Friday, August 14, 2015

Braided streams

  1. What is a Braided stream?

    Simply, it is a stream consisting of multiple small, shallow channels that divide and recombine numerous times forming a pattern resembling the strands of a braidBraided streams form where the sediment load is so heavy that some of the sediments are deposited as shifting islands or bars between the channels.

    braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots. Braided streams occur in rivers with high slope and/or large sediment load.[1] Braided channels are also typical of environments that dramatically decrease channel depth, and consequently channel velocity, such as river deltasalluvial fansand peneplains.


    Braided rivers, as distinct from meanderingrivers, occur when a threshold level of sedimentload or slope is reached. Geologically speaking, an increase in sediment load will over time increase in the slope of the river, so these two conditions can be considered synonymous; and, consequently, a variation of slope can model a variation in sediment load. A threshold slope was experimentally determined to be 0.016 (ft/ft) for a 0.15 cu ft/s (0.0042 m3/s) stream with poorly sorted coarse sand.[1] Any slope over this threshold created a braided stream, while any slope under the threshold created a meandering stream or— for very low slopes—a straight channel. So the main controlling factor on river development is the amount of sediment that the river carries; once a given system crosses a threshold value for sediment load, it will convert from a meandering system to a braided system. Also important to channel development is the proportion of suspended load sediment to bed load. An increase in suspended sediment allowed for the deposition of fine erosion-resistant material on the inside of a curve, which accentuated the curve and in some instances caused a river to shift from a braided to a meandering profile.[1] The channels and braid bars are usually highly mobile, with the river layout often changing significantly during flood events.[2] Channels move sideways via differential velocity: On the outside of a curve, deeper, swift water picks up sediment (usually gravel or larger stones), which is re-deposited in slow-moving water on the inside of a bend.
    The braided channels may flow within an area defined by relatively stable banks or may occupy an entire valley floor. The Rakaia River in Canterbury, New Zealand has cut a channel 100 metres wide into the surrounding plains; this river transports sediment to a lagoon located on the river-coast interface.
    Conditions associated with braided channel formation include:
    • an abundant supply of sediment[3]
    • high stream gradient[4]
    • rapid and frequent variations in water discharge[4]
    • erodible banks
    • a steep channel gradient
    However, the critical factor that determines whether a stream will meander or braid is bank erodibility. A stream with cohesive banks that are resistant to erosion will form narrow, deep, meandering channels, whereas a stream with highly erodible banks will form wide, shallow channels, inhibiting helical flow and resulting in the formation of braided channels.[5]


    Extensive braided river systems are found in AlaskaCanadaNew Zealand's South Island, and the Himalayas, which all contain young, rapidly eroding mountains.
    • The enormous Brahmaputra-Jamuna River in Asia is a classic example of a braided river.[6]
    • Braided river system are present in Africa, for example in the Touat Valley.
    • A notable example of a large braided stream in the contiguous United States is the Platte River in central and western Nebraska. The sediment of the arid Great Plains is augmented by the presence of the nearby Sandhills region north of the river.
    • A portion of the lower Yellow River takes a braided form.[7]
    • The Sewanee Conglomerate, a Pennsylvanian coarse sandstone and conglomerate unit[8] present on the Cumberland Plateau near the University of the South, may have been deposited by an ancient braided and meandering river that once existed in the eastern United States.[9]Others have interpreted the depositional environment for this unit as a tidal delta.[10]
    Notable braided rivers in Europe:
    • Italy
      • Tagliamento (Northeastern Italy)
      • Piave (river)
      • Brenta (river)
      • Cellina
      • Meduna
      • Fella
      • Magra
    • Narew (Poland and Belarus)

Monday, August 10, 2015

What is Anthracite?

Coal 101: What is Anthracite?

Coal 101: What is Anthracite?

Anthracite is a type of coal that is made almost entirely of carbon, and as a result is much harder than other forms of coal. 

Its low pollutant content allows it to burn cleaner than other types of coal, according to United Coal Holdings (TSXV:UCL), an ability that makes it preferred in many applications. As a result, companies that mine it tend to advertise those capacities.

How is anthracite used?

Anthracite is mainly used for heating — while it’s difficult to burn, anthracite produces more heat than other varieties of coal. It is also a common charcoal ingredient. By itself, anthracite is used in steam-based power generators and in liquid form can be used to power internal combustion engines. Anthracite also plays a role in steel production, and is often used to make coal-fired food.

Despite these myriad uses, anthracite does have some disadvantages. For instance, it is quite expensive due to its high quality, and as such isn’t often used in power plants or as a replacement fuel for gasoline. It’s also difficult to ignite, though for industrial applications that barrier is easy to overcome.

Where is anthracite mined?

Anthracite is most commonly found in mountainous regions, as well as near volcanoes and in areas where earthquakes are the norm. Unsurprisingly, there is a large supply of anthracite in the Appalachian Mountains in the United States, with 6 billion tons in that region alone, as per United Coal. There are also reserves in the Rocky Mountains and the Andes.

In the US, Pennsylvania, which is located in the Appalachian region, is the state with the highest anthracite production, Coal Diver states. Though production declined precipitously in the late 1990s and early 2000s, the region still produces plenty of the fuel — in 2010, the figure was 1,842,857 tons of anthracite. That is a decrease from 1998′s record of 5,234,201 tons, but it is still a significant amount of anthracite.

Which companies mine anthracite?

  • Reading Anthracite is a private Pennsylvania-based mining company that was established in 1871. It concentrates on the mining and distribution of anthracite for many purposes, and delivers standard or custom anthracite to industrial clients that need high-grade carbon. The company also provides products for space heating and water and sewage filtering.

Reading’s projects are surface-mining sites in Pennsylvania, and one of the company’s aims is to make sustainable reclamation plans for each of them. To date, its reclamation projects have resulted in wildlife sanctuaries, parks and housing developments.

  • Blaschak Coal, also a private company based in Pennsylvania, was founded in 1937, acquiring its first mine in 1945. It is one of the top anthracite producers in the US, and produced close to 1 million tons of raw coal in 2012. It holds three mines and two processing facilities.

The company obtains land that was previously mined and reopens it for use in production. Like Reading Anthracite and other coal producers in the area, Blaschak ensures its projects are slated for reclamation after they close, turning them into forest land in most cases.

  • Lehigh Anthracite, another Pennsylvania-based company, is a joint venture between Robindale Energy Services and BET Entities, both of which are privately owned. The company mines from the Mammoth, Forty-Foot, Primrose and Orchard seams at the Lehigh anthracite mine, which is the largest surface-mining permit in Pennsylvania. It processes its products on site and has the capacity to produce up to 500,000 tons of anthracite yearly.