Lake Isabelle
Lake Isabelle is a rockfill dam located in Boulder County, Colorado, built in 1925. It carries a Low hazard potential classification and has a fair condition assessment.
About Lake Isabelle
The primary purpose of Lake Isabelle 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 S F St Vrain Creek near Longmont.
The dam stands 38 feet tall, creates a reservoir covering 36 acres, has a maximum storage capacity of 738 acre-feet, and collects water from a drainage area of 2 square miles. Completed in 1925, the structure is over a century old.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. The most recent inspection on record was 09/24/1990. That was over 35 years ago.
At 38 feet, this dam is taller than 85% of dams nationwide.
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Location
| State | Colorado |
| County | Boulder |
| Nearest City | Longmont |
| River/Stream | S F St Vrain Creek |
| Coordinates | 40.07001, -105.61556 |
Physical Characteristics
| Dam Type | Rockfill |
| NID Height | 38 ft |
| Dam Height | 38 ft |
| Year Completed | 1925 (101 years old) |
Storage & Hydraulics
| NID Storage | 738 acre-ft |
| Max Storage | 738 acre-ft |
| Normal Storage | 594 acre-ft |
| Surface Area | 36 acres |
| Drainage Area | 2 sq mi |
| Max Discharge | 1,262 cfs |
| Spillway Type | None |
Ownership & Safety
| Purpose | Irrigation |
| Owner | LEFT HAND DITCH COMPANY (TERRY PLUMMER) |
| Owner Type | Private |
| Hazard Classification | Low |
| Condition Assessment | Fair |
| Last Inspection | 09/24/1990 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | CO01929 |
| Federal ID | CO01929 |
| More Info | State Dam Safety Program |