MANSFIELD HOLLOW DAM

NATCHAUG RIVER - Thames River Basin - Mansfield, CT

DRAINAGE AREA: 159 sq.mi.

PERMANENT POOL: 450 Acre Recreation Pool
Summer Stage = 16.5 Ft (211.5 Ft NGVD)
Winter Stage = 15 Ft (210 Ft NGVD)

DAM
Type: Rolled Earth Fill
Length: 14,050 Feet
Top Elev = 273.0 Ft NGVD (78 Ft)

FLOOD CONTROL STORAGE
Capacity: 49,200 Acre Feet
5.8 Inches of Runoff
Area at Crest: 1,880 Acres

CONTROL WORKS
Type: 5 Rectangular Conduits
Size: 5.5'W x 7.0'H
Length: 26 Feet
Invert Elev = 195.0 Ft NGVD
Gate 1 Weir Elev = 16.5 ft (211.5 ft NGVD)
Gate 2 Weir Elev = 10.5 ft (205.5 ft NGVD)
Capacity (Full Pool): 9,700 cfs
Gates (Type): Hydraulic Slide
Number: 5
Size: 5.5' X 7.0'
Channel Capacity = 2900 cfs

SPILLWAY
Type: Ogee Weir
Length: 690 Feet
Elev = 257.0 Ft NGVD (62 Ft)

SPILLWAY DESIGN FLOOD

• Original Design Criteria:
  • Rainfall Excess = 20.8 inches
  • Initial Pool Level = Full
  • Flood Control Outlet Gates = Inoperable
  • Peak Inflow = 118,000 cfs
  • Peak Outflow = 106,600 cfs
  • Max. Pool = 268.5 ft-NGVD
  • Freeboard = 4.5 ft
• Current HMR 51 & 52 Criteria:
  • Rainfall Excess = 25.5 inches
  • Initial Pool Level = Full
  • Flood Control Outlet Gates = Operable
  • Peak Inflow = 121,000 cfs
  • Peak Outflow = 103,750 cfs
  • Max. Pool = 268.1 ft-NGVD
  • Freeboard = 4.9 ft

RECREATIONAL FACILITIES: State of Connecticut maintains recreational facilities.

TOTAL COST: $6,447,000

PLACED IN OPERATION: 1952