Overview
Granby Dam, Spillway and Tunnel Outlet Works are located in a steep, narrow canyon composed of Precambrian crystalline rocks. Several small faults and rock with varying degrees of hardness and weathering were encountered in the cutoff trench, spillway and tunnel excavations. Fractured, loose and weathered rocks were removed from foundation areas during construction. The dam outside the limits of the cutoff trench rests on granular alluvium up to 65 feet in thickness; the soil types are unknown. Dikes No. 1, 2 and 4 are founded on siltstone of the North Park Formation. Two faults bound the area of the dikes. One passes from the left abutment of Dike No. 2 down the valley southwestward approximately parallel to the axis of Dike No. 1. The other trends due north and passes under the West End of Dike No. 1. These faults have broken the siltstone.
General
| Project | Colorado-Big Thompson |
| Latitude | 40.1650 |
| Watercourse | Colorado River |
| Original Construction | 1941-1950 |
| Longitude | -105.8633 |
| Reservoir | Lake Granby |
| National ID Number | CO01656 |
Dimensions
| Structural Height | 298.00 ft |
| Crest Length | 861.00 ft |
| Top of Active Conservation Pool (Elevation) | 8279.50 ft |
| Top of Inactive Conservation Pool (Elevation) | 8186.00 ft |
| Spillway Crest Elevation | 8260.00 ft |
| Streambed at Dam Axis | 8059.00 ft |
| Crest Elevation | 8290.00 ft |
| Hydraulic Height (Normal Operating Depth at Dam) | 223.0 ft |
| Top of Joint Use Pool (Elevation) | 8280.00 ft |
| Top of Dead Storage Pool (Elevation) | 8174.63 ft |
Hydraulics & Hydrology
| Spillway Capacity at Elevation | 11500 cfs at 8280.0 ft |
| Outlet Works Capacity at Elevation | 435 cfs at 8280.0 ft |
| Drainage Area | 311.0 sq mi |
| Hydrometeorological Report (HMR) | HMR 49 |
| Normal Water Surface Elevation | 8279.5 ft |
| Auxiliary Spillway | No |
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