Jacobi, Toombs, and Lanz, Inc.

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1 Area 5: Blackiston Mill Road at Dead Man's Hollow Flooding Assessment Jacobi, Toombs, and Lanz, Inc. This document summarizes an assessment of drainage and flooding concerns and provides recommendations for improving storm water management in Area 5 for the Town of Clarksville, Indiana. December 2008

2 AREA 5: BLACKISTON MILL ROAD AT DEADMAN S HOLLOW JTL Consulting Engineers Project Area Overview This report summarizes the project team s assessment and recommendations for Area 5, Blackiston Mill Road at Dead Man s Hollow, which has historically presented maintenance issues and flood hazards for the Town of Clarksville. The existing drainage conduit in this area suffered partial failure and has been slip-lined two times since its original construction. These activities have decreased the effective opening size from a 48-inch x 60-inch concrete box culvert (20.0 ft 2 cross-sectional area) to a 30-inch diameter PVC pipe (4.9 ft 2 cross-sectional area). During rainfall events of significant intensity, the existing 30-inch pipe under Blackiston Mill Road lacks the conveyance capacity to prevent backwater conditions upstream of the road embankment. At times, these high water surface elevations upstream of the structure have led to the overtopping of the roadway and presented public safety hazards and caused road closures. In addition, these conditions present significant challenges to the drainage and roadway maintenance activities of the Clarksville Street Department. The project team comprised of Stantec Consulting Services, Inc. (Stantec) and Jacobi, Toombs and Lanz, Inc. (JTL) conducted physical surveys and performed hydrologic and hydraulic assessments of the project area to determine the nature and extent of the problems and evaluate alternatives for improving drainage and reducing the risk of flooding at this location. Two solutions have been developed and are detailed in this report. These solutions include an in-kind replacement of the existing structure or a structure replacement with roadway improvements. The anticipated costs for improvements to this existing structure under Blackiston Mill Road are estimated to be 425,000. In addition, the anticipated cost for structure replacement and improvements to the roadway alignment is 685,000. E.1

3 AREA 5: BLACKISTON MILL ROAD AT DEADMAN S HOLLOW JTL Consulting Engineers Table of Contents PROJECT AREA OVERVIEW E INTRODUCTION BACKGROUND FLOODING PROBLEMS PROBLEM ASSESSMENT STUDY METHODOLOGY EXISTING CONDITIONS ANALYSIS PROPOSED SOLUTIONS ALTERNATIVE 1: BOX CULVERT ALTERNATIVE 2: BOX CULVERT WITH ROAD IMPROVEMENTS CONCLUSIONS i

4 AREA 5: BLACKISTON MILL ROAD AT DEADMAN S HOLLOW JTL Consulting Engineers 1.0 Introduction This report examines two conceptual alternatives to improve motorist safety and minimize maintenance requirements by reducing the flooding risk along Blackiston Mill Road at Dead Man s Hollow. The project team comprised of Stantec Consulting Services, Inc. (Stantec) and Jacobi, Toombs and Lanz, Inc. (JTL) conducted physical surveys and completed hydrologic and hydraulic assessments to identify the problems in the area and develop alternatives in the project area. Flooding problems in the area of Blackiston Mill Road at Dead Man s Hollow have increased in recent years because of the increased volume and intensity of stormwater runoff. This increased runoff is due to extensive developments in the watershed and degradation and partial failure of the existing structure under Blackiston Mill Road. 1.1 BACKGROUND The project area is located in the central and western portion of the Town of Clarksville, situated between the major intersections of Blackiston Mill Road with Gutford Road and Potters Lane. The existing outfall structure on Blackiston Mill Road is located approximately 600 feet east of Silver Creek. Silver Creek water surface elevations and backwater conditions were considered and incorporated into this design. The structure under Blackiston Mill Road is located in a steeply incised stream valley. The elevation difference from the centerline of the road to the invert of the current structure is approximately 24 feet. This project area is located in the Silver Creek Plum Run HUC14 watershed. According to the Natural Resources Conservation Service (NRCS), soils in this area are composed primarily of hydrologic soil group (HSG) C with some smaller areas containing HSG B. The majority of the area is composed of clayey stratum and silty loams which indicate poor soil infiltration capacity, which often leads to standing stormwater in poorly graded areas or regions with little drainage relief. Only very small regions contain soils which permit moderate infiltration abilities. The 451 acre watershed draining to this structure is composed primarily of residential properties in the lower subcatchments and heavy commercial properties located in the upper subcatchments. The watershed is relatively flat, ranging from 466 feet above sea level (FASL) to 474 FASL. The only area of significant elevation relief is immediately adjacent to the steeply incised ditch. Upstream of Blackiston Mill Road, the central open channel begins at the outlet of a 12-foot x 3-foot concrete box culvert that drains a heavy commercial area along Greentree Boulevard. The existing terrain creates a deep channel with steep slopes on both the upstream and downstream side of Blackiston Mill Road. The significant elevation difference between the channel bed and roadway surface results in a significant amount of storage upstream of the structure prior to flow overtopping the roadway. This causes high flow velocities through the culvert and scour downstream. 1.1

5 AREA 5: BLACKISTON MILL ROAD AT DEADMAN S HOLLOW JTL Consulting Engineers 2.0 Flooding Problems 2.1 PROBLEM ASSESSMENT The drainage structure at Dead Man s Hollow is believed to have originally been a 48-inch x 60- inch box culvert; however, due to structural deterioration, the existing structure was slip-lined with a 42-inch galvanized corrugated metal pipe. Due to further complications, the pipe was slip-lined again with a 30-inch, schedule 35 PVC pipe. These repairs have decreased the effective opening size from a 48-inch x 60-inch (20.0 ft 2 ) box culvert to a 30-inch PVC pipe (4.9 ft 2 ). During large rainfall events, the existing culvert cannot convey enough stormwater to prevent ponding along the upstream embankment of Blackiston Mill Road. Additionally, woody debris and trash accumulate at the structure opening and further reduce the flow capacity. This is a regular maintenance issue for the Clarksville Street Department. Additionally, this inadequate structure has regularly caused backups which overtop the roadway. When this overtopping occurs, it causes hazardous conditions for motorists, and requires immediate action by the Clarksville Street Department to close the roadway to traffic. During these events where overtopping occurs, erosion regularly takes place on the downstream side of the embankment. This also requires regular maintenance by the street department. High entrance and exit velocities occur at this structure due to the elevation of ponded water upstream of the structure. Erosion also occurs when stormwater overtops the roadway and flows down the steep embankment on the downstream side of the roadway. These two erosion problems require regular maintenance from the Clarksville Street Department. 3.0 Study Methodology Hydrologic (HEC-HMS) and hydraulic models (HEC-RAS) were developed to assess the drainage and flooding dynamics of Blackiston Mill Road at Dead Man s Hollow. Soil information from the Natural Resources Conservation Service (NRCS) and land use determined from aerial imagery were used to estimate runoff potential for the subwatersheds in the study area. Peak discharges for 24-hour storm events were estimated using the SCS method. Representative cross sections upstream and downstream of Blackiston Mill Road were surveyed by field crews, and used in the hydraulic model to compute peak water surface elevations. 3.2

6 AREA 5: BLACKISTON MILL ROAD AT DEADMAN S HOLLOW JTL Consulting Engineers 4.0 Existing Conditions Analysis A model representing the downstream portions of the watershed and Silver Creek was developed during this assessment. This model validated observations that the area downstream of Blackiston Mill Road is susceptible to backwater flooding from Silver Creek during a 100-year storm event. Consequently, the proposed improvements will only allow increased stormwater discharges underneath Blackiston Mill Road until the backwater conditions from the Silver Creek reach the same elevation as the proposed box culvert. Refer to Appendix 5A for a map of the watershed draining this area. 5.0 Proposed Solutions 5.1 ALTERNATIVE 1: BOX CULVERT Based upon the hydrologic and hydraulic (H & H) analysis, it was determined that an 8-foot x 10-foot box culvert would control the stormwater in a manner that would allow sufficient flow through the culvert while minimizing backwater conditions and controlling the rate of discharge to a sufficient degree to minimize the potential for downstream flooding. Refer to Appendix 5B for the HEC-HMS and Appendix 5C HEC-RAS results of this assessment. See Appendix 5D for the preliminary construction plan for this structure replacement. The estimated cost for the proposed 8 x10 box culvert is 425,000. A detailed breakdown of the engineer s estimate can be found in Appendix 5E. 5.2 ALTERNATIVE 2: BOX CULVERT WITH ROAD IMPROVEMENTS In addition to the proposed 8-foot x 10-foot box culvert recommended above, further improvements to the grade and alignment of Blackiston Mill Road could be implemented during the installation of the culvert to increase the height of the road and further minimize the potential for overtopping. This would further minimize road closures caused by backwater from Silver Creek. These modifications would also improve the traffic conditions and visibility through this portion of Blackiston Mill Road. The general layout and improved vertical roadway alignment can be found in Appendix 5D. The estimated cost of the proposed box culvert with additional road improvements is 685,000. An engineer s estimate of the proposed stormwater and roadway improvements can be found in Appendix 5F. 5.3

7 AREA 5: BLACKISTON MILL ROAD AT DEADMAN S HOLLOW JTL Consulting Engineers 6.0 Conclusions Blackiston Mill Road at Dead Man s Hollow has historically presented maintenance issues for the Clarksville Street Department and regular flood hazards for motorists. The existing drainage conduit in this area suffered partial failure and has been slip-lined two times since its original construction. These activities have decreased the effective opening of the structure to the point that its ability to sufficiently convey stormwater is no longer adequate, which results in high backwater developing. At times, these high water surface elevations upstream of the structure have led to the overtopping of the roadway and presented public safety hazards and caused road closures. The project team conducted physical surveys and developed hydrologic and hydraulic models to determine the nature and extent of the problems and evaluate alternatives for improving drainage and reducing the risk of flooding at this location. The anticipated costs for improvements to this existing structure under Blackiston Mill Road are estimated to be 425,000. In addition, the anticipated cost for structure replacement and improvements to the roadway alignment is 685,000. It is recommended that Alternative 2 is selected due to the increased roadway elevation. This increased elevation will not only further minimize flooding of Blackiston Mill at Deadman s Hollow, it will also serve to improve roadway geometry, reducing traffic safety hazards during both wet and dry weather. 6.4

8 Appendices

9 Appendix A

10

11 Appendix B

12 Simulation Run Area 5 Blackiston Mill - Existing Culvert Backwater Elevation Q Total (cfs) Min Ch El (ft) W.S. Elev (ft) Crit W.S. (ft) E.G. Elev (ft) Slope (ft/ft) Vel Chnl (ft/s) 24 Hour 1 Year Hour 2 Year Hour 5 Year Hour 10 Year Hour 25 Year Hour 50 Year Hour 100 Year Simulation Run Area 5 Blackiston Mill - Proposed Culvert Backwater Elevation Q Total (cfs) Min Ch El (ft) W.S. Elev (ft) Crit W.S. (ft) E.G. Elev (ft) Slope (ft/ft) Vel Chnl (ft/s) 24 Hour 1 Year Hour 2 Year Hour 5 Year Hour 10 Year Hour 25 Year Hour 50 Year Hour 100 Year

13 Culvert_Analysis Plan: Existing 4/3/2008 River Reach Legend WS 100 Year WS 50 Year WS 25 Year WS 10 Year WS 5 Year WS 2 Year WS 1 Year Ground 450 Elevation (ft) Main Channel Distance (ft)

14 Culvert_Analysis Plan: Proposed Culvert 4/3/2008 River Reach Legend WS 100 Year WS 50 Year WS 25 Year WS 10 Year WS 5 Year WS 2 Year WS 1 Year Ground 450 Elevation (ft) Main Channel Distance (ft)

15 Appendix C

16 Simulation Run Area 5 Blackiston Mill - Existing Conditions HEC-HMS Results Hydrologic Element Drainage Area (MI2) Peak Discharge (CFS) Time of Peak Volume (IN) 24 Hour 1 Year Subbasin Jan2008, 00: Hour 2 Year Subbasin Jan2008, 00: Hour 5 Year Subbasin Jan2008, 00: Hour 10 Year Subbasin Jan2008, 00: Hour 25 Year Subbasin Jan2008, 00: Hour 50 Year Subbasin Jan2008, 00: Hour 100 Year Subbasin Jan2008, 00:

17 Project: DeadMan Simulation Run: 24 Hour 1 Year Start of Run: 01Jan2008, 12:00 Basin Model: Basin 1 End of Run: 03Jan2008, 12:00 Meteorologic Model: 24Hr-1Yr Compute Time: 02Apr2008, 13:22:24 Control Specifications: Control 1 Volume Units: IN Hydrologic Element Drainage Area (MI2) Peak Discharge (CFS) Time of Peak Volume (IN) Subbasin Jan2008, 00:

18 Project: DeadMan Simulation Run: 24 Hour 2 Year Start of Run: 01Jan2008, 12:00 Basin Model: Basin 1 End of Run: 03Jan2008, 12:00 Meteorologic Model: 24Hr-2Yr Compute Time: 02Apr2008, 13:23:17 Control Specifications: Control 1 Volume Units: IN Hydrologic Element Drainage Area (MI2) Peak Discharge (CFS) Time of Peak Volume (IN) Subbasin Jan2008, 00:

19 Project: DeadMan Simulation Run: 24 Hour 5 Year Start of Run: 01Jan2008, 12:00 Basin Model: Basin 1 End of Run: 03Jan2008, 12:00 Meteorologic Model: 24Hr-5Yr Compute Time: 02Apr2008, 13:11:15 Control Specifications: Control 1 Volume Units: IN Hydrologic Element Drainage Area (MI2) Peak Discharge (CFS) Time of Peak Volume (IN) Subbasin Jan2008, 00:

20 Project: DeadMan Simulation Run: 24 Hour 10 Year Start of Run: 01Jan2008, 12:00 Basin Model: Basin 1 End of Run: 03Jan2008, 12:00 Meteorologic Model: 24Hr-10Yr Compute Time: 02Apr2008, 13:21:56 Control Specifications: Control 1 Volume Units: IN Hydrologic Element Drainage Area (MI2) Peak Discharge (CFS) Time of Peak Volume (IN) Subbasin Jan2008, 00:

21 Project: DeadMan Simulation Run: 24 Hour 25 Year Start of Run: 01Jan2008, 12:00 Basin Model: Basin 1 End of Run: 03Jan2008, 12:00 Meteorologic Model: 24Hr-25Yr Compute Time: 02Apr2008, 13:22:52 Control Specifications: Control 1 Volume Units: IN Hydrologic Element Drainage Area (MI2) Peak Discharge (CFS) Time of Peak Volume (IN) Subbasin Jan2008, 00:

22 Project: DeadMan Simulation Run: 24 Hour 50 Year Start of Run: 01Jan2008, 12:00 Basin Model: Basin 1 End of Run: 03Jan2008, 12:00 Meteorologic Model: 24Hr-50Yr Compute Time: 02Apr2008, 13:23:44 Control Specifications: Control 1 Volume Units: IN Hydrologic Element Drainage Area (MI2) Peak Discharge (CFS) Time of Peak Volume (IN) Subbasin Jan2008, 00:

23 Project: DeadMan Simulation Run: 24 Hour 100 Year Start of Run: 01Jan2008, 12:00 Basin Model: Basin 1 End of Run: 03Jan2008, 12:00 Meteorologic Model: 24Hr-100Yr Compute Time: 02Apr2008, 13:21:29 Control Specifications: Control 1 Volume Units: IN Hydrologic Element Drainage Area (MI2) Peak Discharge (CFS) Time of Peak Volume (IN) Subbasin Jan2008, 00:

24 Appendix D

25

26 Appendix E

27 Clarksville Stormwater Improvements BY HLH CHECKED JIL Area 5 Blackiston Mill Road Preliminary Cost Estimate - ALT #1 DATE 11/28/2008 JOB NO ITEM QUANTITY UNIT ENGINEER'S ESTIMATED UNIT COST EXTENSION Mobilization & Demobilization 1 LS 10, , Common Excavation 6800 CY , Borrow 8252 CY , HMA Surface, Type B 18 Ton , HMA Intermediate, Type B 36 Ton , HMA Base, Type B 53 Ton , Compacted Aggregate, No Ton , Clearing and Grubbing 1 LS 7, , Revetment Riprap 44 Ton , Seed and Straw Pavement Markings Guardrail, Remove Guardrail, W-beam 6'-3" spacing Traffic Maintenance Erosion Control Remove Existing Culvert SY LS LF LF LS LS LS , , , , , , , , , , , Construction Subtotal 334, % Contingency 33, % Engineering, Surveying, & Inspection 55, Total Estimated Construction Cost 422, USE 425,000

28 Appendix F

29 Clarksville Stormwater Improvements BY HLH CHECKED JIL Area 5 Blackiston Mill Road Preliminary Cost Estimate - ALT #2 DATE 11/28/2008 JOB NO ITEM QUANTITY UNIT ENGINEER'S ESTIMATED UNIT COST EXTENSION Mobilization & Demobilization 1 LS 10, , Common Excavation 6800 CY , Borrow CY , HMA Surface, Type B 106 Ton , HMA Intermediate, Type B 213 Ton , HMA Base, Type B 319 Ton , Compacted Aggregate, No Ton , Clearing and Grubbing 1 LS 10, , Demo Existing Road Surface 1660 SY , Modify Existing Lift Station 1 LS 10, , Revetment Riprap 44 Ton , Seed and Straw Pavement Markings Guardrail, Remove Guardrail, W-beam 6'-3" spacing Traffic Maintenance Erosion Control Remove Existing Culvert SY LS LF LF LS LS LS , , , , , , , , , , , Construction Subtotal 540, % Contingency 54, % Engineering, Surveying, & Inspection 89, Total Estimated Construction Cost 683, USE 685,000

30 Area 6: Adams Drive Drainage Assessment Jacobi, Toombs, and Lanz, Inc. This document summarizes an assessment of drainage and flooding concerns and provides recommendations for improving storm water management in Area 6 for the Town of Clarksville, Indiana. December 2008