Como Dam


Como Dam was completed in 1910 by local irrigators and rehabilitated on its crest and upstream face by the Bureau of Reclamation in 1954. This semi hydraulic earthfill dam at the end of a natural lake is 70 feet high with a crest length of 2,550 feet and contains 1,114,000 cubic yards of earth and rock. In 1976, the district built concrete protection walls on each side of the spillway section up to elevation 4,249.0 feet, the same elevation as the crest of the dam. Under the Safety of Dams Program, designs for the walls were furnished to the district to correct low points in the dam fill adjacent to the spillway.

Between 1992 and 1994, major modifications to Como Dam were performed to mitigate concerns associated with seepage and piping, liquidfication during a large seismic event, and overtopping during large floods.  During these modifications, the spillway crest was raised to elevation 4246.0 feet increasing the active reservoir capacity from 35,100 acre-feet to 38,500 acre feet.  The State of Montana paid for this work and obtained 3,000 acre-feet of capacity for storing water to use in enhancing minimum streamflows in the Bitterroot River.

RegionFacilities in Pacific Northwest | Pacific Northwest Home Page
ProjectBitter Root
Dam TypeHydraulic Earthfill
ReservoirLake Como
WatercourseRock Creek
Original Construction1908-1910
Modified ConstructionMT00564
National ID Number
Hydrologic Unit Code

Structural Height85.0 ft
Hydraulic Height (Normal Operating Depth at Dam)62.0 ft
Top Parapet (Elevation)
Spillway Crest Elevation4252.8 ft
Crest Elevation4249.0 ft plus parapet wall
Crest Length2550.0 ft
Crest Width
Base Width
Volume of Dam Construction Materials
Streambed at Dam Axis4184.00 ft
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)
Top of Active Conservation Pool (Elevation)4246.0 ft
Top of Inactive Conservation Pool (Elevation)4188.50 ft
Top of Dead Storage Pool (Elevation)4185.75 ft

Hydraulics & Hydrology
Total Water Storage at Elevation38,495 ac-ft
Maximum Water Surface Elevation
Normal Water Surface Elevation4246.0 ft
Spillway TypeUngated
Auxiliary Spillway
Spillway Capacity at Elevation7,700 cfs at 4252.8 ft
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation830 cfs
Diversion Capacity at Elevation
Drainage Area56.4 sq mi
Hydrometeorological Report (HMR)HMR 57
Probable Maximum Flood (PMF) Report

Contact Information
OrganizationBitter Root Project Irrigation District
Address1182 Lazy J Land
CityCorvalis, MT 59828
Phone (Office)406 961-1182
OrganizationBitter Root Project Irrigation District
Address1182 Lazy J Land
CityCorvalis, MT 59828
Phone (Office)406 961-1182

Last updated: Mar 11, 2009