Hydraulic conductivity of quaternary surficial units within the Eklutna Valley, southcentral Alaska

Abstract

Eklutna Lake is the primary water supply for Anchorage, Alaska; therefore the hydrogeologic properties of Eklutna surficial deposits are important to characterize. However, there is limited data on the hydraulic conductivity of surficial deposits in the Eklutna basin. This study presents hydraulic conductivity (Kfs and Ksat) measurements using two methods: the bottomless bucket and particle size distribution methods. Statistically, the two methods produced similar results; however, the large range in values obtained for Kfs and Ksat suggests there is a great degree of natural variation. One method used a bottomless bucket in place of a ring infiltrometer to measure field-saturated hydraulic conductivity (Kfs). The other method used a sieve-derived particle size distribution to solve a modified Hazen equation for Ksat. Of 47 samples collected in nine surficial geologic units, from poorly-sorted to well-sorted soils, the means of the two datasets were statistically similar: 49 m/day (Kfs) vs. 41 m/day (Ksat). Although the variability between the datasets was significantly different, with a standard deviation ranging from 44 m/day (Kfs) to 75 m/day (Ksat), the Wilcoxon paired-samples and paired t-test results suggest the datasets are statistically similar. Additionally, 98% of the 47 paired values were within one order of magnitude of each other. The methods presented herein can be used for surficial geologic unit delineation, planning purposes and optimizing hydrological models.