I’m still reading a lot about rivers, and fish, and dams. Here are some particular standouts from the last week:
1. There is a connection between damming rivers and damage to coastal human communities; without the dam, sediment would end up on the shore, and support wetlands and other plant communities that would absorb storm surges. Without that protective barrier, everything on shore risks much greater destruction during a hurricane, tsunami, or major storm.
Here in the United States, we got a little dam crazy in the last few decades. With an estimated 75,000 dams in this country, many of which are obsolete, these structures have an immense impact. One major issue with dams is the sediment load. As erosion occurs upstream, all of the debris that would normally be washed downstream gets caught behind the dam. Far from merely an engineering issue, a dams nature to trap sediment has some serious ecological impacts as well.
Until humans came along, all major rivers eventually made their way to the coast. A free flowing river continually brings sediments from far inland, down to the mouth where they build up to form the foundation of coastal wetlands. Vegetation such as grasses and mangroves readily take root in these nutrient rich sediments, creating an amazingly rich and productive ecosystem. Less apparent, however, is the fact that these wetlands provide physical protection. Storm surges caused by things like hurricanes can send tons upon tons of water barreling towards the coast. In places where healthy wetland vegetation is present, these surges are absorbed and much of that water never has a chance to hit the coast. In areas where these wetlands have vanished, there is nothing stopping the full brunt of the surge and we end up with a situation like we saw following Katrina or Sandy. (Source)
In Delaware Bay, as in estuaries around the world, the search is on for any kind of hedge against future losses of coastal wetlands. This sense of urgency also comes from a new understanding of the value of wetlands: Coastal communities, faced with increasing storm activity and flooding, have realized that wetlands may provide the only real protection from floodwaters and ever higher tidal surges that can overwhelm once-protective embankments, bulkheads, and sea walls.
Scientists have discovered over the last few years that sea grass beds, salt marshes, and mangroves sequester and store far more carbon than equal areas of tropical forest. And because most of this “blue carbon” is stored in submerged soil, it is released far more slowly than carbon stored in forest vegetation. (Source)
2. Generally dams cause a lot of problems. A few examples from “12 dams that changed the world”:
Hoover: the dam that gave us Las Vegas
The Hoover Dam was the world’s highest and most powerful dam when it was completed in 1936. It spurred the agricultural and industrial development of the US southwest, and destroyed the Colorado river’s rich downstream fisheries. Climate change is greatly affecting the dam’s capacity to supply water and generate power.
Banqiao: the dam that washed away.
When dams are not properly built or maintained, they can break. In the world’s biggest dam disaster, the failure of China’s Banqiao Dam killed an estimated 171,000 people in 1975. In more than 100 cases, scientists have also linked dam building to earthquakes. Strong evidence suggests that China’s Sichuan earthquake, which killed 80,000 people in 2008, may have been triggered by the Zipingpu Dam.
Three Gorges: Mao’s dream come true
China’s Three Gorges Dam is the world’s largest hydropower project and was completed in 2008. It generates as much power as eight large nuclear power plants, displaced more than 1.2 million people, and ravaged the ecosystem of the Yangtze River. The Chinese government has acknowledged the problems of the project, but continues to export its technology overseas. (Source)
And it’s questionable if they are economically worth it:
The outside view suggests that in most countries large hydropower dams will be too costly in absolute terms and take too long to build to deliver a positive risk-adjusted return unless suitable risk management measures outlined in this paper can be affordably provided. Policymakers, particularly in developing countries, are advised to prefer agile energy alternatives that can be built over shorter time horizons to energy megaprojects.
3. In my part of the world, dams are also preventing some populations of orcas – the Southern Resident orcas, now at only 77 members – from having enough to eat, by having a major impact on salmon populations, which puts the orcas at a very high risk of extinction. There’s a petition going around via change.org to ask the Governor of Washington, and several other Washington state congresspersons, to push to have four dams on the Snake River (the biggest tributary of the Columbia) removed (part of many years of effort to have these dams removed). A 2009 article on the situation has this to say (Source):
… chinook, as explained in How Many Fish Do The Orcas Need, are the fish upon which Southern Resident orcas depend.
… Their movements are not well known, but scientists believe they forage along the coast, largely for spring/summer and fall Chinook from the Columbia/Snake, Klamath, and sometimes the Sacramento rivers to get them through the winters. The Columbia/Snake Chinook are close to their home waters and were historically the most abundant.
Since the Corps of Engineers completed the fourth of four dams on the lower Snake River in 1975, wild Snake River spring/summer Chinook have not once reached their extremely low recovery targets (the number of spawning salmon necessary to avoid extinction), which must be met for eight consecutive years before the species may be considered recovered. Fall Chinook have barely met recovery targets some years, but that target is low and the species remains threatened and teetering on extinction.
Most scientists agree that removal of the four lower Snake River dams would result in a big rebound of wild salmon that spawn there, along with a full range of wildlife (see below) and Puget Sound’s resident J, K and L pods. . .
. . .
The decline of Snake River salmon populations matters not only to orcas. As they decline, the entire Snake River watershed, an area the size of France, is gradually deprived of essential marine nutrients and chemicals that have been transported upriver for thousands of years by migrating salmon leaving their spawned-out carcasses alongside rivers and streams throughout the wilderness. Pacific Salmon and Wildlife describes the crucial role salmon play in supporting overall ecosystem health. Bears, eagles, otters and beaver are among the 138 animal species that have evolved with salmon as an important part of their diet, and even trees contain chemicals brought upstream by salmon. Indeed, there are lakes once made fertile by returning salmon that now must be artificially fertilized with custom-mixed batches of nutrients to sustain the food web that thrived there before the Snake River dams were built.