In Search of Living Rivers
By Sabra Purdy
Warning: This is a nerdy post written by a fish dork who actually thinks hydrology is cool. Read it anyway. It is really cool and it is really important, and you should know all about it.
Free flowing rivers are an endangered species on this planet. For most of the developed world, massive clusters of dams control river flow and levees prevent the river from escaping the confines of its channel. This is the anatomy of a modern river. But the consequences for rivers and all of the species that depend on them have been dire. A river’s floodplain, the low lying land immediately adjacent to a river, is a place of unimaginable importance. It is the place where flooding is absorbed and relieved, where water can sink down slowly and recharge the groundwater, filling wells. Floodplains support tremendous biodiversity above ground as well.
In California’s great Central Valley, many rivers come together and there would have once been tremendous seasonal wetlands that covered much of the valley floor. Nearly all of the native fish that live in California’s rivers evolved to use these richly productive seasonal habitats packed with nutritious bugs and zooplankton. These species took advantage of the warmer floodplain temperatures, abundant food, and respite from the strong, cold currents that rip through a flood-swollen river channel.
California’s rivers once teemed with migrating Chinook salmon whose young used the floodplains for some seriously concentrated eating and growing on their way out to the ocean where they spend as many as six years before returning to their natal stream to spawn and die, thus completing their life cycle. Body size at the time of ocean entry is a huge determinant of salmon survival success, so the bigger these little fish grow before going into the ocean, the more likely they are to live.
- Folsom Dam Folsom Dam on the American River blocks upstream migration for thousands of salmon. A hatchery was built here to mitigate the losses, but hatchery fish have been shown to be inferior and losses continue. Photo by U.S. Army Corps of Engineers Digital Visual Library
- Floodplains of the Sacramento River Floodplains of the Sacramento River doing their job. Photo by www.sacramentoriver.org
- Sacramento River Levees Sacramento River Levees. An example of the extensive leveeing that constrains nearly all of the rivers in California’s Central Valley. Note the extensive development in the natural floodplain. Photo by U.S. Army Corps of Engineers Digital Visual Library
This is why places like the Amur River, pictured at the top of this blog, are so very precious. The Amur is the third longest free flowing river in the world. It supports the world’s largest salmonid species, the Taimen, a land locked salmon that can grow to over a meter in length. It supports grazing, agriculture, industry, and commerce, yet it does all this without the constraints of dams.
The loss of floodplains has had a profoundly disastrous impact on salmon. Where California’s rivers once supported millions of adult fish annually, many of the salmon runs are just a faint shadow of their historical numbers and falling. Many rivers no longer even support salmon because dams have blocked their access to the places they need for spawning and floodplains are blocked off from outmigrating young by thousands of miles of levees.
Most rivers in California are not only dammed but sustain multiple dams. The Yuba River, in the northern Sierra Nevada has a whopping 32 dams on it. Flood control and cheap power may seem like a good idea to a lot of people, and indeed, it has allowed unprecedented development to occur in areas that should never have seen houses, shopping malls, gas stations and the like. But so much alteration and control of water flow has made it virtually impossible for many aquatic species to persist. We conservation biologists are doing all that we can to remedy this, but it’s a struggle.
With this hare-brained expedition, we have a rare chance to document the lost phenomenon of a free flowing river and the animals and plants that depend on it. What fascinates me most is to see how people have adapted to the realities of a living river that is wild and unconstrained. As an ecologist I am giddy with excitement at the opportunity to study a wild river in its native state. I cannot wait to wade the floodplains with nets and meters and see everything going on in this most precious and rare environment so we can bring this amazing resource home to inform our care, management, and restoration of our own rivers.
- Lower Amur River The unconstrained floodplain of the Lower Amur River.
- Full floodplain access Another river with full access to it's floodplain
- Salmon spring Healthy Salmonid fish populations-- just one of the many benefits of free-flowing rivers.
- Meandering The natural meander bends and floodplain of an undammed river.
- Full circle An enormous meander bend on the Lower Amur river.
For more information on science and the Nobody’s River Project go to https://nobodysriver.org/science.