APPENDIX E GREATER SPRINGFIELD RELIABILTIY PROJECT DRAINAGE ANALYSIS FOR THE NEWGATE/PHELPS ROAD AND THE HATCHETT HILL ROAD AREAS

Transcription

1 APPENDIX E GREATER SPRINGFIELD RELIABILTIY PROJECT DRAINAGE ANALYSIS FOR THE NEWGATE/PHELPS ROAD AND THE HATCHETT HILL ROAD AREAS

2 New England East-West Solution (NEEWS) Greater Springfield Reliability Project Drainage Analysis for the Newgate/Phelps Road and the Hatchett Hill Road Areas prepared for Northeast Utilities July, 2010 Rev. 0 prepared by Burns & McDonnell Engineering Company, Inc. Wallingford, Connecticut COPYRIGHT 2010 BURNS & McDONNELL ENGINEERING COMPANY, INC GSRP 345-kV Line D&M Plan Appendix E: Page 1 of 36

3 GSRP 345-kV Line D&M Plan Appendix E: Page 2 of 36

4 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Table of Contents TABLE OF CONTENTS Page No. 1.0 PROJECT DESCRIPTION INTRODUCTION Newgate/Phelps Road Area Hatchett Hill Road Area RUNOFF CHARACTERISTICS & FLOW CALCULATIONS Two-, Ten-, and Fifty-Year Storm Event Calculations EROSION & SEDIMENT CONTROL MEASURES Vegetation Removal Newgate/Phelps Road Area Erosion & Sediment Control Hatchett Hill Road Area Erosion & Sediment Control LIST OF TABLES Table No. Page No. Table 3-1 Two-Year Storm Event Table 3-2 Ten-Year Storm Event Table 3-3 Fifty-Year Storm Event Table 3-4 Two-Year Storm Event Table 3-5 Ten-Year Storm Event Table 3-6 Fifty-Year Storm Event Northeast Utilities TOC-1 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 3 of 36

5 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Table of Contents APPENDICES APPENDIX A SITE DRAWINGS APPENDIX B TYPICAL EROSION CONTROL DETAILS Northeast Utilities TOC-2 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 4 of 36

6 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Project Description 1.0 PROJECT DESCRIPTION The Greater Springfield Reliability Project (GSRP or the Project) consists of improvements to the electric transmission systems of The Connecticut Light and Power Company (CL&P) in Connecticut and Western Massachusetts Electric Company (WMECO) in Massachusetts. These improvements are needed to provide safe, reliable, and economic transmission service throughout the north-central Connecticut and the Greater Springfield geographic area. Additionally these improvements will ensure that the Greater Springfield portion of the transmission system will comply with mandatory federal and regional reliability standards. At the same time, the GSRP improvements are part of a comprehensive long-term regional plan for improving electric transmission in southern New England, through extensive coordinated improvements in Connecticut, Massachusetts, and Rhode Island. This comprehensive plan is known as the New England East West Solution (NEEWS). To meet these demands, CL&P and WMECO (both owned and operated by Northeast Utilities (NU)), has proposed the GSRP. In general terms the Project will consist of the following: the construction of a new 345-kilovolt (kv) transmission line between CL&P s North Bloomfield Substation in Bloomfield, Connecticut and WMECO s Ludlow Substation in Ludlow, Massachusetts, improvements to existing 115-kV transmission lines, the expansion and construction of switching stations and substations, and removal of the existing transmission structures within the right-of-way (ROW) from North Bloomfield Substation to Granby Junction. In Connecticut, the Project will traverse the municipalities of Bloomfield, East Granby and Suffield along an existing transmission ROW that currently contains overhead 115-kV transmission line(s), and in some segments a distribution line. Northeast Utilities 1-1 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 5 of 36

7 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Introduction 2.0 INTRODUCTION Based on comments received from residents and town officials through various forums, CL&P initiated this review. Due to a variety of factors some residents along the GSRP ROW have existing drainage/surface water runoff problems on their properties, and are concerned that construction, including the additional tree clearing, will alter/increase the amount and frequency of runoff they currently have. Most of the comments received are from residents along Phelps Road and Newgate Road in East Granby and Suffield. However, one resident on Adams Road in East Granby commented as well. As a result these are the two areas examined and discussed in this report. As designed, the control measures recommended in this report will provide adequate control of surface water flow (sheet and concentrated) across these two areas during construction, and until the areas have been stabilized. Therefore there will be no long-term increase in surface water runoff resulting from the construction in these areas. They will not provide control of ground water within or outside of these areas, nor will they permanently reduce the amount of runoff that ultimately leaves these areas. During the Development and Management (D&M) Plan process, which is mandated by the Connecticut Siting Council (CSC), the location of additional control measures that are needed to protect wetlands and watercourses, prevent sedimentation and erosion issues, and to maintain the stability of all improved surfaces (access roads and crane pads) will be determined. The final D&M Plan, to be submitted to the CSC and each town, will also include all controls identified in this report. All control measures will be inspected regularly and will be repaired, reinforced, and upgraded as needed throughout the Project s duration. Northeast Utilities Transmission Business Unit s Best Management Practices: Construction and Maintenance Environmental Requirements Connecticut (provided under separate cover or as an appendix to the D&M Plan for Construction of the Greater Springfield Reliability Project) will be adhered to when inspecting and maintaining all erosion control measures. 2.1 NEWGATE/PHELPS ROAD AREA The Newgate/Phelps Road area is located within East Granby and Suffield and is generally bounded by Phelps Road on the north, Newgate Road on the west, the western slope of West Suffield Mountain on the east, and the intersection of Copper Hill Road and Newgate Road on the south. Except for residential development to the west of the ROW, and scattered residential development to the east, the area consists of wooded land with varying slopes that are in excess of 30 percent in some areas. This area is shown on Figure 1. Northeast Utilities 2-1 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 6 of 36

8 Apple Ln Copper Hill Rd Old Farms Ln \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_Overview_Phelps_Road.mxd Date: 11/11/09 COPYRIGHT 2007 BURNS & McDONNELL ENGINEERING COMPANY, INC. Phelps Rd Copper Hill Rd Copper Hill Rd Legend Proposed Structures Wetlands Existing Structures NU Owned Property Proposed 345kV Route Centerline Vernal Pool Existing Centerline Contours (5 ft) Parcel Boundary Town Boundary Existing ROW Expanded ROW Source: AECOM, Coler & Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics and CT DOT Griffin Rd Country Club Ln NORTH Woodledge Dr Newgate Rd Wyncairn Newgate/ Phelps Road Locus Map Figure 1 Mountain Rd Ridge Blvd 1, ,500 Feet GSRP 345-kV Line D&M Plan Appendix E: Page 7 of 36

9 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Introduction Public Comments Comments from several home owners along Phelps Road and Newgate Road were received. Most comments reflected that some residents in this area have installed engineered drainage systems to control the water that flows down the hill, through the ROW, before reaching their properties at the base of the slope. These systems are currently effective, but the residents are concerned the construction may result in runoff changes that their engineered systems are not designed to handle. Another resident expressed concern about an existing drainage issue between his home and his neighbor s home. During rain events water flows from the ROW behind their homes to Newgate Road where it freezes during the winter, creating a hazardous situation. According to the resident, the Town is aware of this situation. 2.2 HATCHETT HILL ROAD AREA This area is approximately bounded by Holcomb Road on the north, the western slope of Hatchett Hill on the east, Hatchett Hill Road on the south, and the approximate toe of the slope for Hatchett Hill on the west. Adams Road, a cul-de-sac, ends at the west edge of the ROW. Marsh Pond and its associated wetland system are located to the south of Adams Road. This system receives surface and ground water from the south, from residential development to the west and north, and from Hatchett Hill to the east. The west slope of Hatchett Hill is heavily wooded with steep slopes of 10 percent or greater. This area is shown on Figure Public Comments A resident that lives at the end of Adams Road expressed concern that Marsh Pond and its associated forested wetland system south of his property frequently overflows. If the Project causes more water to drain into the pond during construction, it will exacerbate the problem. The resident states his yard, as well as his street, can be a sheet of ice during the winter. He suggested that the Project consider tying into the Town s existing storm drainage system in the street to capture the runoff leaving the ROW, thereby decreasing the amount of additional water that ultimately reaches his property. Northeast Utilities 2-2 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 8 of 36

10 Holcomb St Lexington Dr Adams Dr \\Espsrv\data\DATA2\Projects\NUS\SNETR_Projects\45063_Springfield_345kV\Environmental\GIS\ARC\ArcMXD\Network\GreaterSpringfield\Analysis\Sediment_Survey\GSRP_Overview_Sediment_Maps.mxd Date: 11/11/09 COPYRIGHT 2007 BURNS & McDONNELL ENGINEERING COMPANY, INC. Concord Dr Hatchett Hill Rd Legend Proposed Structures Wetlands Existing Structures NU Owned Property Proposed 345kV Route Centerline Vernal Pool Existing Centerline Contours (5 ft) Parcel Boundary Town Boundary Existing ROW Expanded ROW Source: AECOM, Coler & Colantonio, ESRI and Burns & McDonnell Engineering. Image Source: Optimal Geomatics and CT DOT NORTH Hatchett Hill Ln Hatchett Hill Locus Map Figure Feet GSRP 345-kV Line D&M Plan Appendix E: Page 9 of 36

11 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Runoff Characteristics & Flow Calculations 3.0 RUNOFF CHARACTERISTICS & FLOW CALCULATIONS To assess current drainage conditions and any adverse impacts the construction may cause, runoff flows for the two, ten, and fifty-year storm events were calculated. The calculations were done per the 2004 Connecticut Stormwater Quality Manual, Chapter 7, the 2003 Connecticut Department of Transportation Drainage Manual, and the 2002 Connecticut Guidelines for Soil Erosion and Sediment Control, and are based on the Rational Method. The Rational Method is a standard equation used, for small drainage areas of up to approximately 200 acres, to calculate and estimate the peak rate of runoff at any location in a watershed. The factors used to calculate this are the size of the drainage area, the runoff coefficient, which is dependent on what type of land use is present (e.g. asphalt parking lot versus green space), and the mean rainfall intensity for the design storm event. The runoff coefficient is an estimate of how much of the rain that hits the ground will run off. It will obviously vary with topography, land use, type and amount of vegetation cover, and moisture content of the soil. For example, a runoff coefficient for asphalt pavement is 0.98, which means 98 percent of the water runs off, whereas green space has a runoff coefficient of 0.30, meaning 30 percent runs off and the remainder soaks in. Runoff coefficients were based on Table 6-3 from the 2003 Connecticut Department of Transportation Drainage Manual. This table includes runoff coefficients for pervious areas based on slope rather than on land use. By looking at aerial photographs and visiting the site it can be seen that the majority of the drainage areas are pervious; therefore, it was determined to be more logical for this particular project to base the coefficient on slope. With this understanding, the pre- and post-project runoff coefficients are expected to be the same because the Project does not have an impact on the overall drainage area slope. The runoff characteristics have been grouped into two flow types, concentrated and sheet flow. Areas of concentrated flows were determined from the USGS maps where an obvious channel or concentration of flow exists. Areas of flow not considered concentrated flow areas were assumed to be sheet flow, which is flow that is not intercepted by the erosion control measures at a specific point. Areas of sheet flow are typically on a hillside prior to the runoff reaching a ditch, swale, or creek. For each area, subbasins were delineated using USGS quad maps (see Figures 3 and 4). Times of concentration were calculated for sheet, shallow concentrated, and open channel flow as required. The time of concentration is equal to the amount of time it takes for runoff to flow from the furthest point in a given watershed to the point of concern. A maximum of 100 linear feet was assumed for the flow length in the sheet flow calculations because the flow path is not always perpendicular to the contour lines. Northeast Utilities 3-1 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 10 of 36

12 LL 1152 LL 1148 LL 1098 LL 1083 Subbasin 10 DA= 78.3ac Subbasin 8 DA= 22.3ac Subbasin 3 DA= 31.2ac Subbasin 1 DA= 50.7ac Subbasin 7 DA= 120.6ac Subbasin 4 DA= 20.3ac Subbasin 2 DA= 128.4ac Hampden M ou n tain ld She Subbasin 12 DA= 36.6ac Subbasin 9 DA= 44.7ac Subbasin 5 DA= 17.0ac Legend Subbasin 168 Hartford Subbasin 11 DA= 35.6ac Subbasin 14 DA= 19.1ac Subbasin 6 DA= 313.1ac Greater Springfield Reliability Project Subbasin Map #2 November 11, 2009 on Hartford Bradley Intl Springfield Center COPYRIGHT 2008 BURNS & McDONNELL ENGINEERING COMPANY, INC. \\kcm-fs-006\data\data2\projects\nus\snetr_projects\45063_springfield_345kv\environmental\gis\arc\arcmxd\network\greaterspringfield\analysis\gsrp_9600_subbasin_9_11_09_map2.mxd Subbasin 13 DA= 21.4ac Source: USGS 1:24,000 Topographic Map, Hartford County, CT (2000); ESRI and Burns & McDonnell Engineering Feet Figure 3 GSRP 345-kV Line D&M Plan Appendix E: Page 11 of 36

13 Sub-basin 3 DA= 13.7ac Sub-basin 2 DA= 67.4ac Sub-basin 1 DA= 64.9ac Hampden M ou n tain Hartford 20 Legend Subbasin ld She Greater Springfield Reliability Project Subbasin Map #1 November 11, 2009 on Hartford Bradley Intl Springfield Center COPYRIGHT 2008 BURNS & McDONNELL ENGINEERING COMPANY, INC. \\kcm-fs-006\data\data2\projects\nus\snetr_projects\45063_springfield_345kv\environmental\gis\arc\arcmxd\network\greaterspringfield\analysis\gsrp_9600_subbasin_9_11_09_map1.mxd LL 1034 Source: USGS 1:24,000 Topographic Map, Hartford County, CT (2000); ESRI and Burns & McDonnell Engineering. GSRP 345-kV Line D&M Plan Appendix E: Page 12 of Feet Figure 4

14 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Runoff Characteristics & Flow Calculations 3.1 TWO-, TEN-, AND FIFTY-YEAR STORM EVENT CALCULATIONS If construction activities occurred for less than a one-year period in each particular subbasin, the Best Management Practices (BMPs) would be considered temporary based on the 2002 Connecticut Guidelines for Soil Erosion and Sediment Control Manual. If the BMPs are assumed to be temporary, the two-year storm is generally used to design the necessary erosion controls, and are then assumed to need maintenance after larger storm events. However, although the BMPs will only be temporary, they will be in place for slightly longer than one year. Therefore, calculations for the ten- and fifty-year storm events were also provided. The associated flows (Total Q) in each sub-basin were calculated based on the time of concentration calculations and average rainfall intensities. The rainfall intensity is the average rainfall rate for a specific duration and a selected frequency. The duration is assumed to be equal to the time of concentration. The flows and associated runoff velocities for both areas are summarized in the subsequent tables Newgate/Phelps Road Area The Newgate/Phelps Road Area has 14 sub-basins (see Figure 3, Subbasin Map #2). The following tables provide a summary of the calculations for a two-, ten-, and fifty-year storm event. Table 3-1 Two-Year Storm Event Subbasin Drainage Area (acres) 2-Year Rainfall Intensity (in./hr.) Pre & Post Construction Runoff Coefficient 2-Year Total Q Subbasin (cu. ft./sec.) 2-Year Single Point Q (cu. ft./sec.) Linear Feet 2-Year Total Q Per Foot (cu. ft./sec.) 2-Year Single Point Velocity (ft./sec.) Northeast Utilities 3-2 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 13 of 36

15 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Runoff Characteristics & Flow Calculations Table 3-2 Ten-Year Storm Event Subbasin Drainage Area (acres) 10-Year Rainfall Intensity (in./hr.) Pre & Post Construction Runoff Coefficient 10-Year Total Q Subbasin (cu. ft./sec.) 10-Year Single Point Q (cu. ft./sec.) Linear Feet 10-Year Total Q Per Foot (cu. ft./sec.) 10-Year Single Point Velocity (ft./sec.) Table 3-3 Fifty-Year Storm Event Subbasin Drainage Area (acres) 50-Year Rainfall Intensity (in./hr) Pre & Post Construction Runoff Coefficient 50-Year Total Q Subbasin (cu. ft./sec.) 50-Year Single Point) Q (cu. ft./sec.) Linear Feet 50-Year Total Q Per Foot (cu. ft./sec.) 50-Year Single Point Velocity (ft./sec.) Northeast Utilities 3-3 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 14 of 36

16 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Runoff Characteristics & Flow Calculations As shown in the previous tables, the calculated Single Point Velocities are generally less than 3.5 feet per second for the two- and ten-year storm events in this area. This velocity is less than the erosive velocity of the existing soil types, which is 5 feet per second. Therefore, the 2- and 10- year storm events should pose no erosive threat. The stone check dam control structures shown on the Site Drawings in Appendix A are designed to withstand the expected concentrated flow for two- and ten-year storm events in this area. The fifty-year storm velocities, however, are 4 to 5 feet per second. Fifty-year storms have more potential to exhibit an erosive behavior, and therefore would likely require the heights and widths of the stone check dam controls shown on the Site Drawings to be increased to handle the peak flows without failure or adverse tail water effects. For the areas where sheet flow occurs (all areas not defined as concentrated flow path), it is recommended that silt fence be installed on the downhill side of the disturbed area. The Total Q Per Foot for the two- and ten-year storm events are the same in this area. For a fifty-year storm event the total Q does increase slightly, but would have no effect on the location or type of silt fence used to control erosion in these areas. Therefore, as designed, the silt fence control structures shown on the Site Drawings will withstand the expected sheet flow for the two-, ten- and fifty-year storm events in this area Hatchett Hill Road Area The Hatchett Hill Road Area has three subbasins (see Figure 4, Subbasin Map #1). The following tables provide a summary of the calculations for the two-, ten-, and fifty-year storm event. Table 3-4 Two-Year Storm Event Subbasin Drainage Area (acres) 2-Year Rainfall Intensity (in./hr.) Pre & Post Construction Runoff Coefficient 2-Year Total Q Subbasin (cu. ft/sec.) Linear Feet 2-Year Total Q Per Foot (cu. ft./sec.) Northeast Utilities 3-4 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 15 of 36

17 Drainage Analysis-Newgate/Phelps & Hatchett Hill Road Areas Rev. 0 Runoff Characteristics & Flow Calculations Table 3-5 Ten-Year Storm Event Sub-basin Drainage Area (acres) 10-Year Rainfall Intensity (in./hr.) Pre & Post Construction Runoff Coefficient 10-Year Total Q Sub-basin (cu. ft/sec.) Linear Feet 10-Year Total Q Per Foot (cu. ft/sec.) Table 3-6 Fifty-Year Storm Event Sub-basin Drainage Area (acres) 50-Year Rainfall Intensity (in./hr.) Pre & Post Construction Runoff Coefficient 50-Year Total Q Sub-basin (cu. ft./sec.) Linear Feet 50-Year Total Q Per Foot (cu. ft./sec.) There were no single point sources identified in any of the subbasins in this area. For the areas where sheet flow occurs down the slope of an embankment (all areas not defined as concentrated flow path), it is recommended that silt fence be installed on the downhill side of the disturbed area. The Total Q per foot for the two- and ten-year storm events are the same in this area. For a fifty-year storm event the total Q does increase slightly, but it would not affect the location or type of silt fence used to control erosion in these areas. Therefore, as designed, the silt fence control structures shown on the Site Drawings will withstand the expected sheet flow for two-, ten- and fifty-year storm events in this area. Northeast Utilities 3-5 Burns & McDonnell GSRP 345-kV Line D&M Plan Appendix E: Page 16 of 36