Emerging Reservoir Delta‐Backwaters: Biophysical Dynamics and Riparian Biodiversity

Malia A Volke,W Carter Johnson,Mark D Dixon,Michael L Scott

doi:10.1002/bes2.1537

Abstract

Dams have been built on most of the world's large rivers. Thousands more are being proposed in countries with developing economies. Dams have major ecological consequences for river systems, including the loss of native riparian forests. Sediment that historically moved downstream and sustained coastal deltas is now accumulating at tributary and mainstem confluences in reservoirs worldwide. Our study found that vegetation communities similar to those destroyed in reservoirs are re-establishing on these emerging delta-backwaters. This understudied expansion of riparian forest is compensating, to a yet unknown degree, for the massive losses of ecosystem services caused by river damming. Photo credit: Gray Tappan. Photo credit: Malia Volke. Photo credit: Malia Volke. Photo credit: Malia Volke. Photo credit: Gray Tappan. These photographs illustrate the article “Emerging reservoir delta-backwaters: biophysical dynamics and riparian biodiversity” by Malia A. Volke, W. Carter Johnson, Mark D. Dixon, Michael L. Scott published in Ecological Monographs. https://doi.org/10.1002/ecm.1363

Highlights

The world’s rivers are regulated by over 59,000 large dams (>15 m high; ICLD 2018)
The downstream portions of this reach were periodically inundated by high reservoir stages, while the upstream portions of this reach experienced increased overbank flooding that resulted from decreases in the White River channel slope as the stream adjusted to a new base level
Valley cross sections indicated that minor amounts of sediment deposition occurred above maximum reservoir stage and as far as 31 rkm upstream of the pre-dam White River–Missouri River confluence

Summary

Introduction

The world’s rivers are regulated by over 59,000 large dams (>15 m high; ICLD 2018). Flow regulation by dams has major ecological consequences for riverine ecosystems and biota. Dams transform rivers by fragmenting river networks (Jansson et al 2000, Nilsson et al 2005), replacing bottomlands with artificial reservoirs, disrupting natural patterns of sediment transport, and altering seasonal variation in stream flow (Poff et al 1997). The physical processes involved in delta formation are well understood from coastal delta research (Giosan and Bhattacharya 2005) with delta form and vegetation assemblages dictated by stream flow, sediment particle size, sediment depositional patterns, and the timing, frequency, and duration of inundation on newly deposited substrates (Johnson et al 1985, White 1993). Reservoir deltas form in response to the same physical processes that produce river mouth deltas, but on different time scales.

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Discussion

Conclusion