Siena
Siena is an earth dam located in Broomfield County, Colorado, built in 2004. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Siena
The primary purpose of Siena is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by City Of Broomfield (middleton, Brennan) (local government). It impounds the Coal Creek-tr near Lafayette.
The dam stands 41 feet tall and stretches 1,250 feet across, creates a reservoir covering 20 acres, and has a maximum storage capacity of 640 acre-feet. Completed in 2004, the structure is relatively new.
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 05/03/2022.
At 41 feet, this dam is taller than 88% 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 | Broomfield |
| Nearest City | Lafayette |
| River/Stream | Coal Creek-tr |
| Coordinates | 39.98164, -105.03020 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 41 ft |
| Dam Height | 40 ft |
| Dam Length | 1,250 ft |
| Year Completed | 2004 (22 years old) |
Storage & Hydraulics
| NID Storage | 640 acre-ft |
| Max Storage | 640 acre-ft |
| Normal Storage | 450 acre-ft |
| Surface Area | 20 acres |
| Max Discharge | 690 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | CITY OF BROOMFIELD (MIDDLETON, BRENNAN) |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 05/03/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CO02859 |
| Federal ID | CO02859 |
| More Info | State Dam Safety Program |