Cottonwood Creek Lower
Cottonwood Creek Lower is a dam located in Ada County, Idaho, built in 1961. It carries a Significant hazard potential classification and has a fair condition assessment.
About Cottonwood Creek Lower
The primary purpose of Cottonwood Creek Lower is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is local government-owned. It impounds the Cottonwood Creek Boise River near Boise.
The dam stands 15 feet tall and stretches 1,710 feet across, creates a reservoir covering 9 acres, has a storage capacity of 88 acre-feet, and collects water from a drainage area of 16 square miles. Completed in 1961, the structure is well into its service life at over 50 years old.
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 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 09/11/2018.
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Location
| State | Idaho |
| County | Ada |
| Nearest City | Boise |
| River/Stream | Cottonwood Creek Boise River |
| Coordinates | 43.61560, -116.18580 |
Physical Characteristics
| NID Height | 15 ft |
| Dam Height | 15 ft |
| Dam Length | 1,710 ft |
| Year Completed | 1961 (65 years old) |
Storage & Hydraulics
| NID Storage | 88 acre-ft |
| Normal Storage | 88 acre-ft |
| Surface Area | 9 acres |
| Drainage Area | 16 sq mi |
| Max Discharge | 3,540 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Fair |
| Last Inspection | 09/11/2018 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | ID00477 |
| Federal ID | ID00477 |
| More Info | State Dam Safety Program |