Graduate Defense: Elizabeth Crowther

Thesis Information

Title: The Drying of Dry Creek: A Paired Catchment Experiment Assessing Non-Perennial Headwater Streams

Program: Master of Science in Hydrologic Sciences

Advisor: Dr. James McNamara, Geosciences

Committee Members: Dr. Sarah Godsey, Idaho State University; and Dr. Anna Bergstrom, Geosciences

Abstract

Intermittent streams make up majority of waterways in the United States and are becoming more common in a changing climate, yet they lack stream gaging and habitat data compared to their perennial counterparts. Headwater streams in the mountain west can be classified as intermittent through seasonal contraction of flowing streams.. Although small, they provide critical habitat for fish species and contribute to larger downstream systems. Predictions models, such as the Probability of Stream Permanence (PROSPER) model, have been created to map dry and intermittent reaches on the regional scale, yet they lack large scale spring data sets as controls for their model. In-field mapping of these headwater streams and springs helps improve the accuracy of these models and enhance water management decisions in the mountain west.

Active stream channel networks within intermittent headwater streams expand and contract within geomorphic channel networks in response to climatic conditions. Relationships between the networks depend on watershed structural characteristics, including underlying geology, climate, and topography. Flowing stream networks expansion and retraction are proposed to be visible representations of these geomorphological conditions. However, the surface channel network can differ from the assumed geomorphic drainage density. Stable springs have been examined to contribute to higher stream permanence in headwater streams and create a more stable flowing stream network across seasons. To further understand of how groundwater characteristics influence surficial water expressions, a controlled paired watershed experiment was conducted to relate active channel network mapping to stable spring input concentrations. Predicting stream behavior in low flow conditions can improve water resource management practices and mapping of critical aquatic habitat in headwater catchments. The Dry Creek Experimental Watershed drying patterns offer a unique opportunity to assess connectivity in spring-fed and non-spring-fed catchments with similar geologic and topographic profiles. To assess for active stream network stability, flowing streams were mapped and discharge measurements were made at high flow, low flow, and Fall ‘re-wetting’ conditions. Active stream networks at low flow conditions were then compared to the PROSPER models wet/dry predictions. Geomorphic and hydrologic analysis was also conducted to assess climatic and topographic controls on stream permanence.

Active stream mapping results found that the spring-fed catchment was more stable than the non-spring fed catchment throughout the 2021 water year. Over a 15 year record, the spring fed catchment had higher annual volumes and more stable flow yearly. With differing flow volumes, topographic and geomorphic metrics did not significantly differ between catchments. When compared to the PROSPER model, the spring-fed catchment had a over-prediction of dry conditions, whereas the non-spring fed catchment was both under and over predicted as dry depending on the water year. Our findings concluded that springs are a driver of stream permanence in headwater streams, which leads to a divergence from topographic and climatic controls on stream permanence. Springs as an added control has led to an over prediction of dry conditions in regional intermittent stream dataset and models. Findings will assist in defining Dry Creek stream expansion-contraction dynamics and improve active drainage network predictive models.