tracer-rockGravel mobility and sediment transport are important river features that influence the quantity and quality of fish habitat. Studying how these processes change over time can help determine the amount of habitat available for fish. At low river flows, sediment transport decreases, and particles suspended in the water settle into the spaces between gravel on the riverbed. Known as sedimentation, this process can negatively affect fishes because it decreases the amount of oxygen in the gravel available to their eggs, reduces the availability of macroinvertabrates for food, and makes it difficult for salmonids to dig redds for spawning. However, if river flows are too high, gravel is swept downstream into deep pools, making the habitat unusable for salmonid spawning. FISHBIO uses tracer rocks to study sediment movement by methodically placing marked rocks in a river channel and measuring the rate of downstream movement at varying flows. Such data can inform management strategies about river flows to maintain suitable salmonid habitat.

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