Oct 2
2009

Science Friday“Meandering rivers are common on Earth and other planetary surfaces, yet the conditions necessary to maintain meandering channels are unclear. As a consequence, self – maintaining meandering channels with cutoffs have not been reproduced in the laboratory…” until now.  Science Friday, a radio show on NPR, has just posted the following video of the first such model, which has been developed by UC Berkeley researchers.

“Experimental channels <like the one in the video above> are needed to explore mechanisms controlling migration rate, sinuosity, floodplain formation, and planform morphodynamics and to test theories for wavelength and bend propagation. Here we report an experiment in which meandering with near-constant width was maintained during repeated cutoff and regeneration of meander bends. We found that elevated bank strength (provided by alfalfa sprouts) relative to the cohesionless bed material and the blocking of troughs (chutes) in the lee of point bars via suspended sediment deposition were the necessary ingredients to successful meandering. Varying flood discharge was not necessary. Scaling analysis shows that the experimental meander migration was fast compared to most natural channels. This high migration rate caused nearly all of the bedload sediment to exchange laterally, such that bar growth was primarily dependent on bank sediment supplied from upstream lateral migration. The high migration rate may have contributed to the relatively low sinuosity of 1.19, and this suggests that to obtain much higher sinuosity experiments at this scale may have to be conducted for several years. Although patience is required to evolve them, these experimental channels offer the opportunity to explore several fundamental issues about river morphodynamics. Our results also suggest that sand supply may be an essential control in restoring self-maintaining, actively shifting gravel-bedded meanders.”

For the complete research article, see the Proceedings of the National Academy of Sciences.

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Jul 2
2009

And now for some local news.  The main source of drinking water in Raleigh, Falls Lake, has had some problems with nutrient levels and algal blooms.  The Neuse River, on which Falls Lake is located, already has a set of rules to regulate nutrient levels in stormwater runoff.  However, due to the sensitivity of the problems at Falls Lake, a combination of state and local officials in Wake County are pushing a plan for a speedier cleanup of the lake through the State Legislature.  This has great potential to affect Durham County, however, as much of the pollution appears to originate there.  The likely result would be an accelerated and expanded plan of retrofits to existing development to treat stormwater runoff.  It is also a potential double whammy for Durham too, as Jordan Lake, to its south, is currently undergoing development of a similar plan.  The difference for Durham, however, is that it uses Jordan Lake as a drinking water source.

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Jun 27
2009

Most people think of dams when they think of hydropower.  Traditionally, the dams have been used in part to build up potential energy by piling up water upstream and convert it to greater kinetic energy by running the water through batteries of turbines.  These structures have fallen out of favor as concern has grown as to their impact on wildlife, most especially as to salmon migration.  As a result, there are many mitigation measures such as fish ladders and some dams have been eliminated altogether.

However, there is another alternative in the use of turbines for hydropower: placement directly into natural currents and tides.  At this time, there are several initiatives to implement this design.  One company, Hydro Green Energy out of Houston, is installing these turbines in the Mississippi River at Hastings, Minnesota and in the East River at New York City. Another company, Free Flow Power Corp out of Massachusetts, is planning to install turbines in the Mississippi River in Louisiana.

This new use of technology does bring its own concerns, especially with river transport.  With dams, it is obvious where the hazard is and a set of locks may be provided in order to travel beyond the man-made obstruction.  These turbines are underwater, however, and the water level changes over time.  As a result, those operating river barges on the Mississippi are concerned that they may at some time run into the structures, thus both causing damage to each and disrupting a main artery of freight traffic.  It is therefore uncertain as to whether or not the Louisiana project will be allowed to proceed.

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Jun 26
2009

Reuters Media The Supreme Court recently upheld a permit issued under the Bush administration by the Army Corps of Engineers to allow a mining company to dump tailings from an Alaskan gold mining operation into Lower Slate Lake, which is located in the Tongass National Forest.  The Clean Water Act is supposed to prevent such discharges into natural waters, which is essentially what the appeals court had said in its previous ruling that the Supreme Court has now overturned.  Instead, the mining company, Coeur d’Alene Mines Corp, argued that the lake was the most practical and environmentally sound method of disposal.  Though this is likely to kill all aquatic life in the lake, it was argued that the lake could always be restocked with fish and restored once mining operations had ceased.  This claim seems suspicious to me, however, as gold mining operations have usually been associated with arsenic and I would suspect that such high levels would persist for some indefinitely long period of time.  Nonetheless, the 6-member court majority had said that deference must be paid to the “reasonable” decision made by the Corps of Engineers.  Unfortunately, what I read into this description is that one can get away with whatever the regulator can be convinced into allowing, however that might be accomplished.

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Apr 22
2009

FrontlineI happened upon this gem last night.  It is an episode of the PBS news magazine Frontline.  It is a summary of what problems face our waters today.  Primary examples of current threats include nutrients, endocrine disruptors, and PCBs.

Nutrients largely enter our waters from wastewater discharge and stormwater runoff contaminated with fertilizer and agricultural byproducts.  However, combustion byproducts found in automobile emissions also contain nutrients and find their way into open water in significant amounts.  These nutrients cause an explosion of microbial growth, which can reduce dissolved oxygen and kill everything that depends on it in the water, such as fish.  In fact, the problem has gotten so bad that oceanic dead zones have spread across the world.  One of the most famous occurs in the Gulf of Mexico around the Mississippi River delta.  It is in order to stop these occurrences that stormwater best management practices (BMPs) are required as part of most urban development, but agriculture is still largely unregulated.

Endocrine disruptors are chemicals that mimic hormones in the body.  They are used for this reason in drugs to treat certain conditions.  It also happens to be that certain industrial products happen to have this property.  A good example is bisphenol a (BPA), which is found in various plastics.  It happens to be used in many drink containers and, for this reason, public pressure has forced many baby bottle makers to go BPA-free.  The fear in this case is that boys will be femenized, possibly to the point of having fertility problems.  When endocrine disruptors make it into the wild, it has been known to make organisms that are genetically of one sex to develop as the other.  As far as I know, there is no current regulation of endocrine disruptors in our water (drinking, waste, or natural).

Polychlorinated biphenyls (PCBs) are an example of a kind of toxic  and possibly carcinogenic chemical that is also very persistent as they do not readily degrade.  PCBs are usually associated with old electrical facilities.  Because they are so persistent, PCBs can accumulate over time in animals from both what they eat and their surroundings.  Exposure can get worse from generation to generation as the PCBs can be passed from mother to baby.  The effect is that an entire population could potentially be killed by PCBs.  I have actually had the occasion to work on the design of road crossings of a stream contaminated by PCBs.  It was necessary to span the stream so as not to disturb it and potentially release any PCBs that might be contained in the soils and sediment.  The site has been designated a superfund site, though no cleanup has yet occurred.

If you watch the following video, it will take you through the history and the process by which Chesapeake Bay, Puget Sound, and other waters have been contaminated.  It will also document the effects this has had on the ecosystem and some of the efforts that have been made to mitigate them.  One obvious take-home message is: be careful where you fish.  Another one might be to be careful what you drink.

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