Dewey is a dam located in Cassia County, Idaho, built in 1913. It carries a Significant hazard potential classification and has a satisfactory condition assessment.
Dam profile
NID height · 30 ft30 ft tall and 2,300 ft long, taller than 68% of U.S. dams with a recorded height. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic embankment section and the water level is illustrative.
About Dewey
The primary purpose of Dewey is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is private-owned. It impounds the Marsh Creek Snake River near Declo.
The dam stands 30 feet tall and stretches 2,300 feet across, creates a reservoir covering 82 acres, has a storage capacity of 225 acre-feet, and collects water from a drainage area of 99 square miles. Completed in 1913, the structure is over a century 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 satisfactory, indicating no existing or potential dam safety deficiencies are recognized. The most recent inspection on record was 07/28/2017.
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Location
| State | Idaho |
| County | Cassia |
| Nearest City | Declo |
| River/Stream | Marsh Creek Snake River |
| Coordinates | 42.50170, -113.51670 |
Physical Characteristics
| NID Height | 30 ft |
| Dam Height | 30 ft |
| Dam Length | 2,300 ft |
| Year Completed | 1913 (113 years old) |
Storage & Hydraulics
| NID Storage | 225 acre-ft |
| Normal Storage | 225 acre-ft |
| Surface Area | 82 acres |
| Drainage Area | 99 sq mi |
| Max Discharge | 687 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Irrigation |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Satisfactory |
| Last Inspection | 07/28/2017 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | ID00033 |
| Federal ID | ID00033 |
| More Info | State Dam Safety Program |