Publication Date

5-2015

Date of Final Oral Examination (Defense)

3-11-2015

Type of Culminating Activity

Thesis - Boise State University Access Only

Degree Title

Master of Science in Hydrologic Sciences

Department

Interdisciplinary Studies

Major Advisor

James P. McNamara, Ph.D.

Advisor

Shawn Benner, Ph.D.

Advisor

Alejandro N. Flores, Ph.D.

Abstract

An hourly water balance was conducted for a period of 12 years to evaluate the relative influence of precipitation, streamflow, evapotranspiration, net recharge, and soil water storage in an experimental watershed. The Penman-Monteith equation was used to calculate hourly reference ET and canopy reference ET rates at various elevations. Precipitation, reference ET rates, and soil water storage were distributed spatially using a hypsometric approach. Reference ET was moderated by defining an active growing season for grasses, forbs, and shrubs to estimate actual ET. Actual ET estimates were used in the water balance to ultimately define net recharge.

The results show that apparent actual ET is significantly lower than potential ET and reference ET on an annual scale in this semi-arid watershed. Seasonal precipitation regimes and limited catchment soil water storage (150 mm) in DCEW during times of high ET demand (up to 8.9 mm/day and 0.56 mm/hour) apparently limits plant productivity and ET rates. Annual ET totals are sensitive to low frequency summer precipitation events (when soil water storage is low and potential ET rates are high), with a single event capable of adding more than 15% to the annual ET total. The timing of surface water inputs is critical for the partitioning of water into biotic and abiotic fluxes. Drought and climatic variability have the potential to significantly alter storage regimes and ecohydrologic patterns in this type of environment. Localized soil water storage heterogeneities could be highly important for vegetation, due to the prevalence of shallow soils, lack of groundwater, and high potential ET rates.

Water balance derived changes in storage were compared to and reconciled with autonomous soil water storage observations. The inter-annual changes in water balance storage are unaccounted for in instrumented soils across the watershed and are attributed to net recharge processes. Net recharge averaged 34% of precipitation during the 12-year study. Surface water inputs in the upper half of the watershed are responsible for much of the net recharge volume, while lower elevations are limited by lack of snow accumulation and decreased precipitation magnitudes.

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