Pennsylvania Department of Transportation
District 3-0
P.O. Box 218, 715 Jordan Avenue
Montoursville, PA 17754

Signature
Date

Introduction and Project Description
Watershed Characteristics
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Watershed Description
Channel Characteristics
Channel Description
Flood History
Project Description
Temporary Channel
Hydrologic Analysis
Hydraulic Analysis
Stormwater Management
Flood Plain Management Analysis
Risk Assessment
Erosion and Sediment Control
Wetland Involvement
Alternative Analysis
Conclusion
Summary Data Sheet
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1

The intent of this report is to present information to the PA Department of Environmental
Protection, the PA Fish and Boat Commission, and any other agencies, for the purpose of obtaining a Water Obstruction and Encroachment Permit. This study will provide information to support the fact that the replacement of the existing bridge and implementation of a new structure will not cause any excessive mean velocities that result in scour or intolerable conditions.
The project involves replacement of the existing reinforced concrete slab, having a clear normal span of 9.0 ft., with a precast reinforced concrete box culvert at the same location. This project is located on State Route 1007-008 at Segment 0180 Offset 0968 over a tributary to Tuscarora Creek,
Middle Creek Township, in Snyder County. S.R. 1007 is classified as a rural minor collector with an average 2005 ADT of 530. The existing structure has a normal clear span of 9.0 ft., a curb-to-curb width of 23.6 ft., an under clear of 5.17 ft. and is on a skew of 90° with the roadway.
Proposed construction consists of a 14.0 ft. x 6.0 ft. precast reinforced concrete box culvert placed with a 90° skew. The proposed structure will be approximately 32.2 ft. long with a curb-to-curb width of 28.0 ft. The culvert bottom will be depressed 1.0 ft. below streambed to provide an effective waterway opening of 14.0 ft. x 5.0 ft.
Due to the relatively low ADT, a detour will be established during replacement of the existing structure.
The tributary to Tuscarora Creek is not listed on the PA Fish & Boat Commission’s listing of stocked trout waters. Tuscarora Creek is listed as a cold-water fishery. Tributaries immediately upstream and downstream are also listed as cold-water fisheries.
Hydrologic and hydraulic analyses are performed for the existing and proposed structures. No detailed FEMA study is available for this site. Therefore, the hydrologic analysis is performed in accordance with the procedures in PennDOT Design Manual, Part 2 for non-FEMA and un-gauged watersheds. The hydraulic analysis is performed using the HEC-RAS v. 3.1 computer program.
The Pennsylvania State Programmatic General Permit #2 (PASPGP-2) applies to the proposed activities.
2

WATERSHED CHARACTERISTICS
Area = 0.53 square miles
Shape = irregular
Terrain = forest, fields, pasture
Elevation Range = 850 to 615 ft.
Land Use = Forest, Agriculture (Pasture& Meadow)
Forest = 10%
The project is not located within a detailed FEMA Study Area and no gage data exists for Tuscarora
Creek. Therefore, the hydrologic analysis is performed in accordance with the procedures in
PennDOT Design Manual, Part 2 for non-FEMA and un-gauged watersheds.
WATERSHED DESCRIPTION
The terrain is composed of rolling hills of forest, meadows, and pasture. Elevation ranges from 850 to 615 ft. Approximately 10% of the watershed is forest.
The drainage area is taken from the Freeburg, PA quadrangle of the USGS 7.5-Minute Series Maps.
CHANNEL CHARACTERISTICS
Top Width = 15.0 ft.
Bottom Width = 10.0 ft.
Bank Height = 5.0 ft.
Alignment = Good – the proposed structure will be constructed on the existing 90º skew.
Stability = Good
Vegetation on Bank = Grasses, Brush
Channel = Highly Vegetated, Sediment
Stream Slope = 0.025 ft/ft
Water Quality = Good
High Water = 1999 – measured 1.58’ below bottom of slab at near right. (adjacent landowner
stated that the water was to the “top of slab”)
CHANNEL DESCRIPTION
The channel cross-section dimensions vary with an average top width of 15.0 ft. and an average depth of 5.0 ft. The average stream flow width varies due to seasonal changes, with an average width of 6.0 ft. and normal flow depth of 6.0 inches. There is no embankment erosion occurring immediately upstream or downstream of the structure. R-8 rock exists upstream of the right inlet wing to stabilize the right bank due to past erosion.
FLOOD HISTORY
The measured high water mark is 1.58’ below the bottom of the slab at the near right corner of the bridge during a 1999 high water event. An adjacent landowner stated that the water surface elevation reached the “top of slab.”
3

PROJECT DESCRIPTION
The subject project is located on State Route 1007 at Segment 0180 Offset 0968 over an unnamed tributary to Tuscarora Creek in Middle Creek Township, Snyder County, PA. The exact location of the project is presented in Attachment F.
The existing structure is a reinforced concrete slab bridge built in 1933 on a 90° skew and a curbto-curb width of 23.6 ft. The structure has a span of 9.0 ft. face-to-face of the abutments and an under clear of 5.17ft. Concrete jackets have been placed at the bottom of each abutment and streambed pavement exists. R-5 rock has been placed behind all wings and R-8 rock upstream of the right inlet wing to mitigate erosion at the bridge. Photographs of the project site are presented in Attachment H.
The proposed structure is a 14.0 ft. x 6.0 ft. precast reinforced concrete box culvert placed on a skew of 90° with a guide rail to guide rail width of 28.0 ft.
The disturbed channel at the inlet and outlet will be reconstructed using R-8 rock choked with R-4 rock. The inlet and outlet channel’s final grade and cross section will provide a defined channel upstream, downstream, and through the structure. The culvert will include baffles spaced evenly with heights of eight inches each. The bottom of the box will be covered with washed gravel to mimic the natural channel and stream bottom.
The following list of work items is proposed:
Replace the existing reinforced concrete slab bridge with the proposed reinforced concrete box culvert. The inlet and outlet of the proposed structure will be precast concrete sections.
The bottom slab of the box culvert will be depressed one foot below the existing streambed.
Natural aggradation over time will provide a natural streambed to allow for fish passage and minimize the impact to the streambed environment.
Rock protection will be placed at all wings.
A detour will be used during construction of the bridge replacement project. The availability of the detour and low traffic volume on S.R. 1007 makes a detour the most feasible alternative for maintaining traffic.
TEMPORARY CHANNEL
During construction the stream flow will be transported around the project site via a temporary rock-lined channel. An Erosion and Sediment Control Plan will be implemented and is currently pending.
HYDROLOGIC ANALYSIS
The project is located in a non-FEMA area and within an un-gauged watershed. Therefore, the hydrologic analysis was performed in accordance with the procedures in PennDOT Design Manual,
Part 2 for non-FEMA and un-gauged watersheds.
4

The drainage area is calculated to be 0.53 mi.² using the Freeburg, PA USGS map. HEC-1 is used in obtaining the peak discharge values for the watershed. This method is the procedure recommended in PennDOT’s Strike-Off Letter 431-99-11 “Criteria for Applicability of Hydrologic and Hydraulic Methodologies” dated April 21, 1999. PSU-IV is used as a comparative method only.
The results are summarized below.
HEC-1
2 year
131 cfs
2.33 year
--
5 year 10 year 25 year 50 year 100 year
500 year
211 cfs 280 cfs 407 cfs 528 cfs 685 cfs 1210 cfs
PSU-IV -- 227 cfs 253 cfs 296 cfs 322 cfs 374 cfs 409 cfs 695 cfs
Utilizing soils maps, a CN value of 69 is calculated for the drainage area composed of rolling hills of forest, meadows, and pasture. The SCS methodology is used in the HEC-1 model in WMS v. 7.0.
The NRCS Type-II 24-hour storm is input for the precipitation, with the following rainfall amounts for Snyder County:
2 Year 5 Year 10 Year 25 Year 50 Year 100 Year 500 Year
2.9 in. 3.7 in. 4.3 in. 5.3 in. 6.2 in. 7.3 in. 10.8 in.
The drainage area centroid is located at latitude 40° 50' 45" and longitude 76° 59' 00". The area is located in Region 2 according to Plate 1 of PSU-IV. Percent of forest is estimated to be 10% from the Freeburg, PA USGS map. The standard deviation is determined to be 0.292 as per Plate 2.
Plate 3 represents the skew coefficient as 0.41. Since the drainage area is less than 3.88 sq. km.
(1.50 mi.2), the small area adjustment is used.
The subject bridge is located approximately 18 feet from the confluence of Tuscarora Creek and its tributary. Therefore, a hydrologic study is conducted for a larger basin for Tuscarora Creek to investigate backwater conditions. The drainage area for this larger basin is 1.44 mi.². HEC-1 is used to determine the peak discharge values for the Tuscarora Creek basin since the drainage area is less than 1.50 mi². Utilizing soils maps, a CN value of 70 is calculated for the second basin. The same SCS methodology, NRCS Type-II 24-hour storm, and rainfall amounts are employed in HEC-1.
The results for the second basin are as follows:
2 year 5 year 10 year 25 year 50 year 100 year 500 year
HEC-1 253 cfs 439 cfs 598 cfs 887 cfs 1165 cfs 1521 cfs 2709 cfs
The Pennsylvania Department of Transportation Design Manual, Part 2 in Section 10.12 and Strike-
Off Letter 439-99-11 (April 21, 1999:page 15) specifies a 25-year design flow with consideration given to the rural location of the project site and the improbability of property damage. The 100year flow is also checked.
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HYDRAULIC ANALYSIS
Flow depths, overtopping frequency, and water velocities for the existing and proposed conditions are determined using the HEC-RAS v. 3.1 computer program. A field study is performed to obtain existing stream and roadway cross-sections and profiles. Manning’s ‘n’ roughness coefficients are based on field observations.
Existing Conditions
- The hydraulic opening of the existing structure is 9.0 ft. wide with an average depth of 5.17 ft. for a total area of 46.5 ft². Roughness Coefficient is 0.035 for the channel bottom and for the structure top and sides. The existing low chord elevation at the inlet is 620.69 ft.
- The 25-year flow of 407 cfs results in a water surface elevation of 620.68 ft. that passes through the structure.
- The 100-year flow of 685 cfs results in a water surface elevation of 623.99 ft., overtopping the roadway by 2.24 ft.
Proposed Conditions
- Proposed conditions (14.0 ft. x 6.0 ft. box culvert with one foot of bottom depression and 6”x 6” haunches at all corners of the concrete box culvert) will provide a hydraulic opening of 69.75 ft².
Roughness Coefficient is 0.035 for the structure. The proposed low chord elevation is 620.41 ft.
This proposed low chord elevation is slightly lower than the existing low chord (approximately
0.27 ft.). It is shown hydraulically that no adverse impacts are expected due to the change in low chord elevations.
- The proposed conditions pass the 25-year design storm with a headwater elevation of 619.97 ft.
- The proposed structure creates a water surface elevation of 622.28 ft. for the 100-year flow, which is 1.87 ft. above the low chord elevation of the proposed structure, or 0.09 ft. above the proposed roadway surface over the structure.
- The proposed structure reduces the 25-year water surface elevation by 0.69 ft. and the 100-year water surface elevation by 1.71 ft. at the inlets.
- The water velocities at the outlet will remain approximately the same with the proposed structure. The proposed structure will create velocities that are a close representation of the velocities upstream of the structure and downstream of the structure. No significant backwater effects from the main reach of Tuscarora Creek are noted in the hydraulic models in HEC-RAS.
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STORMWATER MANAGEMENT
The proposed bridge will be constructed on the existing 90° skew. The project will produce very little to no change in the watershed hydrology. The project will improve the hydraulics within the project area, and the unnamed Tributary to Tuscarora Creek will not be adversely impacted due to the replacement of this structure.
The township and county have been notified of the proposed project in accordance with PA ACT
14, P.L. 834. Middle Creek Township indicated that the project is consistent with the local floodplain and stormwater management plans.
FLOODPLAIN MANAGEMENT ANALYSIS
The project is not part of a FEMA Flood Insurance Study for Middle Creek Township; therefore, no detailed FEMA study area exists. HEC-1 is used to obtain the design flows with PSU-IV being a comparative model only. The 25-year and 100-year storms are modeled using HEC-RAS for both the existing and proposed conditions. The models show that the proposed structure would reduce both the 25-year and 100-year storms’ water surface elevations and velocities, as shown in the Hydraulic
Data Table on the Summary Data Sheet.
The Township and County officials have been notified and no concerns have been raised.
RISK ASSESSMENT
The proposed structure will reduce the flood risk of both the 25-year and the 100-year flood. The
Proposed structure reduces the 25-year water surface elevation at the inlet from 620.66 ft. to
619.97 ft. The 100-year water surface is reduced from 623.99 ft. to 622.28 ft. The construction of the proposed structure should reduce the risk of flooding in the adjacent area.
The resulting hydraulic analysis for the proposed box culvert predicts that the 100-year flood will overtop the roadway by 0.09 ft., compared to 2.24 ft. with the existing structure. Therefore, the proposed structure should reduce the risk of overtopping the road with lower water surface elevations at the completion of this project.
EROSION AND SEDIMENT CONTROL
An erosion and sedimentation plan will be implemented on this project. This plan and approval letter is currently pending.
WETLAND INVOLVEMENT
No wetlands exist within construction limits for this project. Refer to the Environmental
Assessment Form in Attachment I.
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ALTERNATIVES ANALYSIS
The alternative to replacing this structure is to do nothing (no build alternative) or rehabilitation of the existing structure. The existing reinforced concrete slab bridge structure, built in 1933, is in poor condition due to severe deterioration on the abutment walls, wing walls, and deck. The existing structure has a curb-to-curb width of 23.6 ft. that is considered substandard and unsafe by current highway design standards. The rehabilitation alternative will prove to be costly and will not provide any benefit relative to providing a safer roadway or improving the hydraulic capacity of the structure. Replacing this bridge will be more cost effective, provide a wider and safer roadway crossing with a longer design life, and improve the crossing’s hydraulic capacity. Therefore, the replacement alternative is selected because it provides the best cost-benefit ratio to the
Commonwealth’s taxpayers.
CONCLUSION
The proposed reinforced concrete box culvert will replace the existing reinforced concrete slab bridge. Hydraulic computations show that an improvement in the hydraulic capacity for both the
25-year and 100-year flow events will occur. The proposed structure will have no adverse impacts and will reduce the risks to public safety. There is no fill below ordinary high water, and no cultural resource or endangered species impacts or conflicts are expected.
Proper erosion and sediment pollution control measures will be employed during construction. The
Pennsylvania State Programmatic General Permit #2 (PASPGP-2) applies to the proposed activities.
In view of the hydrologic and hydraulic studies, we recommend approval of the proposed structure replacement.
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326
214
160
106
54
Upper Reach
Existing Conditions - 25 year flow
Lower Reach Tributary
Station W.S. Elevation Velocity Station W.S. Elevation Velocity Station W.S. Elevation Velocity
521
492
445
(ft.)
623.42
623.14
622.45
(ft./s)
9.36
8.90
9.11
502
479
448
(ft.)
617.51
616.60
615.82
(ft./s)
8.90
10.90
11.55
533
507
456
(ft.)
628.82
628.12
627.05
(ft./s)
7.56
8.90
9.24
621.75
620.35
619.64
619.13
618.89
8.68
5.33
7.84
8.04
5.21
424
387
340
291
249
203
138
616.46
615.83
615.55
614.94
614.26
613.46
611.51
7.08
8.87
8.40
7.10
8.92
9.37
12.81
410
364
331
297
276
251
221
197
626.48
624.76
624.10
624.07
622.91
623.29
622.60
621.56
8.14
10.82
10.12
7.72
10.74
6.43
8.04
9.88
176
161
137
117
101
77
66
55
Bridge
18
622.14
621.49
620.78
620.92
620.82
621.05
620.95
620.66
618.80
5.16
7.63
8.72
6.85
6.74
4.03
4.52
5.91
4.05
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326
214
160
106
54
Upper Reach
Existing Conditions - 100 year flow
Lower Reach Tributary
Station W.S. Elevation Velocity Station W.S. Elevation Velocity Station W.S. Elevation Velocity
521
492
445
(ft.)
624.03
623.71
623.04
(ft./s)
10.58
10.23
10.20
502
479
448
(ft.)
618.59
617.46
616.51
(ft./s)
10.23
12.81
13.92
533
507
456
(ft.)
630.10
629.19
627.59
(ft./s)
8.22
10.21
11.71
622.29
621.42
620.35
619.97
618.24
10.10
6.22
10.03
9.42
12.92
424
387
340
291
249
203
138
617.61
616.74
616.00
615.93
615.13
614.60
612.19
7.62
10.38
11.47
8.20
10.35
10.03
14.99
410
364
331
297
276
251
221
197
627.31
625.64
624.55
624.33
623.76
624.20
623.82
623.89
9.43
12.20
13.07
11.07
11.60
7.25
7.98
6.27
176
161
137
117
101
77
66
55
Bridge
18
624.05
624.05
624.03
624.01
624.01
624.05
624.04
623.99
616.30
4.48
4.24
4.17
4.14
3.97
3.02
3.14
3.61
20.67
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326
214
160
106
54
Upper Reach
Proposed Conditions - 25 year flow
Lower Reach Tributary
Station W.S. Elevation Velocity Station W.S. Elevation Velocity Station W.S. Elevation Velocity
521
492
445
(ft.)
623.42
623.14
622.45
(ft./s)
9.36
8.90
9.11
502
479
448
(ft.)
617.51
616.60
615.82
(ft./s)
8.90
10.90
11.55
533
507
456
(ft.)
628.82
628.12
627.05
(ft./s)
7.56
8.90
9.24
621.75
620.35
619.64
619.13
618.89
8.68
5.33
7.84
8.04
5.21
424
387
340
291
249
203
138
616.46
615.83
615.55
614.94
614.26
613.46
611.51
7.08
8.87
8.40
7.10
8.92
9.37
12.81
410
364
331
297
276
251
221
197
626.48
624.76
624.10
624.07
622.91
623.29
622.60
621.56
8.14
10.82
10.12
7.72
10.74
6.43
8.04
9.88
176
161
137
117
101
77
66
55
Culvert
18
622.14
621.49
620.78
620.83
620.26
620.17
619.96
619.97
618.79
5.16
7.63
8.72
7.13
8.52
5.42
6.17
5.64
4.19
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326
214
160
106
54
Upper Reach
Proposed Conditions - 100 year flow
Lower Reach Tributary
Station W.S. Elevation Velocity Station W.S. Elevation Velocity Station W.S. Elevation Velocity
521
492
445
(ft.)
624.03
623.71
623.04
(ft./s)
10.58
10.22
10.20
502
479
448
(ft.)
618.59
617.46
616.51
(ft./s)
10.23
12.81
13.92
533
507
456
(ft.)
630.10
629.19
627.59
(ft./s)
8.22
10.21
11.71
622.29
621.41
620.39
619.88
620.14
10.10
6.24
9.89
9.78
5.34
424
387
340
291
249
203
138
617.61
616.74
616.00
615.93
615.13
614.60
612.19
7.62
10.38
11.47
8.20
10.35
10.03
14.99
410
364
331
297
276
251
221
197
627.31
625.64
624.55
624.33
623.76
624.25
623.54
622.34
9.43
12.20
13.07
11.07
11.60
7.13
8.93
11.04
176
161
137
117
101
77
66
55
Culvert
18
622.95
622.43
622.36
622.30
622.26
622.45
622.35
622.28
620.05
6.32
8.06
7.14
6.89
6.73
4.54
4.99
5.27
4.71
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