An adit (from Latin aditus , entrance) or stulm is a horizontal or nearly horizontal passage to an underground mine . Miners can use adits for access, drainage, ventilation, and extracting minerals at the lowest convenient level. Adits are also used to explore for mineral veins . Although most strongly associated with mining, the term adit is sometimes also used in the context of underground excavation for non-mining purposes; for example, to refer to smaller underground passageways excavated for underground metro systems , to provide pedestrian access to stations ( pedestrian adits ), and for access required during construction ( construction adits ).
20-679: Rheidol can refer to: Afon Rheidol , a river in Mid-Wales Vale of Rheidol Railway , a narrow-gauge railway in Mid-Wales Rheidol power station , a hydroelectric scheme on the Afon Rheidol Rheidol (locomotive) , a former locomotive on the Vale of Rheidol Railway Rheidol Falls railway station , a station on the Vale of Rheidol Railway Topics referred to by
40-850: A drainage adit can provide, they have sometimes been driven for great distances for this purpose. One example is the Milwr tunnel in North Wales, which is about ten miles (16 km) long. Other examples are the Great County Adit in Cornwall, a 40-mile (64 km)-long network of adits that used to drain the whole Gwennap mining area, and the 3.9 miles (6.3 km) Sutro Tunnel at the Comstock Lode in Virginia City , Nevada . A side benefit of driving such extensive adits
60-579: A narrow-gauge steam railway, the Vale of Rheidol Railway . This was originally built to ship metal ore from the mines, but now provides a very popular tourist route to the top end of the Rheidol valley. A large stag-like shape on the northern valley wall, above the Cwm Rheidol reservoir, known as the "White Stag", is traditionally said to be a hill figure but it is in fact an industrial feature, formed by
80-480: Is also much safer and can move more people and ore than vertical elevators. In the past horses and pit ponies were used. In combination with shafts, adits form an important element in the ventilation of a mine : in simple terms, cool air will enter through an adit, be warmed by the higher temperature underground and will naturally exhaust from vertical shafts, some of which are sunk specifically for this purpose. Most adits are designed to slope slightly upwards from
100-523: Is different from Wikidata All article disambiguation pages All disambiguation pages Afon Rheidol Afon Rheidol ( Welsh pronunciation: [ˈr̥ei̯dɔl] ; also known as the River Rheidol ) is a river in Ceredigion , Wales , 19 miles (31 km) in length. The source is Plynlimon . Receiving an average annual rainfall of 40 inches (1.02 m), Plynlimon is also
120-533: Is not a substantial stream. There are several other, larger streams, such as the Afon Hengwm, which rises to the south of Llyn Bugeilyn, just across the boundary in Powys . The Afon Llechwedd-mawr rises near Llyn Penrhaeadr and marks the boundary between Ceredigion and Powys along most of its course. There are some other lesser streams, including Nant y Moch, after which the reservoir is named. For many centuries
140-470: Is still in place and can be seen from the road. The reservoir is close to the site of the Battle of Mynydd Hyddgen (1401). The true geographical source of the river is difficult to determine. The traditional source is Llyn Llygad Rheidol, a lake in a high valley near the summit of Pen Pumlumon Fawr , as its name suggests ("Rheidol's Eye Lake"); the stream Nant y Llyn descends from it into the Afon Hengwm, but
160-605: The Wye and Severn . After flowing south to Ponterwyd in the increasingly deep valley, then southwest through Welsh Oak ancient woodland , it veers westwards to its confluence with the Afon Mynach , at Devil's Bridge, Ceredigion ( Welsh : Pontarfynach , lit. "bridge on the Mynach"), and a spectacular waterfall. The river continues, passing the abandoned workings of the Cwm Rheidol lead mine; one of many other metal mines in
180-431: The adit does not become blocked. All mine workings below both the drainage adit ("below adit") and the water table will flood unless mechanical means are used for drainage. Until the invention of the steam engine this was the main restriction on deep mining. Adits are useful for deeper mines. Water only needs to be raised to the drainage adit rather than to the surface. Because of the great reduction in ongoing costs that
200-472: The catchment (the area around Aberystwyth contains 38 of the 50 worst polluting metal mines in Wales), by 1991 the river had regularly broken EEC pollution limits for heavy metal contamination such as zinc . Upland Molinia spp. grassland is common growing on deep deposits of peat . Within the valleys, dense and ancient oak forests with rich understoreys of ferns , mosses and lichens are common. In
220-501: The economy of the Rheidol valley had been based on metal mining. This has now been replaced by forestry , tourism and the farming of beef , dairy cattle and sheep . There are a number of tourist attractions in the Rheidol valley. These include the village of Devil's Bridge and the Mynach Falls , where three bridges, each built over the previous, span the top of a spectacular gorge. Between Devil's Bridge and Aberystwyth runs
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#1732776653092240-526: The entrance so that water will flow freely out of the mine. Mines that have adits can be at least partly drained of water by gravity alone or power-assisted gravity. The depth to which a mine can be drained by gravity alone is defined by the deepest open adit which is known as the "drainage adit". The term mine drainage tunnel is also common, at least in the United States. Workings above this level (known as "above adit") will remain unflooded as long as
260-413: The ground is weak, the cost of shoring up a long adit may outweigh its possible advantages. Access to a mine by adit has many advantages over the vertical access shafts used in shaft mining . Less energy is required to transport miners and heavy equipment into and out of the mine. It is also much easier to bring ore or coal out of the mine. Horizontal travel by means of narrow gauge tramway or cable car
280-399: The mine was closed, a major blowout of water contained in an adit coloured the whole river an ochre orange colour and greatly added to the concentrations of lead and zinc in the river. Today, management of water still draining from the mine is by the use of constructed wetlands . Previous management had included a limestone filter bed installed in the 1960s and now redundant. The filter bed
300-411: The mineral vein outcrops at the surface, the adit may follow the lode or vein until it is worked out, in which case the adit is rarely straight. The use of adits for the extraction of ore is generally called drift mining . Adits can only be driven into a mine where the local topography permits. There will be no opportunity to drive an adit to a mine situated on a large flat plain, for instance. Also if
320-410: The same term [REDACTED] This disambiguation page lists articles associated with the title Rheidol . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Rheidol&oldid=768964254 " Category : Disambiguation pages Hidden categories: Short description
340-453: The source of both the Wye and the Severn . Originally formed at the confluence of the Afon Hengwm and Afon Llechwedd-mawr, the Rheidol now emerges as the outflow of Nant-y-moch Reservoir ( 52°27′32″N 3°50′06″W / 52.4590°N 3.8349°W / 52.4590; -3.8349 ( River Rheidol (source) ) ) on the western flanks of Plynlimon , near the sources of
360-418: The valley bottom, glacial and alluvial deposits have been worked by man into low intensive agriculture. 52°23′28″N 3°57′04″W / 52.391°N 3.951°W / 52.391; -3.951 Adit Adits are driven into the side of a hill or mountain, and are often used when an ore body is located inside the mountain but above the adjacent valley floor or coastal plain. In cases where
380-472: The valley – a source of extracted metal pollution of the river – and flows westwards before reaching its confluence with the Afon Ystwyth and the estuary at Aberystwyth to drain into Cardigan Bay . ( 52°24′26″N 4°05′23″W / 52.4071°N 4.0898°W / 52.4071; -4.0898 ( River Rheidol (mouth) ) ) In the late 1960s, when
400-409: The waste from lead mining at Gellireirin. The landmark has been visible for more than 100 years. The catchment of the Rheidol is dominated by the western maritime exposure of this part of Wales. Rainfall levels are high and ecosystems reflect both high rainfall and the acidic nature of the underlying rocks. Combined with the acid mine drainage from abandoned silver and lead mines that sit within
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