HYDROLOGIC AND HYDRAULIC REPORT
For
State Route 2014 / Section 152
Segment 0080 / Offset 0139
Bridge Replacement Over
A Tributary to Garretts Run
In
Kittanning Township
Armstrong County, Pennsylvania
Bowser Crossroads DFB
October 2007
Prepared by:
Pennsylvania Department of Transportation
Engineering District 10-0
Indiana, Pennsylvania
ENGINEER’S SEAL
“I, Brian Allen, P.E., Assistant District Executive – Design, do herby certify to the best of
my knowledge, information, and belief, that the information contained in the
accompanying plans, specifications, and reports has been prepared in accordance with
accepted engineering practice, is true and correct, and is in conformance with Chapter
105 of the rules and regulations of the Department of Environmental Protection.”
Brian Allen, P.E.
Assistant District Executive – Design
Engineering District 10-0
ii
TABLE OF CONTENTS
REPORT
Engineer’s Seal………………………………………………….……...ii
Table of Contents………………………………………………….…...iii
Site Data …………………………………………………………..…...1
Hydrologic Analysis …………………………………………………...4
Hydraulic Analysis …………………………………………….………6
Risk Assessment ……………………………………………………….10
Summary Data Sheet …….……………………………………...……..10
Preliminary Cost Estimate ..……………………………………………12
Drawings …………...……………………………………………...…...12
Design Considerations Included in Drawings..……………………........12
Additional FEMA Considerations ……………………………………...13
DM-2 Chapter 10 Data Summary Sheet ……………………………......14
APPENDICES
Appendix A:
Location Maps
Appendix B:
Colored Photographs
Appendix C:
Hydrologic Analysis
Appendix D:
Hydraulic Analysis
Appendix E:
Drawings and Plans
Appendix F:
H & H QA Forms and Field View Notes
Appendix G:
FEMA Study
iii
A.
Site Data:
A.1. Project Location
The existing structure carrying State Route 2014, segment 0080, offset 0139 over
a tributary to Garretts Run is located in Kittanning Township, Armstrong County,
Pennsylvania. The two-lane structure is located on a two-lane bituminous paved
roadway, which is west of Blanket Hill, Pennsylvania. Refer to the Type 10 location map
and the U.S.G.S. Topographic Map (Mosgrove, PA, 7 ½ minute quadrangle) for the
location of the structure to be replaced. These maps can be found in Appendix A of this
report. Also, the drainage area and downstream structure can be found on the Type 10
map.
A.2.a Existing Structures
The existing and nearest downstream structure can be found on the Type 10 map
in Appendix A.
A.2.b Existing Structure’s Description
The existing structure, built in 1933, is a single span reinforced concrete slab
bridge. The bridge width is 26’-4” (out-to-out) while the normal span is 12’-0” with an
approximate under clearance of 3’-0”. The normal waterway opening is approximately
30.85 square feet. The bridge is on a 90 degree skew. The existing structure will be
removed due to construction of the proposed structure. There are no flood gauging
stations on the tributary to Garretts Run or historical flood data.
There is not a nearest upstream structure along the tributary to Garrets Run.
The nearest downstream structure is located approximately 370 feet downstream
of the project location. After flowing under the project location, the tributary flows
approximately another 320 feet before flowing into Garretts Run, where it then flows
approximately another 20 feet to the downstream structure. The structure is a steel rolled
I-beam bridge with an open steel grate deck. The clear span of the structure is 14’-8”
with an underclearance of 5’-2”. The hydraulic opening of the structure is 75.84 square
1
feet. The bridge skew is 60 degrees, approach roadway width is 20’-0” and the bridge
deck width is 26’-6” (out to out).
A.2.c Crossing and Stream Locations
The proposed structure will be constructed on the same alignment as the existing
structure. The overall length (reaching upstream to downstream) will increase from 26’4” to 28’-0”.
A.2.d Construction
The existing structure will be removed due to construction of the proposed
structure. Traffic will be detoured around the project site during construction thus
avoiding the need for a temporary stream crossing to maintain Traffic. Refer to Appendix
E for the Detour Map. The upstream and downstream structures will not be impacted by
the construction of the proposed structure.
A.3. High-water Marks
There were no visible high water marks or flood damages seen during the field
view conducted on January 5th, 2007 along the existing structure or stream banks
upstream and downstream of the project location.
A.4. Fish Habitat/Environmental Concerns
There were small fish observed in the field view on January 5th, 2007. Aquatic
life, such as minnows and crawfish, were seen throughout the stream. The fish habitat
will not be permanently affected by the bridge replacement. The proposed structure will
provide fish baffles and be depressed 1 foot to account for fish passage upstream through
the box culvert. The stream had continuous flow upstream, downstream, and near the
structure.
2
A.5. Drift, Ice, Stability
Drift, ice, nature of stream bed, and bank stability do not pose to be a problem on
the surrounding environment or existing structure. After the project is completed
problems with drift, ice, and bank stability are not foreseen to occur in the future.
A.6. Colored Photographs
Refer to Appendix B for photographs of the existing State Route 2014 reinforced
concrete slab bridge floodplain and channel from various views. The arrangement of
each photograph is shown on the photograph orientation map in Appendix B of this
report.
A.7. Water Stage Factor
There are no dams, reservoirs, or flood control projects which affect the water
stage elevations at the structure site. The proposed structure’s waterway opening,
roadway profile, and stream channel conditions control the water surface elevations in the
vicinity of the culvert.
A.8. Debris
Debris was not evident during the field view. Once the project is completed,
debris is not foreseen to cause any future problems. The proposed bridge replacement
will allow water to pass through the structure more efficiently than the existing condition.
A.9. Site Inspection Records
A field view took place on January 5th, 2007; see Appendix F for a copy of the
field view notes. A local resident was talked to and he said that he’s never seen the
existing structure over-top, but the stream has come up over the stream banks. This is
consistent to the hydraulic model that was created in HEC-RAS.
3
A.10. Line and Grade Approval
This project requires no alterations to the vertical alignment. The project will be
completed by the PennDOT maintenance forces and will not require line and grade
approval.
B.
Hydrologic Analysis:
B.1. Drainage Area
The drainage area for the tributary to Garretts Run at the project location is 1.17
square miles (749 acres) and is located within the Mosgrove U.S.G.S. Quadrangles. All
flood discharges shown in this report are discharges associated with the drainage area of
1.17 square miles.
The control area (swamps, reservoirs, lakes, etc.) consists of
approximately 0% of the drainage area. The runoff curve number for this drainage area
was calculated to be 71. The drainage area is delineated in Appendix A and Appendix C
of the report.
B.2. Flood Records
There are no stream flood gauging stations on this tributary to Garretts Run or
historical flood data for use in the hydrologic and hydraulic analyses.
B.3. Flood Discharges for Hydrologic Study
The hydrology of this project has been determined by using the “Engineering
Field Handbook-2” (EFH-2) method. This method is acceptable because the watershed
drainage area is represented by a single curve number between 40 & 98, the watershed
area is between 1 and 2,000 acres, the average slope is between 0.5 % and 64 %, there is
no valley or reservoir routing required and urban land use is less than 10 % of the basin.
The EFH-2 method was compared to PSU-IV. The PSU-IV flows were slightly higher
4
than the EFH-2 flows. Refer to Appendix C for calculations and results of flood
discharge values for the design and comparative methods used.
Results of the EFH-2 analysis are summarized in Table 1 of this report. The
results of the independent hydrologic analysis are also presented in Appendix C.
The design flood for the proposed hydraulic opening is the 10-year storm in
accordance with the Design Manual, Part 2: Highway Design, Chapter 10, Table 10.6.1.
This roadway is classified as a Local Road System. Since development within the
watershed area is not anticipated, there was not an adjustment for urbanization factored
into the stream discharges. Table 1, below, is a summary of the flood discharges for the
appropriate return periods.
Table 1: EFH-2 Flood Discharges for Storm Return Periods
Return Period
Flood Discharge
(years)
(cfs)
2
82
5
125
10 *
185
25
252
50
326
100 **
437
Note: * Design Storm
** Risk Assessment Storm
B.4. Flood-Frequency Curve
A flood-frequency curve has been plotted and is included in Appendix C.
B.5. Stage-Discharge-Frequency Curve
A stage-discharge-frequency curve has been plotted and is included in Appendix D.
5
C.
Hydraulic Analysis:
C.1. Hydraulic Study/Results
The United States Army Corps of Engineers HEC-RAS River Analysis Program,
Version 3.1.2, was used to compute the allowable velocity and permissible backwater of
the existing bridge (see Appendix D for HEC-RAS output). As a result of the HEC-RAS
hydraulic analysis, the proposed hydraulic opening, structure type and length, and
roadway elevations were determined to be adequate conforming to all requirements set
forth by the Department of Environmental Protection and PennDOT. The proposed
structure consists of a precast reinforced concrete box culvert with flared end sections.
The length of the structure will be 28’-0” reaching upstream to downstream in the
channel. The clear span of the culvert will be 11’-0” with a rise of 5’-0” (4’-0”
effective) on a 90-degree skew to the tributary to Garretts Run. The span was decreased
to try to eliminate the sedimentation that was found during a trip out to the field (see
Photo 16 in Appendix B). To fulfill The Pennsylvania Department of Transportation
Bridge Design Standard, BD 632M, to have the concrete box opening in one foot
increments, there will be a minimal rise in roadway profile from existing to the proposed
conditions. The effective waterway opening is approximately 44 square feet. One
additional foot of depth will be allowed for the deposit of sedimentation for fish passage.
There will be alternating fish baffles placed in the box culvert, as per The Pennsylvania
Department of Transportation Bridge Design Standard, BD-632M. The proposed
structure will be built using a temporary stream crossing around the construction. The
District’s recommendation is to filter the construction waters by using sediment filter
bags. Using the sediment filter bags will produce no or little impact on the area.
Determination of the use of this temporary facility will be based on the Department of
Environmental Protection’s (DEP) recommendation. The results of the hydraulic
analysis are found in Table 2 below.
Table 2: Summary of Hydraulic Analysis
6
Existing Bridge
Proposed Bridge
Hydraulic Opening
30.85 S.F.
44 S.F.
Low Chord Elevation
1022.95 ft
1023.86 ft
Overtopping Discharge
326 cfs
437 cfs
Overtopping Frequency
50-year
100-year
Upstream Invert Elevation
1020 ft
1020 ft
1019.86 ft
1019.86 ft
1023.95 ft
1023.48 ft
at Structure
1025.87 ft
1025.51 ft
Q10 Velocity at Structure
3.12 ft/sec
3.77 ft/sec
Q100 Velocity at Structure
2.74 ft/sec
3.22 ft/sec
Downstream Invert Elevation
Q10 Water surface Elevation
at Structure
Q100 Water surface Elevation
C.2. Proposed Culvert AHW
The allowable headwater depth ratios for the 10-year design storm and the 100year assessment storm are 0.74 and 1.00 respectively. See Appendix D for the
calculations performed to determine the HW/D values. Overtopping of the roadway does
occur for the 100-year risk assessment storm for the existing bridge and proposed culvert.
The proposed structure will produce little hydraulic impact on the waterway. The
back water surface elevations of the 10-year design flood and 100-year risk assessment
storm decrease from the existing conditions to the proposed conditions for all upstream
cross-sections. Tables 3 and 4 show the existing and proposed 10-year and 100-year
water surface elevations and channel velocities.
Table 3: 10-year design and 100-year risk assessment storm W.S. Elevation
Comparison
River
Station
824.00
10-year Storm W.S. Elevation
(ft)
Existing Proposed Difference
100-year Storm W.S. Elevation
(ft)
Existing Proposed Difference
1028.13
1028.77
1028.13
0.00
7
1028.77
0.00
799.76
769.97
751.40
729.55
701.86
676.50
648.35
624.12
599.24
580.32
551.61
522.42
496.97
476.63
451.07
422.97
394.11
374.83
350.54
321.72
301.67
293.85
275
251.62
225.79
202.08
178.99
151.28
99.46
76.89
53.92
24.82
0.63
1028.45
1028.20
1028.21
1027.35
1027.41
1026.79
1025.88
1026.47
1025.98
1026.05
1025.48
1025.78
1025.10
1024.32
1024.22
1024.10
1024.03
1023.99
1023.96
1023.95
1023.94
1023.95
Bridge
1022.75
1022.56
1022.61
1021.03
1021.17
1020.21
1020.28
1020.19
1019.78
1018.67
1028.45
1028.20
1028.21
1027.35
1027.41
1026.79
1025.88
1026.47
1025.98
1026.05
1025.48
1025.78
1025.10
1024.32
1024.22
1023.05
1023.76
1023.60
1023.51
1023.46
1023.46
1023.48
Culvert
1022.75
1022.56
1022.61
1021.03
1021.17
1020.21
1020.28
1020.19
1019.78
1018.67
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
-1.05
-0.27
-0.39
-0.45
-0.49
-0.48
-0.47
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
1029.23
1028.87
1028.87
1028.57
1028.04
1027.92
1027.43
1027.72
1027.31
1027.27
1026.95
1026.56
1026.06
1025.78
1025.94
1025.94
1025.91
1025.92
1025.92
1025.90
1025.88
1025.87
Bridge
1023.80
1022.88
1022.83
1022.47
1021.99
1021.76
1021.70
1021.65
1021.66
1020.63
1029.23
1028.87
1028.87
1028.57
1028.04
1027.92
1027.43
1027.72
1027.31
1027.27
1026.95
1026.56
1026.06
1025.15
1025.61
1025.62
1025.57
1025.58
1025.58
1025.56
1025.52
1025.51
Culvert
1023.80
1022.88
1022.83
1022.47
1021.99
1021.76
1021.70
1021.65
1021.66
1020.63
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
-0.63
-0.33
-0.32
-0.34
-0.34
-0.34
-0.34
-0.36
-0.36
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Table 4: 10-year design and 100-year risk assessment storm Velocity Comparison
10-year Storm Velocities (ft/s)
Existing Proposed Difference
River
Station
824.00
799.76
769.97
751.40
729.55
701.86
676.50
648.35
6.30
2.70
4.44
3.84
7.66
5.39
7.50
9.25
6.30
2.70
4.44
3.84
7.66
5.39
7.50
9.25
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8
100-year Storm Velocities (ft/s)
Existing Proposed Difference
9.69
4.14
6.28
5.58
7.11
8.29
8.16
9.05
9.69
4.14
6.28
5.58
7.11
8.29
8.16
9.05
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
624.12
599.24
580.32
551.61
522.42
496.97
476.63
451.07
422.97
394.11
374.83
350.54
321.72
301.67
293.85
275
251.62
225.79
202.08
178.99
151.28
99.46
76.89
53.92
24.82
0.63
4.35
6.47
5.16
7.14
3.93
6.43
8.37
7.28
4.56
4.31
4.35
4.13
3.60
3.28
3.12
Bridge
6.41
6.42
5.16
10.10
7.48
8.47
6.73
6.25
7.06
9.72
4.35
6.47
5.16
7.14
3.93
6.43
8.37
7.28
9.25
4.94
5.44
5.35
4.76
4.14
3.77
Culvert
6.41
6.42
5.16
10.10
7.48
8.47
6.73
6.25
7.06
9.72
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
4.69
0.63
1.09
1.22
1.16
0.86
0.65
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
5.29
7.33
5.80
7.23
5.85
7.57
6.22
3.60
2.77
2.87
2.64
2.33
2.37
2.66
2.74
Bridge
8.62
10.82
9.43
9.38
10.01
4.75
4.67
4.64
3.89
8.52
5.29
7.33
5.80
7.23
5.85
7.57
10.09
4.51
3.33
3.52
3.24
2.82
2.85
3.22
3.22
Culvert
8.62
10.82
9.43
9.38
10.01
4.75
4.67
4.64
3.89
8.52
0.00
0.00
0.00
0.00
0.00
0.00
3.87
0.91
0.56
0.65
0.60
0.49
0.48
0.56
0.48
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
The results of the independent hydraulic analyses are presented in Appendix D.
C.3. Channel Changes
There will be no changes to the channel during the construction of the new
structure. The proposed box culvert will not have an impact on the channel.
C.4. Embankment Encroachments Paralleling Floodplains
There will be no effect on the stability of the roadway embankment. The scour
and erosion of roadway embankment and stream channel do not provide an effect on the
embankment encroachments paralleling floodplains.
C.5. Cost Estimate
9
The preliminary cost for the proposed box culvert is $250,000.
D.
Risk Assessment:
The area surrounding the subject structure can be described as rural. The
proposed culvert does not increase the risk of structural damage or personal injury.
Alternate sizes of culverts were hydraulically analyzed and compared with the proposed
culvert. The proposed culvert provides the most cost effective, hydraulically efficient
type and size of the structure for this particular site. The hydraulic analysis shows that
with a larger waterway opening, backwater surface elevations will decrease for the 10year design storm and the 100-year risk assessment storm events.
The discharge associated with the Q100 storm does overtop the proposed roadway.
The proposed precast box culvert improves the flow up to and including the 100-year
storm events. The backwater elevations for all cross-sections are decreased with the
proposed box culvert compared to the existing structure.
The flood limits of the 100-year flood event did not change significantly upstream
or downstream. There will be no increase in all backwater surface elevations for the
proposed culvert. The water in the stream will overtop the banks of the channel up to and
including the 100-year storm event. The backwater velocities at the proposed structure
will increase slightly compared to the backwater velocities at the existing structure due to
the topography of the project area. For a detailed listing of water surface elevations and
velocity changes, please refer back to Table 3 and 4 on page 7 to 9 of this report. The
overall Ecology and Aquatic Habitat will not be affected for this project.
E.
Summary Data Sheet:
1.
State Route: 2014, Segment 0080, Offset 0139
2.
Station: 1+52
3.
Armstrong County
10
4.
Kittanning Township
5.
Tributary of Garretts Run
6.
Drainage Area: 1.17 SQ. MI.
7.
Project Location:
8.
Existing Stream Top: Width: 14’; Depth: 6”-2’
Existing Stream Bottom: Width: 6’; Depth: 6”-2’
9.
Normal Flow Depth: 6”-2’
USGS Quadrangle: Mosgrove
Latitude: N 40° 46’ 11.13”
Longitude: W 79° 28’ 44.91”
10.
Stream Bed Elevation: 494.97 ft +/- Upstream: 1024.83 ft
274.37 ft +/- Downstream: 1016.47 ft
11.
Peak Flows:
12.
Existing and Proposed Structures
a.
Existing Structure
(1)
Concrete Slab Bridge
(2)
1 Span
(3)
12’-0” span along highway from face to face of abutments
(4)
12’-0” normal span
(5)
3’-0” underclearnce
(6)
Skew: 90°
(7)
10 year WSE = 1023.95 ft
25 year WSE = 1024.60 ft
50 year WSE = 1025.46 ft
100 year WSE = 1025.87 ft
(8)
Hydraulic Opening: 30.85 sq ft
b.
10-year: 185 cfs
25-year: 252 cfs
50-year: 326 cfs
100-year: 437 cfs
Proposed Structure
(1)
Precast Concrete Box Culvert
(2)
1 Cell
(3)
11’-0” span along highway from face to face of abutments
(4)
11’-0” normal span
(5)
5’-0” Full Height; 4’-0” Effective Height due to depression
(6)
Skew: 90°
(7)
10 year WSE = 1023.48 ft
25 year WSE = 1024.11 ft
11
(8)
50 year WSE = 1024.86 ft
100 year WSE = 1025.51 ft
Hydraulic Opening: 44 sq ft
13.
Wetland Impact: No wetlands will be impacted by the proposed project.
14.
Other Information
a.
pH: 7.5
b.
Rip-rap size: R-6 (See Appendix D for calculations)
c.
Headwater/Depth Ratio (See Appendix D for calculations)
(1)
10 year = 0.87 (design year)
(2)
100 year = 1.38
F.
Preliminary Cost Estimate:
The preliminary cost estimate for the construction of the proposed box culvert is
$250,000. The Pennsylvania Department of Transportation maintenance forces will
perform the work.
G.
Drawings:
The following drawings can be found in Appendix E.
H.
1.
Roadway Plans and Profile
2.
Cross-sections perpendicular to flood flow
3.
Plan Drawing
4.
Fish Baffle Details
5.
Detour Map
Design Considerations Included in Drawings:
H.1. Backwater Computations
Backwater computations were performed by HEC-RAS to analyze the proposed
structure’s opening. A comparison, in backwater surface elevations from existing
conditions to the proposed conditions, shows the proposed hydraulic opening does not
increase any backwater surface elevations.
H.2. Temporary Drainage Facilities
12
Details of the temporary water diversion can be found in the E&S Plan submitted
with the H&H Report in the GP-11 Package. This project will use a detour around the
construction site to maintain traffic.
H.3. Occasional Flowage Easements
There will be no temporary or occasional flowage easements necessary for the
proposed project. The flood plains will remain the same or slightly decrease.
H.4. Fish Passage
The proposed box culvert will be depressed 1 foot below the stream bed and
contain fish baffles. Details regarding the fish baffles can be found in Appendix E.
H.5. Multi-Cell Structures
The proposed box culvert consists of 1 cell.
H.6. Alternate Structure Types
Various span and height configurations were analyzed in HEC-RAS. The
proposed box culvert with a span of 11’-0” and full effective height of 4’-0” is the most
cost effective design that meets all the design criteria set forth by the Department of
Environmental Protection and PennDOT.
I.
Additional FEMA Considerations:
The project lies within a FEMA Flood Map. See Appendix G for attachments.
The project was in Zone A, so there were no base flood elevations determined for this
area. There are no increases in the 100-year floodplain due to the construction of the
proposed project.
13