Date of Award:

12-2023

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Committee Chair(s)

Sarah E. Null

Committee

Sarah E. Null

Committee

Robert W. Van Kirk

Committee

Courtney Flint

Committee

Phaedra Budy

Committee

Patrick Belmont

Abstract

Multi-user water management is a challenging arena further complicated by climate change. This research is based in the Henrys Fork, Snake River, Idaho—an agricultural watershed that exemplifies those throughout the semi-arid American West. This dissertation uses an integrated approach that considers groundwater-river relationships, farm-scale decisions and basin-scale outcomes, upstream reservoir operation for downstream aquatic habitat, water rights, and collaborative stakeholder management to identify drought adaptation strategies accordingly.

Chapter 2 uses an interdisciplinary approach to quantify how improvements to irrigation efficiency at the farm-scale (i.e., converting from flood to sprinkler irrigation) can add up to affect hydrology at the landscape-scale and alter groundwater-surface water relationships. Motivated to improve economic efficiency, irrigators began converting from surface to center-pivot sprinkler irrigation in the 1950s, with rapid adoption of center-pivot sprinklers through 2000. Between 1978–2000 and 2001–2022, annual surface-water diversion decreased by 2,521 acre-ft (23%) and annual return flow to the river decreased by 2,431 acre-ft.

Chapter 3 uses streamflow predictions, local reservoir operation standards, and the relationship between groundwater and river flows to quantify 1) the potential to conduct aquifer recharge in the lower watershed under a warming climate and 2) resulting streamflow response from groundwater. Water for recharge was largely available in April and October, reducing peak springtime streamflow at the watershed outlet by 10–14% after accounting for groundwater return. Streamflow contribution from recharge peaked in July and November, increasing July–August streamflow by 6–14% and November–March streamflow by 9–14%. I demonstrate recharge can recover groundwater return flows when applied as flood irrigation on agricultural land with senior water rights.

Chapter 4 developed relationships between streamflow and habitat for three fish species in a reach where irrigation-season flows are managed by releases from an upstream reservoir. I used these relationships to 1) quantify aquatic habitat at different streamflows and 2) assess the differences in aquatic habitat across two different streamflow management histories. Using these relationships, I demonstrated that moving the management target's location and flow amount will contribute to more consistently suitable fish habitat in the reach while continuing to meet upstream management objectives.

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