A river is a natural flowing watercourse freshwater, flowing towards an ocean, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, brook and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location. Sometimes a river is defined as being larger than a creek, but not always: the language is vague. Rivers are part of the hydrological cycle. Potamology is the scientific study of rivers, while limnology is the study of inland waters in general. Most of the major cities of the world are situated on the banks of rivers, as they are, or were, used as a source of water, for obtaining food, for transport, as borders, as a defensive measure, as a source of hydropower to drive machinery, for bathing, as a means of disposing of waste.
A river begins at a source, follows a path called a course, ends at a mouth or mouths. The water in a river is confined to a channel, made up of a stream bed between banks. In larger rivers there is also a wider floodplain shaped by flood-waters over-topping the channel. Floodplains may be wide in relation to the size of the river channel; this distinction between river channel and floodplain can be blurred in urban areas where the floodplain of a river channel can become developed by housing and industry. Rivers can flow down mountains, through valleys or along plains, can create canyons or gorges; the term upriver refers to the direction towards the source of the river, i.e. against the direction of flow. The term downriver describes the direction towards the mouth of the river, in which the current flows; the term left bank refers to the left bank in the direction of right bank to the right. The river channel contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river.
Extensive braided rivers are now found in only a few regions worldwide, such as the South Island of New Zealand. They occur on peneplains and some of the larger river deltas. Anastamosing rivers are quite rare, they have multiple sinuous channels carrying large volumes of sediment. There are rare cases of river bifurcation in which a river divides and the resultant flows ending in different seas. An example is the bifurcation of Nerodime River in Kosovo. A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. In 1757, the German hydrologist Albert Brahms empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed; this formulation is sometimes called Airy's law. Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks.
A river valley, created from a U-shaped glaciated valley, can easily be identified by the V-shaped channel that it has carved. In the middle reaches where a river flows over flatter land, meanders may form through erosion of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake or billabong. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths. Rivers whose mouths are in saline tidal waters may form estuaries. Throughout the course of the river, the total volume of water transported downstream will be a combination of the free water flow together with a substantial volume flowing through sub-surface rocks and gravels that underlie the river and its floodplain. For many rivers in large valleys, this unseen component of flow may exceed the visible flow. Most but not all rivers flow on the surface. Subterranean rivers flow underground in caverns; such rivers are found in regions with limestone geologic formations.
Subglacial streams are the braided rivers that flow at the beds of glaciers and ice sheets, permitting meltwater to be discharged at the front of the glacier. Because of the gradient in pressure due to the overlying weight of the glacier, such streams can flow uphill. An intermittent river only flows and can be dry for several years at a time; these rivers are found in regions with limited or variable rainfall, or can occur because of geologic conditions such as a permeable river bed. Some ephemeral rivers flow during the summer months but not in the winter; such rivers are fed from chalk aquifers which recharge from winter rainfall. In England these rivers are called bournes and give their name to places such as Bournemouth and Eastbourne. In humid regions, the location where flow begins in the smallest tributary streams moves upstream in response to precipitation and downstream in its absence or when active summer vegetation diverts water for evapotrans
The Marchantiophyta are a division of non-vascular land plants referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information, it is estimated. Some of the more familiar species grow as a flattened leafless thallus, but most species are leafy with a form much like a flattened moss. Leafy species can be distinguished from the similar mosses on the basis of a number of features, including their single-celled rhizoids. Leafy liverworts differ from most mosses in that their leaves never have a costa and may bear marginal cilia. Other differences are not universal for all mosses and liverworts, but the occurrence of leaves arranged in three ranks, the presence of deep lobes or segmented leaves, or a lack of differentiated stem and leaves all point to the plant being a liverwort. Liverworts are small from 2–20 mm wide with individual plants less than 10 cm long, are therefore overlooked.
However, certain species may cover large patches of ground, trees or any other reasonably firm substrate on which they occur. They are distributed globally in every available habitat, most in humid locations although there are desert and Arctic species as well; some species can be a weed in gardens. Most liverworts are small, measuring from 2–20 millimetres wide with individual plants less than 10 centimetres long, so they are overlooked; the most familiar liverworts consist of a prostrate, ribbon-like or branching structure called a thallus. However, most liverworts produce flattened stems with overlapping scales or leaves in two or more ranks, the middle rank is conspicuously different from the outer ranks. Liverworts can most reliably be distinguished from the similar mosses by their single-celled rhizoids. Other differences are not universal for all mosses and all liverworts. Unlike any other embryophytes, most liverworts contain unique membrane-bound oil bodies containing isoprenoids in at least some of their cells, lipid droplets in the cytoplasm of all other plants being unenclosed.
The overall physical similarity of some mosses and leafy liverworts means that confirmation of the identification of some groups can be performed with certainty only with the aid of microscopy or an experienced bryologist. Liverworts have a gametophyte-dominant life cycle, with the sporophyte dependent on the gametophyte. Cells in a typical liverwort plant each contain only a single set of genetic information, so the plant's cells are haploid for the majority of its life cycle; this contrasts with the pattern exhibited by nearly all animals and by most other plants. In the more familiar seed plants, the haploid generation is represented only by the tiny pollen and the ovule, while the diploid generation is the familiar tree or other plant. Another unusual feature of the liverwort life cycle is that sporophytes are short-lived, withering away not long after releasing spores. In other bryophytes, the sporophyte is persistent and disperses spores over an extended period; the life of a liverwort starts from the germination of a haploid spore to produce a protonema, either a mass of thread-like filaments or else a flattened thallus.
The protonema is a transitory stage in the life of a liverwort, from which will grow the mature gametophore plant that produces the sex organs. The male organs produce the sperm cells. Clusters of antheridia are enclosed by a protective layer of cells called the perigonium; as in other land plants, the female organs are known as archegonia and are protected by the thin surrounding perichaetum. Each archegonium has a slender hollow tube, the "neck", down which the sperm swim to reach the egg cell. Liverwort species may be either monoicous. In dioicous liverworts and male sex organs are borne on different and separate gametophyte plants. In monoicous liverworts, the two kinds of reproductive structures are borne on different branches of the same plant. In either case, the sperm must move from the antheridia where they are produced to the archegonium where the eggs are held; the sperm of liverworts is biflagellate, i.e. they have two tail-like flagellae that enable them to swim short distances, provided that at least a thin film of water is present.
Their journey may be assisted by the splashing of raindrops. In 2008, Japanese researchers discovered that some liverworts are able to fire sperm-containing water up to 15 cm in the air, enabling them to fertilize female plants growing more than a metre from the nearest male; when sperm reach the archegonia, fertilisation occurs, leading to the production of a diploid sporophyte. After fertilisation, the immature sporophyte within the archegonium develops three distinct regions: a foot, which both anchors the sporophyte in place and receives nutrients from its "mother" plant, a spherical or ellipsoidal capsule, inside which the spores will be produced for dispersing to new locations, a seta which lies between the other two
Tywyn spelled to Towyn, is a town and seaside resort on the Cardigan Bay coast of southern Gwynedd, Wales. It was in the historic county of Merionethshire, it is famous as the location of the Cadfan Stone, a stone cross with the earliest known example of written Welsh, the home of the Talyllyn Railway. The name derives from the Welsh tywyn: extensive sand dunes are still to be found to the north and south of the town. In Middle Welsh, the spelling was Tywyn. In the Early Modern period, the spelling Towyn became common in order to reflect a slight change in pronunciation at that time; the modern spelling Tywyn better reflects the current pronunciation in modern Welsh as spoken in north Wales. With the standardisation of the orthography of the Welsh language in the first part of the 20th century, the spelling Tywyn came to dominate, was accepted as the official name of the town in both languages in the 1970s. In Welsh, the town is sometimes referred to as Tywyn Meirionnydd. In origin, this usage refers to the cantref of Meirionnydd, but is now understood as referring to the historical county of the same name.
In English, during the late 19th century and until the middle of the 20th century, the town was sometimes called Towyn-on-Sea. The place-name element tywyn is found in many other parts of Wales, most notably Towyn near Abergele. Tywyn was the location of the first religious community administered by the Breton saint Cadfan upon his arrival in Gwynedd, prior to his departure to found a monastery on Bardsey Island off the Llyn Peninsula; the church contains some early material. The town's historic centre lies around the church of St Cadfan's. In the second half of the 19th century the town expanded mainly towards the sea. To the north of the town lie the reclaimed salt marshes of Morfa Tywyn and Morfa Gwyllt, beyond which lie the Broad Water lagoon and the mouth of the Afon Dysynni. To the north-east lie the rich farmland of Bro Dysynni and the village of Bryncrug, to the east the hills of Craig y Barcud and Craig Fach Goch. To the south towards Aberdyfi is the mouth of the Afon Dyffryn Gwyn and Penllyn Marshes.
The Tywyn coastal defence scheme, a £7.6m civil engineering project, to provide a new rock breakwater above the low-tide level, rock groynes, rock revetment to protect 80 sea-front properties was unveiled by Jane Davidson, the Minister for Environment and Housing in the Welsh Assembly Government, on 24 March 2011. At the time of the 2001 census, 40.5% of the population were recorded as Welsh speakers. By the 2011 census this had decreased to 37.5%. These high figures reflect the use of both Welsh and English as the medium of instruction in Ysgol Penybryn, the town's primary school. An Estyn inspection report in 2010 noted that about 11% of the children at the school came from homes where Welsh was the main language; the town's Welsh dialect has several notable features, with one Victorian observer stating that three languages were spoken there: English, Welsh and'Tywynaeg'. During the 1860s, in the town's British School, a'Welsh stick' was used to punish children who were caught speaking Welsh.
Yet Welsh was the dominant language in Tywyn until the middle of the 20th century. Tywyn is now a anglicised town, with the majority of its population having been born in England according to the 2011 census. More respondents claimed an English-only identity than a Welsh-only identity; the church is of interest for two medieval effigies, for a stone inscribed with what is believed to be the oldest known writing in the Welsh language, dating back to the 8th century AD, rescued from a local gateway in the 18th century. Improved transport links during the 19th century increased Tywyn's appeal as a tourist destination. In the early decades of thatcentury, a creek of the river Dysynni allowed ships to approach the town's northern fringes, where there was a shipbuilding yard; the draining of the salt marsh and the channelling of the river brought this industry to an end, but during the early part of that century the town was made more accessible by building new roads along the coast to Aberdyfi and Llwyngwril.
The railway arrived in the mid-1860s, had a significant effect on the town. Tywyn railway station opened in 1863; the station is still open, is served by the Cambrian Line. Slate-quarrying in the Abergynolwyn area led to the building in 1865 of the Talyllyn Railway, a narrow-gauge line designed to carry slates to Tywyn. Two stations were opened in the town. Tywyn Wharf railway station was opened to enable slates to be unloaded onto a wharf adjacent to the main railway line, it is now the Talyllyn's western terminus and principal station. Pendre railway station was the passenger station, now houses the locomotive and carriage sheds and works. Notable visitors who stayed at Tywyn in the 19th century include: Thomas Love Peacock Thomas Fremantle, 1st Baron Cottesloe Ignatius Spencer Charles Darwin William Morris Elizabeth Blackwell The beach and its extensive promenade have long been key attractions. In 1877, a pier was built at Tywyn; the street called'Pier Road', which leads from the town to the beach, offers a suggestion as to its location.
The promenade was completed in 1889 at the cost of some £30,000, paid for by John Corbett of Ynysymaengwyn. There has been extensive bungalow
Salmon is the common name for several species of ray-finned fish in the family Salmonidae. Other fish in the same family include trout, char and whitefish. Salmon are native to tributaries of the North Pacific Ocean. Many species of salmon have been introduced into non-native environments such as the Great Lakes of North America and Patagonia in South America. Salmon are intensively farmed in many parts of the world. Salmon are anadromous: they hatch in fresh water, migrate to the ocean return to fresh water to reproduce. However, populations of several species are restricted to fresh water through their lives. Folklore has it. Tracking studies have shown this to be true. A portion of a returning salmon run may spawn in different freshwater systems. Homing behavior has been shown to depend on olfactory memory. Salmon date back to the Neogene; the term "salmon" comes from the Latin salmo, which in turn might have originated from salire, meaning "to leap". The nine commercially important species of salmon occur in two genera.
The genus Salmo contains the Atlantic salmon, found in the north Atlantic, as well as many species named trout. The genus Oncorhynchus contains eight species which occur only in the North Pacific; as a group, these are known as Pacific salmon. Chinook salmon have been introduced in New Patagonia. Coho, freshwater sockeye, Atlantic salmon have been established in Patagonia, as well. † Both the Salmo and Oncorhynchus genera contain a number of species referred to as trout. Within Salmo, additional minor taxa have been called salmon in English, i.e. the Adriatic salmon and Black Sea salmon. The steelhead anadromous form of the rainbow trout migrates to sea, but it is not termed "salmon". A number of other species have common names which refer to them as being salmon. Of those listed below, the Danube salmon or huchen is a large freshwater salmonid related to the salmon above, but others are marine fishes of the unrelated Perciformes order: Eosalmo driftwoodensis, the oldest known salmon in the fossil record, helps scientists figure how the different species of salmon diverged from a common ancestor.
The British Columbia salmon fossil provides evidence that the divergence between Pacific and Atlantic salmon had not yet occurred 40 million years ago. Both the fossil record and analysis of mitochondrial DNA suggest the divergence occurred by 10 to 20 million years ago; this independent evidence from DNA analysis and the fossil record rejects the glacial theory of salmon divergence. Atlantic salmon reproduce in northern rivers on both coasts of the Atlantic Ocean. Landlocked salmon live in a number of lakes in eastern North America and in Northern Europe, for instance in lakes Sebago, Ladoga, Saimaa, Vänern, Winnipesaukee, they are not a different species from the Atlantic salmon, but have independently evolved a non-migratory life cycle, which they maintain when they could access the ocean. Chinook salmon are known in the United States as king salmon or blackmouth salmon, as spring salmon in British Columbia. Chinook are the largest of all Pacific salmon exceeding 14 kg; the name tyee is used in British Columbia to refer to Chinook over 30 pounds, in the Columbia River watershed large Chinook were once referred to as June hogs.
Chinook salmon are known to range as far north as the Mackenzie River and Kugluktuk in the central Canadian arctic, as far south as the Central California coast. Chum salmon are known as dog, keta, or calico salmon in some parts of the US; this species has the widest geographic range of the Pacific species: south to the Sacramento River in California in the eastern Pacific and the island of Kyūshū in the Sea of Japan in the western Pacific. Coho salmon are known in the US as silver salmon; this species is found throughout the coastal waters of Alaska and British Columbia and as far south as Central California. It is now known to occur, albeit infrequently, in the Mackenzie River. Masu salmon or cherry salmon are found only in the western Pacific Ocean in Japan and Russia. A land-locked subspecies known as the Taiwanese salmon or Formosan salmon is found in central Taiwan's Chi Chia Wan Stream. Pink salmon, known as humpies in southeast and southwest Alaska, are found from northern California and Korea, throughout the northern Pacific, from the Mackenzie River in Canada to the Lena River in Siberia in shorter coastal streams.
It is the smallest of the Pacific species, with an average weight of 1.6 to 1.8 kg. Sockeye salmon are known in the US as red salmon; this lake-rearing species is found south as far as the Klamath River in California in the eastern Pacific and northern Hokkaidō island in Japan in the western Pacific and as far north as Bathurst Inlet in the Canadian Arctic in the east and the Anadyr River in Siberia in the west. Although most adult Pacific salmon feed on small fish and squid, sockeye feed on plankton they filter through gill rakers. Kokanee salmon are the land-locked form of sockeye salmon. Danube salmon, or huchen, are the largest permanent freshwater salmonid species. Salmon eggs are laid in freshwater streams at high latitudes; the eggs hatch into alevin or sac fry
The Rhinogydd are a range of mountains located east of Harlech in North Wales. The name Rhinogydd derives from the names of two of the more famous peaks, Rhinog Fawr and Rhinog Fach, although the greatest elevation in the range is reached by Y Llethr, 756 m. Foel Penolau, the northernmost summit of the range, was promoted to a Hewitt in 2018 due to a new survey; the Rhinogydd are notably rocky and heather-clad towards the northern end of the range around Rhinog Fawr, Rhinog Fach and towards Moel Ysgyfarnogod. The southern end, around Y Llethr and the Ysgethin Valley has a softer, grassy character. A population of feral goats are in the range. Over 30 km ² are protected as a Special Area of a National Nature Reserve; the Rhinogydd are formed of hard sedimentary rocks of Cambrian age which occur as a major anticlinal structure known to geologists as the Harlech Dome. This structure which originated during the Caledonian Orogeny extends from Cadair Idris in the south to Blaenau Ffestiniog in the north.
Its erosion by successive ice ages has left the peaks of the Rhinogydd visible today. The core of the area is formed from the hard-wearing greywackes of the Rhinog Formation; the formation contains and is overlain by some siltstones and mudstones which form a broken zone of softer scenery around the periphery of the area's rugged core. In places, swarms of dolerite dykes cut through the country rocks in a northwest-southeast direction. Much of the lower ground is mantled by a legacy of the last ice age; the geology of the area was first characterised by Adam Sedgwick and Roderick Murchison in 1835. The Geological Survey began work in the area in 1846 and their first maps were published in 1855. With the discovery of gold in the area in 1846, the state of geological knowledge increased dramatically. At least a dozen major publications appeared between 1844 and 1939; the Rhinogydd are far less well known than the areas in the north of the Snowdonia National Park, such as the Glyderau and the Snowdon massif itself.
This is due to the rugged nature of the landscape in the Rhinogydd and the fame of Snowdon as the highest peak in Wales. The Rhinog mountains are popular with hillwalkers looking for a more isolated, wilder walking experience; the peaks of the range are most accessed from the west side. Two valleys - Cwm Nantcol and Cwm Bychan - lead deep into the mountains and may be reached from the village of Llanbedr; the most popular walking route in this area begins at the Roman Steps at 52°51′16.76″N 4°0′18.43″W, which leads from Cwm Bychan through Bwlch Tyddiad and around Rhinog Fawr. Despite the name, these steps are not Roman and are in fact the well preserved remains of a medieval packhorse trail leading from Chester to Harlech Castle. At the top of the Roman Steps, the route curves around the eastern end of Rhinog Fawr and enters Cwm Nantcol via Bwlch Drws Ardudwy. A different path leads from Cwm Nantcol, passing around the western end of Rhinog Fawr back to Cwm Bychan via Gloywlyn, completing a circular route that can be completed in a day.
The range contains the following Marilyns: Y Llethr 756 m Rhinog Fawr 720 m Y Garn 629 m Moel Ysgyfarnogod 623 m Moelfre 589 mthe following Hewitts: Rhinog Fach 712 m Diffwys 750 m Foel Penolau 614 mand the following Nuttalls: Crib-y-rhiw 670 m Diffwys West Top 642 m Time Out - Wales. The new Umbria? 9 Walks in the Rhinog Mountains
Dolgellau is a market town and community in Gwynedd, north-west Wales, lying on the River Wnion, a tributary of the River Mawddach. It is traditionally the county town of the historic county of Merionethshire, which lost its administrative status when Gwynedd was created in 1974. Dolgellau is the main base for climbers of Cadair Idris; the site of Dolgellau was, in the pre-Roman Celtic period, part of the tribal lands of the Ordovices, who were conquered by the Romans in AD 77–78. Although a few Roman coins from the reigns of Emperors Hadrian and Trajan have been found near Dolgellau, the area is marshy and there is no evidence that it was settled during the Roman period. There are, three hill forts in the vicinity of Dolgellau, of uncertain origin. After the Romans left, the area came under the control of a series of Welsh chieftains, although Dolgellau was not inhabited until the late 11th or 12th century, when it was established as a "serf village" by Cadwgan ap Bleddyn — it remained a serf village until the reign of Henry Tudor.
A church was built in the 12th century, although Cymer Abbey, founded in 1198 in nearby Llanelltyd, remained the most important religious centre locally. Dolgellau gained in importance from this period onwards, was mentioned in the Survey of Merioneth ordered by Edward I. In 1404 it was the location of a council of chiefs under Owain Glyndŵr. After a visit by George Fox in 1657, many inhabitants of Dolgellau converted to Quakerism. Persecution led a large number of them to emigrate to Pennsylvania in 1686, under the leadership of Rowland Ellis, a local gentleman-farmer; the Pennsylvanian town of Bryn Mawr, home to a prestigious women's liberal arts college, is named after Ellis's farm near Dolgellau. The woollen industry was long of the greatest importance to the town's economy; the industry declined in the first half of the 19th century, owing to the introduction of mechanical looms. Another important contributor to the local economy was tanning, which continued into the 1980s in Dolgellau, though on a much reduced scale.
The town was the centre of a minor gold rush in the 19th century. At one time the local gold mines employed over 500 workers. Clogau St. David's mine in Bontddu and Gwynfynydd mine in Ganllwyd have supplied gold for many royal weddings. Dolgellau was the county town of Merionethshire until 1974 when, following the Local Government Act of 1972, it became the administrative centre of Meirionnydd, a district of the county of Gwynedd; this was abolished in 1996 by the Local Government Act 1994. Today, the economy of Dolgellau relies chiefly on tourism, it is believed that Dolgellau Cricket Club, founded in 1869 by Frederick Temple, is one of the oldest cricket clubs in Wales. For nearly a century Dolgellau was the home of Dr Williams School, a pioneering girls' secondary school; this was funded from the legacy of Daniel Williams the Welsh nonconformist of the 17th/18th century. The name of the town is of uncertain origin, although dôl is Welsh for "meadow" or "dale", gelli means "grove" or "spinney", is common locally in names for farms in sheltered nooks.
This would seem to be the most derivation, giving the translation "Grove Meadow". It has been suggested that the name could derive from the word cell, meaning "cell", translating therefore as "Meadow of cells", but this seems less considering the history of the name; the earliest recorded spelling is "Dolkelew", although a spelling "Dolgethley" dates from 1285. From until the 19th century, most spellings were along the lines of "Dôlgelly" "Dolgelley", "Dolgelly" or "Dolgelli". Thomas Pennant used the form "Dolgelleu" in his Tours of Wales, this was the form used in the Church Registers in 1723, although it never had much currency. In 1825 the Registers had "Dolgellau", which form Robert Vaughan of Hengwrt adopted in 1836. While this form may derive from a false etymology, it became standard in Welsh and is now the standard form in both Welsh and English, it was adopted as the official name by the local rural district council in 1958. Shortly before the closure of the town's railway station it displayed signs reading variously Dolgelly and Dolgellau.
Dolgellau is home to Coleg Meirion-Dwyfor. The site it occupies was home to Dr Williams' School, a direct grant grammar school for girls aged 7–18 established in 1875, it was named after its benefactor Dr Daniel Williams, a Nonconformist minister from Wrexham, who gave his name to Dr Williams's Library in Euston, London. The school closed in 1975. Dolgellau Grammar School, a boys' school, had been established in 1665 by the Rector of Dolgellau, Dr John Ellis, at Pen Bryn, before moving to its present site on the Welshpool road. In 1962, it became a comprehensive school under the name Ysgol y Gader, it has 310 pupils and, according to the latest inspection report by Estyn, it has a GCSE pass rate of 75%, which puts it in joint 11th place in Wales, makes it o