BLACKWATER DAM

BLACKWATER RIVER - Merrimack River Basin - Webster, NH

DRAINAGE AREA: 128 sq.mi.

PERMANENT POOL: None

DAM
Type: Rolled earth
Length: 1,150 Feet
Top Elev = 584.0 Ft NGVD

FLOOD CONTROL STORAGE Capacity: 46,000 Acre Feet
6.7 Inches of Runoff
Area at Crest: 3,280 Acres

CONTROL WORKS Type: 4 Conduits thru spillway (3 gated 1 plugged)
Size: 3'- 6" x 5'- 3"
Length: 65 Feet
Invert Elev = 515.0 Ft NGVD
Capacity (Full Pool): 2,800 cfs
Gates (Type): Hydraulic Slide
Number: 3
Size: 3'-6" x 5'-3"
Channel Capacity = 2300 cfs

SPILLWAY

Type: Ogee Weir, Concrete Gravity
Length: 240 Feet
Elev = 566.0 Ft NGVD

SPILLWAY DESIGN FLOOD

• Original Design Criteria:
• Rainfall Excess = 22.0 inches
• Initial Pool Level = Full
• Flood Control Outlet Gates = Inoperable
• Peak Inflow = 49,300 cfs
• Peak Outflow = 32,200 cfs
• Max. Pool = 579.0 ft-NGVD
• Freeboard = 5.0 ft
• Current HMR 51 & 52 Criteria:
• Rainfall Excess = 21.8 inches
• Initial Pool Level = Full
• Flood Control Outlet Gates = Operable
• Peak Inflow = 65,800 cfs
• Peak Outflow = 48,500 cfs
• Max. Pool = 579.0 ft-NGVD
• Freeboard = 5.0 ft

RECREATIONAL FACILITIES: Hunting, fishing, canoeing and parking areas.

TOTAL COST: $1,319,700

PLACED IN OPERATION: November 1941

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