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.


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    
 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
  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:  
  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.