Misplaced Pages

#865134

88-665: In casual usage it typically describes the Fraser River basin downstream of the Fraser Canyon . The term is sometimes used outside British Columbia to refer to the entire Fraser River sections including the Fraser Canyon and up from there to its headwaters , but in general British Columbian usage the term refers to the stretch of Lower Mainland west of the Coquihalla River mouth at the inland town of Hope , and includes all of

176-449: A drainage basin, and there are different ways to interpret that data. In the unlikely event that the gauges are many and evenly distributed over an area of uniform precipitation, using the arithmetic mean method will give good results. In the Thiessen polygon method, the drainage basin is divided into polygons with the rain gauge in the middle of each polygon assumed to be representative for

264-540: A drainage boundary is referred to as watershed delineation . Finding the area and extent of a drainage basin is an important step in many areas of science and engineering. Most of the water that discharges from the basin outlet originated as precipitation falling on the basin. A portion of the water that enters the groundwater system beneath the drainage basin may flow towards the outlet of another drainage basin because groundwater flow directions do not always match those of their overlying drainage network. Measurement of

352-617: A few days. Ground-level ozone tends to be from local sources in the valley and varies with prevailing winds. With prevailing winds from the northeast during the late fall and winter, air quality is seldom a problem. Air quality in the Fraser Valley at times exceeds the Canada-Wide Standard (CWS) for ozone (at Hope) and is close to exceeding the CWS for Particulate Matter. In colloquial usage, "Fraser Valley" usually refers only to that part of

440-543: A flood-prone property to qualify for government-subsidized insurance, a local community must adopt an ordinance that protects the floodway and requires that new residential structures built in Special Flood Hazard Areas be elevated to at least the level of the 100-year flood. Commercial structures can be elevated or floodproofed to or above this level. In some areas without detailed study information, structures may be required to be elevated to at least two feet above

528-445: A floodplain. The quantity of sediments in a floodplain greatly exceeds the river load of sediments. Thus, floodplains are an important storage site for sediments during their transport from where they are generated to their ultimate depositional environment. When the rate at which the river is cutting downwards becomes great enough that overbank flows become infrequent, the river is said to have abandoned its floodplain. Portions of

616-426: A point where surface water is lost underground . Drainage basins are similar but not identical to hydrologic units , which are drainage areas delineated so as to nest into a multi-level hierarchical drainage system . Hydrologic units are defined to allow multiple inlets, outlets, or sinks. In a strict sense, all drainage basins are hydrologic units but not all hydrologic units are drainage basins. About 48.71% of

704-428: A succession of elevated features, such as ridges and hills . A basin may consist of smaller basins that merge at river confluences , forming a hierarchical pattern . Other terms for a drainage basin are catchment area , catchment basin , drainage area , river basin , water basin , and impluvium . In North America, they are commonly called a watershed , though in other English-speaking places, "watershed"

792-546: Is a problem in freshwater systems. Much of the phosphorus in freshwater systems comes from municipal wastewater treatment plants and agricultural runoff. Stream connectivity controls whether phosphorus cycling is mediated by floodplain sediments or by external processes. Under conditions of stream connectivity, phosphorus is better able to be cycled, and sediments and nutrients are more readily retained. Water in freshwater streams ends up in either short-term storage in plants or algae or long-term in sediments. Wet/dry cycling within

880-406: Is advantageous for the rapid colonization of large areas of the floodplain. This allows them to take advantage of shifting floodplain geometry. For example, floodplain trees are fast-growing and tolerant of root disturbance. Opportunists (such as birds) are attracted to the rich food supply provided by the flood pulse. Floodplain ecosystems have distinct biozones. In Europe, as one moves away from

968-498: Is any area subject to inundation by a 100-year flood. A problem is that any alteration of the watershed upstream of the point in question can potentially affect the ability of the watershed to handle water, and thus potentially affects the levels of the periodic floods. A large shopping center and parking lot, for example, may raise the levels of 5-year, 100-year, and other floods, but the maps are rarely adjusted and are frequently rendered obsolete by subsequent development. In order for

SECTION 10

#1732829648866

1056-583: Is considered the head of the Fraser Delta . From there the river passes through some of the most fertile agricultural land in British Columbia—as well as the heart of the Metro Vancouver region—on its way through the valley to its mouth at Georgia Strait . During the last ice age , the area that would become the Fraser Valley was covered by a sheet of ice, walled in by the surrounding mountains. As

1144-488: Is defined as ending at Yale, Hope is generally to be considered the southern end of the canyon, partly because of the change in the character of the highway from that point, and perhaps also because it is at Hope that the first floodplains typifying the course of the Lower Fraser are found. Downstream from Hope, the river and adjoining floodplains widen considerably in the area of Rosedale , Chilliwack and Agassiz , which

1232-456: Is described as vertical accretion , since the deposits build upwards. In undisturbed river systems, overbank flow is frequent, typically occurring every one to two years, regardless of climate or topography. Sedimentation rates for a three-day flood of the Meuse and Rhine Rivers in 1993 found average sedimentation rates in the floodplain of between 0.57 and 1.0 kg/m . Higher rates were found on

1320-615: Is included within the Lower Fraser Valley. The Upper Fraser Valley means from Chilliwack and Agassiz to Hope. The phrases "Fraser Valley towns" and "Fraser River municipalities" include Delta and Richmond, though the colloquial "in the Valley" means from Surrey and Coquitlam eastwards. The "Tidal Fraser area" is usually defined as the area of the Fraser from the mouth at the Pacific Ocean to

1408-565: Is largely a result of flood control, hydroelectric development (such as reservoirs), and conversion of floodplains to agriculture use. Transportation and waste disposal also have detrimental effects. The result is the fragmentation of these ecosystems, resulting in loss of populations and diversity and endangering the remaining fragments of the ecosystem. Flood control creates a sharper boundary between water and land than in undisturbed floodplains, reducing physical diversity. Floodplain forests protect waterways from erosion and pollution and reduce

1496-402: Is most common in sections of rivers where the river bed is accumulating sediments ( aggrading ). Repeated flooding eventually builds up an alluvial ridge, whose natural levees and abandoned meander loops may stand well above most of the floodplain. The alluvial ridge is topped by a channel belt formed by successive generations of channel migration and meander cutoff. At much longer intervals,

1584-434: Is now possible to compare BC communities on a variety of measures. Comparative data on four measures— fine particulate matter , ground-level ozone , nitrogen dioxide and sulphur dioxide —shows the Fraser Valley to have better air quality than Vancouver on several measures. For example, Fraser Valley communities had less than half the levels of nitrogen dioxide, and were lower in fine particulate matter and sulphur dioxide (on

1672-511: Is one of the largest tidal freshwater lakes in the world . Oxbow lakes and side-sloughs are a common feature of the Lower Fraser's geography. The two main oxbows are those of Hatzic Lake and the Stave River on opposite sides of Mission, although that of the Stave has been silted in and part of it drained for a man-made lake. Around Fort Langley is an oxbow formation, mostly swamped in at the time of

1760-480: Is referred to as " watershed management ". In Brazil , the National Policy of Water Resources, regulated by Act n° 9.433 of 1997, establishes the drainage basin as the territorial division of Brazilian water management. When a river basin crosses at least one political border, either a border within a nation or an international boundary, it is identified as a transboundary river . Management of such basins becomes

1848-600: Is the Dead Sea . Drainage basins have been historically important for determining territorial boundaries, particularly in regions where trade by water has been important. For example, the English crown gave the Hudson's Bay Company a monopoly on the fur trade in the entire Hudson Bay basin, an area called Rupert's Land . Bioregional political organization today includes agreements of states (e.g., international treaties and, within

SECTION 20

#1732829648866

1936-550: Is the northernmost area of rice cultivation in the world. As the valley population grows and traffic increases, air pollution becomes an increasingly important issue; various controversies have risen over the years (most recently over " Sumas 2 ", a defeated proposal for a power plant just south of the Canadian/USA border) as to whether or not air pollution is a problem, and if it is a problem, how this should be addressed. Air quality monitoring has improved in recent years and it

2024-404: Is used only in its original sense, that of the drainage divide line. A drainage basin's boundaries are determined by watershed delineation , a common task in environmental engineering and science. In a closed drainage basin, or endorheic basin , rather than flowing to the ocean, water converges toward the interior of the basin, known as a sink , which may be a permanent lake, a dry lake , or

2112-682: The African Great Lakes , the interiors of Australia and the Arabian Peninsula , and parts in Mexico and the Andes . Some of these, such as the Great Basin, are not single drainage basins but collections of separate, adjacent closed basins. In endorheic bodies of water where evaporation is the primary means of water loss, the water is typically more saline than the oceans. An extreme example of this

2200-792: The Continental Divide , northern Alaska and parts of North Dakota , South Dakota , Minnesota , and Montana in the United States, the north shore of the Scandinavian peninsula in Europe, central and northern Russia, and parts of Kazakhstan and Mongolia in Asia , which totals to about 17% of the world's land. Just over 13% of the land in the world drains to the Pacific Ocean . Its basin includes much of China, eastern and southeastern Russia, Japan,

2288-473: The Fraser Valley Regional District , though that consists of only about half of the actual Fraser Valley, and is made up of the municipalities and incorporated areas from Abbotsford and Mission eastwards to Hope. It also includes areas not in the Fraser Valley, particularly the lower Fraser Canyon from Boston Bar to Hope. The term "Central Fraser Valley" refers to Mission and Abbotsford and

2376-681: The Korean Peninsula , most of Indochina, Indonesia and Malaysia, the Philippines, all of the Pacific Islands , the northeast coast of Australia , and Canada and the United States west of the Continental Divide (including most of Alaska), as well as western Central America and South America west of the Andes. The Indian Ocean 's drainage basin also comprises about 13% of Earth's land. It drains

2464-547: The Yellow River in China – see list of deadliest floods . The worst of these, and the worst natural disaster (excluding famine and epidemics), was the 1931 China floods , estimated to have killed millions. This had been preceded by the 1887 Yellow River flood , which killed around one million people and is the second-worst natural disaster in history. The extent of floodplain inundation depends partly on flood magnitude, defined by

2552-674: The groundwater . A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. Floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river . Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high discharge . The soils usually consist of clays, silts , sands, and gravels deposited during floods. Because of regular flooding, floodplains frequently have high soil-fertility since nutrients are deposited with

2640-647: The return period . In the United States, the Federal Emergency Management Agency (FEMA) manages the National Flood Insurance Program (NFIP). The NFIP offers insurance to properties located within a flood-prone area, as defined by the Flood Insurance Rate Map (FIRM), which depicts various flood risks for a community. The FIRM typically focuses on the delineation of the 100-year flood inundation area, also known within

2728-448: The 2011 Census, 76.47% of the Fraser Valley regional district in BC have English as mother tongue ; Punjabi is the mother tongue of 10.02% of the population, followed by German (3.49%), Dutch (1.39%), French (1.07%), Korean (0.69%), Spanish (0.66%), Tagalog (0.35%), Chinese, n.o.s. (0.33%), and Vietnamese (0.30%). Today, the Fraser Valley has a mix of land uses, ranging from

Fraser Valley - Misplaced Pages Continue

2816-887: The Canadian portion of the Fraser Lowland as well as the valleys and upland areas flanking it. It is divided into the Upper Fraser Valley and Lower Fraser Valley by the Vedder River mouth at the eastern foothills of Sumas Mountain , although the Lower Valley section upstream of McMillan Island and the Salmon River mouth (at Fort Langley ) used to be called the Central Fraser Valley up until 1995 (see Central Fraser Valley Regional District ). Administratively,

2904-463: The Fraser Valley comprises parts of the regional districts of Metro Vancouver and the Fraser Valley Regional District . The main population centres in the Fraser Valley are Greater Vancouver , Abbotsford and Chilliwack . This section of the Fraser River is known by local indigenous peoples as "Sto:lo" in the Halqemeylem language of the area, and this term has been adopted to refer to all of

2992-448: The Fraser but help drain its lowland. The Fraser is tidal as far upstream as the town of Mission and, across the river, the City of Abbotsford , which is at the Fraser's closest approach to the international boundary, about 6 miles north of Sumas, Washington . Pitt Lake , one of the Fraser's last tributaries and among its largest, is so low in elevation, despite its mountain setting, that it

3080-654: The Fraser's lower tributaries have floodplains of their own, shared in common with the Fraser freshet. Of varying size these include the Harrison River , Chilliwack River ( Vedder River ), Hatzic Creek and Hatzic Lake, the Stave , Alouette , Pitt and Coquitlam Rivers . Also incorporated in the Fraser delta region are the Nicomekl and Serpentine River floodplains and the Sumas River drainage, which flow to saltwater independently of

3168-684: The Mission bridge. Everything in between there is influenced greatly by ocean tides, including the largest tidal lake in North America, Pitt Lake. The south shore of the Central and Upper Fraser Valley is also known colloquially as the " Bible Belt " of British Columbia and is home to many of Canada's largest churches, notably the Mennonite Brethren and the Dutch Reformed Church , a reflection of

3256-545: The NFIP as the Special Flood Hazard Area. Where a detailed study of a waterway has been done, the 100-year floodplain will also include the floodway, the critical portion of the floodplain which includes the stream channel and any adjacent areas that must be kept free of encroachments that might block flood flows or restrict storage of flood waters. Another commonly encountered term is the Special Flood Hazard Area, which

3344-598: The US, interstate compacts ) or other political entities in a particular drainage basin to manage the body or bodies of water into which it drains. Examples of such interstate compacts are the Great Lakes Commission and the Tahoe Regional Planning Agency . In hydrology , the drainage basin is a logical unit of focus for studying the movement of water within the hydrological cycle . The process of finding

3432-558: The West Coast in both Canada and the United States. The interaction of indigenous peoples and settlers led to the growth of Chinook Wawa , a pidgin language that was used throughout the Fraser River Valley until the early 1900s. Industrialization of the river began with the use of the traditional trade waterway by steamboats and eventually, roads and railways were built, fueled by and in turn fuelling further population growth. Today,

3520-400: The abandoned floodplain may be preserved as fluvial terraces . Floodplains support diverse and productive ecosystems . They are characterized by considerable variability in space and time, which in turn produces some of the most species-rich of ecosystems. From the ecological perspective, the most distinctive aspect of floodplains is the flood pulse associated with annual floods, and so

3608-511: The advantages provided by the richness of the alluvial soil of the floodplain are severely offset by frequent floods brought on by cyclones and annual monsoon rains. These extreme weather events cause severe economic disruption and loss of human life in the densely-populated region. Floodplain soil composition is unique and varies widely based on microtopography. Floodplain forests have high topographic heterogeneity which creates variation in localized hydrologic conditions. Soil moisture within

Fraser Valley - Misplaced Pages Continue

3696-490: The air mass collides with the Olympic Mountains . The cold air from the Fraser Valley can also flow out over the Pacific Ocean. Lanes of convective ocean-effect clouds and showers are produced as heat and moisture modify the very dry, frigid air mass. These then typically organize as a low pressure system which returns the showers to the coast south of Canada, often bringing snow to unusually low elevations. According to

3784-406: The basin, it can form tributaries that change the structure of the land. There are three different main types, which are affected by the rocks and ground underneath. Rock that is quick to erode forms dendritic patterns, and these are seen most often. The two other types of patterns that form are trellis patterns and rectangular patterns. Rain gauge data is used to measure total precipitation over

3872-461: The channel shifts varies greatly, with reported rates ranging from too slow to measure to as much as 2,400 feet (730 m) per year for the Kosi River of India. Overbank flow takes place when the river is flooded with more water than can be accommodated by the river channel. Flow over the banks of the river deposits a thin veneer of sediments that is coarsest and thickest close to the channel. This

3960-430: The discharge of water from a basin may be made by a stream gauge located at the basin's outlet. Depending on the conditions of the drainage basin, as rainfall occurs some of it seeps directly into the ground. This water will either remain underground, slowly making its way downhill and eventually reaching the basin, or it will permeate deeper into the soil and consolidate into groundwater aquifers. As water flows through

4048-441: The drainage area is dependent on the soil type. Certain soil types such as sandy soils are very free-draining, and rainfall on sandy soil is likely to be absorbed by the ground. However, soils containing clay can be almost impermeable and therefore rainfall on clay soils will run off and contribute to flood volumes. After prolonged rainfall even free-draining soils can become saturated , meaning that any further rainfall will reach

4136-692: The drainage basin to the mouth, and may accumulate there, disturbing the natural mineral balance. This can cause eutrophication where plant growth is accelerated by the additional material. Because drainage basins are coherent entities in a hydrological sense, it has become common to manage water resources on the basis of individual basins. In the U.S. state of Minnesota , governmental entities that perform this function are called " watershed districts ". In New Zealand, they are called catchment boards. Comparable community groups based in Ontario, Canada, are called conservation authorities . In North America, this function

4224-821: The eastern coast of Africa, the coasts of the Red Sea and the Persian Gulf , the Indian subcontinent , Burma, and most parts of Australia . The five largest river basins (by area), from largest to smallest, are those of the Amazon (7 million km ), the Congo (4 million km ), the Nile (3.4 million km ), the Mississippi (3.22 million km ), and the Río de la Plata (3.17 million km ). The three rivers that drain

4312-422: The flood waters. This can encourage farming ; some important agricultural regions, such as the Nile and Mississippi river basins , heavily exploit floodplains. Agricultural and urban regions have developed near or on floodplains to take advantage of the rich soil and freshwater. However, the risk of inundation has led to increasing efforts to control flooding . Most floodplains are formed by deposition on

4400-448: The floodplain ecosystem is defined as the part of the river valley that is regularly flooded and dried. Floods bring in detrital material rich in nutrients and release nutrients from dry soil as it is flooded. The decomposition of terrestrial plants submerged by the floodwaters adds to the nutrient supply. The flooded littoral zone of the river (the zone closest to the river bank) provides an ideal environment for many aquatic species, so

4488-462: The floodplain has a big impact on phosphorus availability because it alters water level, redox state, pH, and physical properties of minerals. Dry soils that were previously inundated have reduced availability of phosphorus and increased affinity for obtaining phosphorus. Human floodplain alterations also impact the phosphorus cycle. Particulate phosphorus and soluble reactive phosphorus (SRP) can contribute to algal blooms and toxicity in waterways when

SECTION 50

#1732829648866

4576-579: The floodplain. Other smaller-scale mitigation efforts include acquiring and demolishing flood-prone buildings or flood-proofing them. In some floodplains, such as the Inner Niger Delta of Mali , annual flooding events are a natural part of the local ecology and rural economy , allowing for the raising of crops through recessional agriculture . However, in Bangladesh , which occupies the Ganges Delta ,

4664-419: The fort's foundation, which was drained and made part of the fort's farm and remains farmland today. The system of sloughs and side-channels of the river is complicated, but important sloughs include those around Nicomen Island , Sea Bird Island and flanking the river from Rosedale to Sumas Mountain , on the western side of Chilliwack . In winter, the Fraser Valley occasionally plays a significant role in

4752-516: The greatest portion of western Sub-Saharan Africa , as well as Western Sahara and part of Morocco . The two major mediterranean seas of the world also flow to the Atlantic. The Caribbean Sea and Gulf of Mexico basin includes most of the U.S. interior between the Appalachian and Rocky Mountains , a small part of the Canadian provinces of Alberta and Saskatchewan , eastern Central America ,

4840-435: The ground and along rivers it can pick up nutrients , sediment , and pollutants . With the water, they are transported towards the outlet of the basin, and can affect the ecological processes along the way as well as in the receiving water body . Modern use of artificial fertilizers , containing nitrogen (as nitrates ), phosphorus , and potassium , has affected the mouths of drainage basins. The minerals are carried by

4928-744: The ground at its terminus, the area can go by several names, such playa, salt flat, dry lake , or alkali sink . The largest endorheic basins are in Central Asia , including the Caspian Sea , the Aral Sea , and numerous smaller lakes. Other endorheic regions include the Great Basin in the United States, much of the Sahara Desert , the drainage basin of the Okavango River ( Kalahari Basin ), highlands near

5016-462: The heavy settlement of the Valley by post-war Dutch and German immigrants, as well as the Canadian headquarters of many Christian/ Evangelical para-church organisations such as Focus on the Family and Power to Change, the Canadian branch of Cru_(Christian_organization) , formerly known as Campus Crusade for Christ. Voters in south shore ridings typically elect right-wing candidates, while in ridings on

5104-456: The ice receded, land that had been covered by glaciers became covered by water instead, then slowly rose above the water, forming the basin that exists today. The valley is the largest landform of the Lower Mainland ecoregion, with its delta considered to begin in the area of Agassiz and Chilliwack, although stretches of floodplain flank the mountainsides between there and Hope. Several of

5192-465: The impact of floodwaters. The disturbance by humans of temperate floodplain ecosystems frustrates attempts to understand their natural behavior. Tropical rivers are less impacted by humans and provide models for temperate floodplain ecosystems, which are thought to share many of their ecological attributes. Excluding famines and epidemics , some of the worst natural disasters in history (measured by fatalities) have been river floods, particularly in

5280-579: The indigenous peoples of the Fraser Lowland , other than the Squamish and Musqueam . The indigenous peoples of the area have long made use of the river valley for agricultural and commercial exploits and continue to do so today. The Indigenous people were not consulted in the Treaty of Oregon , which saw the United States and Great Britain define and recognize each other's claims to the area. This overstepping of jurisdiction inevitably led to conflict as Great Britain

5368-448: The inside of river meanders and by overbank flow. Wherever the river meanders, the flowing water erodes the river bank on the outside of the meander. At the same time, sediments are simultaneously deposited in a bar on the inside of the meander. This is described as lateral accretion since the deposition builds the point bar laterally into the river channel. Erosion on the outside of the meander usually closely balances deposition on

SECTION 60

#1732829648866

5456-417: The inside so that the channel shifts in the direction of the meander without changing significantly in width. The point bar is built up to a level very close to that of the river banks. Significant net erosion of sediments occurs only when the meander cuts into higher ground. The overall effect is that, as the river meanders, it creates a level flood plain composed mostly of point bar deposits. The rate at which

5544-619: The islands of the Caribbean and the Gulf, and a small part of northern South America. The Mediterranean Sea basin, with the Black Sea , includes much of North Africa , east-central Africa (through the Nile River ), Southern , Central, and Eastern Europe , Turkey , and the coastal areas of Israel , Lebanon , and Syria . The Arctic Ocean drains most of Western Canada and Northern Canada east of

5632-438: The latter measure, Abbotsford and Chilliwack were among the lowest of all BC sites). In certain weather conditions during the summer, prevailing westerly winds blow air pollution from vehicles and from ships in Vancouver harbour east up the triangular delta, trapping it between the Coast Mountains on the north and the Cascades on the southeast. Air quality suffers. This usually occurs during a temperature inversion , and lasts for

5720-457: The levees (4 kg/m or more) and on low-lying areas (1.6 kg/m ). Sedimentation from the overbank flow is concentrated on natural levees, crevasse splays , and in wetlands and shallow lakes of flood basins. Natural levees are ridges along river banks that form from rapid deposition from the overbank flow. Most of the suspended sand is deposited on the levees, leaving the silt and clay sediments to be deposited as floodplain mud further from

5808-617: The makeup towards ash (49%) with maple increasing to 14% and oak decreasing to 25%. Semiarid floodplains have a much lower species diversity. Species are adapted to alternating drought and flood. Extreme drying can destroy the ability of the floodplain ecosystem to shift to a healthy wet phase when flooded. Floodplain forests constituted 1% of the landscape of Europe in the 1800s. Much of this has been cleared by human activity, though floodplain forests have been impacted less than other kinds of forests. This makes them important refugia for biodiversity. Human destruction of floodplain ecosystems

5896-406: The most important transportation through the region are the Canadian Pacific Railway and Canadian National Railway transcontinental main lines, the Lougheed Highway (Hwy 7), and the Trans-Canada Highway ( Hwy 1 ). After descending through the rapids of the Fraser Canyon , the Fraser River emerges almost at sea level at Yale , over 100 km inland. Although the canyon in geographic terms

5984-409: The most water, from most to least, are the Amazon, Ganges , and Congo rivers. Endorheic basin are inland basins that do not drain to an ocean. Endorheic basins cover around 18% of the Earth's land. Some endorheic basins drain to an Endorheic lake or Inland sea . Many of these lakes are ephemeral or vary dramatically in size depending on climate and inflow. If water evaporates or infiltrates into

6072-694: The nitrogen-to-phosphorus ratios are altered farther upstream. In areas where the phosphorus load is primarily particulate phosphorus, like the Mississippi River, the most effective ways of removing phosphorus upstream are sedimentation, soil accretion, and burial. In basins where SRP is the primary form of phosphorus, biological uptake in floodplain forests is the best way of removing nutrients. Phosphorus can transform between SRP and particulate phosphorus depending on ambient conditions or processes like decomposition, biological uptake, redoximorphic release, and sedimentation and accretion. In either phosphorus form, floodplain forests are beneficial as phosphorus sinks, and

6160-418: The rainfall on the area of land included in its polygon. These polygons are made by drawing lines between gauges, then making perpendicular bisectors of those lines form the polygons. The isohyetal method involves contours of equal precipitation are drawn over the gauges on a map. Calculating the area between these curves and adding up the volume of water is time-consuming. Isochrone maps can be used to show

6248-414: The regulation of immigration and the continuation of mining on the river by the indigenous inhabitants and the new immigrants. This war was part of a series of local conflicts surrounding the arrival of settlers ahead of American and British capacity to maintain order and refusal to cooperate with or recognize indigenous land claims and demands. These conflicts were pivotal in many aspects to the settlement of

6336-625: The responsibility of the countries sharing it. Nile Basin Initiative , OMVS for Senegal River , Mekong River Commission are a few examples of arrangements involving management of shared river basins. Management of shared drainage basins is also seen as a way to build lasting peaceful relationships among countries. The catchment is the most significant factor determining the amount or likelihood of flooding . Catchment factors are: topography , shape, size, soil type, and land use (paved or roofed areas). Catchment topography and shape determine

6424-580: The river may abandon the channel belt and build a new one at another position on the floodplain. This process is called avulsion and occurs at intervals of 10–1000 years. Historical avulsions leading to catastrophic flooding include the 1855 Yellow River flood and the 2008 Kosi River flood . Floodplains can form around rivers of any kind or size. Even relatively straight stretches of river are capable of producing floodplains. Mid-channel bars in braided rivers migrate downstream through processes resembling those in point bars of meandering rivers and can build up

6512-461: The river rather than being absorbed by the ground. If the surface is impermeable the precipitation will create surface run-off which will lead to higher risk of flooding; if the ground is permeable, the precipitation will infiltrate the soil. Land use can contribute to the volume of water reaching the river, in a similar way to clay soils. For example, rainfall on roofs, pavements , and roads will be collected by rivers with almost no absorption into

6600-408: The river's north side elections sway between left-wing and right-wing parties regularly. Drainage basin A drainage basin is an area of land in which all flowing surface water converges to a single point, such as a river mouth , or flows into another body of water , such as a lake or ocean . A basin is separated from adjacent basins by a perimeter, the drainage divide , made up of

6688-511: The river, the successive plant communities are bank vegetation (usually annuals); sedge and reeds; willow shrubs; willow-poplar forest; oak-ash forest; and broadleaf forest. Human disturbance creates wet meadows that replace much of the original ecosystem. The biozones reflect a soil moisture and oxygen gradient that in turn corresponds to a flooding frequency gradient. The primeval floodplain forests of Europe were dominated by oak (60%) elm (20%) and hornbeam (13%), but human disturbance has shifted

6776-418: The river. Levees are typically built up enough to be relatively well-drained compared with nearby wetlands, and levees in non-arid climates are often heavily vegetated. Crevasses are formed by breakout events from the main river channel. The river bank fails, and floodwaters scour a channel. Sediments from the crevasse spread out as delta -shaped deposits with numerous distributary channels. Crevasse formation

6864-408: The spawning season for fish often coincides with the onset of flooding. Fish must grow quickly during the flood to survive the subsequent drop in water level. As the floodwaters recede, the littoral experiences blooms of microorganisms, while the banks of the river dry out and terrestrial plants germinate to stabilize the bank. The biota of floodplains has high annual growth and mortality rates, which

6952-418: The speed with which the runoff reaches a river. A long thin catchment will take longer to drain than a circular catchment. Size will help determine the amount of water reaching the river, as the larger the catchment the greater the potential for flooding. It is also determined on the basis of length and width of the drainage basin. Soil type will help determine how much water reaches the river. The runoff from

7040-459: The surrounding grade. Many State and local governments have, in addition, adopted floodplain construction regulations which are more restrictive than those mandated by the NFIP. The US government also sponsors flood hazard mitigation efforts to reduce flood impacts. California 's Hazard Mitigation Program is one funding source for mitigation projects. A number of whole towns such as English, Indiana , have been completely relocated to remove them from

7128-415: The time taken for rain to reach the river, while catchment size, soil type, and development determine the amount of water to reach the river. Generally, topography plays a big part in how fast runoff will reach a river. Rain that falls in steep mountainous areas will reach the primary river in the drainage basin faster than flat or lightly sloping areas (e.g., > 1% gradient). Shape will contribute to

7216-477: The time taken for runoff water within a drainage basin to reach a lake, reservoir or outlet, assuming constant and uniform effective rainfall. Drainage basins are the principal hydrologic unit considered in fluvial geomorphology . A drainage basin is the source for water and sediment that moves from higher elevation through the river system to lower elevations as they reshape the channel forms. Drainage basins are important in ecology . As water flows over

7304-672: The upper 30 cm of the soil profile also varies widely based on microtopography which affects oxygen availability. Floodplain soil stays aerated for long stretches of time in between flooding events, but during flooding, saturated soil can become oxygen-depleted if it stands stagnant for long enough. More soil oxygen is available at higher elevations farther from the river. Floodplain forests generally experience alternating periods of aerobic and anaerobic soil microbe activity which affects fine root development and desiccation. Floodplains have high buffering capacity for phosphorus to prevent nutrient loss to river outputs. Phosphorus nutrient loading

7392-595: The urban and industrial centres of Vancouver , Surrey , and Abbotsford through golf courses and parks to dairy farms and market gardens . Agricultural land in the valley – much of it protected by the Agricultural Land Reserve – is intensively farmed: the Fraser Valley brings in nearly 40% of British Columbia's annual agricultural revenue, although it makes up a small percentage of the province's total land area. The Fraser Valley, specifically in Abbotsford ,

7480-414: The valley beyond the continuously built-up urban area around Vancouver, up to and including Chilliwack and Agassiz, about 80 km east, and abutting the border with Washington's Whatcom County ; news media typically also include the built-up eastern suburban areas of Vancouver which a few decades ago were mixed farmland and forest, typical of "the Valley". The Fraser Valley region is also the namesake of

7568-532: The weather regime along the west coast of North America as far south as California , acting as a natural outlet for the intensely cold Arctic air mass which typically sits over Western Canada during winter. Under certain meteorological conditions strong winds pour out of the Fraser Valley and over the relatively warmer waters of the Strait of Georgia and the Strait of Juan de Fuca . This can cause ocean-effect snow, especially between Port Angeles and Sequim , where

7656-641: The world's land drains to the Atlantic Ocean . In North America , surface water drains to the Atlantic via the Saint Lawrence River and Great Lakes basins, the Eastern Seaboard of the United States, the Canadian Maritimes , and most of Newfoundland and Labrador . Nearly all of South America east of the Andes also drains to the Atlantic, as does most of Western and Central Europe and

7744-601: Was incapable of exercising the control they claimed over the river valley. As a wave of immigrants flooded into the Fraser River Valley because of the Fraser Canyon Gold Rush , the British were unable to maintain order without the cooperation of the local indigenous peoples, and the Fraser Canyon War broke out. The war was resolved with a series of treaties, none of which remain to this day, but which evidently included

#865134