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 River compared with the Yellowstone River. The differences we observed in SSCV patch dynamics between rivers may have implications for fish populations and community structure through affecting the survival of early life stages. At a larger scale, the smaller area of vegetation inundated in the Missouri River suggests that nutrient cycling and the ecological benefits associated with a moving littoral zone are reduced by the altered flow and sediment regime in that river. Accurate assessments of the effects of flow alteration and successful efforts to restore riverine ecosystems will require consideration of physical and biotic processes that operate at multiple spatial and temporal scales.

Metric-Resolution 2D River Modeling at the Macroscale: Computational Methods and Applications in a Braided River

“…Several studies have used rasterized 2D hydrodynamic model outputs to classify hydraulic habitat types such as riffles, pools, glides, and runs according to constant or adaptive ranges of hydraulic variables (Bowen et al, 2003;Legleiter and Goodchild, 2005;Moir and Pasternack, 2008;Wyrick et al, 2014). Classification of habitat based on local hydraulics is challenging.…”

Larval fish abundance in relation to environmental variables in two Texas Gulf Coast rivers

“…Flood pulses may provide spawning cues and floodplain inundation creates temporary but productive aquatic habitats for spawning and larval growth and survival (Junk et al 1989). As flood pulses recede, they leave behind shallow, low-velocity habitats that often are 'hot spots' for aquatic primary production (Bowen et al 2003;Hoagstrom & Turner 2013). Spawning during flood pulses allows larvae and their predators to disperse at low densities within a greatly expanded volume of aquatic habitat, which should reduce both predation mortality and competition for food resources (Hoagstrom & Turner 2013).…”

Impacts of flow regulation on slackwaters in river channels

“…Terms including ''backwater,'' ''still littoral habitats'' [King, 2004;Price, 2007], ''inshore nursery zone,'' ''dead zone'' [Reynolds et al, 1991;Schiemer et al, 2001], and ''still-water patches'' [Price, 2007] are used to describe similar hydraulic environments characterized by low velocity and often shallow depths, irrespective of the international context [Schiemer et al, 2001;Bowen et al, 2003;King, 2004]. We describe slackwaters as small, shallow areas of water that exhibit little or no discernible current, relative to the main flow thread within the channel.…”