Request for Proposals

TECHNICAL STUDY:

Comprehensive Stormwater Modeling,

Assessment, and Plan Development for

Blind Brook and Beaver Swamp Brook Watersheds

July 1, 1999

Project Impact Technical Study

1.0 Study Purpose and Background

1.1 Purpose of Study

The City of Rye, New York, in cooperation with the Federal Emergency Management Agency (FEMA), is seeking proposals from a qualified consultant, or team of consultants, to prepare a comprehensive GIS-based technical study to identify actions needed to create a flood-resistant community and improve stormwater quality. Specifically, the technical study will develop comprehensive hydrologic and hydraulic models for the Blind Brook and Beaver Swamp Brook watersheds to update the Federal Flood Insurance Study maps for the City, and to identify flooding and water quality problems and solutions.

The study will emphasize environmentally feasible flood control initiatives that minimize or eliminate repetitive property losses. Such initiatives may include acquiring land and easements to prevent increased flooding, reclaiming wetlands, and modifying or constructing new stormwater structures. The study also will stress improving the quality of interior waterways and the receiving waters of Long Island Sound.

The City encourages respondents to consider a multi-disciplinary team approach to ensure balance between master planning for flood control, and the water quality, habitat and biological components of the study.

Related field surveys and GIS-based inventories will be prepared to inform the modeling effort, facilitate implementation of stormwater management projects, and support the emergency planning objectives of Project Impact. The City of Rye also intends to use the technical study to apply for FEMA Hazard Mitigation Grants and to support future applications for Clean Water Act water quality funding.

1.2 Project Background & Setting

The City of Rye is located on Long Island Sound in Westchester County, New York, approximately 7 miles north of the New York City line. It is bordered on the west by the Village of Mamaroneck, on the north by the Village of Rye Brook, on the northwest by the Town/Village of Harrison, and on the northeast by the Village of Port Chester. Long Island Sound forms the City’s southern and eastern boundaries. Rye is a small residential community of 15,000 people, with single-family homes occupying 60 percent of its 6 square miles. Less than 10 percent of the City is in commercial use: Campus-type office buildings that are headquarters for businesses and corporations are the main large economic enterprises in the community; the central business district consists of about 200 small businesses that serve local residents.

In 1998, the City of Rye was designated a Project Impact community by the Federal Emergency Management Agency. The purpose of Project Impact is to build disaster-resistant communities through private and public sector partnerships. As a result of its shoreline and watershed position, Rye experiences chronic flooding and wind damage from coastal and inland storm events. Flooding causes repetitive property losses; as a result, approximately 500 residents hold federal flood insurance policies.

As part of Project Impact, the City is working closely with the New York State Emergency Management Office (SEMO), the Westchester County Emergency Management Office and Chamber of Commerce, and major private corporations, including Consolidated Edison, Inc. to improve its disaster preparedness. FEMA, through its Hazard Mitigation Grant Program, has provided substantial funds to improve a local breakwater and the pier at Westchester County’s Playland Park. The City also has initiated several flood mitigation projects addressing erosion control, elevation and relocation of structures, and stream bank improvements, and has partnered with more than a dozen local businesses and community organizations to enhance disaster response.

The Technical Study component of Project Impact will provide a comprehensive watershed database to identify and implement the structural and institutional measures needed to create a disaster-resistant community.

1.3 Project Study Area

The City of Rye occupies the shore of Long Island Sound and the lower reaches of the Blind Brook and Beaver Swamp Brook watersheds; both basins are tributary to Long Island Sound. In addition to the City of Rye, the Blind Brook watershed contains portions of the Village of Rye Brook, the Town/Village of Harrison, the City of White Plains and the Village of Port Chester. In addition to Rye, the Beaver Swamp Brook watershed contains portions of the Town/Village of Harrison and the Village of Mamaroneck; the west branch of the Beaver Swamp Brook is entirely within the Town/Village of Harrison and is known as Brentwood Brook or Beaver Swamp Brook West.

Rye is located in the Hudson Valley climatological division in New York State. The average annual precipitation is 49 inches.

The Project Study Area will comprise the Blind Brook and Beaver Swamp-Brentwood Brook watersheds for purposes of developing the stormwater management models and GIS databases, except where otherwise noted in Section 2.2. The Project Study Area will emphasize the watershed area within the incorporated boundaries of the City of Rye for purposes of developing project outputs and performing selected surveys; however, flood control solutions that benefit the City should be presented regardless of watershed position.

1.3.1 Blind Brook Watershed

Blind Brook drains an area of 10.91 square miles. It originates as two distinct branches well north of the City, at the Westchester County Airport in the Town of Harrison. All of the airport runways drain to the Brook. The two branches of the Brook flow south to a confluence at the Hutchinson River Parkway. A second tributary to the east joins the main branch south of the Bowman Avenue Dam in the Village of Rye Brook. From the dam, the Brook flows south, under the New England Thruway and through the City of Rye business district to Milton Harbor.

Principal land uses in the upper Blind Brook Watershed within the Town of Harrison and the Village of Rye Brook, are the airport, large campus office, educational and religious institutions, golf courses, residential areas and several New York State-designated and federal- and local-jurisdictional wetlands. Within the City of Rye, the watershed is dominated by low and medium density residential development, institutional and recreational uses, open space, and a small central business district; areas along the Brook are highly developed, with many residences, businesses and public buildings adjacent to the watercourse. State-protected tidal wetlands and other federally and locally jurisdictional wetlands also occupy the lower watershed.

1.3.1.1 Principal Flooding Problems

Flooding occurs along the coast during unusually high tides associated with major storms and hurricanes; large-scale flooding has occurred on numerous occasions this century, most notably in 1938, 1944, 1955, 1962, 1972, 1975, 1977, 1979, and through the ‘80’s and ‘90’s. Interior portions of the Blind Brook watershed also have experienced flooding at these times. Hurricane Agnes (June 1972; approximate frequency 60 years) produced the largest flow ever recorded at the Blind Brook gauge, and the 1975 storm discharge was only slightly smaller. These storms caused extensive damage to properties and public infrastructure, but no lives were lost.

Flooding on Blind Brook is caused by narrow channel width, obstructions, bridge openings constricted by sediment, historical wetland filling and floodplain encroachment and in the lower reaches, tidal backwater (tidal influence extends upstream to Central Avenue). The principal areas within the City that experience significant repeated flooding are all coastal locations, including sections of Kirby Lane, Manursing Island, Pine Island, and the Rye Road-Greenhaven Road-Lake Road section of Greenhaven; Indian Village; Loewen Court and vicinity; and properties in the vicinity of Playland Parkway, from Pine Lane south to Milton Harbor. During severe events, access to Manursing Island, Kirby Lane south, Pine Island and Hen Island is cut off.

1.3.1.2 Prior Flood Control Efforts

The Blind Brook Watershed is one of the most intensively studied drainage basins in Westchester County. Initially evaluated in the early 1960’s as part of the US Army Corps of Engineers flood control program, the watershed failed the cost-benefit test established for federal flood control projects. In 1967, the Westchester County Soil and Water Conservation District (SWCD) was created by the County Board of Legislators to pursue a USDA Soil Conservation Service Public Law 83-566 Small Watershed Protection Plan for Blind Brook. Under PL-566, the federal government would provide funds for major structural flood controls; the City of Rye, partnered with USDA and the County through the SWCD, would form a watershed protection district to underwrite selected project costs.

The Blind Brook PL-566 project proposed to construct two dams to create regional stormwater detention facilities in the upper portion of the watershed, one on property owned by the State University of New York, the other on private land, within the Town of Harrison. The project also proposed dikes in the vicinity of Loewen Court and modifications to the Oakland Beach Avenue bridge in the City of Rye. The estimated 1977 project cost was $3.7 million for design and construction, relocation payments, and a percentage of ongoing district administration. Due to litigation by the owner of one of the dam sites, the PL-566 initiative failed and was formally deactivated by its sponsors in the early 1990’s.

Non-federal flood control efforts include the City’s construction of the Bowman Avenue dam and reservoir in the early 1960’s; since then, initiatives have been largely non-structural, consisting of planning studies and regulations governing new development.

In 1978, the City qualified for the National Flood Insurance Program by adopting floodplain zoning which exceeds the requirements of the federal Flood Insurance Administration. In 1991, Rye adopted a wetland and watercourses protection law to govern land uses in and near streams and wetlands.

1.3.1.3 Water Quality Considerations

Federal Initiatives The Blind Brook watershed is part of the larger Long Island Sound drainage basin which was designated an Estuary of National Significance in 1988 by the US Environmental Protection Agency. As a result of the designation, the Long Island Sound Study (LISS), a federal-state-public partnership begun in 1985, was reconfigured in 1988 as the LISS Management Conference. In 1994, the Management Conference issued a Comprehensive Conservation and Management Plan (CCMP) which identified seven primary areas of concern, most notably low oxygen (hypoxic) conditions, toxics, pathogen contamination, and habitat degradation. The CCMP also established 11 watershed management zones, based on natural drainage basin and political boundaries, to identify nitrogen sources and develop reduction plans; Blind Brook is within Management Zone 7.

To address the most pressing problem, low oxygen caused by nitrogen enrichment, EPA, New York and Connecticut first agreed to cap nitrogen loadings from sewage treatment plants and nonpoint sources at 1990 levels. The 1994 CCMP committed to reduce nitrogen loads further, and in 1997, the LISS issued a "Proposal for Phase III Actions for Hypoxia Management," calling for a 58.5% reduction in nitrogen over 15 years. The Phase III Proposal was adopted by EPA and the states in February 1998, and LISS has developed Sound-wide total maximum daily loads (TMDL’s) for nitrogen by management zone. The nitrogen reduction target for nonpoint sources is 10% for each management zone; the nitrogen reduction target for point sources (sewage treatment plants) varies depending on the nonpoint component, but ranges between 60-63%.

The LISS also calls for a Sound-wide habitat restoration initiative to re-establish the ecological functions of degraded or lost wetlands, intertidal flats, riverine migratory corridors, and other ecological communities. The Study has proposed 162 projects in New York State, including the following within the Blind Brook watershed: Freshwater wetland restoration along the brook; tidal wetland, estuarine embayment, and freshwater wetland restoration at Westchester County’s Edith G. Read Sanctuary at Playland Park; and tidal wetland and intertidal flat restoration at the County’s Marshlands Conservancy.

County Initiatives In 1992, as a result of the Long Island Sound initiative, increasing NPDES requirements for nonpoint pollution, and strengthened nonpoint efforts under the Coastal Zone Reauthorization Act of 1990, the County of Westchester initiated a nonpoint source planning program for its Long Island Sound watersheds. The County program established 6 watershed areas to be studied under the guidance of intermunicipal "Watershed Advisory Committees." The WAC studies developed ARCInfo GIS data layers for land use, soils, hydrology, tidal and freshwater wetlands (existing and filled), detention facilities, and 100-foot buffers for streams and wetlands; this information is being used to develop nonpoint source pollution plans for each study area. The Blind Brook and Beaver Swamp Brook watersheds make up Watershed Advisory Committee 3 (WAC 3).

New York State Programs Certain segments and waterbodies within the Blind Brook watershed have been identified by New York State as threatened, stressed, or impaired by nonpoint source pollution. Several reaches of the Brook, Mead Pond, and Milton Harbor are listed on the State’s Priority Water Problem List due to nutrients, urban runoff, and construction-related activities.

In addition to the primary pollutants identified by the State, Blind Brook is substantially affected by excessive sedimentation, particularly in its tidal reaches (Central Avenue and south); one of two culverts under Playland Parkway has been completely filled in recent years and the need to dredge Milton Harbor has increased substantially in frequency.

1.3.2 Beaver Swamp Brook

Beaver Swamp Brook drains an area of approximately 4.83 square miles (4.7 sm. at the USGS Short Street gauge); its two main branches originate north of the City in the Town of Harrison. The headwaters of the Beaver Swamp Brook branch which drains approximately 3.3 square miles, are in a wetland complex north of Polly Park Road; from there, the brook flows south through the Westchester and Willow Ridge country clubs and golf courses, and enters the City of Rye north of Locust Avenue. It continues south through the Greenwood Union Cemetery, under the New England Thruway, and through City-owned Parcels A and B, a State-designated wetland. South of Theodore Fremd Avenue, the brook runs through corporate office parks and residential neighborhoods, including three State-designated wetlands, to its confluence with Brentwood Brook at the Rye Neck High School. Immediately downstream from the confluence, the brook enters a residential area in the Village of Mamaroneck, flows south under US Route 1 and a distance of 0.5 miles into the tidal wetland complex, Guion Creek, and Mamaroneck Harbor (Maps available upon request).

Brentwood Brook drains approximately 1.5 square miles. It rises as two arms north of Stratford and Woodlands roads in the Town of Harrison; each flows south and the two converge at the High School north of the New England Thruway. Brentwood Brook continues south through densely residential neighborhoods to its confluence with Beaver Swamp Brook at the Rye Neck High School just north of the Short Street gauge.

Land uses in the upper reaches of the Beaver Swamp Brook Watershed are primarily low density residential neighborhoods, golf course/country clubs, corporate office parks and institutional facilities. The lower watershed is more densely developed, particularly within the Town of Harrison, and includes ¼-acre or smaller residential lots, commercial and industrial areas. Much of the 100-year floodplain has been developed in the lower reaches of both branches and, in many cases, buildings are within limited distances from the brooks.

1.3.2.1 Principal Flooding Problems

Beaver Swamp Brook has experienced significant flooding during many of the same storm events as Blind Brook. The USGS gauge at Short Street recorded the largest flow of its history during the 1975 storm.

Significant flooding occurs along Beaver Swamp Brook in the City of Rye from Belmont Avenue south to Bradford Avenue and Hunt Place, and in the Town/Village of Harrison upstream of Broad Street. Significant flooding also has occurred along Brentwood Brook on portions of the Harrison High School upstream of I-95 and between Union and Harrison avenues.

Flooding along Beaver Swamp and Brentwood brooks is caused primarily by low-lying adjacent lands and floodplain development. In some areas, flooding has been exacerbated by silted bridge openings and resultant backwater effects, such as at Park Avenue; ironically, these constrictions reduce flood potential for downstream properties. Five significant obstructions to flow were identified in a 1986 stormwater management study of the brooks: North Street bridge over Beaver Swamp Brook; Penn Central Railroad bridge over Beaver Swamp Brook; Park Avenue over Beaver Swamp Brook; floodplain construction on Beaver Swamp Brook just north of the confluence with Brentwood Brook; and the Penn Central Railroad over Brentwood Brook.

1.3.2.2 Prior Flood Control Efforts

In 1984, at the request of the City of Rye, Town/Village of Harrison and Village of Mamaroneck, the Westchester County Soil and Water Conservation District retained a consultant to prepare a comprehensive stormwater management plan for Beaver Swamp Brook. The work was conducted under the guidance of the Beaver Swamp Brook Watershed Advisory Committee which consisted of elected officials and staff members from each of the three municipalities and the District.

The Beaver Swamp Brook study developed a hydrologic simulation model based on the Penn State Runoff Model (PSRM) and a watershed database that included existing land use (1985), future land use (build-out under zoning), hydrologic soil groups, land surface slopes, and watershed and subarea delineations. The model results were analyzed to develop stormwater control alternatives which included a detention facility upstream of I-95 on Brentwood Brook, a detention facility upstream of North Street on Beaver Swamp Brook (now known as "The Ives"), and, of much less benefit, a revised hydraulic structure for the Penn Central railroad crossing on Brentwood Brook. With the exception of a modified extended dry basin at "The Ives," none of the proposed improvements was implemented, either due to cost or insubstantial benefit. The model also was used as a planning tool to guide detention requirements for new development within the watershed.

The Beaver Swamp Brook Stormwater Plan did not develop water surface elevation data for specific storm events, nor did it identify or evaluate water quality issues within the basin.

Since the preparation of the Beaver Swamp Brook Stormwater Management Plan, the Town/Village of Harrison has channeled most of the length of Brentwood Brook into a concrete culvert; this action apparently has alleviated some of the more serious flooding along the Brentwood segment within Harrison.

1.3.2.3 Water Quality Considerations

As discussed in relation to Blind Brook, the Beaver Swamp Brook Watershed is part of the larger Long Island Sound drainage basin which was designated an Estuary of National Significance in 1988 by the US Environmental Protection Agency and is located in the LISS Management Zone 7. The Beaver Swamp Brook Watershed also is part of Westchester County’s Watershed Advisory Committee 3 Study Area for nonpoint source pollution planning (see Section 1.3.1.3).

The Long Island Sound Study’s habitat restoration initiative targeting 162 projects in New York State includes freshwater wetlands restoration along Beaver Swamp Brook, specifically including the Cowperwood office site on Theall Road in the City of Rye, and New York State-designated wetlands J-1, -2, -3 and -4.

Segments of Beaver Swamp Brook and Guion Creek also are listed on the New York State Priority Water Problem List. Primary pollutants in Beaver Swamp Brook are sediment and urban stormwater runoff; primary pollutants in Guion Creek are pathogens and urban runoff.

In addition to the primary pollutants listed by the State, Beaver Swamp Brook is substantially affected by sedimentation throughout its length, a condition exacerbated by the relatively flat gradient of the stream in its lower reaches.

2.0 Technical Study

The Technical Study will develop GIS databases and hydraulic and hydrologic models for the Blind Brook and Beaver Swamp Brook watersheds to address both flooding and water quality. The study also will include a detailed hydrologic assessment of the Bowman Avenue Dam and reservoir on Blind Brook in the Village of Rye Brook, and a hurricane wind simulation model to evaluate potential property loss from high winds associated with coastal storms.

2.1 Literature Review

The Consultant will review existing studies and relevant maps of both watersheds available from the City and other agencies as noted:

2.2 Watershed GIS Database Development

The City of Rye uses an ARCInfo Geographic Information System (GIS). All databases, including those specific to the hydrologic models, are to be developed as ARCInfo GIS digital files that the City can use and update as necessary.

Database elements that are asterisked (*) are to be developed for the entire watershed. Database elements without asterisks are to be developed for the area incorporated by the City of Rye.

The City may provide the services of a West Point Academy engineering intern to the Consultant to assist in conducting field surveys and mapping.

2.2.1 Benchmark Grid Survey

The Consultant will prepare a benchmark grid survey for the City of Rye using existing US Geological Survey markers. This survey is pre-requisite for the surveys identified below. The benchmark grid also will facilitate the individual surveys that may be required to substantiate challenges to floodplain occupancy and the need for flood insurance.

2.2.2 Repetitive Property Loss Survey and Mapping

The City of Rye has received from the Federal Emergency Management Agency claims data identifying properties that have suffered repeated damage from flooding. The Consultant will obtain this information from the City and prepare GIS maps depicting the location of the properties and the frequency of loss (i.e., 4 times, 3 times, 2 times, once). Eliminating repetitive property loss is the primary focus of the stormwater quantity modeling effort.

2.2.3 Lowest Opening Survey (Habitable Structures)

The Consultant will field survey and map the elevations of the lowest opening for each structure occurring within the updated 100-year floodplain. The Consultant also will provide digital photographs of each structure from all four sides for purposes of correlating survey measurements.

2.2.4 Lowest Member Survey (Bridges)

The Consultant will field survey and map the location and elevation of the lowest member of all bridges within the City limits in both watersheds; the Consultant also will note structural geometry for computing backwater effects. The purpose of the survey will be to identify impediments to flow for various storm events and to evaluate flood control opportunities associated with elevating bridges and/or dredging accumulated sediments.

Under the New York State Department of Transportation bridge improvements program, several structures within the City have been rebuilt and several others are slated for reconstruction.

Blind Brook Watershed The Oakland Beach Avenue, Highland Road, and Elm Place bridges over Blind Brook have been rebuilt and opportunities for flood control modifications at these sites are limited; however, the Locust Avenue, Orchard Avenue, Central Avenue, Boston Post Road, and Playland Parkway crossings are scheduled for reconstruction in the near future. These locations should be carefully evaluated for flood control purposes.

Beaver Swamp Brook Watershed Within the Beaver Swamp Brook Watershed, the Osborn Road and Park Avenue bridges, co-owned by the City and the Town/Village of Harrison, are scheduled to be rebuilt. These structures should be evaluated for flood control opportunities.

2.2.5 SPDES Outfalls Survey and Mapping

The Consultant will survey and map the locations and types of stormwater outfalls to all coastal and interior streams within the City of Rye. The Consultant will recommend, if necessary, additional tasks to position the City to meet the requirements of the Phase II NPDES program as summarized below.

Since the passage of the Clean Water Act, the quality of the Nation’s waters has improved. However, according to the 1996 National Water Quality Inventory, approximately 40% of surveyed US waterbodies do not meet water quality standards; a leading source of this continued impairment is polluted storm water runoff.

Phase I of the US EPA’s storm water program was promulgated in 1990 under the Clean Water Act. Phase I relies on the National Pollutant Discharge Elimination System (NPDES) permit program to address storm water runoff from medium and large municipal separate storm sewer systems (MS4s), construction sites larger than 5 acres, and 10 categories of industrial sources.

In January 1998, EPA published the Storm Water Phase II Proposed Rule to expand the Phase I program by requiring all unregulated storm water dischargers to apply for NPDES permit coverage no later than 3 years and 90 days from the publication of the final rule (anticipated November 1999). The Phase II program would require permits for owners and operators of currently unregulated MS4s located in "urbanized areas," as well as for owners or operators of construction activities that disturb land areas greater than or equal to 1 acre. Small MS4s outside of urbanized areas, construction activities disturbing less than 1 acre, and non-Phase I industrial sources, could be designated for NPDES coverage on a case-by-case basis where watershed plans, TMDL analyses, or other local water quality assessments identify a need to control these sources of storm water runoff. Additional requirements could apply to the Blind Brook and Beaver Swamp Brook watersheds given their location within the Long Island Sound Study Management Zone 7 for which TMDL’s have been developed.

Under Phase II, a regulated small MS4 owner or operator will need to develop and implement a storm water management program designed to reduce the discharge of pollutants from their MS4 to the "maximum extent practicable. The permit application would need to include the selection of BMPs and measurable goals for each minimum measure in the permit application.

Under Phase II, a construction activity would be governed by specific requirements developed by the State. If the Phase I general permits are used as a guide, these requirements likely would require preparation of a storm water pollution prevention plan (SWPPP).

2.2.6 Wetland Survey and Mapping

In 1991, the City of Rye adopted a local law governing land uses in and near wetlands and watercourses; the law defines wetlands in accordance with the 1989 Unified Federal Manual. Several wetlands within the City also are regulated by the State of New York pursuant to Environmental Conservation Law Article 24 (freshwater wetlands) and Article 25 (tidal wetlands). All wetlands within the City are subject to the federal Clean Water Act Section 404 program.

As part of its local wetland program, the City prepared wetland inventory maps based on USDA NRCS Soil Survey information and field surveys by City staff. These maps are used for information purposes. The New York State Department of Environmental Conservation also maintains freshwater and tidal wetland maps for informational purposes, and the Westchester County Planning Department has prepared GIS-based hydric soils maps from the 1986 Soil Survey for Westchester and Putnam counties; the soil survey was mapped at a scale of 1" = 1000’ and is accurate to within +/- 2 acres.

Using available wetland mapping, the Consultant will field-survey and delineate on GIS-based maps all freshwater and tidal wetlands within the City of Rye in accordance with the 1989 Unified Federal Manual. The Consultant also will map filled wetlands for evaluation for flood control and water quality remediation.

2.2.7 Model Input Data*

The Consultant will be responsible for preparing ARCInfo bases for all model input data layers. The data layers will depend on the model(s) selected to complete the stormwater quantity and quality requirements outlined in Section 2.3. Most hydrologic models require minimum data layers, including topography and slope (obtainable from digital elevation data), watershed boundaries, hydrologic elements, watershed subareas, existing and future land use and hydrologic soil groups (to generate curve numbers).

The Consultant will prepare watershed boundary maps for the Blind Brook and Beaver Swamp Brook watersheds and will identify subareas to reflect the following points of interest: (1) known areas of significant flooding within the City as identified in sections 1.3.1.1 and 1.3.2.1; (2) potential land acquisition/easement sites and/or wetland restoration sites to be identified by the City; (3) areas identified by the Consultant as potentially suitable for stormwater management measures for flood control or water quality enhancement.

Digital Elevation Data The Consultant will estimate the cost and time to prepare or have prepared a grid-based, spatially distributed, digital set of elevation data for both watersheds at a 1-foot contour interval. These items should be discussed with the City Engineer who is responsible for maintaining current map inventory. The Beaver Swamp Brook Watershed is 4.83 square miles and the Blind Brook Watershed comprises 10.91 square miles. The digital elevation model is intended to improve the quality of the modeling, to increase map detail and graphical imaging capabilities, and to substantially improve the City’s planning base for implementing all phases of Project Impact.

Soils/Land Use/Hydrologic Features Using ARCInfo, the Westchester County Planning Department has digitized a broad array of coverages including transportation, the County Soil Survey (1" = 1000’), land use, freshwater wetlands (by hydric soils), USGS-based hydrologic features, and 100-foot buffers around streams and wetlands. Several of the coverages, including the hydrologic features, will need refinement for modeling purposes, and land use data should be updated to reflect 1999 conditions. The Consultant will generate future land use from the watershed communities’ current zoning. The City of Rye Planner will act as a liaison to Westchester County Planning.

Water Quality Data The Consultant will develop the water quality database necessary to model nonpoint sources of nutrient, sediment and pathogen pollution. Land uses associated with generating these pollutants will be identified and mapped, as will any related information required to implement the water quality model selected.

The Consultant will present to the City its database development plans for the watershed model(s) it proposes to use.

2.3 Stormwater Modeling

2.3.1 Hydrologic Modeling

2.3.1.1 General Purpose

The Consultant will prepare stormwater quantity and quality models for the Blind Brook and Beaver Swamp Brook watersheds for the following purposes:

2.3.1.2 Selection of Models

The Consultant will propose the model(s) to develop a GIS-based hydrologic simulation of stormwater quantity and quality for the Blind Brook and Beaver Swamp Brook watersheds under existing and future conditions. The Consultant may propose a single model to combine quantity and quality, or separate models; however, the City prefers that the same model or set of models be used for both watersheds.

Water quality models proposed must be classified as mid-range or detailed by the US EPA; simple models will not be accepted.

The Consultant must provide a detailed justification to support the model(s) selected. Models may combine multiple data sources including field measurement and existing data maintained by the City of Rye or Westchester County.

2.3.1.3 GIS Compatibility

All modeling inputs and results are to be produced in ARCInfo GIS file and mapped format. The Consultant may use, as appropriate, existing GIS pre- and post-processing packages (e.g., HEC-PrePro v. 2.0, SWMMDuet, etc.), or may create the necessary automated macro language (AML) script.

2.3.1.4 Calibration of Models

The model or models selected for use and approved by the City and FEMA must be calibrated to minimize under- or over-estimating peak flows and storm volumes.

Until 1996, rainfall-flow gauges were in place on both Blind Brook and Beaver Swamp Brook. The City, in cooperation with FEMA, USGS and Westchester County, is working to reactivate the two gauges on Blind Brook (one flow, one precipitation) and the two gauges on Beaver Swamp Brook (one flow, one precip/flow). It is probable that these gauges will not be activated till after this project is completed.

The Consultant will evaluate the adequacy of gauging records for purposes of calibrating the stormwater model(s), and will consult with the City regarding the need for gauges at additional locations for calibration and to enhance the emergency preparedness response intended by Project Impact.

2.3.1.5 Anticipated Products

The City anticipates the products associated with elements (1) through (7) in Section 2.3.1.1.

2.3.2 Hydraulic Modeling

2.3.2.1 General Purpose

The Consultant will develop a hydraulic model for each watershed to update the stillwater storm elevations in the 1979 Flood Insurance Study, to generate water surface elevation maps for additional storm events, and to serve as the basis for the hydrologic modeling described in Section 2.3.2. For Blind Brook, this work will include, if determined necessary by FEMA, updating the Flood Insurance Study Supplement - Wave Height Analysis dated November 1, 1984; the estimated wave crest elevations associated with storm surges will be reported as the base flood elevations for the coastal portions of the Blind Brook watershed. All elevations must be based on the National Geodetic Vertical Datum of 1929 (NGVD).

Model(s) used for this element of the Technical Study, cross-section locations for field survey and study, use of Manning’s "n" values, and starting water surface elevations for floods of the selected recurrence intervals must be approved by the Federal Emergency Management Agency. A list of numerical models accepted by FEMA for NFIP usage can be reviewed at http://www.fema.gov/mit/tsd/EN_modl.htm.

2.3.2.2 Anticipated Products

The City anticipates the following products from the hydraulic modeling:

  1. Water surface elevations within the incorporated City area for the 2-, 5-, 10-, 25-, and 100-year storm events;
  2. Identification of the depth and extent of flooding at major road intersections and key access routes within the City for each recurrence interval;
  3. Identification and mapping of inhabited areas isolated by flooding for each recurrence interval;
  4. Identification and mapping of properties at risk for flooding for each recurrence interval;
  5. Graphical imaging capability (inundation sequencing graphics) for storm and coastal surge events.

2.3.3 Bowman Avenue Dam Study

The Bowman Avenue Dam is located in the central portion of the Blind Brook Watershed, north of I-287 in the Village of Rye Brook. The dam was constructed in the early 1960’s as a flood control measure and is owned by the City of Rye. The dam primarily benefits downstream residents in Rye, but also reduces flooding in Rye Brook between White Plains Road and Wyman Street.

The City wishes to identify the potential costs and benefits associated with excavating the area behind the dam, and/or constructing a second dam downstream from the first, at the lower end of the reservoir, to increase flood storage.

The Consultant will prepare a detailed evaluation, cost estimate, and preliminary environmental assessment for the above modifications at the Bowman Avenue Dam.

2.3.4 Hurricane Wind Simulation Modeling

The Consultant will propose a study methodology to simulate hurricane winds and assess their impact on inland sites, buildings and above-ground transmission lines.

2.4 Watershed Plan Development

The Consultant will prepare separate Watershed Plans for Blind Brook and Beaver Swamp Brook. Each report will summarize the results of the stormwater modeling and will present a comprehensive flood control and water quality enhancement plan based on those findings.

Each plan will contain at minimum the narrative and maps to support the objectives set forth in sections 2.3.1 and 2.3.2, and will attach the appropriate databases outlined in Section 2.2. The Blind Brook Watershed Plan will include the Bowman Avenue Dam Study.

3.0 Procedural Requirements

3.1 General Requirements for the Scope of Services

The selected Consultant will meet with the City to review project requirements, identify issues, transfer information and review the Technical Study Scope of Services. The Consultant also will meet monthly with the City to report progress and identify and resolve issues as they arise.

The Technical Study may include a public participation component, and will require input from federal and other agencies, under the direction of the City.

Proposals will provide individual cost estimates for each component of the Technical Study. The cost to prepare the hydrologic models and related databases will be presented separately for each watershed.

All databases and input parameters for the selected hydrologic model(s) are to be automated using GIS ARCInfo; any necessary automated macro language (AML) will be developed as needed for this purpose. Modeling outputs are to be provided in hard copy and digital (GIS ARCInfo) format.

Preliminary assessments of environmental feasibility will be prepared for all management measures recommended in the Draft Watershed Plans.

All study products, models, software and computerized elements will be Y2K compliant.

3.2 Required Deliverables

Project Deliverables include those identified in the Scope of Work and the following:

  1. Fifteen (15) copies of each Draft Watershed Plan and accompanying maps, suitable for reproduction. Following City and agency review and comment, and working with the City and FEMA, the Consultant will modify each Draft Watershed Plan and provide the City fifteen (15) copies of each Final Plan and accompanying maps, suitable for reproduction.
  2. The Consultant will provide and install for the City copies of the watershed models, and will train City staff in their use and update, as appropriate.
  3. The Consultant will provide the City copies of all GIS digital files and will provide City staff one day of orientation and training in transferring digital database files to the City GIS system - this may including interacting with the City’s GIS Consultants. GIS training will include use of the graphical imaging program.
  4. All study products, models, software and computerized elements will be Y2K compliant.

3.3 Timing

Work on the Technical Study will begin September 1, 1999 and will be completed no later than April 15, 2000. The Consultant will provide a detailed project schedule that meets this timeframe and identifies key benchmarks and interim reporting in the planning process.

3.4 Content of Submissions

Respondents will prepare a detailed proposal identifying each topic outlined in the Technical Study Scope of Services and presenting a specific plan to address each topic. Respondents also should identify additional topics, if any, that the City should consider in preparing the Technical Study.

All proposals will provide cost estimates by task as specified in Section 3.1.

All proposals must identify the individual or individuals who will prepare the Technical Study, the nature and extent of their specific roles, and their qualifications to perform the task(s) assigned to them. Substitutions of personnel after the consultant selection process is complete must be agreed upon by the City and its designates.

3.5 Evaluation and Selection of Proposer

The successful proposer must fully understand the scope of the Technical Study and communicate that understanding in its submission. The proposer’s approach and recommendations will be reviewed to determine responsiveness to the needs presented in the Scope of Services. On the basis of that review and the City’s judgment, selected firms will be invited to present their proposals orally.

The City is seeking innovation and a multidisciplinary approach to assessing and managing the amount and quality of stormwater runoff within the study watersheds. The successful proposer will present and justify a well-organized and creative approach to prepare the watershed plans.

Specific additional selection criteria include:

3.6 Legal and Financial Requirements

The City of Rye reserves the right to reject any or all proposals; to issue additional solicitations for proposals and/or addenda to this Scope of Services; to waive any irregularities in proposals received after notification to affected proposers; to select any proposal as the basis for negotiation of a contract and to negotiate with proposers for amendments or other modifications to their proposals; to conduct investigations with respect to the qualifications of each proposer; to exercise its discretion and apply its judgment with respect to any aspect of the Scope of Services, the evaluation of proposals, and the negotiation and award of any contract; to enter into an agreement for only portions (or not to enter into an agreement for any) of the services contemplated by the proposals; to select the proposal that best satisfies the interests of the City of Rye and not necessarily on the basis of price or any other single factor.

The City of Rye assumes no responsibility or liability for costs incurred in the preparation or submission of any proposal. The City is not responsible for any internal or external delivery delays which may cause any proposal to arrive beyond the stated deadline. To be considered, proposals must arrive at the City Manager’s office and be time-stamped prior to the deadline.

Requests for clarification of the Scope of Services must be written and submitted to City Manager Frank Culross no later than Friday, July 9, 1999. Written responses will be distributed by the City to all proposers by Monday, July 19, 1999.

Proposals must be signed. Unsigned proposals will be rejected.

Proposers may be required to give an oral presentation to the City.

3.7 Responses

Responses must be sent to Mr. Frank Culross, Rye City Manager, at City Hall, Rye, New York, 10580. The deadline for receipt of information is noon on Monday, July 26, 1999.

Y2K - GIS Requirements

All computerized information must be certified as virus free and Y2K compliant prior to installation on City of Rye computers. This will be determined by the City of Rye Coordinator of Computer Services or his designee. A full description of the City of Rye’s network architecture, GIS system software and GIS/Server storage/access capacity are available upon request.

For More Information:

Call Jeffrey Stonehill, City Manager's Office (914) 967-4603 or email jstonehill@ryeny.gov

RFP Prepared by: Laura Tessier, Tessier Environmental Consultants

Top of RFP

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