1-1 HB-Section 1.doc Section 1 Introduction 1.1 Project Description This study presents recommended drainage improvements to alleviate flooding in the Horseneck Brook watershed in Greenwich, Connecticut (Figure 1.1). The 3,900-acre watershed includes Putnam Lake, Horseneck Pond (also known as West Fork Pond), Greenwich Hospital, the commercial and industrial area along Route 1 and the surrounding residential areas. Horseneck Brook discharges to the tidally-influenced Greenwich Harbor on Long Island Sound. Prompted by the significant flooding that occurred in the spring of 2007, the Town of Greenwich and Camp Dresser & McKee Inc. (CDM) prepared the following scope of work to address the Horseneck Brook flooding problems. 1. Investigate existing conditions within the watershed. 2. Develop hydrologic and hydraulic models of the watershed. 3. Create a future conditions model based on land use, zoning regulations and future development. 4. Evaluate various improvements to address existing and future flooding. 5. Provide recommendations to alleviate flooding. 6. Provide cost estimates for the recommended improvements. This document summarizes the results of the drainage evaluation within the Horseneck Brook watershed. 1.2 Project Location The Town of Greenwich, Connecticut is located on Long Island Sound, 30 miles east of New York City. The Town is bounded by the state of New York to the west and north; Stamford, Connecticut to the east; and Long Island Sound to the south. Greenwich is a diverse community with approximately 61,000 residents, 8,000 acres of protected land, and 32 miles of coastline. The Horseneck Brook watershed is located in the central portion of Greenwich. The watershed boundary is shown on Figure 1.1. The watershed consists of 3,900 acres surrounding Horseneck Brook and its tributary streams. Land use within the Horseneck Brook watershed is predominantly residential with commercial and industrial areas in the south.
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� 1-1HB-Section 1.doc
Section 1 Introduction 1.1 Project Description This study presents recommended drainage improvements to alleviate flooding in the Horseneck Brook watershed in Greenwich, Connecticut (Figure 1.1). The 3,900-acre watershed includes Putnam Lake, Horseneck Pond (also known as West Fork Pond), Greenwich Hospital, the commercial and industrial area along Route 1 and the surrounding residential areas. Horseneck Brook discharges to the tidally-influenced Greenwich Harbor on Long Island Sound.
Prompted by the significant flooding that occurred in the spring of 2007, the Town of Greenwich and Camp Dresser & McKee Inc. (CDM) prepared the following scope of work to address the Horseneck Brook flooding problems.
1. Investigate existing conditions within the watershed.
2. Develop hydrologic and hydraulic models of the watershed.
3. Create a future conditions model based on land use, zoning regulations and future development.
4. Evaluate various improvements to address existing and future flooding.
5. Provide recommendations to alleviate flooding.
6. Provide cost estimates for the recommended improvements.
This document summarizes the results of the drainage evaluation within the Horseneck Brook watershed.
1.2 Project Location The Town of Greenwich, Connecticut is located on Long Island Sound, 30 miles east of New York City. The Town is bounded by the state of New York to the west and north; Stamford, Connecticut to the east; and Long Island Sound to the south. Greenwich is a diverse community with approximately 61,000 residents, 8,000 acres of protected land, and 32 miles of coastline.
The Horseneck Brook watershed is located in the central portion of Greenwich. The watershed boundary is shown on Figure 1.1. The watershed consists of 3,900 acres surrounding Horseneck Brook and its tributary streams. Land use within the Horseneck Brook watershed is predominantly residential with commercial and industrial areas in the south.
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Stamford, CT
Horseneck Brook Watershed
0 4,200 Feet
1
95
Horseneck Brook
Greenwich Drainage StudyFigure 1.1
Horseneck Brook Watershed LimitsNovember 2009
Westchester County, N
Y
Westchester County, NY
Section 1 Introduction
1.3 Existing Flooding Problems The Town of Greenwich experienced several historical storm events over the last century, including the flood of 1955, a significant storm event in 1972 and more recently the spring storm events of 2007. With the most recent storm events, the Town received several flooding complaints within the Horseneck Brook watershed. Figure 1.2, “Documented Flooding Locations” shows the locations within the Horseneck Brook watershed where flooding concerns have been documented.
Based on the recorded flooding complaints, discussions with Town officials, and public input, the following areas have been identified as having flooding problems:
Brookside Drive Maher Avenue
Field Point Road Railroad Avenue
Glen Road Round Hill Road at Pecksland Avenue
Glenville Road at Valley Drive Winding Lane
Hamilton Avenue Woodland Drive
Lake Avenue Zaccheus Mead Lane at Winding Lane
Putnam Avenue at Church Street
The areas listed above are distributed throughout the Horseneck Brook watershed with the most frequent flooding found within the southern section. Based on reports by residents and as supported by modeling results, the backyards of a number of homes and some of the local roadways flood during smaller storm events, while more serious flooding occurs during larger storm events. In response to flooding concerns from citizens in this area, CDM met with Town officials and local residents to discuss flooding concerns associated with the March and April storms of 2007. The Engineering Department and Highway Division also provided valuable information relative to the type and severity of flooding at various locations.
A number of problematic areas listed above are subject to flooding due to inadequate drainage networks. Several of these areas and their associated drainage networks were studied as part of this report, including Brookside Drive, Calhoun Drive, Glenville Road, Glen Road, Grove Lane and Volunteer Lane. The flooding problems along Putnam Avenue at Church Street and Sherwood Avenue are also the result of an inadequate drainage network. This area was previously studied by CDM and the results are presented in the “Church Street Hydrologic and Hydraulic Study” dated October 10, 2008.
� 1-3 HB-Section 1.doc
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Greenwich Drainage StudyFigure 1.2
Documented Flooding LocationsNovember 2009
Stamford, CT
0 3,000 FeetFlood Complaint
Horseneck Brook Watershed&
1
95
Westchester County, N
Y
Westchester County, NY
Section 1 Introduction
CDM compared the rainfall records from the March 2 and April 15, 2007 storms to historical rainfall data. The results are shown on Figure 1.3, “Comparison of Rainfall – Spring 2007 Storm Events.” The comparison showed that the March storm correlated to a 5-year storm event (which would statistically occur once every 5 years or have a 20% chance of occurring in any given year), and the April storm event correlated to a 25-year storm (which would statistically occur once every 25 years or have a 4% chance of occurring in any given year). As shown in the figure, the two storms tracked closely to the statistical storm events. The information shown in Figure 1.3 compares statistical rainfall amounts to the actual rainfall recorded during the 2007 spring rain events. This information does not take into consideration runoff conditions, which are affected by actual ground conditions, such as impervious surfaces, snow accumulation or frozen ground. The actual site conditions would impact the amount of runoff produced from a particular rainfall event.
The two storms that occurred in the spring of 2007 were the driving force behind this study as well as the studies being performed in other watersheds within the Town of Greenwich.
1.4 Summary of Previous Studies In response to many of the flooding events within the last several decades, the Town and various regulatory agencies have evaluated several of the watersheds within the Town and surrounding areas. Appendix A provides a full list of all the documents that were collected and reviewed as part of this study. The following provides an abbreviated chronological list of the documents that were most applicable to the evaluation of the Horseneck Brook watershed:
Preliminary Report on Flood Control, Gannett Fleming Corddry & Carpenter, Inc., December 1956
Engineering Report on Flood Control Improvements, Gannett Fleming Corddry and Carpenter, Inc., October 1973.
Design Flood Discharges for Horseneck Brook & Strickland Brooks, Gannett Fleming Corddry and Carpenter, Inc., January 1974
Preliminary Engineering Report for Horseneck and Strickland Brooks, Gannett Fleming Corddry and Carpenter, Inc., March 1974
Engineering Report on Flood Control Projects Horseneck and Strickland Brooks,Gannett Fleming Corddry and Carpenter, Inc., December 1975.
Engineering Report on Modified Horseneck Brook, Gannet, Fleming, Corddry & Carpenter, Inc., January 1979
Town of Greenwich Water Quality Study, Milone & MacBroom, Inc., January 26, 2004.
Hydraulic and Scour Analysis, Horseneck Brook Culvert System, Parsons Brinkerhoff Inc., May, 2009.
Horseneck Brook Culverts From Railroad Avenue Inlet Through Field Point Road Outlet, Preliminary Engineering Report, Parsons Brinkerhoff Inc., May, 2009.
� 1-5 HB-Section 1.doc
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