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61-519: The permanent swamp is surrounded by a seasonally-inundated floodplain , varying from about 5 to 25 km wide in the south and east, up to 40 km in the north, and reaching the Kafue River and its swamps 25 km to the west and north-west. When the Kafue floods it overflows north-west through the normally dry Mwinuna channel and into the lower Lukanga River, while another channel drains out of

122-589: A 1980 estimate of 2600 t for the fish catch, sold in the markets of Lusaka, Kabwe, and the Copperbelt . A more recent report puts the figure at 1,200 t and notes declining catches due to over-fishing. There are some smaller commercial farms especially near the Great North Road which passes within 10 km of the floodplain at the south-eastern edge. Several large commercial farms and plantations, some with dry-season irrigation, have been established on

183-554: 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

244-445: 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

305-411: A maximum of 8000 km at the peak flooding of a good rainy season. There are several inhabited islands of higher ground which stay dry through the rainy season, mainly in an arc along the western edge of the permanent swamp, such as Chilwa Island and Chiposha Island. In addition the swamp contains floating islands of papyrus which support temporary fishing camps. No seasonal roads or bridges reach into

366-462: A regression developed from water samples that are filtered, dried, and weighed), multiplying the concentration with the discharge as above, and integrating over the entire plume. To distinguish the spill contribution, the background turbidity is subtracted from the spill plume turbidity. Since the spill plume in open water varies in space and time, an integration over the entire plume is required, and repeated many times to get acceptably low uncertainty in

427-414: Is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay . It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary or permanent) of fine sediments on bottoms where they are undesirable. Siltation is most often caused by soil erosion or sediment spill. It is sometimes referred to by

488-546: 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

549-406: 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

610-401: 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

671-498: 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

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732-460: 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

793-565: 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

854-402: 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,

915-582: Is visited by elephant , buffalo , eland and roan antelope . In 2000 the Department of National Parks and Wildlife Service (NPWS) was reported to be under-resourced in the area and the swamps "are virtually unprotected, and poaching is excessive". Deforestation for charcoal production and for ' slash and burn ' and other types of farming is also reported as a major threat to the Lukanga Swamp ecosystem mainly because it results in erosion of

976-504: The Kafue River is a game management area stretching as far as Kafue National Park . Lukanga Swamp therefore could be considered a potential extension of that rich wildlife haven. Lukanga Swamp is home to 316 reported bird species. It supports populations of hippopotamus , and crocodile , and is considered an important site for conservation of lechwe , oribi , marsh mongoose , sitatunga , bushbuck , and python . The western side

1037-557: 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

1098-475: The offshore dumping of material dredged from harbours and navigation channels. The deposition may also be to build up the coastline, for artificial islands , or for beach replenishment . Climate change also affects siltation rates. Another important cause of siltation is the septage and other sewage sludges that are discharged from households or business establishments with no septic tanks or wastewater treatment facilities to bodies of water. While

1159-747: 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

1220-455: The sediment in transport is in suspension , it acts as a pollutant for those who require clean water, such as for cooling or in industrial processes, and it includes aquatic life that are sensitive to suspended material in the water. While nekton have been found to avoid spill plumes in the water (e.g. the environmental monitoring project during the building of the Øresund Bridge ), filtering benthic organisms have no way of escape. Among

1281-462: The Lukanga Swamp remains relatively inaccessible and even today government authorities in Kabwe and Lusaka have relatively little knowledge of or effect on the area. The inhabitants of villages mainly around the north-east, east and southern floodplain practise traditional methods of fishing in the swamps and farm the edge of the floodplain. There is no commercial fishing of any size, but FAO reported

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1342-560: 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

1403-400: 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

1464-511: 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

1525-426: The ambiguous term " sediment pollution ", which can also refer to a chemical contamination of sediments accumulated on the bottom, or to pollutants bound to sediment particles. Although "siltation" is not perfectly stringent, since it also includes particle sizes other than silt, it is preferred for its lack of ambiguity. The origin of the increased sediment transport into an area may be erosion on land or activities in

1586-467: 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

1647-429: The first line of defense is to maintain land cover and prevent soil erosion in the first place. The second line of defense is to trap the material before it reaches the stream network (known as sediment control ). In urban areas, the defenses are to keep land uncovered for as short a time as possible during construction and to use silt screens to prevent the sediment from getting released in water bodies. During dredging,

1708-472: 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

1769-448: 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

1830-462: 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

1891-599: 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 ,

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1952-410: The food gathering of filtering organisms, and the sediment accumulation on the bottom may bury organisms to the point that they starve or even die. It is only if the concentration is extreme that it decreases the light level sufficiently for impacting primary productivity. An accumulation of as little as 1 mm (0.039 in) may kill coral polyps. While the effect of the siltation on the biota (once

2013-455: The harm is already done) can be studied by repeated inspection of selected test plots, the magnitude of the siltation process in the impact area may be measured directly by monitoring in real time. Parameters to measure are sediment accumulation, turbidity at the level of the filtering biota, and optionally incident light. Siltation of the magnitude that it affects shipping can also be monitored by repeated bathymetric surveys. In rural areas,

2074-401: The human-caused disconnect between floodplains and rivers exacerbates the phosphorus overload. Floodplain soils tend to be high in eco-pollutants, especially persistent organic pollutant (POP) deposition. Proper understanding of the distribution of soil contaminants is difficult because of high variation in microtopography and soil texture within floodplains. Siltation Siltation

2135-465: 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

2196-448: 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

2257-417: 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

2318-558: The land, turbidity of the water and siltation . In nearly all areas north-east of the swamp forests have been cleared especially for charcoal production, and land clearing for farming has been extensive on the north-east, east and southern sides of the swamp. Only the western side remains relatively untouched. The development of a tourism industry in the area, which (as has been seen for the national parks) results in greater wildlife conservation efforts, depends on providing access to this part from Mumbwa or Kabwe. The nearly circular shape of

2379-457: 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

2440-556: The main permanent swamp has led to speculation that Lukanga Swamp may be an impact crater (astrobleme) formed by the impact of a meteorite . However research on the ground in 2002 found no evidence of impact shock in rocks of the area, concluding that the Lukanga Swamp is not an astrobleme. In the absence of other research data the origin of the swamp is unknown. 14°13′14″S 27°38′25″E  /  14.22046°S 27.64023°E  / -14.22046; 27.64023 Floodplain A floodplain or flood plain or bottomlands

2501-617: 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

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2562-476: The most difficult conflicts of interest to resolve, as regards siltation mitigation, is perhaps beach nourishment . When sediments are placed on or near beaches in order to replenish an eroding beach, any fines in the material will continue to be washed out for as long as the sand is being reworked. Since all replenished beaches are eroding or they would not need replenishment, they will contribute to nearshore siltation almost for as long as it takes to erode away what

2623-436: The most sensitive organisms are coral polyps. Generally speaking, hard bottom communities and mussel banks (including oysters) are more sensitive to siltation than sand and mud bottoms. Unlike in the sea, in a stream, the plume will cover the entire channel, except possibly for backwaters, and so fish will also be directly affected in most cases. Siltation can also affect navigation channels or irrigation channels. It refers to

2684-762: 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

2745-606: The north side of the floodplain. The floodplain is classed as the Zambezian flooded grasslands ecoregion, and the surrounding woodland savanna is the Central Zambezian miombo woodlands ecoregion, except on the south-east side which is Zambezian and mopane woodlands ecoregion. Flooded grasslands are considered to be productive and diverse owing to the nutrients brought by the flood and the fact they provide both grazing and aquatic habitats. The miombo woodland west of

2806-403: The original land-covering vegetation and temporarily creating something akin to an urban desert from which fines are easily washed out during rainstorms. In water, the main pollution source is sediment spill from dredging , the transportation of dredged material on barges, and the deposition of dredged material in or near water. Such deposition may be made to get rid of unwanted material, such as

2867-401: The permanently swampy areas, and only one road crosses any part of the floodplain to any extent, a dry-season road from Kabwe (with a feeder from Mpongwe ) going through Mukobwe and Ibondo to a ferry across the Kafue and on to Ngabwe. Two other dirt tracks come from Mumbwa in the south to the river near Mswebe and to the floodplain at Mwanamulambo. Despite its central location in the country,

2928-474: The proportion of fines in sediments typically increases in the offshore direction, the deposited sand will inevitably contain a significant percentage of siltation-contributing fines. It is desirable to minimize the siltation of irrigation channels by hydrologic design, the objective being not to create zones with falling sediment transport capacity, as that is conducive to sedimentation. Once sedimentation has occurred, in irrigation or navigation channels, dredging

2989-474: The results. The measurements are made close to the source, in the order of a few hundred meters. Anything beyond a work area buffer zone for sediment spill is considered the potential impact area. In the open sea, the impact of concern is almost exclusively with the sessile bottom communities since empirical data show that fish effectively avoid the impacted area. The siltation affects the bottom community in two main ways. The suspended sediment may interfere with

3050-580: 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

3111-511: 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

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3172-418: 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

3233-408: 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

3294-409: The spill can be minimized but not eliminated completely by the way the dredger is designed and operated. If the material is deposited on land, efficient sedimentation basins can be constructed. If it is dumped into relatively deep water, there will be a significant spill during dumping but not thereafter, and the spill that arises has minimal impact if there are only fine-sediment bottoms nearby. One of

3355-445: The stream, by measuring the sediment concentration and multiplying that with the discharge ; for example, 50 mg/L (1.8 × 10  lb/cu in) times 30 m /s (1,100 cu ft/s) gives 1.5 kg/s (200 lb/min). Also, sediment spill is better measured in transport than at the source. The sediment transport in open water is estimated by measuring the turbidity , correlating turbidity to sediment concentration (using

3416-459: 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

3477-454: The swamp back into the Kafue in the south-west. The Kafue meanders through its own swamps which are up to 10 km wide and extend for 90 km along the river. Numerous short rivers and streams flow into the swamp from the south, east and north, of which the Lukanga is the largest. In the rainy season the floodplains are inundated increasing the area of the wetland to 6000 km, reaching

3538-409: The undesired accumulation of sediments in channels intended for vessels or for distributing water. One may distinguish between measurements at the source, during transport, and within the affected area. Source measurements of erosion may be very difficult since the lost material may be a fraction of a millimeter per year. Therefore, the approach taken is typically to measure the sediment in transport in

3599-672: 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

3660-400: The water. In rural areas, the erosion source is typically soil degradation by intensive or inadequate agricultural practices, leading to soil erosion , especially in fine-grained soils such as loess . The result will be an increased amount of silt and clay in the water bodies that drain the area. In urban areas, the erosion source is typically construction activities, which involve clearing

3721-422: Was added, albeit with somewhat decreasing intensity over time. Since the leakage is detrimental to coral reefs, the practice leads to a direct conflict between the public interest of saving beaches, and preserving any nearshore coral reefs. To minimize the conflict, beach replenishment should not be done with sand containing any silt or clay fractions. In practice the sand is often taken from offshore areas, and since

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