Bathymetry of New York City’s East of Hudson Reservoirs

Background: The New York City Department of Environmental Protection (DEP) maintains an extensive network of reservoirs and aqueducts for water collection, storage, and transport; it supplies more than one billion gallons of drinking water daily to more than nine million people. The East of Hudson (EOH) network (fig. 1) includes thirteen reservoirs – Amawalk, Bog Brook, Boyd Corners, Cross River, Croton Falls, Diverting, East Branch, Kensico, Middle Branch, Muscoot, New Croton, Titicus, and West Branch – and three regulated lakes – Kirk Lake, Lake Gilead, and Lake Gleneida.  The EOH reservoirs were put into service from 1873 to 1915 and have an estimated combined storage capacity of more than 117 billion gallons.

Problem: The daily and seasonal management of the EOH reservoirs by DEP depends on accurate bathymetry information in several forms, including the mapped bathymetric surface and contours and stage-area-capacity tables. The bathymetric surface and tabular data are used in several water-quality models, the stage-capacity tables are used to determine current and available reservoir storage, and contours are used in mapping applications. The bathymetry of the reservoirs was initially determined from pre-inundation land surface maps more than 100 years ago. More recent bathymetric surveys were conducted in West Branch Reservoir in 1998. Since the initial filling of the reservoirs, bed morphology has likely changed as a result of sedimentation. An updated detailed bathymetric survey of the EOH reservoirs is therefore required – the USGS proposes to perform a detailed analysis of reservoir geometry in the thirteen EOH reservoirs and three regulated lakes to provide updated bathymetric surfaces and corresponding stage-area-capacity tables.

Objective: Provide the bathymetric data, data analysis, and interpretation needed to better manage water use and availability in the watersheds of the thirteen EOH reservoirs and three regulated lakes.

Relevance and Benefits: This study will benefit (1) Federal, State, County, and local governments, (2) residents whose drinking water is supplied from the thirteen EOH reservoirs, and (3) residents of the drainage basins which contain the thirteen EOH reservoirs. An important part of the USGS mission is to provide scientific information to manage the water resources of the Nation to enhance and protect quality of life. The information provided as part of this study will help DEP, as manager of the reservoirs, to improve water-quality models used in reservoir management and to more accurately regulate storage in the reservoirs, and thereby facilitate DEP’s mission to provide drinking water to its many customers. It will allow improved water management for human and ecological needs within New York State. 

Approach:

Bathymetry data will be collected with a multibeam echosounder with real-time kinematic (RTK) global navigation satellite system (GNSS) positioning. Collected bathymetry data will be merged with existing lidar data to produce raster surface maps of the reservoirs, 2-foot interval contour maps, and elevation-area-capacity tables.

Project Location by County

Putnam County, NY, Westchester County, NY