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64-724: Physiographically, the Interior Plateau is a section of the larger Northern Plateaus province, which in turn is part of the Intermontane Plateaus physiographic division. (The Interior Plateau is not part of the Interior Mountains , a huge area that constitutes most of the northern two thirds of the Canadian province of British Columbia between the Coast Mountains, Rocky Mountains and

128-442: A dam is designed specifically to impound water behind a wall, whilst a weir is designed to alter the river flow characteristics. A common distinction between dams and weirs is that water flows over the top (crest) of a weir or underneath it for at least some of its length. Accordingly, the crest of an overflow spillway on a large dam may therefore be referred to as a weir. Weirs can vary in size both horizontally and vertically, with

192-406: A derivative of the root of the verb werian, meaning "to defend, dam". The German cognate is Wehr , which means the same as English weir. Commonly, weirs are used to prevent flooding , measure water discharge, and help render rivers more navigable by boat. In some locations, the terms dam and weir are synonymous, but normally there is a clear distinction made between the structures. Usually,

256-488: A negative effect on fish species that migrate as part of their breeding cycle (e.g., salmonids ), but it also can be useful as a method of preventing invasive species moving upstream. For example, weirs in the Great Lakes region have helped to prevent invasive sea lamprey from colonising farther upstream. Mill ponds are created by a weir that impounds water that then flows over the structure. The energy created by

320-415: A range of biota , including poor swimmers. Even though the water around weirs can often appear relatively calm, they can be extremely dangerous places to boat, swim, or wade, as the circulation patterns on the downstream side—typically called a hydraulic jump —can submerge a person indefinitely. This phenomenon is so well known to canoeists, kayakers, and others who spend time on rivers that they even have

384-416: A rueful name for weirs: "drowning machines". The Ohio DNR recommends that a victim should "tuck the chin down, draw the knees up to the chest with arms wrapped around them. Hopefully, conditions will be such that the current will push the victim along the bed of the river until swept beyond the boil line and released by the hydraulic." The Pennsylvania State Police also recommends to victims, "curl up, dive to

448-406: A temporary shallow sheet on a dead level of clay, or playa, in a basin center, but the sheet of water vanishes in the warm season ( dry lake ) and the stream shrinks far up its course, the absolutely barren clay floor of the playa, impassable when wet, becomes firm enough for crossing when dry. One of the southwestern basins, with its floor below sea-level, has a plain of salt in its center. A few of

512-449: A weir is broad-crested for much of its length, but has a section where the weir stops or is 'open' so that small boats and fish can traverse the structure. A notch weir is any weir where the physical barrier is significantly higher than the water level except for a specific notch (often V-shaped) cut into the panel. At times of normal flow all the water must pass through the notch, simplifying flow volume calculations, and at times of flood

576-480: Is a large igneous province of flood basalts erupted in Miocene and early Pliocence epochs across the states of Washington , Oregon , Idaho , Nevada , and California . The province was uplifted and divided into great blocks by faults or monoclinal flexures which were exposed to long-lasting denudation in a mid-Tertiary cycle of erosion. They were then broadly elevated again with renewed movement on some of

640-405: Is a flat-crested structure, where the water passes over a crest that covers much or all of the channel width. This is one of the most common types of weir found worldwide. A compound weir is any weir that comprises several different designs into one structure. They are commonly seen in locations where a river has multiple users who may need to bypass the structure. A common design would be one where

704-473: Is a generic relationship and specific calculations are available for the many different types of weir. Flow measurement weirs must be well maintained if they are to remain accurate. The flow over a V-notch weir (in ft /s) is given by the Kindsvater–Shen equation: where As weirs are a physical barrier, they can impede the longitudinal movement of fish and other animals up and down a river. This can have

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768-603: Is cut by the basins and tributaries of two rivers: the Columbia and the Fraser . The northern region is largely wooded, except in lowland and more southerly areas which resemble the sagebrush grasslands which typify the southern part of the plateau in the Columbia drainage. The first documented human presence was in 8500 BC . Bison remains, Clovis and other fluted points date back to this time frame. An important sites in

832-858: Is in the Lower Colorado River Valley that an irrigation project, involving the diversion of some of the river water to the low plain of the Imperial Valley , led to disaster in 1904. The river flooded through a deliberately engineered breach of the Alamo Canal and flowed across the Imperial Valley plain into the Salton Sink , forming the Salton Sea . The endorheic Salton Sea remains, now supplied by subterranean flow from over-irrigated fields draining into

896-779: Is located in all or parts of Oregon , Idaho , Nevada , California , Utah , New Mexico , Arizona in the Western United States; and Sonora , Chihuahua , Sinaloa , and other states southwards to the Trans-Mexican Volcanic Belt in Mexico . It involves some novel problems in its description, especially in Southern California and central Mexico. The province is characterized by numerous disconnected mountain ranges trending north and south, from 30–100 miles (48–161 km) in length,

960-821: Is the Quanchus Range. Also, the Cariboo Mountains are sometimes included as part of the Interior Plateau. Three areas liminal to the plateau, i.e. sometimes considered part of it rather than the adjoining mountain ranges, are the Shuswap Highland , Okanagan Highland and Quesnel Highland . The location of the Interior Plateau in North America is between the Rocky Mountains and the Pacific Coast Ranges. It

1024-644: Is to this newly introduced cycle of physiographic evolution that the deep canyons of the Plateau province are due. Thus the Virgin River , a northern tributary of the Colorado River , has cut a vertical slit, 1000 ft. deep, hardly wider at the top than at the bottom, in the heavy Triassic sandstones of southern Utah. However the most famous example is the Grand Canyon of Arizona , eroded by

1088-477: The Cascade Range on the northwest. The river followed the temporary course long enough to erode a deep gorge, known as Grande Coulee , along part of its length. The lava plains are treeless and for the most part too dry for agriculture. However they support wildlife, and cattle and horses. Along parts of their eastern border, where the rainfall is a little increased by the approach of the westerly winds to

1152-497: The Colorado river across the uplifted platform of Carboniferous limestone. During the current cycle of erosion, several of the faults , whose scarps had been worn away in the previous cycle, have been brought to light again as topographic features by the removal of the weak strata along one side of the fault line, leaving the harder strata on the other side in relief. Such scarps are known as fault-line scarps, in distinction from

1216-869: The Mexican Plateau to central Mexico at the Trans-Mexican Volcanic Belt . Only a small part of the Basin and Range province is drained to the sea. A few intermont areas in the north-west part of the province have outlets westward via the Klamath River through the Cascade range. The Sacramento and San Joaquin Rivers from the Sierra Nevada pass through the Central Valley and California Coast Ranges to San Francisco Bay . A few basins in

1280-669: The Omineca Mountains and the Cassiar Mountains , which are two major subdivisions of the Interior Mountains . Several mountain ranges and hill-systems are included in the definition of this region such as the following: Some classifications systems assign the Pattullo Rangez to the Hazelton Mountains , which are part of the larger Skeena Mountains complex, but then theoretically so zalso

1344-732: The Rocky Mountains on the east and the Cascade and Sierra Nevada Mountains on the west. It is subdivided into three physiographic provinces : the Columbia Plateau in the north, the Basin and Range Province in the central and southwestern portions, and the Colorado Plateau in the southeast. In turn, each of these provinces are each subdivided into a number of physiographic sections. The Columbia Plateau Province

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1408-733: The Carboniferous platform one ascends in succession the Chocolate Cliffs ( Triassic sandstones), Vermilion and White Cliffs ( Jurassic sandstones), the Gray Cliffs ( Cretaceous sandstones, of remarkably cross-bedded structure, interpreted as the dunes of an ancient desert), and finally the Pink Cliffs ( Eocene strata of fluviatile and lacustrine origin) of the high, forested plateaus. Associated with these irregular escarpments are occasional rectilinear ridges,

1472-403: The Rocky Mountains, there is a belt of very deep, impalpably fine soil, supposed to be a dust deposit brought from the drier parts of the plains farther west. Weir A weir / w ɪər / or low-head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control

1536-504: The aquifer. Many streams descend from the ravines only to wither away on the desert basin floors before uniting in a trunk river along the axis of a depression. Others succeed in uniting in the winter season, when evaporation is much reduced, and then their trunk flows for several additional miles only to disappear by sinking (evaporating) farther on. A few of the large streams, such as the Mojave River , when in flood may spread out in

1600-640: The area is at Wenatchee site (located in Washington ). The Windust phase is dated between 10600 BC and 7100 BC. At the Lind Coulee Archaeological Site in east-central Washington, leaf-shaped projectile points and knives date between 8500 and 5500 BC. Based on archaeological evidence, it is suggested that these people were hunters, subsisting also from fishing and plant gathering. The presence of sea shells gives an indication that trading took place. A small, oval-shaped dwelling

1664-542: The basins are occupied by endorheic lakes without outlet, of which Great Salt Lake , in north-west Utah, is the largest. Other examples are Owens Lake and Mono Lake in California. Several smaller lakes occur in the basins of western Nevada, immediately east of the Sierra Nevada. During Pleistocene times all these lacustrine basins were occupied by lakes of much greater depth and larger size. The outlines of

1728-523: The blocks are monoclinal in structure as well as in attitude. Here, the amount of dissection is relatively moderate, for some of the fault faces are described as ravined but not yet deeply dissected. Hence these dislocations appear to be of recent date. In the Great Basin of western Utah and through most of Nevada , many of the blocks exhibit deformed structures involving folds and faults of relatively ancient ( Jurassic ) date. In fact so ancient that

1792-502: The bottom, and swim or crawl downstream". As the hydraulic jump entrains air, the buoyancy of the water between the dam and boil line will be reduced by upward of 30%, and if a victim is unable to float, escape at the base of the dam may be the only option for survival. There are many different types of weirs and they can vary from a simple stone structure that is barely noticeable, to elaborate and very large structures that require extensive management and maintenance. A broad-crested weir

1856-501: The change in height of the water can then be used to power waterwheels and power sawmills, grinding wheels, and other equipment. Weirs are commonly used to control the flow rates of rivers during periods of high discharge. Sluice gates (or in some cases the height of the weir crest) can be altered to increase or decrease the volume of water flowing downstream. Weirs for this purpose are commonly found upstream of towns and villages and can either be automated or manually operated. By slowing

1920-414: The design of a weir that ensure that fish can bypass the barriers and access upstream habitats. Unlike dams, weirs do not usually prevent downstream fish migration (as water flows over the top and allows fish to bypass the structure in that water), although they can create flow conditions that injure juvenile fish. Recent studies suggest that navigation locks have also potential to provide increased access for

1984-446: The development of a series of cuestas : huge, south-facing, retreating escarpments of irregular outline on the edges of the higher formations farther north. Each escarpment stands forth where a resistant formation overlies a weaker, less resistant one. Each escarpment is separated from the next higher one by a broad step of weaker strata. A series of these geologic formations occurs in southern Utah , where in passing northward from

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2048-462: The eastern Lake Bonneville and the western Lake Lahontan water bodies are well recorded by shore lines and deltas on the enclosing slopes, hundreds of feet above the present lake surfaces. The abandoned shore lines have yielded evidence of past climatic changes second in importance only to those of the Pleistocene glaciated areas. The duration of the Pleistocene lakes was brief as compared with

2112-502: The face of the Vermilion Cliffs, so that huge slices of the cliff face have slid down and forward 1–2 miles (1.6–3.2 km), all shattered into a confused tumult of forms for a 20 miles (32 km) or more along the cliff base. Volcanic features occur in abundance in the Plateau province. Some of the high plateaus in the north are capped with remnants of heavy lava flows of early eruption. A group of large volcanoes occurs on

2176-480: The fault face. They are already somewhat battered and dissected by erosion. The most important line of cliffs of this class is associated with the western and southern boundary of the Plateau Province where it was uplifted from the lower ground. The few rivers of the region must have reached the quiescence of old age in the earlier cycle, but were revived by uplift to a vigorous youth in the current cycle. It

2240-417: The faults. The current erosion cycle started in the late Tertiary, when the deep canyons of the region were trenched. The results of the first cycle of erosion are seen in the widespread exposure of the resistant Carboniferous limestone as a broad platform in the southwestern area of greater uplift through central Arizona where the less resistant overlying formations have been eroded away. They are also seen in

2304-478: The flow of water for outlets of lakes, ponds, and reservoirs. There are many weir designs, but commonly water flows freely over the top of the weir crest before cascading down to a lower level. There is no single definition as to what constitutes a weir. Weir can also refer to the skimmer found in most in-ground swimming pools, which controls the flow of water pulled into the filtering system. The word likely originated from Middle English were , Old English wer ,

2368-425: The higher ranges reaching altitudes of 8,000–10,000 feet (2,400–3,000 m), separated by broad, intermontane desert plains or basins at altitudes varying from sea-level (or a little less) in the southwest, to 4,000–5,000 feet (1,200–1,500 m) farther inland. It is an arid region. Many of the intermontane plains , occurring mostly in the north, appear to be heavily aggraded with mountain waste. Others, mostly in

2432-637: The historic era, plants and salmon were the staple foods, which give us an indication that Cascade groups harvested salmon runs in the summer and fall. The Late Period, dated to about 2500 BC , the pithouse ( quiggly hole ) came into existence, such as those at the Keatley Creek Archaeological Site . Other markers of this period include the increasing number of pithouses and settlements. Fishing continued to increase, and technology advanced, introducing more specialized barb fish spears and composite toggling harpoons. Other technology

2496-462: The initial form of the uplifted blocks can hardly be perceived. Some of them still retain along one side the highly significant feature of a relatively simple base-line, transecting hard and soft structures alike indicating the faulted margin of a tilted block. Here the less uplifted blocks are now heavily aggraded with waste from the dissected ranges. The waste takes the form of huge alluvial fans, formed chiefly by occasional boulder-bearing floods from

2560-583: The limestone platform south of the Grand Canyon, culminating in Mount San Francisco (Humphreys Peak) (12,794 feet (3,900 m), a moderately dissected cone, and associated with many more recent smaller cones and freshlooking lava flows. Mount Taylor in western New Mexico is of similar age, but here dissection seems to have advanced farther, probably because of the weaker nature of the underlying rocks. The dissection has resulted in removing

2624-423: The maximum height a species can jump or creates flow conditions that cannot be bypassed (e.g., due to excessive water velocity) effectively limits the maximum point upstream that fish can migrate. In some cases this can mean that huge lengths of breeding habitat are lost, and over time this can have a significant impact on fish populations. In many countries, it is now a legal requirement to build fish ladders into

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2688-410: The mountains formed by the folding were worn down to the lowland stage of old age before the block-faulting occurred. When this old-mountain lowland was broken into blocks and the blocks were tilted, their attitude, but not their structure, was monoclinal. In this new attitude, they have been so maturely re-dissected in the current new cycle of erosion as to have gained elaborately carved forms in which

2752-472: The mountains. Each fan heads in a ravine at the mountain base and becomes laterally confluent with adjacent fans as it stretches several miles forward with decreasing slope and increasing fineness of material. In the upper southern part of the Basin and Range Province, in the Mojave Desert of California, and Sonoran Desert of southern California and Arizona (U.S.) and northern Sonora (Mexico) states,

2816-441: The original fault scarps . They are peculiar in having their altitude dependent on the depth of revived erosion, instead of the amount of faulting, and they are sometimes topographically reversed, in that the revived scarp overlooks a lowland worn on a weak formation in the upheaved fault-block. Another consequence of revived erosion is seen in the occurrence of great landslides , where the removal of weak ( Permian ) clays has sapped

2880-545: The plains are higher and has disclosed the many lava sheets which build up the plains, occasionally revealing a buried mountain in which the superposed river has cut an even narrower canyon. One of the most remarkable features of the Intermediate Province is seen in the temporary course taken by the Columbia River across the plains, while its canyon was obstructed by Pleistocene glaciers that came from

2944-403: The pre-existent land forms over most of its extent. Some of the flows are still so young as to preserve their scoriaceous surface. Here, the shore-line of the lava contours evenly around the spurs and enters, bay-like, into the valleys of the enclosing mountains, occasionally isolating an outlying mass. Other parts of the lava flood are much older and have been more or less deformed and eroded. Thus

3008-402: The present cycle introduced, inequalities of surface due to renewed faulting were again introduced. These still appear as cliffs, of more nearly rectilinear front than the retreating escarpments formed in the previous cycle. These cliffs are peculiar in gradually passing from one formation to another, and in having a height dependent on the displacement of the fault rather than on the structures in

3072-423: The ranges are well dissected and some of the intermontane depressions have rock floors with gentle, centripetal slopes. This area also has huge alluvial fans , with heads at canyons exiting the mountains, and laterally confluent with adjacent fans as they extend for miles with rather consistent slopes. The Basin and Range Province extends southeast down into Chihuahua state in northeast Mexico, and far south along

3136-413: The rate at which water moves downstream even slightly, a disproportionate effect can be had on the likelihood of flooding. On larger rivers, a weir can also alter the flow characteristics of the waterway to the point that vessels are able to navigate areas previously inaccessible due to extreme currents or eddies . Many larger weirs will have construction features that allow boats and river users to "shoot

3200-427: The river bottom) that reduces the water oxygen content and smothers invertebrate habitat and fish spawning sites. The oxygen content typically returns to normal once water has passed over the weir crest (although it can be hyper-oxygenated), although increased river velocity can scour the river bed causing erosion and habitat loss. Weirs can have a significant effect on fish migration . Any weir that exceeds either

3264-480: The smaller cones and exposing many lava conduits or pipes in the form of volcanic necks or buttes. The Henry Mountains in southwestern Utah are peculiar in owing their relief to the doming or blistering up of the plateau strata by the underground intrusion of large bodies or cisterns (laccolites) of lava, now more or less exposed by erosion. The large Basin and Range Province is a basin and range topography resulting from crustal extension ( extensional tectonics ). It

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3328-422: The smallest being only a few centimetres in height whilst the largest may be many metres tall and hundreds of metres long. Some common weir purposes are outlined below. Weirs allow hydrologists and engineers a simple method of measuring the volumetric flow rate in small to medium-sized streams/rivers or in industrial discharge locations. Since the geometry of the top of the weir is known and all water flows over

3392-417: The south, are valleys also heavily aggraded by mountain erosion. The structure of the region previous to faulting was dependent on long antecedent processes of accumulation and deformation and the surface of the region then was dependent on the amount of erosion suffered in the prefaulting cycle. When the region was broken into fault blocks and the blocks were uplifted and tilted, the back slope of each block

3456-534: The southeast have outlet by the Rio Grande to the Gulf of Mexico . A much larger but still narrow medial area is drained southwestward by the Colorado River to the head of the Gulf of California , where this large and very turbid river has formed the extensive Colorado River Delta , north of which the former head of the gulf is now cut off from the sea and laid bare by evaporation as a plain below sea-level. It

3520-713: The time since the dislocation of the faulted blocks, as is shown by the small dimensions of the lacustrine beaches compared to the great volume of the ravine-heading fans on which the beaches often lie. The Intermediate Province is located in parts of Washington , Oregon and Idaho . The lava plains of the Columbia River Basin are among the most extensive volcanic outpourings in the world. They cover over 210,000 square kilometres (81,000 sq mi) in southeastern Washington, eastern Oregon, and southwestern Idaho, and are known to be 4,000 feet (1,200 m) deep in some river gorges. The lava completely buries

3584-526: The uplifted, dislocated and dissected lava sheets of Yellowstone National Park in the Rocky Mountains on the east (at the headwaters of the Snake River ) are associated with the older lavas of the Columbian plains. The Columbia River has entrenched itself in a canyon-like valley around the northern and Western side of the lava plains. The Snake River has cut a deeper canyon farther southeast where

3648-891: The various small ranges on the inland lea of the Coast Mountains between the Bulkley Ranges and the Bella Coola River ). It has several subdivisions, these being: The Cariboo and Chilcotin Plateaus are separated by the Fraser River . The Nechako Plateau flanks the Fraser on both sides; its southern boundary is defined by the West Road River (aka the Blackwater River) and the Quesnel River , and its northern boundary consists of

3712-515: The water level can rise and submerge the weir without any alterations made to the structure. A polynomial weir is a weir that has a geometry defined by a polynomial equation of any order n . In practice, most weirs are low-order polynomial weirs. The standard rectangular weir is, for example, a polynomial weir of order zero. The triangular (V-notch) and trapezoidal weirs are of order one. High-order polynomial weirs are providing wider range of Head-Discharge relationships, and hence better control of

3776-546: The weir" and navigate by passing up or down stream without having to exit the river. Weirs constructed for this purpose are especially common on the River Thames , and most are situated near each of the river's 45 locks . Because a weir impounds water behind it and alters the flow regime of the river, it can have an effect on the local ecology . Typically, the reduced river velocity upstream can lead to increased siltation (deposition of fine particles of silt and clay on

3840-532: The weir, the depth of water behind the weir can be converted to a rate of flow. However, this can only be achieved in locations where all water flows over the top of the weir crest (as opposed to around the sides or through conduits or sluices) and at locations where the water that flows over the crest is carried away from the structure. If these conditions are not met, it can make flow measurement complicated, inaccurate, or even impossible. The discharge calculation can be summarised as where However, this calculation

3904-674: The work of extensive erosion on monoclinal structures. A good example of this is Echo Cliffs lying east of the Painted Desert . The Mogollon Rim escarpment is part of the transition zone between the Mogollon Plateau of the Colorado Plateau Province and the Sonoran Desert of the Basin and Range Province . With the renewal of uplift by which the earlier cycle of erosion was interrupted and

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3968-418: Was a part of the previously eroded surface and the face of the block was a surface of fracture. The present form of the higher blocks is more or less affected by erosion since faulting, while many of the lower blocks have been buried under the waste of the higher ones. In the north, where dislocations have invaded the field of the horizontal Columbian lavas, as in southeastern Oregon and northeastern California,

4032-573: Was also found at the Paulina Lake site in Oregon , dating to 7100 BC . The Cascade phase took place from 7100 to 4300 BC, and was marked by a slight change in toolkit technology from the Windust peoples. A residential structure was found for this group, dating between 5500 and 4300 BC. Other pithouses followed between 4000 and 2000 BC. Most residential structures are located on rivers. During

4096-475: Was used as well, including nets and weirs . Trade networks also flourished during this time, using sea shells, turquoise, fish grease and others. Intermontane Plateaus In the context of physical geography , the Intermontane Plateaus is one of eight physiographic regions of the contiguous United States . The region consists mostly of plateaus and mountain ranges lying between

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