The gravel-bed river floodplain as affected by human structures. (A to D) Illustration shows the loss of floodplain natural complexity as a result of human infrastructure shoreline housing and transportation corridor (A), rip-rap as a bank-hardening structure (B), geomorphic modification of levee construction (C), and a dam at the top of the floodplain (D). Note that, in this cutaway view, the hyporheic zone is highly reduced and modified from that shown in Figs. 2 and 5 as the river is converted into a functional single-thread river with little cut-and-fill alluviation across the floodplain. This results in the loss of highly sorted, open-network cobble substrata and further loss of the interstitial flow pathways of the hyporheic zone. When modified, most ecosystem components illustrated in Fig. 5 are significantly reduced or eliminated from the floodplain system. Graphic: E. Harrington

By Jim Robbins
4 January 2017 (Yale e360) – The Yellowstone River has its headwaters in the mountain streams and snowy peaks of the famous U.S. national park with the same name, and makes an unfettered downhill run all the way to the Missouri River, nearly 700 miles away. It is the longest undammed river in the Lower 48 states. Last August, the Yellowstone made national headlines when a parasite killed thousands of fish, mostly whitefish. Fear of spreading the parasite to other waterways forced Montana officials to close the river to fishermen, rafters, and boaters. At the height of summer, the stunningly scenic, trout-rich river was eerily deserted. Fishing re-opened in the fall, but the parasite has been found in other Montana waterways. That a non-native parasite somehow got into a river may seem like an unremarkable occurrence. But a new, expansive model of gravel-bed river systems in mountainous areas, such as the Yellowstone, depicts a more complex scenario in which a host of human activities combine to degrade river systems and render them more vulnerable to destructive outside influences such as parasites. This body of research — 40 years in the making, but much of it summed up in a recent paper — rewrites the understanding of the ecological dynamics of these rivers. And it casts a harsh light on human river valley activities such as homebuilding, dam construction, irrigation, and channelization that may be slowly choking highly dynamic river systems — and the biodiversity that depends on them — to death. […] Most of the world’s gravel-bed rivers have experienced degradation, and in many places managers are trying to walk back the damage. On the Snake River near Jackson, Wyoming, for example, local and federal officials are working to restore riparian habitat damaged by the construction of 22 miles of 15-foot-high flood-control levees in the mid-20th century. The levees enabled some construction to take place in the floodplain, but deprived the river of its ability to flood and carry out other ecological functions. In Europe, most mountain rivers have been tamed dramatically over the past several centuries. The Drava River — which flows out of the Alps through Croatia and Austria and into the Danube — has been constrained historically by farming, hydroelectric dams, and flood control. In recent years, however, conservationists and government officials have launched major restoration programs to reconnect tributaries and floodplains and to restore riparian areas of the Drava. The life that depends on healthy, mountain river systems is legion. The recent paper, published in the journal Science Advances, brought together an array of researchers from different disciplines, from bear biologists, to ornithologists, to ungulate biologists. They were surprised to find the large number of species that rely heavily on the biodiversity generated by the Yellowstone ecosystem, not just fish and other aquatic species. [more]

New Look at Rivers Reveals The Toll of Human Activity

ABSTRACT: Gravel-bed river floodplains in mountain landscapes disproportionately concentrate diverse habitats, nutrient cycling, productivity of biota, and species interactions. Although stream ecologists know that river channel and floodplain habitats used by aquatic organisms are maintained by hydrologic regimes that mobilize gravel-bed sediments, terrestrial ecologists have largely been unaware of the importance of floodplain structures and processes to the life requirements of a wide variety of species. We provide insight into gravel-bed rivers as the ecological nexus of glaciated mountain landscapes. We show why gravel-bed river floodplains are the primary arena where interactions take place among aquatic, avian, and terrestrial species from microbes to grizzly bears and provide essential connectivity as corridors for movement for both aquatic and terrestrial species. Paradoxically, gravel-bed river floodplains are also disproportionately unprotected where human developments are concentrated. Structural modifications to floodplains such as roads, railways, and housing and hydrologic-altering hydroelectric or water storage dams have severe impacts to floodplain habitat diversity and productivity, restrict local and regional connectivity, and reduce the resilience of both aquatic and terrestrial species, including adaptation to climate change. To be effective, conservation efforts in glaciated mountain landscapes intended to benefit the widest variety of organisms need a paradigm shift that has gravel-bed rivers and their floodplains as the central focus and that prioritizes the maintenance or restoration of the intact structure and processes of these critically important systems throughout their length and breadth.

Gravel-bed river floodplains are the ecological nexus of glaciated mountain landscapes