A Synthesis of Long-Term Hydrometeorological Data Series for Eklutna Watershed, Alaska

Authors: Ostman, Johnse, Alaska Pacific University; Geck, Jason, Alaska Pacific University; Loso, Mike, National Park System; Conaway, Jeff, US Geological Survey

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Abstract

Anchorage, Alaska's 300,000 residents are critically dependent on the Eklutna Lake watershed for hydropower and drinking water. Eklutna Lake receives runoff from the thinning and retreating Eklutna Glacier, with resulting mass loss enhancing short-term runoff. The headwater catchment contributes ~80% of the total runoff into Eklutna Lake, and yet historically the hydrometeorology has not been monitored. Here we present the 2008-2021 continuous seasonal on- and off-glacier West Fork catchment weather, and West Fork Eklutna River and East Fork Eklutna River discharge time series based on a combined 112 discrete discharge measurements and their associated stage-discharge relationships. Although not significantly correlated, air temperatures increased at a rate of 0.5 degC per decade on-glacier at the equilibrium line altitude and 1.2 degC per decade off-glacier, and rainfall was variable with no trends observed. Hydrometeorological comparison showed positive significant correlation between air temperature and basin runoff, although annual flood peaks more strongly correlated with Gulf of Alaska atmospheric rainfall events. Average June-September discharge in the West Fork Eklutna River was 4% greater than in the East Fork Eklutna River, whereas water yield from the West Fork produced 58% greater specific discharge. Average day of year when half the runoff season total flow volume had accumulated and hydrographic daily maximum were ~9 days earlier in the East Fork. Distributions of accumulated annual specific discharge highlighted how glacier buffering contributes to lower interannual variability, providing insight into future runoff patterns from the West Fork as Eklutna Glacier dividends diminish. The data presented here together with continuation of this robust hydrometeorological monitoring program are essential for informing water resource utility management strategies into the future.

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