Six Mile - Main
Six Mile - Main is an earth dam located in Boulder County, Colorado, built in 1892. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Six Mile - Main
The primary purpose of Six Mile - Main is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is owned by Boulder & White Rock Ditch & Reservoir Co. (grant, (private). It impounds the Little Dry Creek-tr near Boulder.
The dam stands 52 feet tall and stretches 3,050 feet across, creates a reservoir covering 124 acres, has a maximum storage capacity of 2,186 acre-feet, and collects water from a drainage area of 3 square miles. Completed in 1892, the structure is over a century old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 08/09/2022.
At 52 feet, this dam is taller than 93% of dams nationwide.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Colorado dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Colorado |
| County | Boulder |
| Nearest City | Boulder |
| River/Stream | Little Dry Creek-tr |
| Coordinates | 40.06751, -105.21807 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 52 ft |
| Dam Height | 35 ft |
| Dam Length | 3,050 ft |
| Year Completed | 1892 (134 years old) |
Storage & Hydraulics
| NID Storage | 2,186 acre-ft |
| Max Storage | 2,186 acre-ft |
| Normal Storage | 1,367 acre-ft |
| Surface Area | 124 acres |
| Drainage Area | 3 sq mi |
| Max Discharge | 11,552 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Irrigation |
| Owner | BOULDER & WHITE ROCK DITCH & RESERVOIR CO. (GRANT, |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 08/09/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CO00250 |
| Federal ID | CO00250 |
| More Info | State Dam Safety Program |