Closure begins about 9 hours before a dangerous high tide reaches the barrier. Messages give orders to stop river traffic, close subsidiary gates and alert other river users. As well as the Thames Barrier, the smaller gates along the Thames Tideway must be closed. Once river navigation has been stopped and all gates closed, then the Thames Barrier itself can be closed. The smaller gates are closed first, then the main navigable spans in succession. The gates remain closed until the tide downstream of the barrier falls to the same level as the water level upstream.
After heavy rain west of London, floodwater flows down the Thames upstream (before London). Because the river is tidal from Teddington weir all the way through London, "this is only a problem at high tide", which prevents the floodwater from escaping out to sea. From Teddington the river is opening out into its estuary, and at low tide it can take much greater flow rates the further one goes downstream.
When the river is in flood upstream, if the gates are closed shortly after low tide, a huge empty volume holds behind the barrier which can act as a reservoir to hold the floodwater coming over Teddington weir. Most river floods will not fill this volume in the few high tide hours when the barrier needs to be closed. If the barrier was not there, the high tide would fill up this volume instead, and the floodwater could then spill over the river banks in London. About a third of the closures up to 2009 were to prevent flooding caused by heavy rain to the west of London.
In the 1980s there were four closures, 35 closures in the 1990s, and 75 closures in the first decade of this century. The rate of closures is above that predicted, and is increasing rapidly.
An incident that was potentially catastrophic for London occurred on 27 October 1997. The dredger, MV "Sand Kite", sailing in thick fog, collided with one of the Thames Barrier's piers. As the ship started to sink she dumped her 3,300 tonne load of aggregate, finally sinking by the bow on top of one of the barrier's gates where she lay for several days. Initially the gate could not be closed as it was covered in a thick layer of gravel. A longer term problem was the premature loss of paint on the flat side of the gate caused by abrasion. One estimate of the cost of flooding damage, had it occurred, was around £13 billion. The vessel was refloated in mid-November 1997.
The barrier was closed twice on 9 November 2007 after a storm surge in the North Sea which was compared to the one in 1953. The main danger of flooding from the surge was on the coast above the Thames Barrier, where evacuations took place, but the winds abated a little and, at the Thames Barrier, the 9 November 2007 storm surge did not completely coincide with high tide.
The barrier was originally designed to protect London against a big flood level. The defence level included long-term changes in sea and land levels as understood at that time (~1970). Despite global warming, and a higher predicted rate of sea level rise, recent analysis suggested the barrier could last until around 2060–2070.
Released in 2005, a study by four respected academics contained a proposal to replace the Thames Barrier with a more ambitious 16 km (10 mi) long barrier across the Thames Estuary from Sheerness in Kent to Southend in Essex.
Environmental chemistry
Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. Environmental chemistry can be defined as the study of the sources, reactions, transport, effects, and fates of chemical species in the air, soil, and water environments; and the effect of human activity on these. Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as uses analytical chemistry. It is related to environmental and other areas of science. It is different from green chemistry, which tries to reduce potential pollution at its source.
Environmental chemistry starts by understanding how the uncontaminated environment works. It identifies the chemicals that are present naturally. It studies the concentration and effects of those chemicals. Then, it accurately study the effects humans have on the environment through the release of chemicals.
Environmental chemists draw on a range of concepts from chemistry and various environmental sciences to assist in their study of what is happening to a chemical in the environment. Important general concepts from chemistry include understanding chemical reactions and equations, solutions, units, sampling, and analytical techniques. Chemists study compounds with biological activity such as pheromones.
A contaminant is a substance present in nature at a level higher than typical levels or that would not otherwise be there. This may be due to human activity. The term contaminant is often used interchangeably with "pollutant", which is a substance that hurts the surrounding environment. While a contaminant is sometimes defined as a substance present in the environment as a result of human activity, but without harmful effects, it is sometimes the case that toxic or harmful effects from contamination only become apparent at a later date.
The "medium" (for example, soil) or organism (for example, fish) affected by the pollutant or contaminant is called a "receptor". A "sink" is a chemical medium or species that retains and interacts with the pollutant.
Chemical measures of water quality include dissolved oxygen (DO), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total dissolved solids (TDS), pH, nutrients nitrates and phosphorus, heavy metals (including copper, zinc, cadmium, lead and mercury), and pesticides.
Environmental chemistry is used by the Environment Agency (in England and Wales), the Environmental Protection Agency (in the United States) the Association of Public Analysts, and other environmental agencies and research bodies around the world to detect and identify the nature and source of pollutants. These can include:
Quantitative chemical analysis is a key part of environmental chemistry, since it provides the data that frame most environmental studies.
Common analytical techniques used for quantitative determinations in environmental chemistry include classical wet chemistry, such as gravimetric, titrimetric and electrochemical methods. More sophisticated approaches are used in the determination of trace metals and organic compounds. Metals are commonly measured by atomic spectroscopy and mass spectrometry: Atomic Absorption Spectrophotometry (AAS) and Inductively Coupled Plasma Atomic Emission (ICP-AES) or Inductively Coupled Plasma Mass Spectrometric (ICP-MS) techniques. Organic compounds are commonly measured also using mass spectrometric methods, such as gas chromatography–mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC/MS). Non-MS methods using GCs and LCs having universal or specific detectors are still staples in the arsenal of available analytical tools.
Other parameters often measured in environmental chemistry are radiochemicals. These are pollutants which emit radioactive materials, such as alpha and beta particles, posing danger to human health and the environment. Particle counters and Scintillation counters are most commonly used for these measurements. Bioassays and immunoassays are utilized for toxicity evaluations of chemical effects on various organisms.
Peer-reviewed test methods have been published by government agencies
Foster the People
Foster the People is an American indie pop band from Los Angeles, California. Foster the People have four members: Mark Foster, Isom Innis, Mark Pontius, and Sean Cimino. Their best known song is "Pumped Up Kicks" which was released on September 14, 2010 and reached #1 on Billboard's Alternative Songs chart, #3 on the Rock Songs tally and #3 on the Billboard Hot 100.