Hansen Dam
Hansen Dam
Hansen Dam is an essential element for flood control in the Los Angeles County Drainage Area (LACDA). In conjunction with Sepulveda Dam and Lopez Dam, it is vital for the flood control protection of the lower portions of the San Fernando Valley and the City of Los Angeles. The project was built by the Corps of Engineers, Los Angeles District between September 1939 and September 1940. The project is located near the northern edge of the San Fernando Valley on Tujunga Wash, about one mile below the confluence of the Big Tujunga Wash and the Little Tujunga Wash, and about four miles southeast of the City of San Fernando. Hansen Dam is approximately 3.5 miles northwest of Lopez Dam.
Hansen Dam was authorized by the Flood Control Act, approved 22 June 1936 (Public Law 738, 74th Congress) and extended and amended by subsequent Flood Control Acts of 1937, 1938, 1941, 1944, and 1946. The plan for construction, in accordance with the recommendations contained in the report dated 11 April 1940 by the Chief of Engineers, and submitted in House Document 838, 76th Congress, 3rd session, was authorized by the Flood Control Act, approved 18 August 1941.
The current water control manual for Hansen Dam was approved in November 1990, and is scheduled for revision by September 2001.
HANSEN DAM AND RESERVOIR
LOS ANGELES, CALIFORNIA
PERTINENT DATA - JUNE 2016
Operational Objectives
Flood Control
Incidental Water Conservation
Original Completion Date
September 1940
Stream System
Tujunga Wash
LACDA
Drainage Area
149.87
mi2
Significant Upstream Flood Control Facilities
Big Tujunga Dam
LACDPW
DSAC Rating
3
Reservoir:
Elevation
NGVD 1929
+ 2.21 ft =
NAVD 1988
Original Streambed Elecation
990.0
ft
992.2
Intake Invert
1,010.5
ft
1,012.7
Spillway crest
1,060.0
ft
1,062.2
Revised Spillway design surcharge level2
1,081.2
ft
1,083.4
Top of dam
1,087.0
ft
1,089.2
Area1
Debris Pool
372
acres
Spillway crest
826
acres
Revised Spillway design surcharge level2
1084
acres
Top of dam
1154
acres
Capacity1, Gross
Debris Pool
3,756
af
Spillway crest
33,348
af
Revised Spillway design surcharge level2
52,964
af
Top of dam
59,299
af
Allowance for sediment (100-year)2
21,000
af
Dam
Type:
Earthfill
Height above original streambed
97
ft
Top length
10,4758
ft
West Dike top length / max. height9
~1,525 / 22
ft
Spillway2
Type:
Detached Concrete Ogee Weir on left under Associated Rd.
Crest length, net [302ft - (6 piers @ 3ft ea)]
284
ft
Revised spillway surcharge2
21.2
ft
Revised freeboard2
5.8
ft
Outlets2
Type:
Uncontrolled
Number and size
2 - 8'W x 6'H
ft
Entrance invert elevation
1,011.0
ft
1,013.2
Conduits' (2) length
265
ft
Conduits' dimensions
8'W x 8'H opening
ft
Maximum capacity at spillway crest
4,900
cfs
Controlled
Type:
Hydraulic lift vertical slide gates
Number and Size
8 - 5'W x 8'H
Entrance / Discharge invert elevation
990.0 / 989.0
ft
Conduits' (8) length
265
ft
992.2 / 991.2
Maximum capacity at spillway crest
17,000
ft
Revised downstream channel capacity4
20,800
ft
Reservoir Design Flood ➜
Original3
Resived SPP2
Duration (Inflow)
5
days
4
Total volume
70,700
af
57,200
Inflow peak
64,800
cfs
53,000
Outflow peak
12,0005
cfs
22,000
Maximum water surface elevation
1059.7 (1061.9 NAVD)
ft
1064.8 (1067 NAVD)
Spillway Design Flood ➜
Original2
Resived PMP2
Duration (Inflow)
1
days
5
Total volume
76,800
af
246,000
Inflow peak
129,600
cfs
105,000
Outflow peak
99,800
cfs
99,700
Maximum water surface elevation
1081.8 (1084 NAVD)
ft
1081.2 (1083.4 NAVD)
Historic Maximums
Date
Local Datum
NAVD 1988
Maximum water surface elevation
3/2/1983
1039.7
ft
1,041.9
Maximum storage (50% full)6
3/2/1983
13,260
af
Maximum outflow
3/2/1983
15,200
cfs
1. Based on November 2004 Survey
2. Interim Report on H & H Review of Design Features of Existing Dams for LACDA, June 1978
3. Tujunga Wash Improvement, Hansen Dam, Analysis of Design, June 1940
4. LACDA Feasibility Interim Report, Hydrology Technical Report, December 1991
5. Available d/s channel capacity at time of dam construction. [See Hydrology, ULAR & Tribs, Burbank-Western to Sepulveda Dam, Dec1946 for Reservoir Design Routing with improved channel]
6. Survey of July 1982, computed 16 Feb 1983
7. Original drainage area of 147.4 mi2 plus addition of 2.4 mi2 with completion of Lopez Canyon Diversion Channel in 1960.
8. Original design documents list crest length of 9,050 ft. The value of 10,475 ft comes from the 1963 O&M Manual and is more consistent with existing dam.
9. Estimated from drawing 425 / 1, Plan and Elevation of Dam, revised 3-6-1939.
