Allen Lake
Allen Lake is an earth dam located in Boulder County, Colorado, built in 1928. It carries a Significant hazard potential classification and has a satisfactory condition assessment.
About Allen Lake
The primary purpose of Allen Lake is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is owned by Left Hand Ditch Company (terry Plummer) (private). It impounds the Left Hand Creek-os near Longmont.
The dam stands 24 feet tall and stretches 1,525 feet across, creates a reservoir covering 36 acres, and has a maximum storage capacity of 865 acre-feet. Completed in 1928, the structure is well-established, with more than 75 years of service.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. 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 06/23/2022.
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Location
| State | Colorado |
| County | Boulder |
| Nearest City | Longmont |
| River/Stream | Left Hand Creek-os |
| Coordinates | 40.14047, -105.28410 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 24 ft |
| Dam Height | 24 ft |
| Dam Length | 1,525 ft |
| Year Completed | 1928 (98 years old) |
Storage & Hydraulics
| NID Storage | 865 acre-ft |
| Max Storage | 865 acre-ft |
| Normal Storage | 700 acre-ft |
| Surface Area | 36 acres |
| Max Discharge | 8,821 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Irrigation |
| Owner | LEFT HAND DITCH COMPANY (TERRY PLUMMER) |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Satisfactory |
| Last Inspection | 06/23/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CO00169 |
| Federal ID | CO00169 |
| More Info | State Dam Safety Program |