How much water is being taken?

The collection system above Gold Park

Five existing collectors and Homestake Reservoir feed the tunnel carrying water east to Turquoise Lake. Below the collectors and reservoir, Gold Park records water continuing down Homestake Creek toward the Eagle River.

Map key: C Sopris · D East Fork · E Upper Homestake and reservoir · G French · H Fancy · I remaining Missouri Creek area.

The colors distinguish upper creek drainage areas. All five existing intakes and Homestake Reservoir lie upstream of the Gold Park gauge. French Creek joins Homestake Creek above the gauge.

More water through Homestake Tunnel than past Gold Park.

Across WY2007-2024, Homestake Tunnel carried about 23,400 acre-feet a year to Turquoise Lake, while about 21,500 acre-feet a year passed Gold Park down Homestake Creek. Whitney would add another reservoir and collection works to this existing diversion system.

Exports exceeded recorded Gold Park flow by 8.7%. Another view of those same volumes is their combined share: about 52% through the tunnel and 48% past Gold Park. The denominator is the sum of these two measured routes.

The tunnel share compares these two recorded routes over the same 18 water years. The mapped drainage used for the basin calculation below covers about 35.9 square miles.

Why we believe the middle ground is already here

Homestake already supplies Aurora and Colorado Springs. The water that remains supports the creek, its wetlands and fens, and the wildlife and communities connected to them. We believe the existing diversion is already a major compromise.

The available streamflow records and ecological evidence have not established an ecologically safe margin for taking more water from Homestake. Protecting what remains is a reasonable place to draw the line, for our children and future generations.

Learn more about the math behind these calculations

How the amounts were calculated

Where the rest of the basin’s water goes

For water years 2007-2020, PRISM climate estimates put average rain and snow over the mapped basin at about 61,500 acre-feet a year. About 23,300 acre-feet went through the tunnel and another 23,300 passed the Gold Park gauge. After accounting for the change in Homestake Reservoir storage, roughly 14,900 acre-feet a year remains.

Estimates for snow turning directly to vapor, reservoir evaporation and water released to the air by mapped fens could explain about 7,900-10,600 acre-feet of that remainder each year. Snow accounts for most of the estimate. The other 4,300-6,900 acre-feet could reflect evaporation and plant use elsewhere, changes in storage, groundwater movement and uncertainty in the inputs.

What the letters mean

P is the estimated rain and snow falling across the basin. E is tunnel export. Q is creek flow past Gold Park. ΔS is the change in Homestake Reservoir storage from beginning to end. R is the amount left after those quantities are accounted for.

For the two recorded routes, the tunnel percentage is 100 × E / (E + Q). Using the summed volumes for WY2007-2024 gives about 52%. Dividing each total by 18 gives its annual average. The exact figures are in the Water Technical Companion.

For the whole-basin calculation, R = P − E − Q − ΔS. For WY2007-2020, the reservoir ended about 640 acre-feet lower than it began. That negative storage change increases the remainder: water released from storage also helped supply the recorded outflows. Calculating with the full source values and dividing by 14 gives about 14,900 acre-feet a year. The companion gives the exact figures and calculations.

The estimated return to the air includes roughly 7,100-9,400 acre-feet a year from snow sublimation, 800-1,000 from reservoir evaporation and 55-191 from partial-season evapotranspiration on mapped fens. These are estimates of processes within R, not additional recorded exports.

Read the full calculations, annual records and source data in the Water Technical Companion.

Historical September 24 scenario: 247-353 mm of fen evapotranspiration in normal years. The current figures above include the drought year, using 101-353 mm.

Collection, export and timing

Together, these five intakes captured about 13,100 acre-feet a year on average from 2014 to 2024. About 88% of their capture happened in May and June, and more than 99% between May and July. These seasonal withdrawals change when water remains in the creeks. Runoff also connects side channels and wet ground before summer levels fall. Its timing matters to pond persistence, streamside vegetation and later refuge. The collector record measures capture timing; the ecological studies explain the habitat processes. The intakes feed the reservoir and tunnel, so adding intake capture to tunnel export would count water from the same system twice. State intake records

Farther downstream at Red Cliff

The Red Cliff gauge offers a second view farther down Homestake Creek: tunnel exports compared with creek flow after more tributaries have joined. Its 58.2-square-mile drainage is larger than Gold Park’s, and the available matched record covers WY2007-2011. During those years, tunnel export made up about 43% of those two recorded routes together. The added drainage and different years explain why this percentage differs from the Gold Park comparison.

Read the Water Technical Companion for the annual figures, sources and full methods.