.
105-728: The Trabancos is a river in Spain that flows between the Zapardiel and the Guareña rivers, and is a tributary of the Duero river . The source of the Trabancos is in Moraña , a region in the north of the province of Ávila , near Blascomillán. The Trabancos is at an elevation of approximately 1,100 metres (3,600 ft), is approximately 85 kilometres (53 mi) long and, although its river bed
210-495: A colluvium buildup of gravels with rounded stones of quartz and quartzite . The terraces of the Trabancos River only occur on the left hand side of the valley. Their sediments overlie Miocene sediments . This is the result of a hard slope in the opposite margin, where the terrain is heavily eroded, which renders the formation and maintenance of river terraces impossible. Of the previously mentioned river terraces,
315-465: A characteristic of Spanish steppes , which are only water-filled during the winter. From a conservation standpoint, such ponds, like nearby segments of the Trabancos River's banks, are in a precarious ecological state. Nevertheless, the areas are still capable of sustaining the flora and fauna commensurate with a natural riverside environment. The Trabancos region stands out for its concentration of great bustards (more than 2000); as well as having
420-575: A confined channel and is free to spread out and infiltrate the surface. This reduces the carrying capacity of the flow and results in deposition of sediments. The flow can take the form of infrequent debris flows or one or more ephemeral or perennial streams. Alluvial fans are common in the geologic record , such as in the Triassic basins of eastern North America and the New Red Sandstone of south Devon . Such fan deposits likely contain
525-484: A conflict of interest since the region was under Castilian rule, and Salamanca belonged to the crown of León. In fact, the Salmantinos created new parishes, like Siete Iglesias de Trabancos in 1167, and Alaejos in 1185. Looking at the Trabancos today and at a time when it is dry, it might seem preposterous that at one time it held a position of strategic importance for the town of Medina del Campo , and also, for
630-558: A debris flow can come to a halt while still on moderately tilted ground. The flow then becomes consolidated under its own weight. Debris flow fans occur in all climates but are more common where the source rock is mudstone or matrix-rich saprolite rather than coarser, more permeable regolith . The abundance of fine-grained sediments encourages the initial hillslope failure and subsequent cohesive flow of debris. Saturation of clay-rich colluvium by locally intense thunderstorms initiates slope failure. The resulting debris flow travels down
735-401: A document found in the 'Book of Loans' of Salamanca cathedral, which records the result of a new conflict: the battle between the dioceses of Salamanca and Segovia for the possession of the parishes to the east of the Trabancos; an area that hitherto had been accorded little worth. Salamanca had made use of the frontier struggles to take possession of the towns of Medina del Campo, provoking
840-514: A hiatus of 70,000 to 80,000 years between the old and new fans, with evidence of tectonic tilting at 45,000 years ago and an end to fan deposition 20,000 years ago. Both the hiatus and the more recent end to fan deposition are thought to be connected to periods of enhanced southwest monsoon precipitation. Climate has also influenced fan formation in Death Valley , California , US, where dating of beds suggests that peaks of fan deposition during
945-664: A lag of gravel deposits that have the appearance of a network of braided streams. Where the flow is more continuous, as with spring snow melt, incised-channel flow in channels 1–4 meters (3–10 ft) high takes place in a network of braided streams. Such alluvial fans tend to have a shallower slope but can become enormous. The Kosi and other fans along the Himalaya mountain front in the Indo-Gangetic plain are examples of gigantic stream-flow-dominated alluvial fans, sometimes described as megafans . Here, continued movement on
1050-443: A million people were rendered homeless, about a thousand lost their lives and thousands of hectares of crops were destroyed. Buried alluvial fans are sometimes found at the margins of petroleum basins. Debris flow fans make poor petroleum reservoirs, but fluvial fans are potentially significant reservoirs. Though fluvial fans are typically of poorer quality than reservoirs closer to the basin center, due to their complex structure,
1155-502: A minimum, major structural flood control measures are required to mitigate risk, and in some cases, the only alternative is to restrict development on the fan surface. Such measures can be politically controversial, particularly since the hazard is not obvious to property owners. In the United States, areas at risk of alluvial fan flooding are marked as Zone AO on flood insurance rate maps . Alluvial fan flooding commonly takes
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#17327733046121260-426: A narrow canyon emerging from an escarpment . They are characteristic of mountainous terrain in arid to semiarid climates , but are also found in more humid environments subject to intense rainfall and in areas of modern glaciation . They range in area from less than 1 square kilometer (0.4 sq mi) to almost 20,000 square kilometers (7,700 sq mi). Alluvial fans typically form where flow emerges from
1365-409: A part of the fan with a steeper gradient, where deposition resumes. As a result, normally only part of the fan is active at any particular time, and the bypassed areas may undergo soil formation or erosion. Alluvial fans can be dominated by debris flows ( debris flow fans ) or stream flow ( fluvial fans ). Which kind of fan is formed is controlled by climate, tectonics , and the type of bedrock in
1470-485: A prosperous tourist industry has developed based on river excursions from Porto to points along the Upper Douro valley. The Douro railway line ( Linha do Douro ) was completed in 1887; it connects Porto, Rio Tinto, Ermesinde, Valongo, Paredes, Penafiel, Livração, Marco de Canaveses, Régua, Tua and Pocinho. Pocinho is near the very small city of Foz Côa, which is close to Côa Valley Paleolithic Art site. This
1575-498: A short truce in 1204 thanks to the marriage of Alphonse IX of León to his niece, Berenguela of Castile); but the marriage was annulled by her father because of the close blood-relationship of the spouses. Finally, the Crowns of both kingdoms were taken by King Ferdinand III of Castile . The logical conclusion of these events was that the border was heavily militarized, involving the building of castles and reinforcements of troops in
1680-473: A streamflow-dominated alluvial fan shows nearly the same depositional facies as ordinary fluvial environments, so that identification of ancient alluvial fans must be based on radial paleomorphology in a piedmont setting. Alluvial fans are characteristic of mountainous terrain in arid to semiarid climates , but are also found in more humid environments subject to intense rainfall and in areas of modern glaciation. They have also been found on other bodies of
1785-538: A striking plate fragment with red gloss, resembling those that were carried by Roman legionaries on military campaigns . In the Middle Ages , the area remained a zone of little interest. No written documents exist prior to the 12th century that mention the region. It is known, however, that between 711 and 740 AD the Berbers had stationed troops in the valley of the Duero , but the majority of these peoples left
1890-419: A water content between 40 and 80 weight percent. Floods may transition to hyperconcentrated flows as they entrain sediments, while debris flows may become hyperconcentrated flows if they are diluted by water. Because flooding on alluvial fans carries large quantities of sediment, channels can rapidly become blocked, creating great uncertainty about flow paths that magnifies the dangers. Alluvial fan flooding in
1995-517: Is a result of the severity of the land and weather in the Trabancos valley and its surrounding regions. Possibly, during the pre-Roman period the territory was a no-man's-land between the Hispanic tribes of the Vaccei and Vettoni . Some archaeological remains have been found in the municipality of Siete iglesias de Trabancos ( Valladolid ), but they are not well preserved, having been situated on
2100-686: Is a town names Zorita de la Frontera ("Zorita on the Border") in memory of those times). These fortresses were reinforced in the 12th and 13th centuries due to conflicts between the two kingdoms; but it appears that they are more plentiful on the Castilian side (near the Trabancos) than on the Leonese side (near the River Guareña). This has been seen as indicative of a certain independence on
2205-489: Is also host to numerous gamebirds , including the red-legged partridge ( Alectoris rufa ). Despite their importance, the population of little bustard ( Tetrax tetrax ) in the region appear to be diminishing. Although not all the species protected in this ZEPA SPA can be listed, the protected area is a migratory crossing site and wintertime nesting area that, along with the Riberas de Castronuño (Valladolid) nature reserve,
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#17327733046122310-525: Is an accumulation of sediments that fans out from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment . This accumulation is shaped like a section of a shallow cone , with its apex at the source of sediments. Alluvial fans vary greatly in size, from only a few meters across at the base to as much as 150 kilometers across, with a slope of 1.5 to 25 degrees. Some giant alluvial fans have areas of almost 20,000 square kilometres (7,700 sq mi). The slope measured from
2415-438: Is approximately in equilibrium with erosion, so the river annually carries some 100 million cubic meters (3.5 × 10 ^ cu ft) of sediment as it exits the mountains. Deposition of this magnitude over millions of years is more than sufficient to account for the megafan. In North America , streams flowing into California's Central Valley have deposited smaller but still extensive alluvial fans, such as that of
2520-824: Is cognate with modern Breton dour and Cornish dur "water" and results from a later typical Brittonic evolution of *dubro- , unknown in the Continental Celtic languages . The possible origin is the hydronymic root *dur- , which is Pre-Indo-European or Pre-Celtic . Albert Dauzat linked this river name to a Pre-Celtic hydronymic root *dor- , which is well attested in Western Europe : in France Doire , Doron , Douron, etc. and in Italy Dora , etc. The meaning of this element is, however, unknown. A folk-etymological derivation suggests that
2625-569: Is considered important to the archaeological pre-historic patrimony, and it has been designated as a UNESCO World Heritage Site . Fifteen dams have been built on the Douro to regulate the water flow, generate hydroelectric power , and allow navigation through locks . Beginning at the headwaters, the first five dams are in Spain: Cuerda del Pozo , Los Rábanos , San José , Villalcampo and Castro Dams . The next five downstream are along
2730-432: Is described as fanglomerate . Stream flow deposits tend to be sheetlike, better sorted than debris flow deposits, and sometimes show well-developed sedimentary structures such as cross-bedding. These are more prevalent in the medial and distal fan. In the distal fan, where channels are very shallow and braided, stream flow deposits consist of sandy interbeds with planar and trough slanted stratification. The medial fan of
2835-539: Is frequented by many waterfowl ( cranes , geese , etc.), some of which even take advantage of the area ephemeral ponds for nesting during humid winters. 41°26′56″N 5°11′02″W / 41.449°N 5.184°W / 41.449; -5.184 Douro The Douro ( UK : / ˈ d ʊər oʊ , ˈ d ʊər uː / , US : / ˈ d ɔːr uː , ˈ d ɔːr oʊ / , Portuguese: [ˈdo(w)ɾu] , Mirandese : [ˈdowɾʊ] ; Spanish : Duero [ˈdweɾo] ; Latin : Durius )
2940-469: Is greatly eroded; although some sections survive to the south of the municipality of Alaejos ( Valladolid ), they are very difficult to differentiate from the colluvium floor that covers the Superficie de Alaejos . Entering into land in the municipality of Pollos , the stream stops to form river terraces, cutting traversely and lowering enough (between 40 and 60 meters) to meet the terrace deposits of
3045-568: Is located adjacent to low-relief terrain. In Nepal , the Koshi River has built a megafan covering some 15,000 km (5,800 sq mi) below its exit from Himalayan foothills onto the nearly level plains where the river traverses into India before joining the Ganges . Along the upper Koshi tributaries, tectonic forces elevate the Himalayas several millimeters annually. Uplift
3150-438: Is most likely composed of round grains of water ice or solid organic compounds about two centimeters in diameter. Alluvial fans are the most important groundwater reservoirs in many regions. Many urban, industrial, and agricultural areas are located on alluvial fans, including the conurbations of Los Angeles, California ; Salt Lake City, Utah ; and Denver, Colorado , in the western United States, and in many other parts of
3255-585: Is stable, only has a constant water flow during and immediately after torrential rains . From its source in the province of Ávila, to its mouth in the village of Pollos ("Village of Chickens" in Spanish) in the Vallisoletana ( "confluence of waters" ) region, the course of the Trabancos is markedly affected by a geologic fault originating in the Tertiary era —likely pre- Pliocene that, like most of
Trabancos (river) - Misplaced Pages Continue
3360-760: Is the largest in the Autonomous Community of Castile and León , since it covers almost 1,400 square kilometres, including the Campo de Peñaranda (in Salamanca ), the Moraña (in Ávila) and, especially, a large part of the Tierra de Medina del Campo . In all, 73% of the territory of the Trabancos ZEPA SPA corresponds to the province of Valladolid. The designated region is largely uninhabited —97% of
3465-648: Is the largest river of the Iberian Peninsula by discharge. It rises near Duruelo de la Sierra in the Spanish province of Soria , meanders briefly south, then flows generally west through the northern part of the Meseta Central in Castile and León into northern Portugal . Its largest tributary (carrying more water than the Douro at their confluence) is the right-bank Esla . The Douro flows into
3570-562: The Acheulean period are found on the surface (not as a result of archeological excavation), including centripetally knapped lithic cores , others displaying non-arranged lithic reduction , as well as lithic flakes characteristic of both the Levallois and Kombewa techniques, chopping tools , and handaxes . Only ambiguous archaeological evidence has been found dating from the late Roman period . It has been suggested by some that this
3675-753: The Aldeadávila Dam impounds the river, there are protected areas: the International Douro Natural Park (on the Portuguese side) and the Arribes del Duero Natural Park (on the Zamoran margin). The Douro fully enters Portuguese territory just after the confluence with the Águeda River ; once the Douro enters Portugal, major population centres are less frequent along the river. Except for Porto and Vila Nova de Gaia at
3780-625: The Apennine Mountains of Italy have resulted in repeated loss of life. A flood on 1 October 1581 at Piedimonte Matese resulted in the loss of 400 lives. Loss of life from alluvial fan floods continued into the 19th century, and the hazard of alluvial fan flooding remains a concern in Italy. On January 1, 1934, record rainfall in a recently burned area of the San Gabriel Mountains , California , caused severe flooding of
3885-585: The Atlantic Ocean at Porto , the second largest city of Portugal. The scenic Douro railway line runs close to the river. Adjacent areas produce port (a mildly fortified wine) and other agricultural produce. A small tributary of the river has the Côa Valley Paleolithic Art site which is considered important to the archaeological pre-historic patrimony, designated a UNESCO World Heritage Site . Within Spain, it flows through
3990-571: The Douro Valley in Portugal, long devoted to vineyards , has been designated by UNESCO as a World Heritage Site . The wine was taken downriver in flat-bottom boats called rabelos , to be stored in barrels in cellars in Vila Nova de Gaia , just across the river from Porto . Nowadays port is transported there in tanker trucks. In the 1960s and 1970s, dams with locks were built along
4095-525: The Duero River . The TT-3 platform features a very compact and thick Miocene epoch conglomerate formed of river-smoothed pebbles of quartzite , most likely cut by the Trabancos River ages ago, and cemented together by chalk and sandstone materials. While this Miocene conglomerate emerges from the banks of each river terrace, the quartzite in the conglomerate on the TT-2 platform, just northwest of
4200-737: The Kings River flowing out of the Sierra Nevada . Like the Himalayan megafans, these are streamflow-dominated fans. Alluvial fans are also found on Mars . Unlike alluvial fans on Earth, those on Mars are rarely associated with tectonic processes, but are much more common on crater rims. The crater rim alluvial fans appear to have been deposited by sheetflow rather than debris flows. Three alluvial fans have been found in Saheki Crater . These fans confirmed past fluvial flow on
4305-518: The Main Boundary Thrust over the last ten million years has focused the drainage of 750 kilometres (470 miles) of mountain frontage into just three enormous fans. Alluvial fans are common in the geologic record, but may have been particularly important before the evolution of land plants in the mid-Paleozoic. They are characteristic of fault-bounded basins and can be 5,000 meters (16,000 ft) or thicker due to tectonic subsidence of
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4410-487: The Ribera del Duero wine region. Sheep rearing is also still important. The drainage basin borders those of Miño to the north, Ebro to the east, and Tajo to the south. For 112 kilometres (70 mi), the river forms part of the border between Spain and Portugal , in a region of narrow canyons . It formed a historical barrier to invasions, creating a cultural/linguistic divide. In these isolated areas, in which
4515-678: The Solar System . Alluvial fans are built in response to erosion induced by tectonic uplift . The upwards coarsening of the beds making up the fan reflects cycles of erosion in the highlands that feed sediments to the fan. However, climate and changes in base level may be as important as tectonic uplift. For example, alluvial fans in the Himalayas show older fans entrenched and overlain by younger fans. The younger fans, in turn, are cut by deep incised valleys showing two terrace levels. Dating via optically stimulated luminescence suggests
4620-698: The Valles Marineris canyon system. These provide evidence of the existence and nature of faulting in this region of Mars. Alluvial fans have been observed by the Cassini-Huygens mission on Titan using the Cassini orbiter's synthetic aperture radar instrument. These fans are more common in the drier mid-latitudes at the end of methane/ethane rivers where it is thought that frequent wetting and drying occur due to precipitation, much like arid fans on Earth. Radar imaging suggests that fan material
4725-691: The conservation of bird species threatened with extinction, in accordance with the criteria established by the community board Birds Directive 79/409/CEE and subsequent modifications by the (Directiva de Aves) "Aviary Regulation Board" of the EU. Although the designation also includes a portion of the Guareña River's course to the west, and the Zapardiel River's course to the east, the Trabancos River ZEPA SPA designated area
4830-522: The floodplain ); and the TT-4 platform (at +10 meters, the last and most recent). The right hand margin of the designated chart depicts a gravel plateau present along the middle and final courses of the Trabancos River. The scientist Alfredo Pérez-Gonzalez named this formation "Superficie de Alaejos" ("The Plateau of Alaejos", after a nearby village). The Alaejos Plateau incorporates a number of different types of materials, including red argillic soil and
4935-724: The 11th century; that is to say, previous to any official resettlement. Specifically, more than ten defensive structures of various sizes were verified along the course of the Trabancos River in the province of Valladolid. Almost all the torrejones are in areas now uninhabited (except those in Castrejón and Alaejos, both of which were turned into castles, in later history). The torrejones were relatively simple square or egg-shaped structures, with several floors, built of limestone or brick . At least two categories of torrejones can be identified: The first have small peepholes in their walls and are built in regions that were in isolated areas at
5040-720: The 13th century, it played an important role in the history of the North Spanish Plateau. Evidence of prehistoric human habitation has been unearthed in hillsides in some areas of Narros del Castillo ( Ávila ), and in Siete Iglesias de Trabancos ( Valladolid ), dating from the Quaternary period, and have been further pinpointed as originating in the Lower Paleolithic era. At both sites, collections of lithic stone artifacts knapped during
5145-580: The Bronze Age. In addition, some prehistoric remains have been found near the mouth of the Trabancos River, in Pollos village that originated from the Duero River . These include relics of the Spanish Bronze Age classified as Cogotas pottery, as well as Proto-Cogotas pottery, both featuring incised decoration. The Romans likely came to the Trabancos region in the 2nd century, during
5250-615: The Douro River are Valladolid and Zamora in Spain, and Porto and Vila Nova de Gaia in Portugal. The latter two are located at the mouth of the Douro at the Atlantic Ocean. In Portugal, the Douro flows through the districts of Bragança , Guarda , Viseu , Vila Real , Aveiro and Porto . Porto is the main hub city in northern Portugal. Its historic centre has been designated as a UNESCO World Heritage Site because of its significant architecture and history. These reaches of
5355-431: The Douro have a mesoclimate allowing for cultivation of olives , almonds , and especially grapes , which are important for making port . The region around Pinhão and São João da Pesqueira is considered to be the centre of port, with its quintas (or farms/estates) that extend along the steep slopes of the river valleys. In the 21st century, many of these are owned by multinational, reputed wine companies. Recently,
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#17327733046125460-602: The Fortress of Cast'cam (Castrejón), which led to the signing of a peace treaty between Alphonse VIII of Castille and Ferdinand II of León . But in fact peace came to a swift end in the year 1183, when the Kings of Castille and Leon made camp on the outskirts of the towns of Carpio and Fresno el Viejo (both towns in the Province of Valladolid) respectively. After the death of Ferdinand II, fighting resumed (interspersed with
5565-553: The Iberian Peninsula after the Tagus and Ebro . Its total length is 897 kilometres (557 mi), of which only sections of the Portuguese section, being below a fall/rapids line, are naturally navigable, by modest rivercraft. The Douro River basin encompasses an area of approximately 97,290 square kilometres. In its Spanish section, the Douro crosses the great Castilian meseta and meanders through five provinces of
5670-524: The Portuguese-Spanish border; the first three are owned and operated by Portugal: ( Miranda , Picote and Bemposta Dams ), while the next two belong to Spain: ( Aldeadávila and Saucelle Dams ). The Douro's last five dams are in Portugal, and allow for navigation: Pocinho , Valeira , Régua , Carrapatelo , and Crestuma–Lever dams. Vessels with a maximum length of 83 metres (272 ft) and width of 11.4 metres (37 ft) can pass through
5775-542: The affected Duero River terraces are younger than those not formed from activity of the waters of this river. The "superficie de Alaejos" carve-out intrudes 4 to 6 meters into the Duero River terrace designated TD-7 (+74/80 m) to the northwest of Siete Iglesias de Trabancos village. Likewise, the TT-2 fluvial terrace of Trabancos cuts some Duero River terraces. Since the previously mentioned Duero River terrace named TD-7 has been dated by Alfredo Pérez-González (op.cit.) to
5880-604: The alluvial fan on which the towns of Montrose and Glendale were built. The floods caused significant loss of life and property. The Koshi River in India has built up a megafan where it exits the Himalayas onto the Ganges plain . The river has a history of frequently and capriciously changing its course, so that it has been called the Sorrow of Bihar for contributing disproportionately to India's death tolls in flooding. These exceed those of all countries except Bangladesh . Over
5985-409: The apex is generally concave, with the steepest slope near the apex (the proximal fan or fanhead ) and becoming less steep further out (the medial fan or midfan ) and shallowing at the edges of the fan (the distal fan or outer fan ). Sieve deposits , which are lobes of coarse gravel, may be present on the proximal fan. The sediments in an alluvial fan are usually coarse and poorly sorted, with
6090-410: The area because of a severe drought that occurred sometime between 750 and 753 AD. Only the most important centers of habitation survived ( Medina del Campo , Olmedo, Alcazarén , Tordesillas , etc.). During the Christian conquest , little emphasis was placed on resettling the region, as it was essential for the sovereigns of the time to consolidate more strategic zones (in the 11th century, priority
6195-422: The area during the Middle Ages , despite its history as a fortified border from the tenth century, the area was unimportant until the thirteenth. The King of the (now united) Kingdom of Castile and Leon, Alphonse VII (1126–1157), made a series of internal territorial changes that transferred Leonese territories to the Crown of Castille: specifically, The Tierra de Campos to the north of the Duero, an area valued at
6300-431: The area feeding the flow onto the fan. Debris flow fans receive most of their sediments in the form of debris flows. Debris flows are slurry-like mixtures of water and particles of all sizes, from clay to boulders, that resemble wet concrete . They are characterized by having a yield strength, meaning that they are highly viscous at low flow velocities but become less viscous as the flow velocity increases. This means that
6405-406: The area is agricultural land, with an emphasis on cereal crops and other irrigation farming purposes. The areas of ecological interest are found in the remaining 3% percent of the terrain. The region is characterized by tilled land and pastures, small pine woods and holm oak woods , with interspersed wasteland areas covered in halophile bushes. There are also many small ephemeral ponds;
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#17327733046126510-648: The areas surrounding the Trabancos River, with some castles being erected in the west, such as in Alaejos. Paradoxically, the wars increased the value of the region, and for the first time there began to appear documents recording the area in the files of the cathedrals of Zamora , Salamanca and Segovia including documents regarding: Siete Iglesias de Trabancos ("Seven Churches at Trabancos") in 1178, Alaejos ( Falafeios ) in 1167, and in 1180, Eván de Arriba, Eván de Abajo, Valdefuentes and Pedroso (which are now deserted villages ), together with Nava del Rey in 1265, among others. This last date, 1265, corresponds to
6615-483: The autonomous community of Castile and León : Soria , Burgos , Valladolid , Zamora , and Salamanca , passing through the towns of Soria , Almazán , Aranda de Duero , Tordesillas , and Zamora . The most important tributaries in this region are the Pisuerga , passing through Valladolid , and the Esla , which passes through Zamora . This region is generally semi-arid plains, with wheat and in some places, especially near Aranda de Duero , with vineyards , in
6720-430: The basin and uplift of the mountain front. Most are red from hematite produced by diagenetic alteration of iron-rich minerals in a shallow, oxidizing environment. Examples of paleofans include the Triassic basins of eastern North America and the New Red Sandstone of south Devon, the Devonian Hornelen Basin of Norway, and the Devonian- Carboniferous in the Gaspé Peninsula of Canada. Such fan deposit likely contain
6825-403: The beginning of the Middle Pleistocene , meaning the river terraces of Trabancos River are younger than the "Superficie de Alaejos", it appears plausible that this postdates the creation of Trabancos valley: the proposed date could, thus, be halfway through the Middle Pleistocene or later. Although the eastern portion of the river is of insignificant hydrographic importance, at least until
6930-478: The bottom. Multiple braided streams are usually present and active during water flows. Phreatophytes (plants with long tap roots capable of reaching a deep water table ) are sometimes found in sinuous lines radiating from arid climate fan toes. These fan-toe phreatophyte strips trace buried channels of coarse sediments from the fan that have interfingered with impermeable playa sediments. Alluvial fans also develop in wetter climates when high-relief terrain
7035-426: The campaigns of Lucius Licinius Lucullus (152 BC), but the area was peripheral to the regions of principal occupation, as well as to the creation of early towns and more importantly, trade routes : most travel routes were in the east of this region, which followed the river Eresma from the town of Coca ( Cauca , in Roman times) and Matapozuelos village ( Nivaria in Roman times), up to Simancas ( Septimanca ); and at
7140-423: The coarsest sediments found on the proximal fan. When there is enough space in the alluvial plain for all of the sediment deposits to fan out without contacting other valley walls or rivers, an unconfined alluvial fan develops. Unconfined alluvial fans allow sediments to naturally fan out, and the shape of the fan is not influenced by other topological features. When the alluvial plain is more restricted, so that
7245-456: The control of the area, especially Tierra de Campos , but also, though less importantly, over the area of Medina del Campo . The wars over the area intensified between 1178 and 1181. The Leonese Alfoz de Toro was heavily defended, thanks to the Fortress of Castronuño , with a vicious battle taking place even on the shores of the Trabancos River itself. Of particular note is an encounter in 1179 between Leonese and Castilian forces, just outside
7350-420: The fan comes into contact with topographic barriers, a confined fan is formed. Wave or channel erosion of the edge of the fan ( lateral erosion ) sometimes produces a "toe-trimmed" fan, in which the edge of the fan is marked by a small escarpment. Toe-trimmed fans may record climate changes or tectonic processes, and the process of lateral erosion may enhance the aquifer or petroleum reservoir potential of
7455-400: The fan. Toe-trimmed fans on the planet Mars provide evidence of past river systems. When numerous rivers and streams exit a mountain front onto a plain, the fans can combine to form a continuous apron. This is referred to as a bajada or piedmont alluvial plain . Alluvial fans usually form where a confined feeder channel exits a mountain front or a glacier margin. As the flow exits
7560-745: The fan: Finer sediments are deposited at the edge of the fan, but as the fan continues to grow, increasingly coarse sediments are deposited on top of the earlier, less coarse sediments. However, a few fans show normal grading indicating inactivity or even fan retreat, so that increasingly fine sediments are deposited on earlier coarser sediments. Normal or reverse grading sequences can be hundreds to thousands of meters in thickness. Depositional facies that have been reported for alluvial fans include debris flows, sheet floods and upper regime stream floods, sieve deposits, and braided stream flows, each leaving their own characteristic sediment deposits that can be identified by geologists. Debris flow deposits are common in
7665-516: The feeder channel and onto the surface of the fan. Debris flow fans have a network of mostly inactive distributary channels in the upper fan that gives way to mid- to lower-level lobes. The channels tend to be filled by subsequent cohesive debris flows. Usually only one lobe is active at a time, and inactive lobes may develop desert varnish or develop a soil profile from eolian dust deposition, on time scales of 1,000 to 10,000 years. Because of their high viscosity, debris flows tend to be confined to
7770-554: The feeder channel onto the fan surface, it is able to spread out into wide, shallow channels or to infiltrate the surface. This reduces the carrying power of the flow and results in deposition of sediments. Flow in the proximal fan, where the slope is steepest, is usually confined to a single channel (a fanhead trench ), which may be up to 30 meters (100 ft) deep. This channel is subject to blockage by accumulated sediments or debris flows , which causes flow to periodically break out of its old channel ( nodal avulsion ) and shift to
7875-400: The feeder channel. This results in sheetfloods on the alluvial fan, where sediment-laden water leaves its channel confines and spreads across the fan surface. These may include hyperconcentrated flows containing 20% to 45% sediments, which are intermediate between sheetfloods having 20% or less of sediments and debris flows with more than 45% sediments. As the flood recedes, it often leaves
7980-667: The final vowel sound often changes with context, as in Latin). However, were that the case, the - b -, of which there remains no trace, would not have disappeared, as evidenced by place-names derived from Gaulish *dubron (plural dubra ), such as French Douvres and English Dover (3rd/4th-century Dubris ; Douvres in French), Spanish Dobra, German Tauber ( Dubra-gave 807), and Gaelic/ Old Irish dobur "water" and river name Dobhar in Ireland and Scotland. Modern Welsh dŵr "water"
8085-435: The five locks . The highest lock, at Carrapatelo Dam, has a maximum lift of 35 metres (115 ft). The waters of Pocinho lake reach 125 metres (410 ft) above sea level. Unannounced releases of water from upstream Spanish dams occasionally causes navigation issues in these locks. Alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as
8190-530: The form of short (several hours) but energetic flash floods that occur with little or no warning. They typically result from heavy and prolonged rainfall, and are characterized by high velocities and capacity for sediment transport. Flows cover the range from floods through hyperconcentrated flows to debris flows, depending on the volume of sediments in the flow. Debris flows resemble freshly poured concrete, consisting mostly of coarse debris. Hyperconcentrated flows are intermediate between floods and debris flows, with
8295-402: The form of stream flow rather than debris flows. They are less sharply distinguished from ordinary fluvial deposits than are debris flow fans. Fluvial fans occur where there is perennial, seasonal, or ephemeral stream flow that feeds a system of distributary channels on the fan. In arid or semiarid climates, deposition is dominated by infrequent but intense rainfall that produces flash floods in
8400-617: The largest accumulations of gravel in the geologic record. Alluvial fans have also been found on Mars and Titan , showing that fluvial processes have occurred on other worlds. Some of the largest alluvial fans are found along the Himalaya mountain front on the Indo-Gangetic plain . A shift of the feeder channel (a nodal avulsion ) can lead to catastrophic flooding, as occurred on the Kosi River fan in 2008. An alluvial fan
8505-450: The largest accumulations of gravel in the geologic record. Several kinds of sediment deposits ( facies ) are found in alluvial fans. Alluvial fans are characterized by coarse sedimentation, though the sediments making up the fan become less coarse further from the apex. Gravels show well-developed imbrication with the pebbles dipping towards the apex. Fan deposits typically show well-developed reverse grading caused by outbuilding of
8610-568: The largest reproductive concentration of black-bellied sandgrouses ( Pterocles orientalis ) in Castile and León (with more than 200 mating pairs). It is also the winter season nesting ground of more than 1,500 red kites ( Milvus milvus ). There are also numerous birds of prey ; the most abundant are Montagu's harriers ( Circus pygargus , 50 mating pairs) and lesser kestrels ( Falco naumanni ; almost 150 mating pairs), but there are also hawks , goshawks , falcons , owls , and others. The region
8715-411: The last 25,000 years occurred during times of rapid climate change, both from wet to dry and from dry to wet. Alluvial fans are often found in desert areas, which are subjected to periodic flash floods from nearby thunderstorms in local hills. The typical watercourse in an arid climate has a large, funnel-shaped basin at the top, leading to a narrow defile , which opens out into an alluvial fan at
8820-471: The last few hundred years, the river had generally shifted westward across its fan, and by 2008, the main river channel was located on the extreme western part of the megafan. In August 2008 , high monsoon flows breached the embankment of the Koshi River . This diverted most of the river into an unprotected ancient channel and flooded the central part of the megafan. This was an area with a high population density that had been stable for over 200 years. Over
8925-424: The likely flood path, the likelihood of abrupt deposition and erosion of sediments carried by the flood from upstream sources, and a combination of the availability of sediments and of the slope and topography of the fan that creates extraordinary hazards. These hazards cannot reliably be mitigated by elevation on fill (raising existing buildings up to a meter (three feet) and building new foundations beneath them ). At
9030-453: The middle of the autonomous community of Castile and León , with the basin spanning through the northern half of the Meseta Central . The latter includes wine producing areas such as the Ribera del Duero DOP. The Latin name Durius might have been a Celtic name before the overwhelming Romanization of Iberia. If so, the Celtic root could have been *dubro- (in that family of languages
9135-408: The municipality of Siete Iglesias de Trabancos, likely derives from the action of the Duero River rather than the Trabancos River, as a slope in the terrain is thought to have caused the formation of an alluvial fan that deposited quartzite on the fluvial fossil river bed of the Trabancos. The fact that the river terraces of the Trabancos River cut and cross some terraces of the Duero River indicates
9240-431: The name comes from the Portuguese or Spanish term for "golden". In Roman times, the river was personified as a god, Durius . Part of the drainage basin might have been severely depopulated in the 8th century. According to Claudio Sánchez-Albornoz this was a deliberate act by Alfonso I of Asturias for the defence of his Kingdom , which led the area to be named Repoblación . The Douro vinhateiro (vine-land) of
9345-590: The observed faults of that geological era , follows a NNE-SSW direction. As shown in the graph below, the fault separates material laid down during the Oligocene epoch on the right margin, from material laid down during the Miocene epoch on the left margin. The surface level represents material deposited during the Quaternary period. Archeological research in areas that surround the Trabancos River, between
9450-402: The one known as TT-4 is only visible near Narros del Castillo ( Ávila ). Terrace TT-3 is the best preserved of the lot; although its height on the bed of the stream is not constant, it clearly stands out on the floodplain . Terrace TT-2 is quite well preserved as well, although it has been more heavily sculptured by other small tributaries of the Trabancos River. By contrast, terrace TT-1
9555-640: The part of the militia of the Community of Medina del Campo and surrounding areas, which was thereby forced to defend itself without outside help, while the Leonese side would have been able to rely on the help of Royal troops, and the Knights Hospitaller of the Order of Saint John of Jerusalem , billeted in Castronuño and Torrecilla de la Orden. As indicated at the start of the discussion of
9660-722: The planet and further supported the theory that liquid water was once present in some form on the Martian surface. In addition, observations of fans in Gale crater made by satellites from orbit have now been confirmed by the discovery of fluvial sediments by the Curiosity rover . Alluvial fans in Holden crater have toe-trimmed profiles attributed to fluvial erosion. The few alluvial fans associated with tectonic processes include those at Coprates Chasma and Juventae Chasma, which are part of
9765-465: The proximal and medial fan even in a debris-flow-dominated alluvial fan, and streamfloods dominate the distal fan. However, some debris-flow-dominated fans in arid climates consist almost entirely of debris flows and lag gravels from eolian winnowing of debris flows, with no evidence of sheetflood or sieve deposits. Debris-flow-dominated fans tend to be steep and poorly vegetated. Fluvial fans (streamflow-dominated fans) receive most of their sediments in
9870-473: The proximal and medial fan. These deposits lack sedimentary structure, other than occasional reverse-graded bedding towards the base, and they are poorly sorted. The proximal fan may also include gravel lobes that have been interpreted as sieve deposits, where runoff rapidly infiltrates and leaves behind only the coarse material. However, the gravel lobes have also been interpreted as debris flow deposits. Conglomerate originating as debris flows on alluvial fans
9975-583: The river mouth, the only population centres of any note are Foz do Tua, Pinhão and Peso da Régua . Tributaries here are small, merging into the Douro along the canyons; the most important are Côa , Tua , Sabor , Corgo , Tavora , Paiva , Tâmega , and Sousa . None of these small, fast-flowing rivers is navigable. Major Spanish riverside towns include Soria , Almazán , Aranda de Duero , Tordesillas , Zamora and major Portuguese towns include Miranda do Douro , Foz Côa , Peso da Régua , Lamego , Vila Nova de Gaia , and Porto . The most populous cities along
10080-489: The river, allowing river traffic into the upper regions in Spain and along the border. In 1998, Portugal and Spain signed the Albufeira Convention, an agreement on the sharing of trans-boundary rivers to include the Douro, Tagus and Guadiana . The convention superseded an agreement on the Douro, signed in 1927, that was expanded in 1964 and 1968 to include tributaries. It is the third-longest river in
10185-638: The so-called "Extremadura Catellana" (the wildest border of Castile ). However, the area's archaeological heritage is fast disappearing. The middle and final course of the river Trabancos has been included in the Special Protection Area (SPA or in Spanish ZEPA) Tierra de Campiñas (Land of champaigns). ZEPA SPAs, are catalogued by the member states of the European Union as natural zones of special interest for
10290-428: The surface of the terrain. Such remains consist of, for instance, broken pieces of comb-decorated pottery that appear to date from Spain's Iron Age . There are few other examples of prehistoric findings directly along the Trabancos river. However, in the surrounding regions, such as the municipality of Alaejos ( Valladolid ), archaeological investigation has unearthed several human burials sites that have been dated to
10395-573: The time for its riches, and the alfoz de Medina del Campo (to the south of the Duero), a poor and sparsely populated zone, although it possessed a certain strategic value in terms of the defense of the passes of the Duero valley. During the time of the union of the two crowns, the question of who owned these areas was of little importance; however, upon the death of Alphonse VII and the division of his possession amongst his sons, continuous conflicts arose over
10500-469: The time of use, and the other are small castles located in what were rural farming villages (though today they are deserted ). Nevertheless, the typological similarity of the structures and the relatively short distance between them (ideal for visual communication), has led some to think that they were on opposite sides of the frontier line between the Kingdoms of León and Castile (in Salamanca there
10605-538: The villages of Castrejón and Pollos ( Valladolid province ) have been compared with the specialized bibliography and the published geological charts ( infra ). This produced identified a sequence of river terraces as follows, on the left hand margin of the chart: TT-1 platform (the most ancient, at +35/40 meters over the flood plain ); the TT-2 platform (the second one at +25/30 meters); the TT-3 platform (at +15 meters over
10710-754: The west, for the " Vía de la Plata " (" silver road"), the most important Roman route in Lusitania Province. Nevertheless, it is known that in the Vallisoletan area, there were several villages that probably are of pre-Roman origin. In fact, the etymology of the word 'Trabancos' suggests a name originating before the Roman occupation. At the Lavachicha site (municipality of Castrejón, Valladolid ) several pieces of typical Roman pottery named terra sigillata hispanica have been unearthed and there
10815-574: The world. However, flooding on alluvial fans poses unique problems for disaster prevention and preparation. The beds of coarse sediments associated with alluvial fans form aquifers that are the most important groundwater reservoirs in many regions. These include both arid regions, such as Egypt or Iraq, and humid regions, such as central Europe or Taiwan. Alluvial fans are subject to infrequent but often very damaging flooding, whose unusual characteristics distinguish alluvial fan floods from ordinary riverbank flooding. These include great uncertainty in
10920-590: Was also an archaeological excavation in the 1980s that revealed a necropolis from late Roman times or, perhaps, from Visigothic times. Similar remains of late Roman pottery, have been found in Carpio ( Valladolid ), but only at ground level, and not from archaeological excavation. Another municipality crossed by the Trabancos River is Nava del Rey (a small town located in Valladolid ), where, once again, are found superficial pieces of terra sigillata hispanica and
11025-549: Was placed on the south of the Sistema Central , a mountain range located in the center of the Iberian Peninsula ), which is why Medina del Campo remained intact into the 12th century. Nevertheless, Tomas Mañanes, a professor at the University of Valladolid , who investigated the Trabancos valley and Guareña area, found numerous defensive turrets or "Torrejones" (according to the local dialect ) that were dated to
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