River ecosystems are flowing waters that drain the landscape, include the biotic interactions amongst plants and micro-organisms, as well as abiotic physical and chemical interactions of its many parts. River ecosystems are part of larger watershed networks or catchments, where smaller headwater streams drain into mid-size streams, which progressively drain into larger river networks. River ecosystems are prime examples of lotic ecosystems. Lotic refers from the Latin lotus, meaning washed. Lotic waters range from springs only a few centimeters wide to major rivers kilometers in width. Much of this article applies to lotic ecosystems in general, including related lotic systems such as streams and springs. Lotic ecosystems can be contrasted with lentic ecosystems, which involve still terrestrial waters such as lakes and wetlands. Together, these two ecosystems form the more general study area of freshwater or aquatic ecology; the following unifying characteristics make the ecology of running waters unique among aquatic habitats.
Flow is unidirectional. There is a state of continuous physical change. There is a high degree of temporal heterogeneity at all scales. Variability between lotic systems is quite high; the biota is specialized to live with flow conditions. The non living components of an ecosystem are called abiotic components. E.g stone,air,soil,etc. Unidirectional water flow is the key factor in lotic systems influencing their ecology. Stream flow can be intermittent, though. Stream flow is the result of the summative inputs from groundwater and overland flow. Water flow can vary between systems, ranging from torrential rapids to slow backwaters that seem like lentic systems; the speed or velocity of the water flow of the water column can vary within a system and is subject to chaotic turbulence, though water velocity tends to be highest in the middle part of the stream channel. This turbulence results in divergences of flow from the mean downslope flow vector as typified by eddy currents; the mean flow rate vector is based on variability of friction with the bottom or sides of the channel, sinuosity and the incline gradient.
In addition, the amount of water input into the system from direct precipitation, and/or groundwater can affect flow rate. The amount of water in a stream is measured as discharge; as water flows downstream and rivers most gain water volume, so at base flow, smaller headwater streams have low discharge, while larger rivers have much higher discharge. The "flow regime" of a river or stream includes the general patterns of discharge over annual or decadal time scales, may capture seasonal changes in flow. While water flow is determined by slope, flowing waters can alter the general shape or direction of the stream bed, a characteristic known as geomorphology; the profile of the river water column is made up of three primary actions: erosion and deposition. Rivers have been described as "the gutters down which run the ruins of continents". Rivers are continuously eroding and depositing substrate and organic material; the continuous movement of water and entrained material creates a variety of habitats, including riffles and pools.
Light is important to lotic systems, because it provides the energy necessary to drive primary production via photosynthesis, can provide refuge for prey species in shadows it casts. The amount of light that a system receives can be related to a combination of internal and external stream variables; the area surrounding a small stream, for example, might be shaded by surrounding forests or by valley walls. Larger river systems tend to be wide so the influence of external variables is minimized, the sun reaches the surface; these rivers tend to be more turbulent and particles in the water attenuate light as depth increases. Seasonal and diurnal factors might play a role in light availability because the angle of incidence, the angle at which light strikes water can lead to light lost from reflection. Known as Beer's Law, the shallower the angle, the more light is reflected and the amount of solar radiation received declines logarithmically with depth. Additional influences on light availability include cloud cover and geographic position.
Most lotic species are poikilotherms whose internal temperature varies with their environment, thus temperature is a key abiotic factor for them. Water can be heated or cooled through radiation at the surface and conduction to or from the air and surrounding substrate. Shallow streams are well mixed and maintain a uniform temperature within an area. In deeper, slower moving water systems, however, a strong difference between the bottom and surface temperatures may develop. Spring fed systems have little variation as springs are from groundwater sources, which are very close to ambient temperature. Many systems show strong diurnal fluctuations and seasonal variations are most extreme in arctic and temperate systems; the amount of shading and elevation can influence the temperature of lotic systems. Water chemistry in river ecosystems varies depending on which dissolved solutes and gases are present in the water column of the stream. River water can include, apart from the water itself, dissolved inorganic matter and major ions dissolved inorganic nutrients suspended and dissolved organic matter gases (nitrogen, nitrous oxide, carbon dioxide, oxyge
Hydrology is the scientific study of the movement and quality of water on Earth and other planets, including the water cycle, water resources and environmental watershed sustainability. A practitioner of hydrology is a hydrologist, working within the fields of earth or environmental science, physical geography, geology or civil and environmental engineering. Using various analytical methods and scientific techniques, they collect and analyze data to help solve water related problems such as environmental preservation, natural disasters, water management. Hydrology subdivides into surface water hydrology, groundwater hydrology, marine hydrology. Domains of hydrology include hydrometeorology, surface hydrology, drainage-basin management and water quality, where water plays the central role. Oceanography and meteorology are not included because water is only one of many important aspects within those fields. Hydrological research can inform environmental engineering and planning. Chemical hydrology is the study of the chemical characteristics of water.
Ecohydrology is the study of interactions between the hydrologic cycle. Hydrogeology is the study of the movement of groundwater. Hydroinformatics is the adaptation of information technology to hydrology and water resources applications. Hydrometeorology is the study of the transfer of water and energy between land and water body surfaces and the lower atmosphere. Isotope hydrology is the study of the isotopic signatures of water. Surface hydrology is the study of hydrologic processes that operate near Earth's surface. Drainage basin management covers water storage, in the form of reservoirs, floods protection. Water quality includes the chemistry of water in rivers and lakes, both of pollutants and natural solutes. Calculation of rainfall. Calculating surface precipitation. Determining the water balance of a region. Determining the agricultural water balance. Designing riparian restoration projects. Mitigating and predicting flood and drought risk. Real-time flood forecasting and flood warning. Designing irrigation managing agricultural productivity.
Part of the hazard module in catastrophe modeling. Providing drinking water. Designing dams for hydroelectric power generation. Designing bridges. Designing sewers and urban drainage system. Analyzing the impacts of antecedent moisture on sanitary sewer systems. Predicting geomorphologic changes, such as erosion or sedimentation. Assessing the impacts of natural and anthropogenic environmental change on water resources. Assessing contaminant transport risk and establishing environmental policy guidelines. Estimating the water resource potential of river basins. Hydrology has been a subject of engineering for millennia. For example, about 4000 BC the Nile was dammed to improve agricultural productivity of barren lands. Mesopotamian towns were protected from flooding with high earthen walls. Aqueducts were built by the Greeks and Ancient Romans, while the history of China shows they built irrigation and flood control works; the ancient Sinhalese used hydrology to build complex irrigation works in Sri Lanka known for invention of the Valve Pit which allowed construction of large reservoirs and canals which still function.
Marcus Vitruvius, in the first century BC, described a philosophical theory of the hydrologic cycle, in which precipitation falling in the mountains infiltrated the Earth's surface and led to streams and springs in the lowlands. With adoption of a more scientific approach, Leonardo da Vinci and Bernard Palissy independently reached an accurate representation of the hydrologic cycle, it was not until the 17th century. Pioneers of the modern science of hydrology include Pierre Perrault, Edme Mariotte and Edmund Halley. By measuring rainfall and drainage area, Perrault showed that rainfall was sufficient to account for flow of the Seine. Marriotte combined velocity and river cross-section measurements to obtain discharge, again in the Seine. Halley showed that the evaporation from the Mediterranean Sea was sufficient to account for the outflow of rivers flowing into the sea. Advances in the 18th century included the Bernoulli piezometer and Bernoulli's equation, by Daniel Bernoulli, the Pitot tube, by Henri Pitot.
The 19th century saw development in groundwater hydrology, including Darcy's law, the Dupuit-Thiem well formula, Hagen-Poiseuille's capillary flow equation. Rational analyses began to replace empiricism in the 20th century, while governmental agencies began their own hydrological research programs. Of particular importance were Leroy Sherman's unit hydrograph, the infiltration theory of Robert E. Horton, C. V. Theis's aquifer test/equation describing well hydraulics. Since the 1950s, hydrology has been approached with a more theoretical basis than in the past, facilitated by advances in the physical understanding of hydrological processes and by the advent of computers and geographic information systems; the central theme of hydrology is that water circulates throughout the Earth through different pathways and at different rates. The most vivid image of this is in the evaporation of water from the ocean; these clouds produce rain. The rainwater flows into rivers, or aquifers; the water in lakes and aquifers either evaporates back to the atmosphere or flows back to the ocean, completing a cycle.
Water changes its state of being several times throughout this cycle. The areas of research within hydrology concern the moveme
Mayflies are aquatic insects belonging to the order Ephemeroptera. This order is part of an ancient group of insects termed the Palaeoptera, which contains dragonflies and damselflies. Over 3,000 species of mayfly are known worldwide, grouped into over 400 genera in 42 families. Mayflies exhibit a number of ancestral traits that were present in the first flying insects, such as long tails and wings that do not fold flat over the abdomen, their immature stages are aquatic fresh water forms, whose presence indicates a clean, unpolluted environment. They are unique among insect orders in having a winged terrestrial adult stage, the subimago, which moults into a sexually mature adult, the imago. Mayflies "hatch" from spring to autumn, not in May, in enormous numbers; some hatches attract tourists. Fly fishermen make use of mayfly hatches by choosing artificial fishing flies that resemble the species in question. One of the most famous English mayflies is Rhithrogena germanica, the fisherman's "March brown mayfly".
The brief lives of mayfly adults have been noted by naturalists and encyclopaedists since Aristotle and Pliny the Elder in classical times. The German engraver Albrecht Dürer included a mayfly in his 1495 engraving The Holy Family with the Mayfly to suggest a link between heaven and earth; the English poet George Crabbe compared the brief life of a daily newspaper with that of a mayfly in the satirical poem "The Newspaper", both being known as "ephemera". Immature mayflies are referred to as nymphs or naiads. In contrast to their short lives as adults, they may live for several years in the water, they have an elongated, cylindrical or somewhat flattened body that passes through a number of instars and increasing in size each time. When ready to emerge from the water, nymphs vary depending on species, from 3 to 30 mm; the head has a tough outer covering of sclerotin with various hard ridges and projections. There are two large compound eyes, three ocelli and a pair of antennae of variable lengths, set between or in front of the eyes.
The mouthparts are designed for chewing and consist of a flap-like labrum, a pair of strong mandibles, a pair of maxillae, a membranous hypopharynx and a labium. The thorax consists of three segments – the hindmost two, the mesothorax and metathorax, being fused; each segment bears a pair of legs which terminate in a single claw. The legs are robust and clad in bristles, hairs or spines. Wing pads develop on the mesothorax, in some species, hindwing pads develop on the metathorax; the abdomen consists of ten segments, some of which may be obscured by a large pair of operculate gills, a thoracic shield or the developing wing pads. In most taxa up to seven pairs of gills arise from the top or sides of the abdomen, but in some species they are under the abdomen, in a few species the gills are instead located on the coxae of the legs, or the bases of the maxillae; the abdomen terminates in a pair of, or slender thread-like projections. The final moult of the nymph is not to the full adult form, but to a winged stage called a subimago that physically resembles the adult, but, sexually immature and duller in colour.
The subimago has cloudy wings fringed with minute hairs. Subimagos are poor fliers, lack the colour patterns used to attract mates. After a period lasting one or two days but in some species only a few minutes, the subimago moults to the full adult form, making mayflies the only insects where a winged form undergoes a further moult. Adult mayflies, or imagos, are primitive in structure, exhibiting traits that were present in the first flying insects; these include long wings that do not fold flat over the abdomen. Mayflies are delicate-looking insects with one or two pairs of membranous, triangular wings, which are extensively covered with veins. At rest, the wings are held upright, like those of a butterfly; the hind wings may be vestigial or absent. The second segment of the thorax, which bears the forewings, is enlarged to hold the main flight muscles. Adults have short, flexible antennae, large compound eyes, three ocelli and non-functional mouthparts. In most species, the males' eyes are large and the front legs unusually long, for use in locating and grasping females during the mid-air mating.
In the males of some families, there are two large cylindrical "turban" eyes that face upwards in addition to the lateral eyes. They are capable of detecting ultraviolet light and are thought to be used during courtship to detect females flying above them. In some species, all the legs are functionless, apart from the front pair in males; the abdomen is long and cylindrical, with ten segments and two or three long cerci at the tip. Uniquely among insects, mayflies possess paired genitalia, with the male having two aedeagi and the female two gonopores. Mayflies are hemimetabolous, they are unique among insects. Mayflies at the subimago stage are a favourite food of many fish, many fishing flies are
Gravel is a loose aggregation of rock fragments. Gravel is classified by particle size range and includes size classes from granule- to boulder-sized fragments. In the Udden-Wentworth scale gravel is categorized into granular pebble gravel. ISO 14688 grades gravels as fine and coarse with ranges 2 mm to 6.3 mm to 20 mm to 63 mm. One cubic metre of gravel weighs about 1,800 kg. Gravel is an important commercial product, with a number of applications. Many roadways are surfaced with gravel in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with tarmac. Both sand and small gravel are important for the manufacture of concrete. Large gravel deposits are a common geological feature, being formed as a result of the weathering and erosion of rocks; the action of rivers and waves tends to pile up gravel in large accumulations. This can sometimes result in gravel becoming compacted and lithified into the sedimentary rock called conglomerate. Where natural gravel deposits are insufficient for human purposes, gravel is produced by quarrying and crushing hard-wearing rocks, such as sandstone, limestone, or basalt.
Quarries where gravel is extracted are known as gravel pits. Southern England possesses large concentrations of them due to the widespread deposition of gravel in the region during the Ice Ages; as of 2006, the United States is consumer of gravel. The word gravel comes from the Breton language. In Breton, "grav" means coast. Adding the "-el" suffix in Breton denotes the component parts of something larger, thus "gravel" means the small stones which make up such a beach on the coast. Many dictionaries ignore the Breton language, citing Old French gravelle. Gravel has the meaning a mixture of different size pieces of stone mixed with sand and some clay. In American English, rocks broken into small pieces by a crusher are known as crushed stone. Types of gravel include: Bank gravel: deposited gravel intermixed with sand or clay found in and next to rivers and streams. Known as "bank run" or "river run". Bench gravel: a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level.
Creek rock or river rock: this is rounded, semi-polished stones of a wide range of types, that are dredged or scooped from stream beds. It is often used as concrete aggregate and less as a paving surface. Crushed stone: rock crushed and graded by screens and mixed to a blend of stones and fines, it is used as a surfacing for roads and driveways, sometimes with tar applied over it. Crushed stone may be made from granite, limestone and other rocks. Known as "crusher run", DGA QP, shoulder stone. Fine gravel: gravel consisting of particles with a diameter of 2 to 8 mm. Stone dust: fine, gravel from the final stage of screen separation, such that the gravel is not separated out from fine dust particles. Lag gravel: a surface accumulation of coarse gravel produced by the removal of finer particles. Pay gravel: known as "pay dirt"; the metals are recovered through gold panning. Pea gravel: known as "pea shingle" is gravel that consists of small, rounded stones used in concrete surfaces. Used for walkways, driveways and as a substrate in home aquariums.
Piedmont gravel: a coarse gravel carried down from high places by mountain streams and deposited on flat ground, where the water runs more slowly. Plateau gravel: a layer of gravel on a plateau or other region above the height at which stream-terrace gravel is found. In locales where gravelly soil is predominant, plant life is more sparse; this outcome derives from the inferior ability of gravels to retain moisture, as well as the corresponding paucity of mineral nutrients, since finer soils that contain such minerals are present in smaller amounts. Construction aggregate Pebble Rock Media related to Gravel at Wikimedia Commons
Topography is the study of the shape and features of land surfaces. The topography of an area could refer to the surface shapes and features themselves, or a description. Topography is a field of geoscience and planetary science and is concerned with local detail in general, including not only relief but natural and artificial features, local history and culture; this meaning is less common in the United States, where topographic maps with elevation contours have made "topography" synonymous with relief. Topography in a narrow sense involves the recording of relief or terrain, the three-dimensional quality of the surface, the identification of specific landforms; this is known as geomorphometry. In modern usage, this involves generation of elevation data in digital form, it is considered to include the graphic representation of the landform on a map by a variety of techniques, including contour lines, hypsometric tints, relief shading. The term topography originated in ancient Greece and continued in ancient Rome, as the detailed description of a place.
The word comes from the Greek τόπος and -γραφία. In classical literature this refers to writing about a place or places, what is now called'local history'. In Britain and in Europe in general, the word topography is still sometimes used in its original sense. Detailed military surveys in Britain were called Ordnance Surveys, this term was used into the 20th century as generic for topographic surveys and maps; the earliest scientific surveys in France were called the Cassini maps after the family who produced them over four generations. The term "topographic surveys" appears to be American in origin; the earliest detailed surveys in the United States were made by the “Topographical Bureau of the Army,” formed during the War of 1812, which became the Corps of Topographical Engineers in 1838. After the work of national mapping was assumed by the U. S. Geological Survey in 1878, the term topographical remained as a general term for detailed surveys and mapping programs, has been adopted by most other nations as standard.
In the 20th century, the term topography started to be used to describe surface description in other fields where mapping in a broader sense is used in medical fields such as neurology. An objective of topography is to determine the position of any feature or more any point in terms of both a horizontal coordinate system such as latitude and altitude. Identifying features, recognizing typical landform patterns are part of the field. A topographic study may be made for a variety of reasons: military planning and geological exploration have been primary motivators to start survey programs, but detailed information about terrain and surface features is essential for the planning and construction of any major civil engineering, public works, or reclamation projects. There are a variety of approaches to studying topography. Which method to use depend on the scale and size of the area under study, its accessibility, the quality of existing surveys. Surveying helps determine the terrestrial or three-dimensional space position of points and the distances and angles between them using leveling instruments such as theodolites, dumpy levels and clinometers.
Work on one of the first topographic maps was begun in France by Giovanni Domenico Cassini, the great Italian astronomer. Though remote sensing has sped up the process of gathering information, has allowed greater accuracy control over long distances, the direct survey still provides the basic control points and framework for all topographic work, whether manual or GIS-based. In areas where there has been an extensive direct survey and mapping program, the compiled data forms the basis of basic digital elevation datasets such as USGS DEM data; this data must be "cleaned" to eliminate discrepancies between surveys, but it still forms a valuable set of information for large-scale analysis. The original American topographic surveys involved not only recording of relief, but identification of landmark features and vegetative land cover. Remote sensing is a general term for geodata collection at a distance from the subject area. Besides their role in photogrammetry and satellite imagery can be used to identify and delineate terrain features and more general land-cover features.
They have become more and more a part of geovisualization, whether maps or GIS systems. False-color and non-visible spectra imaging can help determine the lie of the land by delineating vegetation and other land-use information more clearly. Images can be in other spectrum. Photogrammetry is a measurement technique for which the co-ordinates of the points in 3D of an object are determined by the measurements made in two photographic images taken starting from different positions from different passes of an aerial photography flight. In this technique, the common points are identified on each image. A line of sight can be built from the camera location to the point on the object, it is the intersection of its rays which determines the relative three-dimensional position of the point. Known control points can be used to give these relative positions absolute values. More sophisticated algorithms can exploit other information on the scene known a priori. Satellite RADAR mapping is one of the major techniques of generating Digital E
A floodplain or flood plain is an area of land adjacent to a stream or river which stretches from the banks of its channel to the base of the enclosing valley walls, which experiences flooding during periods of high discharge. The soils consist of levees and sands deposited during floods. Levees are the heaviest materials and they are deposited first. Floodplains are formed; when a river breaks its banks, it leaves behind layers of alluvium. These build up to create the floor of the plain. Floodplains contain unconsolidated sediments extending below the bed of the stream; these are accumulations of sand, loam, and/or clay, are important aquifers, the water drawn from them being pre-filtered compared to the water in the river. Geologically ancient floodplains are represented in the landscape by fluvial terraces; these are old floodplains that remain high above the present floodplain and indicate former courses of a stream. Sections of the Missouri River floodplain taken by the United States Geological Survey show a great variety of material of varying coarseness, the stream bed having been scoured at one place and filled at another by currents and floods of varying swiftness, so that sometimes the deposits are of coarse gravel, sometimes of fine sand or of fine silt.
It is probable that any section of such an alluvial plain would show deposits of a similar character. The floodplain during its formation is marked by meandering or anastomotic streams, oxbow lakes and bayous, marshes or stagnant pools, is completely covered with water; when the drainage system has ceased to act or is diverted for any reason, the floodplain may become a level area of great fertility, similar in appearance to the floor of an old lake. The floodplain differs, because it is not altogether flat, it has a gentle slope downstream, for a distance, from the side towards the center. The floodplain is the natural place for a river to dissipate its energy. Meanders form over the floodplain to slow down the flow of water and when the channel is at capacity the water spills over the floodplain where it is temporarily stored. In terms of flood management the upper part of the floodplain is crucial as this is where the flood water control starts. Artificial canalisation of the river here will have a major impact on wider flooding.
This is the basis of sustainable flood management. Floodplains can support rich ecosystems, both in quantity and diversity. Tugay forests form an ecosystem associated with floodplains in Central Asia, they are a category of riparian systems. A floodplain can contain 100 or 1,000 times as many species as a river. Wetting of the floodplain soil releases an immediate surge of nutrients: those left over from the last flood, those that result from the rapid decomposition of organic matter that has accumulated since then. Microscopic organisms thrive and larger species enter a rapid breeding cycle. Opportunistic feeders move in to take advantage; the production of nutrients falls away quickly. This makes floodplains valuable for agriculture. River flow rates are undergoing change following suit with climate change; this change is a threat to other floodplain forests. These forests have over time synced their seedling deposits after the spring peaks in flow to best take advantage of the nutrient rich soil generated by peak flow.
Many towns have been built on floodplains, where they are susceptible to flooding, for a number of reasons: access to fresh water. The worst of these, the worst natural disaster were 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, is the second-worst natural disaster in history. The extent of floodplain inundation depends in part on the flood magnitude, defined by the return period. In the United States the Federal Emergency Management Agency manages the National Flood Insurance Program; the NFIP offers insurance to properties located within a flood prone area, as defined by the Flood Insurance Rate Map, which depicts various flood risks for a community. The FIRM focuses on delineation of the 100-year flood inundation area known within the NFIP as the Special Flood Hazard Area. Where a detailed study of a waterway has been done, the 100-year floodplain will 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 encountered term is the Special Flood Hazard Area, any area subject to inundation by the 100-year flood. A problem is that any alteration of the watershed upstream of the point in question can affect the ability of the watershed to handle water, thus affects the levels of the periodic floods. A large shopping center and parking lot, for example, may raise the levels of the 5-year, 100-year, other floods, but the maps are adjusted, are rendered