NSF Rapid Proposal: Flows of the future: Capitalizing on an extreme weather year to evaluate future summer streamflows in the Cascades

Oregon State University, Corvallis OR

Investigators

Abstract

Snow is a crucial moisture source for forests, aquatic ecosystems, and communities in the Pacific Northwest and across the western US. The winter of 2014-2015 was the warmest winter on record followed by an anomalously warm, dry spring resulting in historically low streamflows and early declarations of drought conditions across western Oregon. This hydrologic drought represents an overall decrease in streamflow that can be monitored conveniently by downstream gages. However the upstream impact of decreased streamflow is difficult to assess from downstream gages. It is therefore necessary to assess how headwater streams react to decreased rainfall and meteorologic drought. Understanding how headwater streams react (and by what mechanisms) to meteorologic drought will enable the interpretation of stream gage records in terms of upstream ecological response. The field campaign will provide undergraduates with valuable field training, conducting scientifically exciting and societally relevant research. This research effort will also provide the post-doctoral researcher with an opportunity to mentor and train undergraduates. The investigators will capitalize on this opportunity through a coordinated set of activities including: 1) meeting with public and private water supply and power utilities to provide a framework for future flow forecasting; 2) meeting with Federal and State land and water managers to share findings and discuss implications for water availability and ecological consequences of low flows; and 3) working with journalists to disseminate accurate real-time findings (similar to the monthly snow report). This proposal posits that headwater streams can respond to drought by contracting laterally or longitudinally. And that spring fed streams will respond with "jumps" from sequential spring outflow levels whereas surface flow fed stream will contract. These source regions for water will have chemically differing signatures which they can track. The study region includes (a) surface-flow dominated Western Cascades watersheds, representing a flashy streamflow regime with rapid baseflow recession and very low summer flows; and (b) the spring-fed High Cascades watersheds, representing a slow-responding streamflow regime with a long and sustained baseflow recession that maintains late summer streamflow through deep-groundwater contributions to high-volume coldwater springs. The investigators will use a field-based approach to collect and analyze data from both spring-fed and surface flow-dominated watersheds throughout the dry season, from approximately June through October (or first rainfall event of consequence). Summer streamflow recession will be monitored using USGS mainstem gages and project stage height/stream discharge relationships developed for our small streams. The longitudinal contraction hypotheses will be tested by repeat measurements of channel head locations in each watershed and continuous monitoring of water temperature (an indication of presence/absence of water) at headwater springs. The lateral contraction hypotheses of streams will be tested by repeat surveys of multiple transects per stream.