DRAFT LOCATION HYDRAULIC REPORT

Transcription

1 DRAFT LOCATION HYDRAULIC REPORT West Bay Parkway (CR 388) Segment 2 From SR 79 to SR 77 in Bay County FPID No Florida Department of Transportation District Three 1074 Highway 90 East Chipley, FL March 2010

2 LOCATION HYDRAULIC REPORT West Bay Parkway Segment 2 From SR 79 in Bay County To SR 77 in Bay County Prepared for FDOT District Three FPID No Prepared by: 2940 East Park Avenue Suite 200 Tallahassee FL, Certificate of Authorization No. 894

3 TABLE OF CONTENTS SECTION 1 INTRODUCTION SECTION 2 PROJECT DESCRIPTION SECTION 3 EXISTING CONDITIONS Existing Conditions Surface Water Drainage Existing Cross Drains Soils Existing Roadway Drainage Floodplains Floodways SECTION 4 REGULATORY REQUIREMENTS FDEP/ NWFWMD FDOT Local Government Federal Emergency Management Agency (FEMA) SECTION 5 EVALUATION OF HYDRAULIC STRUCTURES SECTION 6 FLOODPLAIN IMPACTS SECTION 7 CONCLUSION Location Hydraulic Report West Bay Parkway - Segment 2 i March 2010

4 LIST OF EXHIBITS Exhibit 1.1 Project Location Map Exhibit 2.1 Existing Land Uses LIST OF TABLES Table 3.1 Table 5.1 Table 6.1 Summary of Existing Cross Drains Bridges/ Cross Drains Required Longitudinal Encroachments LIST OF APPENDICES Appendix A Appendix B Appendix C Appendix D Appendix E FEMA Flood Insurance Rate Maps (FIRM) NRCS Soils Maps & Details Approach to Estimating Bridge Lengths & Cross Drain Size Longitudinal Encroachments FDOT Straight Line Diagram Location Hydraulic Report West Bay Parkway - Segment 2 ii March 2010

5 SECTION 1 INTRODUCTION This Location Hydraulics Report has been prepared to assess the floodplain encroachments for each alignment alternative for the proposed West Bay Parkway (CR 388). This study is required by the Federal-Aid Policy Guide 23 CRF 650A Sec and has been prepared in accordance with Part 2, Chapter 24 of the FDOT Project Development and Environment Manual, The intent of these regulations is to avoid or minimize highway encroachments within the 100-year (base) floodplains, where practicable, and to avoid supporting land use development which is incompatible with floodplain values. The project is located in the Florida Panhandle within Bay County between Panama City and Wewahitchka. The project is located within Township 2 South and Ranges 14, 15 and 16 West. The project alignment extends from SR 79 to SR 77 in southwestern Bay County. See Project Location Map, Exhibit 1.1. Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

6 Exhibit 1.1 Project Location Map Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

7 SECTION 2 PROJECT DESCRIPTION The existing land uses for the area around CR 388 were obtained from Bay County and can be generally characterized as agricultural and conservation, except in the planned area around the new Northwest Florida Beaches International Airport, known as the West Bay Sector Plan. An overview of the Existing Land Uses is shown in Exhibit 2.1 From SR 79, north of CR 388 and to the eastern border of the Northwest Florida Beach International Airport, an area sector plan was developed by Bay County. Land uses identified within this area are denoted at the end of their description on the Land Use Map as sector plan and include: Airport/Industrial, Regional Employment Center, Village Center, West Bay Preservation Area, and Business Center. South of CR 388 from SR 79 to SR 77 is designated almost entirely as Conservation, mostly as a result of the wetland mitigation plans enacted during the airport permitting. In this area a few small blocks of Agriculture Timberland also exists. From the eastern border of the airport (both north and south of CR 388) the land use designation is also Agriculture Timberland and Conservation. There are some small residential communities surrounding Crooked Creek and Burnt Mill Creek. South of CR 388 between SR 79 and Crooked Creek the Rivercamp sub development is under construction with most of the built areas nearest to SR 79. The Burnt Mill Creek community is located on both the north and south sides of CR 388 and east of Burnt Mill Creek. Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

8 Exhibit 2.1 Existing Land Uses Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

9 SECTION 3 EXISTING CONDITIONS 3.1 Existing Conditions There are numerous storm water drainage crossings along the project, all draining to West Bay. Portions of the alternative alignments traverse FEMA mapped floodplains. Floodplain impacts are traverse unless identified as longitudinal in Section Surface Water Drainage Two surface water outfalls occur along the project. The first is Crooked Creek, located west of the propose Airport Access Road. Crooked Creek drains south to West Bay. The second outfall is Burnt Mill Creek, located approximately mid-point of the project limits. Burnt Mill Creek also drains south to West Bay Existing Cross Drains A review of FDOT straight line diagrams and field investigations produced an inventory of existing cross drains summarized in Table 3.1. The FDOT Straight Line Diagrams are included as Appendix E. The existing roadway overtops at several locations along the corridor. The biggest overtopping concern exists in the vicinity of SR77. This overtopping is occurring mostly for the 100 year events including hurricanes. The existing cross drains will need to be evaluated for conveyance capacity to prevent flooding in the proposed conditions. These cross drains were installed with the original construction of the roadway. Existing service life will need to be evaluated at the time of design to determine if new cross drains will be required. Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

10 Table 3.1 Summary of Existing Cross Drains!" #$% &!" '%!" #$% & (! ) * Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

11 3.2 Soils A review of available literature was conducted for the Segment 2 corridor. The review included the United States Department of Agriculture (USDA) Soil Survey for Bay County, the United States Geological Survey s (USGS) Topographic Survey, Florida Geological Survey s records and publications, and files of past projects conducted in the corridor area. The groundwater along the existing alignment is near the ground surface and could be above the surface for the Pamlico and Rutledge series. There are small regions of Hurricane series soil that have deeper groundwater. Based on the following summary, it is assumed the SHWT is 1 below surface for this evaluation. Predominant soils along existing CR 388: NO. Name Depth to SHWT 13 Leon Pamlico/Dorovan Hurricane Rutledge Pottsburg See Appendix B for Soil Survey information. 3.3 Existing Roadway Drainage Of the several alternate alignments evaluated for this project, the majority of each alignment follows the existing CR 388 alignment. The existing drainage patterns for all alternatives are from north to south and ultimately into West Bay. The existing CR 388 roadway is a rural section with open ditches on both sides. Runoff is conveyed under the roadway at twenty six cross drain locations. The Stormwater Engineer for Bay County was contacted to discuss any existing flooding issues and maintenance concerns. The existing ditches remain wet through the majority of the year and have been classified as wetlands by the FDEP. It has been documented that the roadway goes under water at several locations along the existing corridor with the biggest concern being the SR77 interesection and approximately 200 feet along CR 388. Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

12 Bay County suggested that all existing cross drains be evaluated for remaining service life and existing capacity. All improvements will need to be evaluated to ensure that there will not be a rise in the current flood elevations. 3.4 Floodplains The applicable Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRM) are listed and shown in Appendix A. These and the Bay County Flood Insurance Study indicate that numerous portions of the alternative alignments traverse FEMA mapped floodplains. The flood plains in close proximity to West Bay are storm surge related and have an elevation of 8.0 Ft (NAVD 88). Inland the floodplains are a mix of Zone AE and A. Flood Zone A is classified as an area of the 100-year flood where base flood elevations and flood hazard factors are not determined. Areas identified as Zone AE are areas of the 100-year floodplain where the base flood elevation is determined. There are no regulatory floodways within the limits of this project. The construction of the drainage structures proposed for this project will cause changes in flood stage and flood limits. These changes will not result in any significant adverse impacts on the natural and beneficial floodplain values or any significant changes in flood risk or damage. There will not be significant change in the potential for interruption or termination of emergency service or emergency evacuation routes. Therefore, it has been determined that this encroachment is not significant. 3.5 Floodways A floodway is the channel of a stream, plus any adjacent floodplain areas, that must be kept free of encroachment so that the 1-percent flood (100-year flood) can be carried without substantial increases in flood heights. Minimum Federal standards limit such increases to 1.0 foot, provided that hazardous velocities are not produced. Local agencies often restrict the increase in flood stage even more. Neither Big Crooked Creek nor Burnt Mill Creek have designated FEMA floodways. Neither of these creeks are listed as Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

13 having a detailed study by FEMA in the June 2, 2009 Bay County, Florida Flood Insurance Study. However, flood elevations are given on the FEMA Flood Insurance Rate Maps as shown in Appendix A. All alternative alignments cross both Big Crooked Creek and Burnt Mill Creek waterways and therefore will include a bridge design at each crossing. Closer evaluation will need to occur at the crossing of Burnt Mill Creek. The existing crossing constricts the floodway to 200 feet while the floodway width is approximately 1800 feet. If a new bridge is added at this location the bridge length should be the floodway width, and likely longer to assure no increase in the base flood elevation or change in the floodway limits. Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

14 SECTION 4 REGULATORY REQUIREMENTS 4.1 FDEP/ NWFWMD Floodways and floodplains, and levels of flood flows or velocities of adjacent streams, impoundments or other water courses must not be altered so as to adversely impact the off-site storage and conveyance capabilities of the water resource. 1. A system shall not cause a net reduction in flood storage within a 10-year floodplain except for structures elevated on pilings or traversing works. A system will not cause a net reduction in flood storage within a 10-year floodplain if compensating storage is provided outside the 10-year floodplain. Traversing works, works or other structures shall cause no more than a one foot increase in the 100-year flood elevation immediately upstream and no more than one tenth of a foot increase in the 100-year flood elevation 500 feet upstream. 2. A system shall not cause a reduction in the flood conveyance capabilities provided by a floodway except for structures elevated on pilings or traversing works. Such works or other structures shall cause no more than a one foot increase in the 100-year flood elevation immediately upstream and no more than one tenth of a foot increase in the 100-year flood elevation 500 feet upstream. 4.2 FDOT From FDOT Drainage Manual (Chapter 4): The hydraulic design of cross drains shall be done in accordance with good engineering practice and comply with 23 CFR 650, Subpart A, and the National Flood Insurance Program. Specifically: 1. All cross drains shall be designed to have sufficient hydraulic capacity to convey the selected design frequency flood without damage to the structure and approach embankments, with due consideration to the effects of greater floods. 2. The design of all cross drain structures shall be analyzed for the Design Flood, Base Flood (100 year frequency flood ) and the Greatest Flood (overtopping Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

15 flood or the 500-year frequency flood where overtopping is not practicable) that can be expected to flow to the structure. A summary of this analysis showing the peak stages and discharges for these events shall be shown on the final project plans. 4.3 Local Government This project falls entirely within Bay County. In general, meeting requirements for the ERP and FDOT Drainage Manual will satisfy the County s requirements defined in Bay County Land Development Code Chapter 24 Drainage/Stormwater Management. 4.4 Federal Emergency Management Agency (FEMA) This project must also meet the Code of Federal Regulations Title 44--Emergency Management and Assistance to comply with the requirements of FEMA. These regulations include Part 9 Floodplain Management and Protection of Wetlands, Part 60 Criteria for Land Management and Use and Part 65 - Identification and Mapping of Special Hazard Areas. Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

16 SECTION 5 EVALUATION OF HYDRAULIC STRUCTURES The following approach is felt to provide a reasonable comparison of the alternate alignments, but a much more refined effort using site specific topographic data will need to be done during the design phase to determine the size of the hydraulic structures. During the design phase, the structures will be developed in accordance with FDOT s drainage standards and as such the impacts to floodplains will be minimized. USGS Quadrangle maps and Aerial images were used to delineate drainage basins and to determine locations where cross drains will be needed. Straight Line Diagrams for Bay County were used to determine existing cross drain locations and sizes along the existing alignment. Existing cross drains will be evaluated for performance and service life and modifications or replacements will be made, as necessary. Region C Regression Equations were used to estimate the 50 year design flow rate for watersheds between 0.92 square miles and 4384 square miles. Once flow rates were estimated, bridge lengths and culvert sizes were estimated. Appendix C summarizes the technical approach. Below is a summary of the bridges and cross drains required for each alternative alignment. Since the there are not any basins greater than 590 acres along the new alignment alternatives for Segment 2 no new cross drain calculations were performed. It is assumed that existing culvert locations and sizes are acceptable. Table 5.1 Bridges/ Cross Drains Required!" #()!"#$ #$%"&' #$%"&' "#''"(' +, +, +, Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

17 Scour conditions will be evaluated during final design since crossings will be designed to create minimal backwater. Contraction of the floodway will be kept to a minimum so scour is not anticipated to be significant. Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

18 SECTION 6 FLOODPLAIN IMPACTS All but a few portions of the alternative alignments have transverse crossings of the floodplains. There is not a practical way to avoid these due to there being so many and the roadway design standards requiring gradual curves. As noted above, preliminary evaluations were performed to estimate the structure size for the floodplains having larger watersheds. For those floodplains, and those with smaller watersheds, the hydraulic structures will be sized during design to meet FDOT s drainage standards and as such, the impacts to floodplains will be minimized. Longitudinal encroachments were identified based on an overlay of the alignments on aerial maps showing the floodplain boundaries. One location will be required to be bridged. That location is the longitudinal encroachment on Burnt Mill Creek. The longitudinal encroachments are shown in Appendix D. During design, when field survey is available and detailed hydraulic evaluations are done, it may be determined that some of the encroachments are smaller than indicated in this preliminary report. Table 6.1 Longitudinal Encroachments ("%#&* ++"#, ()#$ # &(-"#(-).$/ ----+! Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

19 SECTION 7 CONCLUSION Proposed cross drains will be designed to pass the 50-year flow without overtopping the roadway. Flows up to and including the 500-year will be analyzed to determine backwater elevations and the cross drains will be designed so that there is no significant change in land use values. There are FEMA mapped floodplains and un-mapped floodplains associated with small hydraulic crossings. Floodplain elevations will be determined during the final design. This type of project has the potential to cause changes in flood stage and flood limits, however, proper application of the FDOT cross drain design criteria will ensure that the changes are minimal and insignificant. This project will have a positive effect on Emergency Services and evacuation as it provides another route to the local communities. In summary, the hydraulic structures proposed along the existing alignment will perform in a manner equal to or better than the existing structure and backwater elevations are not expected to increase. The hydraulic structures proposed along the new alignments will be designed to cause minimal changes in flood stages and flood limits. These changes will not result in any significant adverse impacts in the natural and beneficial floodplain values or any significant changes in flood risk or damage. The project will enhance Emergency services and evacuations. Therefore, it has been determined that the encroachments associated with this project are not significant. Draft Location Hydraulic Report West Bay Parkway - Segment March 2010

20 Appendix A FEMA Flood Insurance Rate Maps (FIRM)

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25 Appendix B NRCS Soils Maps & Details

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35 Appendix C Approach to Estimating Bridge Lengths & Cross Drain Size

36 Approach to Estimating Cross Drain Sizes: The following approach is intended to estimate the number and size of large cross drains for estimating costs and comparing alternative alignments. Since the approach will be applied uniformly to all alternatives, it should provide a reasonable comparison of structure costs for each alternative. This evaluation considers only hydraulic factors. Environmental factors could sometimes necessitate longer structures. A more refined approach may be done after the preferred alignment is selected. On or near Existing Alignments: Where alternative alignments match or are within several hundred feet of existing county or state roads, it is assumed that existing culvert locations and sizes are acceptable unless there is evidence to the contrary. New Alignments: In general the lack of topographic survey prevents detailed determinations of culvert locations and sizes. The remoteness of some of the new alignments also makes it unreasonable to field review the locations. Of primary importance in comparing alternatives is the cost of the large structures. As such this evaluation focuses on relatively large drainage basins that typically would dictate the largest structures. Smaller basins will generally dictate smaller structures that will not have a substantial impact on the costs of a particular alternative and thus should not favor a particular alternative alignment over another. The smallest basin size evaluated will be approximately 590 acres which is the lower limit of the USGS Regression Equation (Region C). Data: In most cases topographic data is limited to USGS quadrangle maps, but Bay County information may provide more detailed information at some locations. The best available topographic data will be used for each area.

37 Aerial images dating back to 1950 will be used to augment the topographic data and current aerial images. The older aerials sometimes provide better delineation of low lying areas, flow paths and drainage patterns. Hydrology: The USGS Regression Equation (Region C) was used for basins 590 acres and larger. Slopes were estimated by interpolation of the contour data. Only the 50 year flow was determined. Hydraulics: After the flow rates were estimated, a cross sectional area of opening was determined based on 2 feet per second (fps) for bridges and 4 fps for culverts. 2 fps is the velocity listed in the FDOT 1996 Cross Drain HB for a trial bridge length. 4 fps is the velocity listed in the 2004 FDOT culvert handbook for trial culvert sizes. After the cross sectional area is determined bridge length is calculated based on an assumed average flow depth of 4 feet unless the topographic data indicates a deeper depth is appropriate. In the case of culverts, a pipe or box configuration is developed that provides the calculated cross sectional area. The height of box culverts was limited to no more than 6 feet unless the topographic data indicated a deeper depth was appropriate. The minimum box culvert height used was 4 feet. Less than 4 feet restricts maintenance access and usually multiple pipe culverts are more economical than shallow box culverts. For moderate size drainage basins there is a decision whether a bridge or culvert should be used. This decision is formally done during the design phase when detail survey is available. For this effort, a minimum bridge size will used and for smaller flows a box culvert or a multiple pipe culvert is sized. The minimum bridge length is assumed to be 60 feet. This is based on an average flow depth of 4 feet, standard abutment slopes, abutment horizontal toes, and drift clearance, while providing a reasonable a main channel width as shown below.

38 60 2 Drift Clr. 4 Avg Depth Horiz. Exist. Main Chan. Horiz. Toe Toe Assumed Minimum Bridge Length It is realized that during design shorter bridge lengths could be considered as part of the bridge hydraulic reports and bridge development reports. As an example of a large basin with obvious needs for a bridge, the bridge length would be determined as follows: Assume the computed flow = 2000 cfs Area of opening = 2000 cfs/2 fps = 1000 sf Bridge length = 1000 sf /4 ft = 250 ft. As an example of a small basin suitable for a culvert, the bridge length would be determined as follows: Assume the computed flow = 150 cfs Area of opening = 150 cfs/4 fps = 37.5 sf Option 1 culvert = 8 x 5 box having 40 sf opening Option 2 culvert = 3-48 pipes having 38 sf opening.

39 Appendix D Longitudinal Encroachments

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41 Appendix E FDOT Straight Line Diagrams

42 ROADWAY FEATURES LANE WIDTHS ARE AVERAGED INTERIM REVISIONS 5 YR INV SLD REV BMP EMP INV SLD REV INT. or US ROUTE NO STATE ROAD NO. COUNTY DISTRICT ROADWAY ID SHEET DATE 10/05/06 11/16/06 NO. 1 BY METRIC METRIC FLORIDA DEPARTMENT OF TRANSPORTATION * * * OFF SYSTEM * * * CR 388 BAY OF. 2 4 x OUTSIDE CITY & URBAN <=CR x 388 x <CR A SR BAY ROAD A A 38.0' ' ' RDWY 2*8.0' LWN SHLD1 TEMPLE AVE O UNSIGNED RD ' ' ' RDWY 13.0' PVD MED 2*5.0' LWN SHLD1 A ' ' ' RDWY 2*5.0' LWN SHLD1 STRAIGHT LINE DIAGRAM OF ROAD INVENTORY PRESERVATION DRIVE A 49.0' ' ' RDWY 11.0' PVD MED 2*8.0' LWN SHLD ' ' ' RDWY 2*8.0' LWN SHLD1 CROOKED CREEK ROADWAY COMPOSITION 28/FC /FC-3 28/FC /FC /FC-3 28/FC /FC-3 HORIZONTAL CURVE DATA IS NOT FIELD VERIFIED ALIGNMENT STRUCTURE DESCRIPTION ' BR 0051 DISTRICT USE SIS FUN CLASS PLANNED EMERGING SIS CONNECTOR RURAL MINOR ARTERIAL LANE WIDTHS ARE AVERAGED ROADWAY FEATURES BURNT MILL CREEK N BURNT MILL CREEK R O S BURNT MILL CREEK R O ROADWAY COMPOSITION 28/FC-3 HORIZONTAL ALIGNMENT CURVE DATA IS NOT FIELD VERIFIED STRUCTURE DESCRIPTION ' BR 0052 DISTRICT USE SIS FUN CLASS PLANNED EMERGING SIS CONNECTOR RURAL MINOR ARTERIAL

43 STRAIGHT LINE DIAGRAM OF ROAD INVENTORY INTERIM REVISIONS 5 YR INV SLD REV BMP EMP INV SLD REV INT. or US ROUTE NO STATE ROAD NO. COUNTY DISTRICT ROADWAY ID SHEET DATE 10/05/06 11/16/06 NO. 2 BY METRIC METRIC FLORIDA DEPARTMENT OF TRANSPORTATION * * * OFF SYSTEM * * * CR BAY OF ROADWAY FEATURES LANE WIDTHS ARE AVERAGED 38.0' ' ' RDWY 2*8.0' LWN SHLD1 28/FC-3 ROADWAY COMPOSITION HORIZONTAL ALIGNMENT CURVE DATA IS NOT FIELD VERIFIED STRUCTURE DESCRIPTION DISTRICT USE SIS FUN CLASS RURAL MINOR ARTERIAL LANE WIDTHS ARE AVERAGED ROADWAY FEATURES x INSIDE URBAN, OUTSIDE CITY x PANAMA CITY x ' ' ' RDWY 2*5.0' PVD SHLD1 2*5.0' LWN SHLD2 A SR A NET ROADWAY ID LENGTH: ROADWAY COMPOSITION 28/FC-3 HORIZONTAL ALIGNMENT CURVE DATA IS NOT FIELD VERIFIED STRUCTURE DESCRIPTION DISTRICT USE SIS FUN CLASS RURAL MINOR ARTERIAL URBAN MINOR ARTERIAL