Water Resources Research Act Program

Details for Project ID 2012ID183B

The geomorphic signature of salmon: quantifying the impact of spawner density on stream bed morphology and habitat for future spawners to inform water resources management

Institute: Idaho
Year Established: 2012 Start Date: 2012-03-01 End Date: 2014-02-28
Total Federal Funds: $29,020 Total Non-Federal Funds: $50,336

Principal Investigators: Alexander Fremier, Elowyn Yager

Abstract: Current physical process models typically lack a coupled understanding of how organisms influence the physical landscape. A coupled understanding of biological and physical processes will improve our ability to predict ecosystem dynamics when environmental (bio-physical) drivers change. Salmon runs worldwide have been in steep decline over the last century, which has had wide reaching economic and cultural impacts. In recent years considerable progress has been made in understanding their decline, specifically the fluvial processes that create and maintain aquatic spawning habitat (NRC 1996). Here, spawning success is contingent upon stream bed grain size distributions and flow regimes (Chapman 1988; Bjornn & Reiser 1991); however, salmon are not passive inhabitants of riverine environments, but actively modify them when they build nests (redds) during spawning. This reciprocal feedback between salmon spawning activities and fluvial processes is increasingly being recognized as having a significant geomorphic effect (Gottesfeld et al. 2004; Hassan et al. 2008). Despite this awareness, we lack a mechanistic understanding of the influence of spawning on stream bed morphology, particle architectures, and importantly, redd stability. Such knowledge is an important scientific contribution because it will enable us to better predict redd removal during peak flow events (regulated or natural) as well as sediment transport rates for key salmon-bearing stream reaches. Accurately predicting sediment flux in salmon-bearing streams, and the potential impact to spawning on future stream habitats, will require a mechanistic understanding of how salmon influence channel bed conditions and sediment motion. In this proposal we ask, what is the influence of redd construction on grain size distributions and bed architecture (particle looseness, protrusion, exposure, and friction angles) and how does spawning affect flow requirements for stream bed mobilization on flow regulated channels? We hypothesize spawned beds will mobilize at lower flow magnitudes than unspawned beds. We further hypothesize that changes to particle architectures and grain size distributions by spawning requires modification of equations that predict friction angles, particle protrusion and exposure from the grain size distribution of an unspawned bed (e.g. Kirchner et al. 1990; Buffington et al. 1992). In this proposal, we will adjust existing force balance equations (e.g. Wiberg & Smith 1987) for predicting stream flow conditions required to mobilize spawned beds. Predictions will be tested in the flume and modifications to the force balance approach will be made to improve its prediction accuracy, if needed. Findings and products of this research will instruct and enable water managers to regulate stream flows to prevent scour of redds while eggs are incubating in the channel bed, and to mobilize the channel bed after eggs have hatched so that sediment conditions for spawning salmon are maintained. The overall goal of the research is to quantify the scale and extent that spawning disturbances to stream beds influence geomorphic processes and to advance a linked understanding of sediment transport, salmon biology, and river ecosystems. The first step in this research project is to refine the procedure for simulating scaled redds in a flume and begin to quantify the effects of redd building on stream bed structure and particle entrainment. This research is currently funded by USDA McIntire-Stennis Formula Funds for the salary of a PhD student and a series of flume and field studies over the next three years. Using the USG Section 104B funds, we will be able to fully support the PhD student (tuition and full summer salary) and hire another technician for the flume work. The USDA grant does not pay tuition, and therefore we request funds to cover tuition for two semesters. With these funds we will (1) perform a full literature review on redd morphologies measured by others; this will also include our existing field measurements of redd surface and subsurface morphology; (2) perform a set of flume experiments to develop a protocol for simulating a redd in a flume; and, (3) use our flume measurements of redd particle architectures to predict initial motion of spawned beds. The funds will support the PhD student‟s research and writing of manuscripts for publication. Moreover, this project initiates a long-term collaboration between investigators in the interdisciplinary field of eco-geomorphology‟.