Earth and Planetary Sciences ETDs

Publication Date

Summer 7-11-2019

Abstract

We develop and implement new tools for assessing the future of surface water supplies in downstream reaches of the Rio Grande, for which Elephant Butte Reservoir is the major storage reservoir. First, a normalization procedure is developed to adjust natural Rio Grande streamflows simulated by dynamical models in downstream reaches. The normalization accounts for upstream anthropogenic impairments to flow that are not considered in the model, thereby yielding downstream flows closer to observed values and more appropriate for use in assessments of future flows in downstream reaches. The normalization is applied to assess the potential effects of climate change on future water availability in the Rio Grande Basin at a gage just above Elephant Butte reservoir. Model simulated streamflow values were normalized force simulated flows to have the same mean and variance as observed flows over a historical baseline period, yielding normalization ratios that can be applied to future flows when water management decisions are unknown. At the gage considered in this study, the effect of the normalization is to reduce all simulated flow values by nearly 72% on average, indicative of the large fraction of natural flow diverted from the river upstream from the gage.

The normalized streamflow scenarios are then implemented as the main boundary condition in a simple water balance model to analyze future policy options, using reservoir storage and downstream releases to compare management choices. It takes four years of twice the average annual inflow to fill Elephant Butte Reservoir to full operating capacity, starting from near-empty initial conditions as occurred in late 2018. In terms of increasing downstream releases and increasing reservoir storage, reducing direct reservoir evaporation was the best option from a strictly hydrologic perspective. Increasing the future inflows by reducing upstream diversions increases reservoir storage and Caballo releases, but there was also an increase in reservoir evaporation. Lastly, maintaining a minimum storage threshold for reservoir storage increases future average storage, but also leads to an increase in reservoir evaporation and a decrease in releases. Water stored in Elephant Butte Reservoir is lost via the positive correlation between increasing reservoir storage, and thus the increased surface area, and the subsequent rise in direct reservoir evaporation. Therefore, the water balance model suggests the most hydrologically efficient policy option involves reducing reservoir evaporation, although the water balance model does not consider the costs of methods to reduce evaporation.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

David Gutzler

Second Committee Member

Alex Mayer

Third Committee Member

Joseph Galewsky

Keywords

Rio Grande, Water Resource Management, Climate, Hydrology, Drought

Document Type

Thesis

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