East Portal Diversion Dam


When water is diverted from Colorado's West Slope through the Alva B. Adams Tunnel to Colorado's East Slope, it is first deposited in East Portal, a small afterbay enclosed by East Portal Dam. East Portal sits to the southwest of Estes Park, Colorado on the boundary of Rocky Mountain National Park.

Water can exit East Portal through the spillway, depositing into Wind River, but it is almost always diverted via the Rams Horn Tunnel to Marys Lake and the Marys Lake Power Plant.

RegionFacilities in Great Plains | Great Plains Home Page
ProjectColorado-Big Thompson
Dam Type
WatercourseWind River
Original Construction1947
Modified Construction
National ID Number
Hydrologic Unit Code

Structural Height76 ft
Hydraulic Height (Normal Operating Depth at Dam)10 ft
Top Parapet (Elevation)
Spillway Crest Elevation
Crest Elevation8265.0 ft
Crest Length245 ft
Crest Width
Base Width
Volume of Dam Construction Materials
Streambed at Dam Axis
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)
Top of Active Conservation Pool (Elevation)
Top of Inactive Conservation Pool (Elevation)
Top of Dead Storage Pool (Elevation)

Hydraulics & Hydrology
Total Water Storage at Elevation
Maximum Water Surface Elevation
Normal Water Surface Elevation
Spillway Type
Auxiliary Spillway
Spillway Capacity at Elevation550 cfs at 8265.0
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation
Diversion Capacity at Elevation
Drainage Area
Hydrometeorological Report (HMR)
Probable Maximum Flood (PMF) Report

Contact Information
OwnerNo value defined
OperatorNo value defined

Last updated: Mar 29, 2013