23, Volume 2, Third

Edition.

Federal Highway Administration, US Army Corps of Engineers (2010) “Hydrologic Engineering Center River Analysis Software (HEC-RAS)” V.

4.1. Developed by USACE, Davis, CA.

USGS National Water Information System: Web Interface http://nwis.waterdata.usgs.gov/nwis/uv/?site_no=06429905

USGS Peak-Flow Characteristics of Wyoming Streams, Miller, Kirk A., Water-Resources Investigations

Report 03-4107, 2003.

Google Earth Pro, 2011.

http://www.aquaveo.com/ file:///C:/Users/bart.bergendahl/AppData/Local/Microsoft/Windows/Temporary%20Internet%20Files/Content.Outlook/1965SCOP/www.fhwa.dot.gov/engineering/hydraulics/index.cfm http://nwis.waterdata.usgs.gov/nwis/uv/?site_no=06429905

APPENDIX A

HYDROLOGY

LOG PEARSON TYPE III ANALYSIS

Rank Discharge (Q-high to low) Log of Q

(Log Q -avg(logQ))^2

(Log Q - avg (LogQ))^3

Return Period Pe % k 1.0 k 1.1 slope k

1.08 Y PE CFS

1 1230 3.089905 1.599495 2.022900 30.00 3.3333 0 2.608 3.025 1060

2 514 2.710963 0.784588 0.694964 15.00 6.6667 0 2.074 2.780 602

294 2.468347 0.413647 0.266038 10.00

10.0000 1.340

1.3409 0.00053

1.340

2.442 277

4 255 2.406540 0.337964 0.196474 7.50 13.3333 0 1.043 2.305 202

5 248 2.394452 0.324055 0.184471 6.00 16.6667 0 0.892 2.236 172

6 164 2.214844 0.151827 0.059160 5.00 20.0000 0.757 0.7453 -0.0122 0.748 2.169 148

7 164 2.214844 0.151827 0.059160 4.29 23.3333 0 0.621 2.111 129

8 130 2.113943 0.083376 0.024075 3.75 26.6667 0 0.495 2.053 113

9 127 2.103804 0.077624 0.021627 3.33 30.0000 0 0.368 1.995 99

10 96 1.982271 0.024673 0.003876 3.00 33.3333 0 0.270 1.949 89

11 71 1.851258 0.000679 0.000018 2.73 36.6667 0 0.172 1.904 80

12 62 1.792392 0.001076 -0.000035 2.50 40.0000 0 0.074 1.859 72

13 56 1.748188 0.005930 -0.000457 2.31 43.3333 0 -0.013 1.819 66

14 47 1.672098 0.023438 -0.003588 2.14 46.6667 0 -0.095 1.782 60

15 44 1.643453 0.033030 -0.006003 2.00 50.0000 -0.164 -0.1797 -0.0157 -0.177 1.744 55

16 43 1.633468 0.036759 -0.007048 1.88 53.3333 0 -0.253 1.709 51

17 37 1.568202 0.066045 -0.016973 1.76 56.6667 0 -0.330 1.674 47

18 35 1.544068 0.079032 -0.022218 1.67 60.0000 0 -0.404 1.639 44

19 34 1.531479 0.086268 -0.025338 1.58 63.3333 0 0.477 2.045 111

20 34 1.531479 0.086268 -0.025338 1.50 66.6667 0 -0.550 1.572 37

21 32 1.505150 0.102428 -0.032781 1.43 70.0000 0 -0.623 1.538 35

22 31 1.491362 0.111444 -0.037203 1.36 73.3333 0 -0.698 1.504 32

23 29 1.462398 0.131621 -0.047751 1.30 76.6667 0 -0.774 1.469 29

24 26 1.414973 0.168281 -0.069032 1.25 80.0000 0 -0.849 1.435 27

25 25 1.397940 0.182546 -0.077993 1.20 83.3333 0 -0.936 1.394 25

26 25 1.397940 0.182546 -0.077993 1.15 86.6667 0 -1.024 1.354 23

27 24 1.380211 0.198009 -0.088111 1.11 90.0000 0 -1.111 1.314 21

22 1.342423 0.233068 -0.112518 1.07

93.3333

0 -1.229 1.260 18

29 21 1.322219 0.252983 -0.127244 1.03 96.6667 0 -1.369 1.195 16

Average Average Sum Sum

135.17 1.825 5.931 2.755 variance 0.2118 std deviation 0.4602 skew coefficient 1.08

TABLE A1. WEIBULL PLOTTING OF GAGE DATA

TABLE A2. PLOT OF WEIBULL PLOTTING RESULTS

0102030405060708090100

D is ch ar ge s

(c fs

Exceedance Probability %

Sand Creek Peak Flow from Gage

LP III peak flows for std return periods

Annual Peak flows

USBS WYOMING REGRESSION EQUATIONS, REGION 4 (BLACK HILLS)

Equation

SEE

SEP

Average Equivalent years of record

95-% prediction interval factor

Lower Limit

Upper Limit

Q2 = 6.26(Area0.506) (MAR1.33)(LAT-40)-0.315 46 53 3.2 .348 2.87

Q10 = 16.9 (Area0.518) (MAR1.12)(LAT-40)0.107 45 54 6.3 .345 2.90

Q25 = 23.5(Area0.536) (MAR1.05)(LAT-40)0.283 43 54 8.9 .345 2.90

Q50 = 29.1(Area0.549) (MAR1.01)(LAT-40)0.403 42 54 11.0 .344 2.91

Q100 = 35.3(Area0562) (MAR0.963)(LAT-40)0.517 42 54 13.1 .342 2.92 Table A3. Equations for estimating peak-flow characteristics (QTR), Eastern Mountains Region, Wyoming Region

4. (SEE, average standard error of estimate; SEP, average standard error of prediction, QT, estimated peak flow for recurrence interval T years; Area, total drainage area in sq. mi.)

The weighted average peak-flow calculation is made with the following equation:

QTW = (nQTS + enQTR)/ (n+en)

Where:

QTW = weighted peak flow in cfs for recurrence interval of T years n = number of annual peaks used to compute QTS

QTS = gaging station peak flow in cfs for recurrence interval of T years, determined from gaging station peak-flow frequency analysis en = average equivalent years of record for QTR

QTR = peak flow in cfs for recurrence interval of T years from regional regression equation

Weighted

(cfs)

Q 2w 64

Q 10w 351

Q 25w 768

Q 50w 1315

Q 100w 2170

Q 500w 6545

Table A4. Calculated Weighted Discharges.

Weighted

(cfs)

LP III

Analysis

(cfs)

WY

Regression Equation

(cfs)

Q 2w 65 55 140

Q 10w 345 277 680

Q 25w 765 594 1315

Q 50w 1315 1025 2050

Q 100w 2170 1737 3095

Q 500w 6545 5623 8015

TABLE A5. Summary of LP III, Regional Regression Equations, and Weighted Discharges.

Gage

#1 Bridge

#6

Return Period weighted cfs Q/sq mi Q (cfs) Q (cfs)

2 65 0.24 64 63

10 345 1.25 342 335

25 765 2.78 758 743

50 1315 4.78 1302 1277

100 2170 7.89 2149 2107

500 6545 23.80 6482 6354

Table A6. Weighted Discharges for Bridges 1 and 6.

APPENDIX B

HYDRAULIC ANALYSIS

PROPOSED HEC RAS RESULTS

BRIDGE 1

Reach River Sta Profile

Q

Total Min Ch El

W.S.

Elev Crit W.S.

E.G.

Elev E.G. Slope Vel Chnl Flow Area

Top

Width

Froude #

Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

XS1 2214 2-yr 65 3668.1 3669.7 3669.7 3669.96 0.024603 4.15 15.65 31.25 1.03

XS1 2214 10-yr 340 3668.1 3670.69 3670.69 3671.19 0.012543 5.86 67.11 71.7 0.88

XS1 2214 25-yr 760 3668.1 3671.41 3671.41 3672.18 0.01212 7.61 121.54 79.77 0.92

XS1 2214 50-yr 1300 3668.1 3672.09 3672.09 3673.14 0.011957 9.1 178.17 87.6 0.96

XS1 2214 incipient 1700 3668.1 3672.53 3672.52 3673.74 0.011659 9.9 217.91 94.55 0.97

XS1 1680 2-yr 65 3654.46 3661.05 3656.47 3661.06 0.000035 0.57 114.24 30.25 0.05

XS1 1680 10-yr 340 3654.46 3662.57 3658.36 3662.64 0.000332 2.04 171.01 45.09 0.17

XS1 1680 25-yr 760 3654.46 3664.01 3659.8 3664.19 0.000642 3.39 246.02 149.76 0.24

XS1 1680 50-yr 1300 3654.46 3665.42 3661.18 3665.72 0.000872 4.53 323.59 232.99 0.29

XS1 1680 incipient 1700 3654.46 3666.69 3662.07 3667.04 0.000837 4.92 393.44 250.93 0.29

XS1 1660 Bridge

XS1 1640 2-yr 65 3654.5 3661.05 3656.65 3661.06 0.000058 0.68 95.98 27.62 0.06

XS1 1640 10-yr 340 3654.5 3662.53 3658.69 3662.62 0.000507 2.4 147.07 62.6 0.2

XS1 1640 25-yr 760 3654.5 3663.91 3660.26 3664.14 0.000943 3.91 220.97 153.17 0.28

XS1 1640 50-yr 1300 3654.5 3665.24 3661.78 3665.61 0.001255 5.16 295.15 213.66 0.34

XS1 1640 incipient 1700 3654.5 3666.05 3662.72 3666.53 0.001417 5.88 340.79 240.16 0.36

XS1 1569 2-yr 65 3659.63 3661.02 3661.04 0.001068 1.17 62.8 97.74 0.23

XS1 1569 10-yr 340 3659.63 3662.52 3661.14 3662.56 0.000587 1.77 234.96 126.64 0.21

XS1 1569 25-yr 760 3659.63 3663.95 3664.01 0.000492 2.25 425.77 139.87 0.21

XS1 1569 50-yr 1300 3659.63 3665.33 3665.42 0.000454 2.66 628.09 152.34 0.21

XS1 1569 incipient 1700 3659.63 3666.19 3666.29 0.00044 2.91 762.06 160.07 0.21

XS1 1088 2-yr 65 3657.69 3659.38 3659.38 3659.79 0.020582 5.17 12.56 15.62 1.02

XS1 1088 10-yr 340 3657.69 3660.89 3660.89 3661.67 0.016412 7.1 47.87 31.19 1.01

XS1 1088 25-yr 760 3657.69 3662.06 3662.06 3663.15 0.014002 8.39 91.41 43.26 0.99

XS1 1088 50-yr 1300 3657.69 3663.05 3663.05 3664.51 0.011497 9.75 139.69 53.54 0.96

XS1 1088 incipient 1700 3657.69 3663.66 3663.66 3665.34 0.010655 10.54 174.26 59.82 0.95

BRIDGE 2

Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude #

Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

XS2 2504 2-yr 65 3680.03 3681.14 3681.14 3681.34 0.025772 3.6 18.13 49.2 1.02

XS2 2504 10-yr 340 3680.03 3681.86 3681.86 3682.33 0.016124 5.72 66.48 74.51 0.96

XS2 2504 25-yr 760 3680.03 3682.52 3682.52 3683.27 0.014416 7.39 118.12 82.69 0.98

XS2 2504 50-yr 1300 3680.03 3683.25 3683.25 3684.21 0.011957 8.49 184.41 103.98 0.95

XS2 2504 incipient 1517 3680.03 3683.48 3683.48 3684.51 0.011699 8.9 208.27 109.17 0.95

XS2 2379 2-yr 65 3674.96 3676.6 3676.81 3677.37 0.038192 7.07 9.2 11.23 1.38

XS2 2379 10-yr 340 3674.96 3678.19 3678.59 3679.6 0.0282 9.54 35.65 22.11 1.32

XS2 2379 25-yr 760 3674.96 3680.18 3679.84 3681.1 0.009541 7.67 99.04 37.7 0.83

XS2 2379 50-yr 1300 3674.96 3681.57 3680.96 3682.65 0.007476 8.33 156.9 59.19 0.77

XS2 2379 incipient 1517 3674.96 3682.11 3681.31 3683.15 0.006139 8.28 199.52 86.83 0.72

XS2 2344.* 2-yr 65 3674.61 3676.53 3676.42 3676.88 0.013939 4.75 13.68 14.3 0.86

XS2 2344.* 10-yr 340 3674.61 3678.12 3678.12 3678.97 0.015243 7.39 45.98 26.46 0.99

XS2 2344.* 25-yr 760 3674.61 3679.44 3679.39 3680.68 0.013236 8.92 85.22 32.47 0.97

XS2 2344.* 50-yr 1300 3674.61 3681.11 3680.57 3682.35 0.008672 8.95 145.33 39.52 0.82

XS2 2344.* incipient 1517 3674.61 3681.66 3680.98 3682.9 0.007328 8.97 177.94 74.72 0.77

XS2 2309.* 2-yr 65 3674.25 3675.88 3675.88 3676.31 0.019386 5.24 12.41 14.41 0.99

XS2 2309.* 10-yr 340 3674.25 3677.26 3677.42 3678.33 0.020746 8.29 41.03 24.87 1.14

XS2 2309.* 25-yr 760 3674.25 3679.12 3678.73 3680.23 0.01034 8.44 90.05 28.81 0.84

XS2 2309.* 50-yr 1300 3674.25 3680.1 3680.1 3681.91 0.013835 10.82 120.17 32.76 1

XS2 2309.* incipient 1517 3674.25 3680.56 3680.56 3682.5 0.013454 11.19 135.63 34.45 0.99

XS2 2274 2-yr 65 3673.9 3675.85 3675.16 3675.93 0.002372 2.39 27.22 20.69 0.37

XS2 2274 10-yr 340 3673.9 3677.51 3676.6 3677.93 0.004663 5.2 65.36 24.08 0.56

XS2 2274 25-yr 760 3673.9 3679.11 3678.03 3679.87 0.00522 6.99 110.72 33.04 0.62

XS2 2274 50-yr 1300 3673.9 3679.82 3679.39 3681.35 0.008582 10.02 135.47 37.57 0.82

XS2 2274 incipient 1517 3673.9 3680.41 3679.87 3681.99 0.007618 10.22 157.18 41.51 0.79

XS2 2250 Bridge

XS2 2240 2-yr 65 3674.38 3675.37 3675.37 3675.69 0.022377 4.54 14.32 22.6 1

XS2 2240 10-yr 340 3674.38 3676.66 3676.66 3677.55 0.016961 7.56 44.96 24.92 0.99

XS2 2240 25-yr 760 3674.38 3677.97 3677.97 3679.41 0.015051 9.61 79.12 27.1 0.99

XS2 2240 50-yr 1300 3674.38 3679.14 3679.29 3681.24 0.015164 11.61 112.61 30.49 1.04

XS2 2240 incipient 1517 3674.38 3679.46 3679.78 3681.89 0.016071 12.52 122.44 32.86 1.08

XS2 2155 2-yr 65 3668.95 3673.11 3670.41 3673.12 0.000052 0.64 124.61 59.52 0.06

XS2 2155 10-yr 340 3668.95 3675.09 3671.57 3675.13 0.000188 1.7 301.78 134.1 0.13

XS2 2155 25-yr 760 3668.95 3676.78 3672.67 3676.83 0.000229 2.27 517.96 183.37 0.15

XS2 2155 50-yr 1300 3668.95 3678.3 3673.71 3678.37 0.000257 2.76 728.25 209.91 0.17

XS2 2155 incipient 1517 3668.95 3678.8 3674.05 3678.88 0.000267 2.92 801.85 219.41 0.17

XS2 2058 2-yr 65 3671.7 3672.77 3672.69 3673.07 0.015016 4.41 14.73 18.53 0.87

XS2 2058 10-yr 340 3671.7 3674.16 3674.13 3674.99 0.015 7.31 46.51 27.14 0.98

XS2 2058 25-yr 760 3671.7 3675.4 3675.4 3676.64 0.014124 8.95 84.95 34.81 1.01

XS2 2058 50-yr 1300 3671.7 3676.57 3676.57 3678.14 0.011844 10.12 131.17 44.5 0.97

XS2 2058 incipient 1517 3671.7 3676.98 3676.98 3678.64 0.010859 10.42 151.19 53.25 0.95

BRIDGE 3

Reach

River

Sta Profile

Q

Tota l

Min Ch

El

W.S.

Elev Crit W.S.

E.G.

Elev

E.G.

Slope

Vel

Chn l

Flow

Area

Top

Width

Froude #

Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft)

(ft/s

) (sq ft) (ft)

XS3 3268 2-yr 65 3706.29 3708.24 3707.76 3708.4 0.005174 3.14 20.68 18.97 0.53

XS3 3268 10-yr 340 3706.29 3710.14 3709.33 3710.5 0.003999 4.87 76.73 45.67 0.54

XS3 3268 25-yr 760 3706.29 3712.03 3710.64 3712.37 0.002159 5.18 195.99 80.57 0.43

XS3 3268 50-yr 1300 3706.29 3714.55 3711.72 3714.74 0.000811 4.28 513.08 178.7 0.29

XS3 3268 incipient 1295 3706.29 3713.71 3711.7 3714.06 0.001613 5.54 372.89 148.92 0.39

XS3 3193 2-yr 65 3706.24 3707.9 3707.5 3708.03 0.004691 2.9 22.43 21.8 0.5

XS3 3193 10-yr 340 3706.24 3709.87 3708.85 3710.21 0.003757 4.69 72.47 26.8 0.5

XS3 3193 25-yr 760 3706.24 3711.63 3710.09 3712.16 0.003519 5.98 139.58 50.16 0.51

XS3 3193 50-yr 1300 3706.24 3714.35 3711.63 3714.65 0.001261 4.99 389.24 172.25 0.33

XS3 3193 incipient 1295 3706.24 3713.26 3711.62 3713.88 0.002825 6.66 224.58 106.23 0.49

XS3 3170

XS3 3164 2-yr 65 3705.58 3707.37 3706.6 3707.45 0.00198 2.27 28.6 20.03 0.34

XS3 3164 10-yr 340 3705.58 3709.39 3708.04 3709.73 0.003379 4.64 73.21 24.1 0.47

XS3 3164 25-yr 760 3705.58 3710.63 3709.5 3711.47 0.005933 7.35 103.49 25.96 0.63

XS3 3164 50-yr 1300 3705.58 3711.17 3711.01 3713.06 0.011659

11.0

5 120.81 33.37 0.9

XS3 3164 incipient 1295 3705.58 3710.75 3711.01 3713.05 0.015674

12.1

5 107 32.47 1.03

XS3 3123 2-yr 65 3705.83 3707.27 3706.69 3707.35 0.002528 2.29 28.39 24.71 0.38

XS3 3123 10-yr 340 3705.83 3709.35 3707.95 3709.56 0.001906 3.79 112.93 86.99 0.38

XS3 3123 25-yr 760 3705.83 3710.84 3709.54 3711.04 0.001452 4.28 267.67 123.49 0.35

XS3 3123 50-yr 1300 3705.83 3711.85 3710.34 3712.11 0.001563 5.07 405.37 160.05 0.38

XS3 3123 incipient 1295 3705.83 3711.84 3710.35 3712.1 0.001562 5.06 404.2 159.5 0.38

XS3 3039 2-yr 65 3704.75 3706.92 3706.53 3707.14 0.007007 3.75 17.32 15.35 0.62

XS3 3039 10-yr 340 3704.75 3708.86 3708.29 3709.36 0.007005 5.66 60.51 32.79 0.69

XS3 3039 25-yr 760 3704.75 3710.01 3709.79 3710.83 0.007001 7.54 123.09 81.96 0.74

XS3 3039 50-yr 1300 3704.75 3710.87 3710.8 3711.87 0.007005 8.84 204.35 107.15 0.77

XS3 3039 incipient 1295 3704.75 3710.86 3710.8 3711.86 0.007004 8.83 203.64 106.96 0.77

BRIDGE 4

Reac h

River

Sta Profile

Q

Total Min Ch El W.S. Elev Crit W.S.

E.G.

Elev E.G. Slope Vel Chnl

Flow

Area

Top

Width

Froude

# Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

XS4 4663 2-yr 65 3725.82 3727.15 3727.15 3727.55 0.021743 5.07 12.86 17.55 1.04

XS4 4663 10-yr 340 3725.82 3728.64 3728.64 3729.4 0.011666 7.3 55.73 44.37 0.9

XS4 4663 25-yr 760 3725.82 3730.13 3729.93 3730.5 0.003912 6.09 235.63 218.04 0.57

XS4 4663 50-yr 1300 3725.82 3732.66 3730.46 3732.71 0.000371 2.68 923.4 327.4 0.19

XS4 4663 Incipient 1100 3725.82 3732.3 3730.32 3732.34 0.000383 2.62 806.63 311.84 0.19

XS4 4495 2-yr 65 3723.4 3725.47 3724.83 3725.57 0.002832 2.61 24.91 18.94 0.4

XS4 4495 10-yr 340 3723.4 3726.81 3726.34 3727.46 0.008315 6.5 52.27 21.78 0.74

XS4 4495 25-yr 760 3723.4 3728.54 3727.76 3729.57 0.006946 8.17 95.95 30.93 0.73

XS4 4495 50-yr 1300 3723.4 3732.2 3729.36 3732.57 0.001325 5.53 379.07 203.03 0.35

XS4 4495 Incipient 1100 3723.4 3731.66 3728.86 3732.18 0.001742 6.03 214.51 172.48 0.4

XS4 4475

XS4 4468 2-yr 65 3723.89 3725.18 3724.88 3725.36 0.00681 3.43 18.97 18.89 0.6

XS4 4468 10-yr 340 3723.89 3726.76 3726.34 3727.43 0.00883 6.56 51.83 22.69 0.76

XS4 4468 25-yr 760 3723.89 3727.34 3727.84 3729.43 0.022654 11.59 65.56 24.6 1.25

XS4 4468 50-yr 1300 3723.89 3729.29 3729.29 3731.11 0.010595 10.89 124.95 49.3 0.92

XS4 4468 Incipient 1100 3723.89 3728.76 3728.76 3730.5 0.011995 10.62 105.61 34.24 0.96

XS4 4376 2-yr 65 3723.53 3725.1 3724.41 3725.15 0.001463 1.74 37.28 32.78 0.29

XS4 4376 10-yr 340 3723.53 3726.8 3725.47 3726.98 0.002242 3.36 101.06 45.29 0.4

XS4 4376 25-yr 760 3723.53 3728.07 3726.58 3728.37 0.002829 4.47 180.37 130.65 0.47

XS4 4376 50-yr 1300 3723.53 3728.93 3727.62 3729.3 0.002706 5.21 323.12 213.81 0.48

XS4 4376 Incipient 1100 3723.53 3728.64 3727.29 3729 0.0028 5.02 271.86 206.95 0.48

XS4 4153 2-yr 65 3722.62 3724.2 3724.05 3724.42 0.012021 3.78 17.21 23.31 0.77

XS4 4153 10-yr 340 3722.62 3725.39 3725.28 3725.97 0.012012 6.16 56.49 43 0.88

XS4 4153 25-yr 760 3722.62 3726.45 3726.45 3727.29 0.009142 7.62 118.38 84.57 0.83

XS4 4153 50-yr 1300 3722.62 3727.24 3727.24 3728.26 0.008534 8.8 193.14 102.04 0.84

XS4 4153 Incipient 1100 3722.62 3726.99 3726.99 3727.94 0.00861 8.39 167.58 96.8 0.83

BRIDGE 5

River

Sta Profile Q Total

Min Ch

El W.S. Elev

Crit

W.S. E.G. Elev

E.G.

Slope

Vel

Chnl

Flow

Area

Top

Width

Froude

# Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

XS5 5406 2-yr 65 3748.95 3751.36 3750.93 3751.67 0.008063 4.44 14.65 10.38 0.66

XS5 5406 10-yr 335 3748.95 3752.91 3752.83 3753.64 0.012349 6.96 51.53 35.11 0.89

XS5 5406 25-yr 745 3748.95 3754.75 3754.03 3755.4 0.004972 6.94 137.8 69.71 0.63

XS5 5406 50-yr 1275 3748.95 3756.34 3755.49 3756.78 0.002596 6.36 314.91 133 0.49

XS5 5406 incipient 950 3748.95 3755.88 3754.46 3756.25 0.002321 5.66 256.5 122.36 0.45

XS5 5324 2-yr 65 3749.29 3750.51 3750.43 3750.78 0.015451 4.16 15.64 21.87 0.87

XS5 5324 10-yr 335 3749.29 3752.6 3752.97 0.004373 4.88 68.58 27.98 0.55

XS5 5324 25-yr 745 3749.29 3754.53 3755.04 0.003178 5.8 140.24 69.86 0.5

XS5 5324 50-yr 1275 3749.29 3756 3756.56 0.002556 6.38 250.32 79.53 0.48

XS5 5324 incipient 950 3749.29 3755.72 3756.09 0.001778 5.14 228.11 77.69 0.39

XS5 5235 2-yr 65 3748.84 3750.24 3749.71 3750.31 0.002427 2.12 30.71 28.76 0.36

XS5 5235 10-yr 335 3748.84 3752.53 3750.8 3752.71 0.001644 3.39 98.69 31.24 0.34

XS5 5235 25-yr 745 3748.84 3754.51 3751.95 3754.81 0.00149 4.43 180.75 123.09 0.35

XS5 5235 50-yr 1275 3748.84 3756.15 3753.24 3756.34 0.000868 4.07 473.02 167.91 0.28

XS5 5235 incipient 950 3748.84 3755.81 3752.44 3755.94 0.000645 3.38 417.99 153.87 0.24

XS5 5220 Bridge

XS5 5197 2-yr 65 3749.1 3750.07 3749.73 3750.17 0.004531 2.6 25.03 27.86 0.48

XS5 5197 10-yr 335 3749.1 3752.43 3750.83 3752.63 0.001889 3.61 92.91 29.5 0.36

XS5 5197 25-yr 745 3749.1 3754.33 3751.97 3754.71 0.002077 4.95 153.56 41.33 0.39

XS5 5197 50-yr 1275 3749.1 3755.15 3753.2 3755.92 0.003508 7.12 193.09 63.82 0.52

XS5 5197 incipient 950 3749.1 3754.83 3752.48 3755.33 0.002399 5.67 176.45 49.84 0.43

XS5 5112 2-yr 65 3747.73 3749.23 3749.23 3749.71 0.020229 5.54 11.74 12.6 1.01

XS5 5112 10-yr 335 3747.73 3751.07 3751.07 3752.18 0.01613 8.47 39.61 18.12 1

XS5 5112 25-yr 745 3747.73 3752.8 3752.8 3754.22 0.010947 9.73 84.13 36.35 0.9

XS5 5112 50-yr 1275 3747.73 3754.48 3754.48 3755.6 0.006172 9.41 205.61 115.34 0.72

XS5 5112 incipient 950 3747.73 3753.68 3753.68 3754.93 0.007602 9.37 130.17 74.19 0.78

BRIDGE 6

River

Sta Profile Q Total

Min Ch

El W.S. Elev Crit W.S. E.G. Elev E.G. Slope

Vel

Chnl

Flow

Area

Top

Width

Froude

# Chl

(cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft)

XS6 6421 2-yr 65 3788.56 3789.93 3789.62 3790.07 0.00625 3.07 21.17 23.74 0.57

XS6 6421 10-yr 335 3788.56 3791.74 3790.89 3792.07 0.003592 4.69 79.29 43.18 0.51

XS6 6421 25-yr 745 3788.56 3793.58 3792.1 3793.95 0.002239 5.3 180.13 64.29 0.44

XS6 6421 50-yr 1275 3788.56 3795.33 3793.19 3795.72 0.001642 5.67 323.01 105.59 0.4

XS6 6421 incipient 1230 3788.56 3795.25 3793.12 3795.63 0.001615 5.58 314.87 102.84 0.4

XS6 6372 2-yr 65 3787.76 3789.14 3789.14 3789.55 0.020733 5.12 12.7 16.05 1.01

XS6 6372 10-yr 335 3787.76 3791.23 3791.8 0.007689 6.05 55.41 24.79 0.71

XS6 6372 25-yr 745 3787.76 3793 3793.76 0.005094 7.11 114.53 41.35 0.63

XS6 6372 50-yr 1275 3787.76 3794.53 3795.53 0.004521 8.35 187.19 66.93 0.63

XS6 6372 incipient 1230 3787.76 3794.51 3795.45 0.004263 8.09 185.89 65.97 0.61

XS6 6314 2-yr 65 3787.66 3789.1 3788.47 3789.16 0.001918 1.97 32.92 28.78 0.33

XS6 6314 10-yr 335 3787.66 3791.41 3789.58 3791.53 0.00118 2.9 129.68 56.42 0.29

XS6 6314 25-yr 745 3787.66 3793.29 3790.79 3793.47 0.001127 3.61 233.51 68.06 0.29

XS6 6314 50-yr 1275 3787.66 3794.94 3791.8 3795.2 0.001119 4.36 335.99 94.48 0.3

XS6 6314 incipient 1230 3787.66 3794.9 3791.69 3795.15 0.001071 4.24 332.98 94.17 0.3

XS6 6290 Bridge

XS6 6278 2-yr 65 3787.54 3789.06 3788.19 3789.09 0.000819 1.44 45.1 33.25 0.22

XS6 6278 10-yr 335 3787.54 3791.33 3789.18 3791.44 0.000941 2.75 121.66 34.37 0.26

XS6 6278 25-yr 745 3787.54 3793.08 3790.22 3793.34 0.001304 4.08 183.31 38.41 0.31

XS6 6278 50-yr 1275 3787.54 3794.17 3791.28 3794.68 0.002009 5.74 226.25 97.07 0.4

XS6 6278 incipient 1230 3787.54 3794.19 3791.2 3794.66 0.001851 5.52 227.04 98.6 0.39

XS6 6219 2-yr 65 3786.21 3788.58 3788.36 3788.89 0.010669 4.47 14.54 13.26 0.75

XS6 6219 10-yr 335 3786.21 3790.29 3790.16 3791.1 0.012193 7.25 46.82 25.97 0.89

XS6 6219 25-yr 745 3786.21 3791.57 3791.57 3792.86 0.011136 9.32 88.49 39.44 0.92

XS6 6219 50-yr 1275 3786.21 3793.16 3793.16 3794.3 0.006463 9.3 204.6 128.07 0.75

XS6 6219 incipient 1230 3786.21 3792.79 3792.79 3794.18 0.008421 10.08 158.71 98.07 0.85

XS6 6146 2-yr 65 3785.84 3787.79 3787.48 3788.1 0.010006 4.46 14.57 12.24 0.72

XS6 6146 10-yr 335 3785.84 3789.5 3789.45 3790.19 0.010013 6.98 59.71 52.79 0.82

XS6 6146 25-yr 745 3785.84 3790 3790.54 3791.63 0.01997 11.27 99.45 95.15 1.19

XS6 6146 50-yr 1275 3785.84 3790.39 3791.17 3792.94 0.029304 14.88 137.19 102.15 1.48

XS6 6146 incipient 1230 3785.84 3790.38 3791.12 3792.79 0.02774 14.45 136.17 101.97 1.44

APPENDIX C

SCOUR ANALYSIS

BRIDGE 1

ABUTMENT SCOUR

PRESSURE SCOUR

Flow

HEC-18 pg 6.25 ys= y2+t-hb t = t/hb= 0.5(hb*ht/hu^2)^0.2 ys = 2.40 ft t = 4.41 y2 = 6.97 from eq. 6-2 for live bed conditions hb= 8.98 existing depth in contracted section before scour (ft) ht= 1.06

Depth of water measured from WSEL to low chord (ft) hu= 3.22 Upstream water depth (ft)

HEC RAS RIVER DATA

BRIDGE 2 – ABUTMENT SCOUR

ys = 2.50 ft t = 2.19 y2 = 5.52 bed conditions hb= 5.21 existing depth in contracted section before scour (ft) ht= 1.37

Depth of water measured from WSEL to low chord hu= 4.12

Upstream water depth (ft)

BRIDGE 3 –ABUTMENT SCOUR

Flow - HEC-18 pg 6.25 ys= y2+t-hb t = t/hb= 0.5(hb*ht/hu^2)^0.2 ys = 3.88 ft t = -1.99 no overtopping of bridge y2 = 9.73 from eq. 6-2 for live bed conditions hb= 5.85 existing depth in contracted section before scour (ft) ht= -0.93 depth of water measured from WSEL to low chord (ft) hu= 6.13 upstream water depth

BRIDGE 4 – ABUTMENT SCOUR

ys = 5.75 ft t = 1.96 y2 = 8.86 bed conditions hb= 5.06 existing depth in contracted section before scour ht= 1.18 hu= 4.63

BRIDGE 5

ys = 1.2 ft t = 2.24 y2 = 5.35 bed conditions hb= 6.39 existing depth in contracted section before scour ht= 0.74 hu= 5.3

BRIDGE 6

ys = -0.57 ft t = 2.49 y2 = 3.55 bed conditions hb= 6.61 existing depth in contracted section before scour ht= 1.0 hu= 5.22

APPENDIX D

RIPRAP ANALYSIS