Detailed Study/Inspection for Reconstruction of the Dams in the Catskill and Delaware Watersheds


The New York City Department of Environmental Protection (NYCDEP) - Bureau of Water Supply, Quality and Protection engaged GZA GeoEnvironmental of New York (GZANY) to provide engineering consulting services for its Detailed Study/Investigation for the Catskill and Delaware System Dams. The focus of this $4.3 million engineering contract, with design and oversight of a $5 million subsurface exploration contract, is the performance of detailed safety inspections, geotechnical and other engineering investigations of six of the NYCDEP's largest water supply reservoirs which provide 90 percent of New York City's current 1.4 billion gallons per day demand. The NYC system is one of the largest municipal surface water storage and supply complexes in the world. Many of these dams served as text-book cases for dam designs in the early to mid-1900's. GZA has completed:

  • detailed record review, physical dam safety and underwater inspections for existing facilities at six reservoirs, 7 earth/ rock fill and gravity dams and dikes 180-250 feet in height; and 5 earth fill dikes up to 75 feet high.
  • geotechnical, geological, seismic, stability, structural, groundwater/seepage, hydraulic, mechanical, and electrical engineering assessments;
  • design, preparation of plans and specifications, resident engineering and geotechnical engineer-of-record services for $5 million subsurface exploration program for 12 large embankment and gravity dams and dikes (test borings and cross-borehole testing) and installation of piezometer and observation well monitoring instrumentation within dams and foundations including central monitoring stations and lightning protection; borehole depths up to 400 feet below dam crest in up to 150 feet of water.
  • extensive laboratory strength testing program to evaluate strength of embankment and foundation soils and bedrock.
  • selection and concept design of rock anchors, toe drainage, etc. as necessary to reduce risk of instability and improve dam safety
  • inspection, instrumentation and dam safety reports
  • hydrologic/hydraulic evaluation of spillway capacities under Probable Maximum flood
  • reservoir dredging feasibility studies; and
  • emergency action plans, dam breach modeling studies and inundation mapping using digital mapping technology to assist in assessing the risk of downstream damage and loss of life in the event of a hypothetical failure.

GZA is providing extensive reports of site geology, site specific seismicity studies, visual inspections, subsurface investigations, cross-hole geophysical testing, permeability and packer tests, laboratory soil and rock strength testing, groundwater, seepage and stability analysis, along with recommendations for modifications and repairs needed to upgrade these critical earth, rock and concrete structures to first-class working condition for the next 50 years of operation.

GZA and its subconsultants evaluated large gates and valves and recommended improvements and/or replacements to restore hydraulic contacts to first close working order.

Project work began in the Summer of 1998. In 2000, GZA designed emergency repairs to fill scoured holes up to 15 feet deep at the base of the 180 foot high Gilboa dam spillway at Schoharie Reservoir. The project was completed in a high quality technical manner on-time and within budget. This project demonstrates GZA's geotechnical engineering and management skills and staff depth to execute large dam engineering project assignments.