c. Effects of the Project on Public Health, Safety and the Environment

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1 INTRODUCTION a. Description of Proposed Activity This report is for the hydrologic and hydraulic analysis for the structure located at Sta on S.R in North Fayette Township, Allegheny County, Pennsylvania. The project includes the replacement and realignment of an existing structure that carries S.R over North Branch Robinson Run and the reconstruction of the roadway approaches to the structure. b. Project Purpose The purpose of this project is to improve the roadway and structure facilities on S.R for public safety. c. Effects of the Project on Public Health, Safety and the Environment This project will improve public health and safety with minimum impact on the environment during construction. d. Statement on Water Dependency This project involves the construction of a structure and is water dependent. e. Purpose of This Report The purpose of this report is to present a hydrologic and hydraulic analysis of the flood stages created by the existing and proposed waterway openings which carry S.R over North Branch Robinson Run. The Pennsylvania Department of Transportation's Design Manual, Part 2, Chapter 10, will be used as a guide in the preparation of this report. f. Structures The existing structure is a single-span steel I-beam bridge, with an underclearance of 6.12 and a clear span of 45.0 at a skew of with a hydraulic opening of The proposed structure is a single-span concrete bridge with an underclearance of 6.67 and a clear span of 66.0 at a skew of with a hydraulic opening of The design of the proposed structure is based on the constraints that the proposed opening be larger than that of the existing opening, that the existing vertical clear be met by the proposed structure, and that the proposed design is cost effective. See the Upstream and Downstream Structures location map on page A16, for the location of the structures. Both the upstream and downstream structures are privately owned and serve as a driveway. ii

2 g. Traffic Control Traffic will be detoured during roadway tie-in construction from S.R to S.R to S.R Otherwise, traffic will be maintained on the existing structure during construction of the new structure. h. Hydrology A detailed FEMA Flood Insurance Study has been prepared for this project. The FEMA data provided was used in the analysis and comparison of the project; the sections from the HEC-2 runs were incorporated with the surveyed sections. The structure being replaced falls between sections F and G of the FIS study. It should be noted that the water surface elevations from the proposed structure analysis ties in with FEMA s printed sections. i. Stream Characteristics North Branch Robinson Run is listed as a stockable warm water or trout stream in PaDOT Design Manual, Part 2, Appendix 10.A. North Branch Robinson Run is listed in the Pennsylvania Code, Title 25. Environmental Resources, Chapter 93, Water Quality Standards. iii

3 SECTION A - SITE DATA 1. PROJECT LOCATION The structure for this project is located at Sta in North Fayette Township, Allegheny County. This project includes the replacement and realignment of an existing bridge that carries S.R over North Branch Robinson Run and the reconstruction of the roadway approaches to the structure. a. Location Map Figures A-1 and A-2 are the Location Maps for this project. Figure A-1 is a portion of the Oakdale, Pennsylvania, seven and one-half minute quadrangle of the U.S.G.S. geological maps. It indicates the location of the project site on S.R in reference to natural areas and landmarks, political boundaries and other geographic and physical features. Figure A-2 is a portion of the General Highway Map of Allegheny County. This map shows the location of the proposed structure replacement on S.R in reference to other state, township, and local roads and other geographic features. 2. EXISTING STRUCTURES a. Location The location of the existing structure at the project site is shown on the Location Map, Figure A-1. b. Structure Descriptions Existing Structure (To Be Replaced) (see Photographs 1-15) Type: Steel I-Beam Bridge No. of Span(s): 1 Clear Span(s): 45.0 Underclearance: 6.12 Skew: c. Stream Comparison There will be no changes made within the channel. The proposed roadway profile grade is increased by 2.08 which results in a fill line encroaching upon the top of bank just downstream of the structure. The fill line is located on the left side of the downstream bank between sections 8.4 and 4.0. The fill line is held outside of the channel itself, but results in slight increases in water surface elevation downstream of structure at section 7.3. The increased water surface elevation comes up to the shoulder but does not encroach onto the proposed roadway. See figure H-3 for flood area. A1

4 d. Status of Existing Structures The existing structure carrying S.R over North Branch Robinson Run will be removed after the construction of the proposed structure. 3. HIGHWATER MARKS AND HISTORICAL FLOOD RECORDS Victor Rogale of North Fayette Township was contacted. He stated that North Branch Robinson Run has never overtopped the bridge as long as he s been with North Fayette Township (23 years). Although the bridge has never been overtopped, he said that right downstream of the structure, the roadway has been inundated. 4. ENVIRONMENTAL HABITATS See page iii, Section i. Stream Characteristics 5. DRIFT, ICE, NATURE OF STREAMBED, AND BANK STABILITY a. Drift and Ice Drift and ice are not considered a detrimental factor in the hydraulic analysis of North Branch Robinson Run. b. Nature of Streambed The streambed composition consists mainly of large particles or rock (Refer to Photo 1, page A8). c. Stream Bank Stability North Branch Robinson Run has continuos flow and stable channel bank slopes. Rock rip-rap, class R-6, is recommended to protect the slopes adjacent to the proposed structure. 6. PHOTOGRAPHS Photographs 1 through 15, inclusive, are photographs of the existing structures, the stream, and the upstream and downstream floodplains. 7. FACTORS AFFECTING WATER STAGES a. High-water From Other Streams Not applicable to this project. b. Reservoirs Not applicable to this project. A2

5 c. Flood Control Projects Not applicable to this project d. Tides Not applicable to this project. e. Other Controls 8. DEBRIS None in the floodplains affected by this project. Debris accumulation is not currently evident at the project site. The proposed opening will not adversely effect debris accumulation. 9. SITE INSPECTION RECORDS March 2003, By Karen Gleason and Carl Buchanan from SPK Engineering, Inc., for preparation of the H&H Report. 10. DATE OF DESIGN FIELD VIEW APPROVAL The Design Field View approval is pending. A3

6 S.R. 0978, Sec. 002 over North Branch Robinson Run VICINITY MAP Figure A-2 Scale 1 = 1 mile Allegheny County

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