Flatiron Afterbay Dam

Overview
The zoned and compacted earthfill-type dam provides for the retention and regulation of water discharged into Chimney Hollow from Flatiron Powerplant. It consists of an impervious central core flanked by zones of relatively free-draining material grading to pervious at the outer slopes of the dam. The upstream zone is designed to resist percolation of the afterbay water and to dissipate internal pressures exerted outwardly during rapid afterbay drawdowns. The downstream zones protects the impervious central core and stabilizes the dam by lowering the saturation line in the downstream area. The cutoff trench beneath the dam is designed to obstruct percolation along the foundation contact to prevent dangerous seepage velocities. The stability of the dam is further safeguarded by the embankment toe drains which intercept seepage along the foundation contact and surface flow from within the dam. The toe drains are designed to permit easy escape of the seepage and to lower the ground water table sufficiently to avoid the formation of boggy areas below the dam.

General
RegionFacilities in Great Plains | Great Plains Home Page
StateColorado
CountyLarimer
ProjectColorado-Big Thompson
Dam Type
ReservoirFlatiron
WatercourseChimney Hollow Creek
Location
Longitude-105.2233
Latitude40.3683
Net Generation187,204,951 kWh
Original Construction1951-1953
Modified Construction
National ID NumberCO01654
Hydrologic Unit Code

Dimensions
Structural Height86.0 ft
Hydraulic Height (Normal Operating Depth at Dam)55.0 ft
Top Parapet (Elevation)
Spillway Crest Elevation5472.8 ft
Crest Elevation5486.0 ft
Crest Length1725.0 ft
Crest Width
Base Width
Volume of Dam Construction Materials
Streambed at Dam Axis4317.0 ft
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)
Top of Active Conservation Pool (Elevation)5472.8 ft
Top of Inactive Conservation Pool (Elevation)5462.0 ft
Top of Dead Storage Pool (Elevation)5454.75 ft

Hydraulics & Hydrology
Volume
Total Water Storage at Elevation
Maximum Water Surface Elevation
Normal Water Surface Elevation5472.8 ft
Spillway Type
Auxiliary Spillway
Spillway Capacity at Elevation23600 cfs at 5480.0 ft
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation930 cfs at 5464.8 ft
Diversion Capacity at Elevation
Drainage Area7.1 sq mi
Hydrometeorological Report (HMR)HMR 55A
Probable Maximum Flood (PMF) Report

Contact Information
Owner
TitleArea Office Manager
OrganizationEastern Colorado Area Office
Address11056 W. County Rd 18E
CityLoveland, CO 80537-9711
Phone (Fax)970 663-3212
Phone (Office)970 667-4410
Operator
TitleArea Office Manager
OrganizationEastern Colorado Area Office
Address11056 W. County Rd 18E
CityLoveland, CO 80537-9711
Phone (Fax)970 663-3212
Phone (Office)970 667-4410


Last updated: Mar 29, 2013