Aquatic Habitat Representation for Robust Water Resources Management and Fish Conservation Decision-Making

We rely on rivers to provide water supply, flood control, and hydroelectricity for people and to sustain aquatic ecosystems. The development of dams and reservoirs to provide water for people did not consider environmental impacts to rivers, leading to widespread decline of freshwater species and habitat. Improving environmental outcomes of water management is needed to protect and restore aquatic ecosystems. However, rivers are complex and variable, making them difficult to represent as objectives for water management. This dissertation explores approaches to improve aquatic habitat representation and environmental objectives for water resources management and river conservation and restoration. Chapter 2 uses economic and environmental modeling to evaluate tradeoffs in Utah’s Bear River Basin between water supply for people, impacts to stream habitat for fish, and changes to Great Salt Lake with proposed water diversions and reservoirs. New diversions and reservoirs reduced summer stream habitat for threatened Bonneville Cutthroat Trout, and water diversions to the metropolitan Wasatch Front decreased Great Salt Lake level by over 4 m (11 ft) between 2000 and 2020. I demonstrate that conflicting economic and environmental objectives for the Bear River exacerbate current threats to Bonneville Cutthroat Trout and pose significant economic, environmental, and human health risks from a declining Great Salt Lake. Chapter 3 evaluates how barrier removals reconnecting stream reaches for Bonneville Cutthroat Trout perform under uncertain stream temperature conditions in Utah’s Weber River Basin. Barrier removals were sensitive to stream temperature data uncertainty for reconnecting summer coldwater stream habitats, and few barrier removals were also selected for reconnecting streams with suitable temperatures for fish growth. I demonstrate that uncertainty stream temperature conditions influence barrier removal selection and should be considered for restoring river connectivity. Chapter 4 compares methods to predict fish passage at road-stream crossings for measuring connectivity in river systems. My methods for predicting road-crossing passability produced similar river connectivity estimates but vary considerably predicting fish passage for individual barriers. I demonstrate that simple methods for predicting fish passage at road crossings are sufficient to characterize river connectivity and highlight limitations for predicting fish passage to support barrier removal and river restoration.