Emerging reservoir delta‐backwaters: biophysical dynamics and riparian biodiversity

Abstract

Deltas and backwater‐affected bottomlands are forming along tributary and mainstem confluences in reservoirs worldwide. Emergence of prograding deltas, along with related upstream hydrogeomorphic changes to river bottomlands in the backwater fluctuation zones of reservoirs, signals the development of new and dynamic riparian and wetland habitats. This study was conducted along the regulated Missouri River, USA, to examine delta‐backwater formation and describe vegetation response to its development and dynamics. Our research focused specifically on the delta‐backwater forming at the confluence of the White River tributary and Lake Francis Case reservoir. Objectives of the research were to: (1) describe and analyze the process of delta‐backwater formation over space and time; (2) determine by field sampling and GIS mapping how vegetation has responded to development of the delta‐backwater; and (3) compare the woody plant communities of the delta‐backwater to those along free‐flowing and regulated remnant river reaches. In response to base level changes caused by reservoir filling, the thalweg of the lower 31 km of the original White River channel and adjacent floodplain aggraded by up to 12 m between 1954 and 2011. The overall channel slope flattened from 0.70 to 0.29 m/km. Riparian Populus–Salix forests increased in area by nearly 50% during the post‐dam period by colonizing new deltaic and floodplain deposits. Many of the native woody species found along natural and regulated river reaches were also found on the delta‐backwater. Woody species sorted along a fluvial to delta gradient; wetland affiliated species (Salix spp., Typha spp.) dominated the delta‐backwater near the reservoir while riparian species (Populus, Fraxinus) dominated in upstream portions of the delta‐backwater. This habitat complex supports young stands of native riparian vegetation now in decline in remnant reaches protected from flooding.

Reservoir fish assemblage structure across an aquatic ecotone: Can river‐reservoir interfaces provide conservation and management opportunities?

“…Despite calls to embrace a more holistic approach incorporating the structural and functional connections between rivers and reservoirs, these systems continue to be managed independently (Buckmeier, Smith, Fleming, & Bodine, 2014; Cowx & Gerdeaux, 2004; Miranda, Habrat, & Miyazono, 2008; Wurtsbaugh et al., 2015). Formation of delta areas in the riverine and transitional zones of reservoirs mimics historically available habitats in unregulated river reaches, such as connected floodplains with submerged terrestrial vegetation and large backwater habitats (Buckmeier et al., 2014; Volke, Johnson, Dixon, & Scott, 2019; Volke, Scott, Johnson, & Dixon, 2015). River‐reservoir interfaces might not be conducive to some species life histories such as drifting early life stages of pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson) (Guy et al., 2015), pelagic broadcast spawning minnows (Dudley & Platania, 2007; Hoagstrom, Archdeacon, Davenport, Propst, & Brooks, 2015; Perkin & Gido, 2011), or periodic strategists and benthic species (Arantes, Fitzgerald, Hoeinghaus, & Winemiller, 2019).…”

“…This leads to shifts in species distributions as lotic‐adapted species are commonly found in upstream riverine and transitionary habitats, while more lentic‐adapted species are found in downstream lacustrine habitats (Matthews, Gido, & Gelwick, 2004; Nobile et al., 2019; Yang, Gao, Li, Ma, & Liu, 2012). Many native species are adapted to lotic habitats, whereas some might use both lentic and lotic habitats and benefit from resources available at the lotic‐lentic interface that are limiting in upstream river fragments, such as low velocity and highly productive nursery habitat (Bestgen et al, 2011; Volke et al., 2019; Volke et al., 2015). There is a need to further understand mechanisms governing species distributions and potential interactions in river‐reservoir systems where native and non‐native species co‐occur (Clarkson, Marsh, Stefferud, & Stefferud, 2005; Gido et al., 2002; Oliveira, Minte‐Vera, & Goulart, 2005).…”

Two Dimensional Model for Backwater Geomorphology: Darby Creek, PA

“…In addition to coastal areas, dammed rivers are also subjected to backwater (BW) conditions. Dams act as blocks on rivers and by forming backwater conditions, change the water surface profile upstream [7][8][9][10][11]. By 2018, there were more than 59,000 large dams built all around the world [8].…”

“…Dams act as blocks on rivers and by forming backwater conditions, change the water surface profile upstream [7][8][9][10][11]. By 2018, there were more than 59,000 large dams built all around the world [8]. In US itself, there are more than 2 million low-head dams [10] which alter the hydraulics, sediment erosion and deposition regime of the rivers due to BW conditions [9].…”

Study on Backwater Effect Due to Polavaram Dam Project under Different Return Periods

“…The upstream of the river affected by this response would exceed several hundreds of kilometers in low slope rivers, which is termed as the backwater zone [1]. Dams act as a block on rivers and by forming backwater conditions, which in turn affect the water surface profile at upstream of the river [2][3][4][5][6]. There have been numerous studies on dams that these hydraulic structures can limit discharge and elevate water level at the upstream by creating backwater [7,8].…”