Why Horsetooth Reservoir got so low so quickly this summer

Jacy Marmaduke
The Coloradoan
Jan Andersen makes her final strokes to the shores of the south bay on Horsetooth Reservoir as she completes the 2.4-kilometer swim on Sunday, September 10, 2017.

If you took a trip to Horsetooth Reservoir this month, you might've noticed the water looked a lot lower than it did just a few weeks ago.

In all, Horsetooth dropped 32 feet between Aug. 1 and Sept. 13. The reason for the decrease is two-fold, according to reservoir manager Northern Water.

One reason for the level change is the approaching end of the irrigation season. Water users often didn't need to take advantage of their water rights earlier in the summer, when storm clouds dropped rain on Northern Colorado several times a week. 

But as the weather's dried up, Northern Water has delivered more water to ditch companies for irrigation, spokesman Brian Werner said. The Poudre and South Platte Rivers are running lower now that snowpack has waned, so irrigation water is coming out of storage at Horsetooth. 

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The releases are also necessary because Northern Water is planning maintenance on the Soldier Canyon Dam outlet works in early November, Werner said. Lower water levels make it easier for divers to access dams for repairs.

Horsetooth stood at 5,391 feet on Wednesday morning, which is about average for this time of year, Werner said. On Aug. 1, Horsetooth's elevation was 5,423 feet, or 7 feet below full.

The level decrease is steeper than usual but not unprecedented, according to Northern Water records dating back to 1999.

Northern Water plans to draw down Horsetooth another 4 feet but will do so more gradually during the coming weeks, Werner said. The reservoir will probably reach more of an "equilibrium" between inflows and outflows this weekend, he added.

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