Terry J. Waddle

Effects of flow regulation on shallow-water habitat dynamics and floodplain connectivity

Abstract Our study examined the effects of flow regulation on the spatiotemporal availability of shallow habitat patches with slow current velocity (SSCV patches) and floodplain inundation in the unregulated Yellowstone River and the regulated Missouri River in Montana and North Dakota. We mapped representative sites and used hydraulic models and hydrograph data to describe the frequency and extent of floodplain inundation and the availability of SSCV habitat over time during different water years. In the Yellowstone River the distribution, location, and size of SSCV patches varied but followed an annual pattern that was tied to the snowmelt runoff hydrograph. There was less variation in patch distribution in the Missouri River, and the pattern of habitat availability was influenced by flow regulation. Regulated flows and their effects on channel morphology and patterns of vegetation establishment resulted in 3.0–3.5 times less area of inundated woody vegetation during normal and dry years in the Missouri...

IMPORTANCE OF THE TEMPORAL ASPECTS OF HABITAT HYDRAULICS TO FISH POPULATION STUDIES

The direct and indirect influences of hydrology and hydraulics on the usability of stream habitats by stream fish are discussed. Most habitat–hydraulic models in use today emphasize the spatial aspects of habitat quality and quantity. It is our contention that the temporal dynamics of habitat quantity are a major influence, determining fish population responses in riverine environments. This may manifest through dramatic shifts in the velocity and temperature distributions over seasons and years as influenced by climatic conditions as well as reservoir operations. Time series simulations of usable habitat available to various life stages of brown and rainbow trout and smallmouth bass populations demonstrate that the usable space and its stability during the early life history is directly translated into year-class-strength for these fish populations. Riverine ecosystems are temporally dynamic due to the stochastic nature of precipitation events. Therefore an understanding of the temporal aspects of streamflow and habitat is essential to designing water management schemes intended to protect, enhance or restore riverine fish populations.