Here's the White Salmon River returning to it's natural course after about 100 years (thanks to an exploding dam!):
Preeeetttty neat. The idea is to restore the river and its surroundings to a more natural state for the wildlife. And also, I hope, for the sake of exploding something.
(io9 via National Geographic.)
Courtesy Azure BevingtonYou might have heard about the terrible flooding that is occurring all along the Mighty Mississippi. As I write this I am sitting in Baton Rouge, Louisiana hoping the levees will hold. Normally the river in Baton Rouge is far below the tops of the levees. Flood stage, which is the water level at which the river would begin to flood surrounding areas without the levees acting as barriers, is 35 ft. Right now the water level is 42.8 ft and has risen 8 ft in just the last week. It is projected to crest at 47.5 ft and remain at that level for 8 to 10 days; this is higher than the previous record set in May 1927 of 47.28 ft. The tops of the levees that protect Baton Rouge are between 47 and 50 ft, they are currently sandbagging in areas less than 48 ft. Besides the possibility of overtopping there are also other problems that we need to look out for. When the river level remains high for an extended period of time the water can seep in and begin to saturate the soil, this can possibly weaken the levee structure. There is also the possibility of water going under the levee; this can result in sand boils, where the water bubbles up through the soil. It is very unlikely that this will happen, as the levees are strong and well constructed, but we need to be on the lookout for any problems.
Here in Baton Rouge we are much better off than many who live in communities within the Atchafalaya Basin, where the expected opening of the Morganza spillway could cause flooding of over 3 million acres (Click here to see a map of projected flooding in the basin) Many of these folks have already begun to sandbag their homes and to prepare to leave the area. The Morganza spillway is a large controlled gated structure that will divert water from the Mississippi River into the Atchafalaya Basin. The Atchafalaya Basin is a low lying cypress swamp that normally receives 30% of the flow of the Mississippi River through the Old River Control structure through the Atchafalaya River that winds its way through the swamp. This flood is projected to be larger than the 1973 flood and possibly even larger than the 1927 flood that devastated communities along the river, and brought about the passage of Flood Control Act of 1928. The magnitude of this year’s flood has already resulted in the opening of the Bonnet Carré spillway which diverts water into Lake Pontchartrain, this reduces the water levels as the River flows past New Orleans.
Stay tuned for updates on the flooding in Louisiana.
Have any of you been affected by the flood waters?
Courtesy Robert and Mihaela VicolFish and tomatoes compete for resources.
Yep, they do, and that resource is water.
The authors of a new report out in this week's issue of the journal Science are reminding folks of that fact.
John Sabo, a biologist at Arizona State University and lead author of the report told NSF News that "Humans may need to make hard decisions about how to allocate water so that we grow the right food, but still leave enough in rivers to sustain fish populations."
His comments stem from the report's findings that human actions--agricultural irrigation, dam construction, and the collective activities that lead to climate change--alter the natural variability of river flows and in the process shorten river food chains, particularly eliminating top predators like many large-bodied fish.
Courtesy Pete McBride
"Floods and droughts shorten the food chain, but they do it in different ways," Sabo explained. "Floods simplify the food web by taking out some of the intermediate players so the big fish begin to eat lower on the chain," Sabo said. "With droughts, it's completely different: droughts eliminate the top predator altogether because many fish can't tolerate the low oxygen and high temperatures that result when a stream starts drying out."
Sabo and co-authors--Jacques Finlay, from the University of Minnesota, Theodore Kennedy from the U.S. Geological Survey Southwest Biological Science Center, and David Post from Yale University--suggest that the fate of large-bodied fishes should be more carefully factored into the management of water use, especially as growing human populations and climate change affect water availability.
According to Sabo, "The question becomes: can you have fish and tomatoes on the same table?"
The Role of Discharge Variation in Scaling of Drainage Area and Food Chain Length in Rivers
John L. Sabo, Jacques. C. Finlay, Theodore Kennedy, and David M. Post (14 October 2010)
Science [DOI: 10.1126/science.1196005]
[It's Blog Action Day 2010, and this year's theme is water.]
Alright, it's absolutely beautiful outside today. So what's up with this predicted flooding?
Remember all that rain the week of September 20th? (We got 2-4" here in the Twin Cities, but areas to the southwest of us got as much as 10".)
Courtesy National Weather Service
It all had to go somewhere, and that somewhere was the Minnesota River. Why does that affect us here in St. Paul? Take a look at another map:
Courtesy NASA (Landsat)
Remember: rivers don't necessarily flow south. The reddish line is the Minnesota River. The blue is the Mississippi. And that little blip just north of where the two rivers come together is downtown St. Paul. (The yellow elipse is the area of highest rainfall.)
All that rain is flowing right past us. And it should be impressive. The river's at 15.4' this morning (moderate flood stage), and predicted to crest at 18' (major flood stage) on Saturday morning. But the recent spate of lovely weather means that the flooding should pass quickly--today's prediction has the water level back under 17" by Monday morning.
St. Paul police have closed all the river roads and parks, and are discouraging people from walking down by the river. But you can get a stellar view of everything from outside the Museum on Kellogg Plaza, or inside the museum from the Mississippi River Gallery on level 5.
Last night, bkennedy, a couple other SMM staff members, and I attended the Bell Museum's Cafe Scientifique at Bryant-Lake Bowl in Minneapolis. Robert Twilley, a principal investigator with the National Center for Earth-Surface Dynamics, came to speak about the endangered environment of the Mississippi Delta and the BP Deep Horizon Oil Spill. I didn't expect to get a history lesson, but it's just this kind of broad-ranging perspective that will help us understand what is happening to our environment.
It was frustrating to hear Dr. Twilley recount how, as a result of the 1928 Flood Control Act, civil engineers literally remade the Mississippi River and its delta in response to severe flooding events. While this had the temporary effect of protecting area residents from flooding, the plan neglected an important quality of all coastlines: they're dynamic. As sea level has risen over the last century, diverted sediments no longer replenish key areas of the delta and vast stretches of wetland are drowning--the same stretches of wetland that would protect people in the event of a strong hurricane. As a result of the levees, regular floods no longer wash sediments into the area. To complicate matters, projects such as dams farther upstream have cut the overall sediment supply to the Mississippi by about 50 percent in the last couple centuries.
Twilley emphasized that it wasn't as if people didn't know the problems these strategies would cause; engineers who opposed flood control tried to call attention to the associated risks. But in the wake of disastrous floods, the public demanded visible public works projects and politicians wanted to please them. Engineers who supported flood control saw it as a noble enterprise to control nature and protect people. And so today we have a tricky situation in the delta area. Disasters increase in intensity, and with them, peoples' insistence on solutions grow. But Twilley cautioned that it is imprudent to act on impulse, especially due to a widespread lack of understanding about how coastal systems work, and to our tendency to favor human safety without consideration for the environment that supports our safety. In short, we undermine ourselves.
"Since 1932, the basin has lost approximately 70% of its total land area."
When Hurricane Katrina hit, the same channel intended to give port access to ships funneled the storm surge farther inland. Twilley described how this perfect storm of civil engineering amplified the devastation brought by the Category 3 hurricane. The response to this devastation, rather than stepping back to reevaluate the situation and consider new ways to accommodate both the delta's needs and humans' needs, was to build a surge barrier that does nothing to restore the natural systems that once built and sustained that landscape over centuries. Contrary to engineers' intentions, Twilley asserted that these strategies will only exacerbate rising sea level and storm surge in the future as the wetlands drown further and the coastline moves inland.
Twilley also explained how, more recently, a lack of recognition of the complex systems in the river delta and along the Gulf Coast exacerbated BP's Deepwater Horizon Oil Spill. BP's front end study on the potential impacts of a spill found no cause for concern that the oil would reach the shore. And yet, in spite of booms placed along the coast, the oil did reach the shore, infiltrating wetlands already threatened by rising sea levels and weakened by lack of sedimentation. Thanks to the use of dispersants, the oil is difficult to find and we may not know the full impact of the spill for some time.
This paints a pretty grim picture of the future, but Twilley left us with cause for hope. In one of the areas to which a significant portion of sediment was diverted, the wetlands are actually growing (Atchafalaya). Twilley and his colleagues hope that this and other examples will demonstrate the importance of these natural wetland-building systems and garner support for their plain to mitigate the wetland loss. They want to add river outlets in strategically important places throughout the delta to rebuild the wetlands and help stabilize the landscape. These outlets would only operate during flooding episodes--an approach called controlled flooding (as opposed to the current strategy of flood control), siphoning off extra water and sediment to starved wetlands AND preventing flooding into human settlements. Currently, they're also involved in a project to pipe sediment to areas that need it.
Of course, the new outlet plan won't be without some compromise on the part of humans--some may have to relocate. But given projections of the area for 2100, relocation isn't far off anyway. And the long-term protective benefits of restoring the wetlands might just be worth it.
With forty-four percent of our 3.5 million miles of rivers and streams degraded due to sedimentation and excess nutrients, stream restoration has become big business in the United States. Estimates show that over $1 billion has been spent on stream restoration projects in the U.S. in every year since 1990.
Trouble is, the field of stream restoration lacks a lot of scientific rigor, making the prediction of successful restoration strategies difficult. Take, for example, one of the most commonly used tools of the trade—the in-stream structure. Man-made, in-stream structures (think small wall jutting out into the water from a stream bank) are frequently used in stream restoration and management to try to stabilize beds and banks or to improve aquatic habitat. Despite the frequency with which they are used however, engineering standards for the design and installation of the structures are inadequate, a problem that would be good to remedy if we are to make reliable predictions about whether a given stream restoration strategy or project will succeed.
Establishing comprehensive, quantitative engineering guidelines for in-stream structure installation and maintenance is far from simple though. The underlying physical processes that govern the behavior of a stream and its inhabitants are very complex. To deal with the complexity, researchers at the National Center for Earth-surface Dynamics (NCED) have come up with a novel approach—build a near-field scale experimental stream and a computational “virtual” stream to help elucidate the underlying interactions of water, sediment, and biota.
The experimental stream is the Outdoor Stream Lab (OSL) that sits right on the Mississippi River. The virtual stream is the (surprise, surprise) “Virtual StreamLab” (VSL) that exits as code within massively parallel supercomputers. This past summer, NCED researchers were able to complete their first simulation of a real stream (the OSL) using the VSL (see the video above). The simulation involved mapping more than 90 million data points into the computer model. The result was the most accurate model of a real stream to date.
The ability to simulate water flow over topography with this degree of realism will provide researchers with the insights necessary to improve sustainable stream restoration strategies and help to optimize techniques to fight erosion, prevent flooding, and restore aquatic habitats. NCED researchers are currently using their simulation to develop comprehensive, quantitative design, installation, and maintenance standards for in-stream structures.
With so many miles of degraded streams and rivers in the United States, the VSL is a good step in the right direction for the design and use of in-stream structures specifically, and for the field of stream restoration generally.
The Outdoor StreamLab is located in one of the most interesting spots in Minneapolis, in fact the very birthplace of the city--the area in and around St. Anthony Falls. This special place has long been important to indigenous people, was the center of a great deal of industrial development, and now is a hub for recreation.
Find out more at the St. Anthony Falls Heritage Zone site
of listen to a wonderful ode to the area from Peter Smith at MPR.
Look out the window or walk down the street to nearly any river or stream in Minnesota right now and you are likely to observe two things about the river:
You can, of course, confirm these observations by investigating reports from gauging stations along these rivers, maintained by the U.S. Geological Survey. (See data for the gauging station serving downtown St. Paul.) But what is really happening?
Courtesy Liza Pryor
Until a river flows over its banks, it is considered to be in a “bankfull” state. In this state, the water flowing through the river is confined to a relatively fixed channel area. Simply put, floods occur because more water is being introduced into this channel from upstream, due to snowmelt, heavy rains, or a dam breach. As this added volume of water moves through a fixed area, it both increases in velocity and in depth until it overflows the banks, at which point some, but not necessarily a lot, of the volume and velocity moving through the channel are reduced.
Scientists call the rate of flow through a channel “discharge." Discharge is defined as the volume of water passing through a given cross-section of the river channel within a specified period of time.A simple equation for determining discharge is
Q = D x W x V
where Q = discharge, D = channel depth, W = channel width and V = velocity.
Looking at this equation, it is easy to see that if discharge becomes greater and channel width is fixed, then an increase in both volume and depth (or height relative to the banks) is likely to be the cause. Discharge can be measured in cubic feet per second or cubic meters per second, for example.
But is the river flowing at the same rate at the surface as it does along its banks and beds? Understanding this requires investigating some more detailed equations, as the banks and bed introduce friction, which affects the rate of flow.
To learn more about rivers and how they flow, you may want to check out the works of Luna Leopold, and M. Gordon Wolman. In particular:
Also, check out our full feature on the 2010 Mississippi River flooding.