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
A river is a natural flowing watercourse freshwater, flowing towards an ocean, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, brook and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location. Sometimes a river is defined as being larger than a creek, but not always: the language is vague. Rivers are part of the hydrological cycle. Potamology is the scientific study of rivers, while limnology is the study of inland waters in general. Most of the major cities of the world are situated on the banks of rivers, as they are, or were, used as a source of water, for obtaining food, for transport, as borders, as a defensive measure, as a source of hydropower to drive machinery, for bathing, as a means of disposing of waste.
A river begins at a source, follows a path called a course, ends at a mouth or mouths. The water in a river is confined to a channel, made up of a stream bed between banks. In larger rivers there is also a wider floodplain shaped by flood-waters over-topping the channel. Floodplains may be wide in relation to the size of the river channel; this distinction between river channel and floodplain can be blurred in urban areas where the floodplain of a river channel can become developed by housing and industry. Rivers can flow down mountains, through valleys or along plains, can create canyons or gorges; the term upriver refers to the direction towards the source of the river, i.e. against the direction of flow. The term downriver describes the direction towards the mouth of the river, in which the current flows; the term left bank refers to the left bank in the direction of right bank to the right. The river channel contains a single stream of water, but some rivers flow as several interconnecting streams of water, producing a braided river.
Extensive braided rivers are now found in only a few regions worldwide, such as the South Island of New Zealand. They occur on peneplains and some of the larger river deltas. Anastamosing rivers are quite rare, they have multiple sinuous channels carrying large volumes of sediment. There are rare cases of river bifurcation in which a river divides and the resultant flows ending in different seas. An example is the bifurcation of Nerodime River in Kosovo. A river flowing in its channel is a source of energy which acts on the river channel to change its shape and form. In 1757, the German hydrologist Albert Brahms empirically observed that the submerged weight of objects that may be carried away by a river is proportional to the sixth power of the river flow speed; this formulation is sometimes called Airy's law. Thus, if the speed of flow is doubled, the flow would dislodge objects with 64 times as much submerged weight. In mountainous torrential zones this can be seen as erosion channels through hard rocks and the creation of sands and gravels from the destruction of larger rocks.
A river valley, created from a U-shaped glaciated valley, can easily be identified by the V-shaped channel that it has carved. In the middle reaches where a river flows over flatter land, meanders may form through erosion of the river banks and deposition on the inside of bends. Sometimes the river will cut off a loop, shortening the channel and forming an oxbow lake or billabong. Rivers that carry large amounts of sediment may develop conspicuous deltas at their mouths. Rivers whose mouths are in saline tidal waters may form estuaries. Throughout the course of the river, the total volume of water transported downstream will be a combination of the free water flow together with a substantial volume flowing through sub-surface rocks and gravels that underlie the river and its floodplain. For many rivers in large valleys, this unseen component of flow may exceed the visible flow. Most but not all rivers flow on the surface. Subterranean rivers flow underground in caverns; such rivers are found in regions with limestone geologic formations.
Subglacial streams are the braided rivers that flow at the beds of glaciers and ice sheets, permitting meltwater to be discharged at the front of the glacier. Because of the gradient in pressure due to the overlying weight of the glacier, such streams can flow uphill. An intermittent river only flows and can be dry for several years at a time; these rivers are found in regions with limited or variable rainfall, or can occur because of geologic conditions such as a permeable river bed. Some ephemeral rivers flow during the summer months but not in the winter; such rivers are fed from chalk aquifers which recharge from winter rainfall. In England these rivers are called bournes and give their name to places such as Bournemouth and Eastbourne. In humid regions, the location where flow begins in the smallest tributary streams moves upstream in response to precipitation and downstream in its absence or when active summer vegetation diverts water for evapotrans
A stream is a body of water with surface water flowing within the bed and banks of a channel. The stream encompasses surface and groundwater fluxes that respond to geological, geomorphological and biotic controls. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams are called rivers. Streams are important as conduits in the water cycle, instruments in groundwater recharge, corridors for fish and wildlife migration; the biological habitat in the immediate vicinity of a stream is called a riparian zone. Given the status of the ongoing Holocene extinction, streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity; the study of streams and waterways in general is known as surface hydrology and is a core element of environmental geography. Brook A stream smaller than a creek one, fed by a spring or seep, it is small and forded. A brook is characterised by its shallowness.
Creek In North America and New Zealand, a small to medium-sized natural stream. Sometimes navigable by motor craft and may be intermittent. In parts of Maryland, New England, the UK and India, a tidal inlet in a salt marsh or mangrove swamp, or between enclosed and drained former salt marshes or swamps. In these cases, the stream is the tidal stream, the course of the seawater through the creek channel at low and high tide. River A large natural stream, which may be a waterway. Runnel the linear channel between the parallel ridges or bars on a shoreline beach or river floodplain, or between a bar and the shore. Called a swale. Tributary A contributory stream, or a stream which does not reach a static body of water such as a lake or ocean, but joins another river. Sometimes called a branch or fork. There are a number of regional names for a stream. Allt is used in Highland Scotland. Beck is used in Lincolnshire to Cumbria in areas which were once occupied by the Danes and Norwegians. Bourne or winterbourne is used in the chalk downland of southern England.
Brook. Burn is used in North East England. Gill or ghyll is seen in Surrey influenced by Old Norse; the variant "ghyll" is used in the Lake District and appears to have been an invention of William Wordsworth. Nant is used in Wales. Rivulet is a term encountered in Victorian era publications. Stream Syke is used in lowland Cumbria for a seasonal stream. Branch is used to name streams in Virginia. Creek is common throughout the United States, as well as Australia. Falls is used to name streams in Maryland, for streams/rivers which have waterfalls on them if such falls have a small vertical drop. Little Gunpowder Falls and The Jones Falls are rivers named in this manner, unique to Maryland. Kill in New York, Pennsylvania and New Jersey comes from a Dutch language word meaning "riverbed" or "water channel", can be used for the UK meaning of'creek'. Run in Ohio, Michigan, New Jersey, Virginia, or West Virginia can be the name of a stream. Run in Florida is the name given to streams coming out of small natural springs.
River is used for larger springs like the Silver Rainbow River. Stream and brook are used in Midwestern states, Mid-Atlantic states, New England. Bar A shoal that develops in a stream as sediment is deposited as the current slows or is impeded by wave action at the confluence. Bifurcation A fork into two or more streams. Channel A depression created by constant erosion. Confluence The point at which the two streams merge. If the two tributaries are of equal size, the confluence may be called a fork. Drainage basin The area of land. A large drainage basin such as the Amazon River contains many smaller drainage basins. Floodplain Lands adjacent to the stream that are subject to flooding when a stream overflows its banks. Gaging station A site along the route of a stream or river, used for reference marking or water monitoring. Headwaters The part of a stream or river proximate to its source; the word is most used in the plural where there is no single point source. Knickpoint The point on a stream's profile where a sudden change in stream gradient occurs.
Mouth The point at which the stream discharges via an estuary or delta, into a static body of water such as a lake or ocean. Pool A segment where the water is deeper and slower moving. Rapids A turbulent, fast-flowing stretch of a stream or river. Riffle A segment where the flow is shallower and more turbulent. River A large natural stream, which may be a waterway. Run A somewhat smoothly flowing segment of the stream. Source The spring, or other point of origin of a stream. Spring The point at which a stream emerges from an underground course through unconsolidated sediments or through caves. A stream can with caves, flow aboveground for part of its course, underground for part of its course. Stream bed The bottom of a stream. Stream corridor Stream, its floodplains, the transitional upland fringe Streamflow The water moving through a stream channel. Thalweg The river's longitudinal section, or the line joining the deepest point in the channel at each stage from source to mouth. Waterfall or cascade The fall of water where the stream goes over a sudden drop called a knickpoint.
The stream expends kinetic energy in "trying" to eliminate the
A hydrograph is a graph showing the rate of flow versus time past a specific point in a river, channel, or conduit carrying flow. The rate of flow is expressed in cubic meters or cubic feet per second, it can refer to a graph showing the volume of water reaching a particular outfall, or location in a sewerage network. Graphs are used in the design of sewerage, more the design of surface water sewerage systems and combined sewers. Discharge: the rate of flow passing a specific location in a river, or other channel; the discharge is measured at a specific point in a river and is time variant. Rising limb: The rising limb of the hydrograph known as concentration curve, reflects a prolonged increase in discharge from a catchment area in response to a rainfall event. Peak discharge: the highest point on the hydrograph when the rate of discharge is greatest. Recession limb: The recession limb extends from the peak flow rate onward; the end of stormflow and the return to groundwater-derived flow is taken as the point of inflection of the recession limb.
The recession limb represents the withdrawal of water from the storage built up in the basin during the earlier phases of the hydrograph. Lag time: the time interval from the center of mass of rainfall excess to the peak of the resulting hydrograph. Time to peak: time interval from the start of the resulting hydrograph. Types of hydrographs include: Storm hydrographs Flood hydrographs Annual hydrographs a.k.a. regimes Direct Runoff Hydrograph Effective Runoff Hydrograph Raster Hydrograph Storage opportunities in the drainage network A stream hydrograph is determining the influence of different hydrologic processes on discharge from the subject catchment. Because the timing and duration of groundwater return flow differs so from that of direct runoff and understanding the influence of these distinct processes is key to analyzing and simulating the hydrologic effects of various land use, water use and climate conditions and changes. However, the process of separating “baseflow” from “direct runoff” is an inexact science.
In part this is because these two concepts are not, themselves distinct and unrelated. Return flow from groundwater increases along with overland flow from saturated or impermeable areas during and after a storm event. Therefore, separation of a purely “baseflow component” in a hydrograph is a somewhat arbitrary exercise. Various graphical and empirical techniques have been developed to perform these hydrograph separations; the separation of base flow from direct runoff can be an important first step in developing rainfall-runoff models for a watershed of interest—for example, in developing and applying unit hydrographs as described below. An unit hydrograph is the hypothetical unit response of a watershed to a unit input of rainfall, it can be defined as the direct runoff hydrograph resulting from one unit of effective rainfall occurring uniformly over that watershed at a uniform rate over a unit period of time. As a UH is applicable only to the direct runoff component of a hydrograph, a separate determination of the baseflow component is required.
A UH is specific to a particular watershed, specific to a particular length of time corresponding to the duration of the effective rainfall. That is, the UH is specified as being the 1-hour, 6-hour, or 24-hour UH, or any other length of time up to the time of concentration of direct runoff at the watershed outlet. Thus, for a given watershed, there can be many unit hydrographs, each one corresponding to a different duration of effective rainfall; the UH technique provides a practical and easy-to-apply tool for quantifying the effect of a unit of rainfall on the corresponding runoff from a particular drainage basin. UH theory assumes that a watershed's runoff response is linear and time-invariant, that the effective rainfall occurs uniformly over the watershed. In the real world, none of these assumptions are true. Application of UH methods yields a reasonable approximation of the flood response of natural watersheds; the linear assumptions underlying UH theory allows for the variation in storm intensity over time to be simulated by applying the principles of superposition and proportionality to separate storm components to determine the resulting cumulative hydrograph.
This allows for a straightforward calculation of the hydrograph response to any arbitrary rain event. An instantaneous unit hydrograph is a further refinement of the concept. Making this assumption can simplify the analysis involved in constructing a unit hydrograph, it is necessary for the creation of a geomorphologic instantaneous unit hydrograph; the creation of a GIUH is possible given nothing more than topologic data for a particular drainage basin. In fact, only the number of streams of a given order, the mean length of streams of a given order, the mean land area draining directly to streams of a given order are required, it is therefore possible to calculate a GIUH for a basin without any data about stream height or flow, which may not
Surface runoff is the flow of water that occurs when excess stormwater, meltwater, or other sources flows over the Earth's surface. This might occur because soil is saturated to full capacity, because rain arrives more than soil can absorb it, or because impervious areas send their runoff to surrounding soil that cannot absorb all of it. Surface runoff is a major component of the water cycle, it is the primary agent in soil erosion by water. Runoff that occurs on the ground surface before reaching a channel is called a nonpoint source. If a nonpoint source contains man-made contaminants, or natural forms of pollution the runoff is called nonpoint source pollution. A land area which produces runoff that drains to a common point is called a drainage basin; when runoff flows along the ground, it can pick up soil contaminants including petroleum, pesticides, or fertilizers that become discharge or nonpoint source pollution. In addition to causing water erosion and pollution, surface runoff in urban areas is a primary cause of urban flooding which can result in property damage and mold in basements, street flooding.
Surface runoff glaciers. Snow and glacier melt occur only in areas cold enough for these to form permanently. Snowmelt will peak in the spring and glacier melt in the summer, leading to pronounced flow maxima in rivers affected by them; the determining factor of the rate of melting of snow or glaciers is both air temperature and the duration of sunlight. In high mountain regions, streams rise on sunny days and fall on cloudy ones for this reason. In areas where there is no snow, runoff will come from rainfall. However, not all rainfall will produce runoff. On the ancient soils of Australia and Southern Africa, proteoid roots with their dense networks of root hairs can absorb so much rainwater as to prevent runoff when substantial amounts of rain fall. In these regions on less infertile cracking clay soils, high amounts of rainfall and potential evaporation are needed to generate any surface runoff, leading to specialised adaptations to variable streams; this occurs when the rate of rainfall on a surface exceeds the rate at which water can infiltrate the ground, any depression storage has been filled.
This is called flooding Hortonian overland flow, or unsaturated overland flow. This more occurs in arid and semi-arid regions, where rainfall intensities are high and the soil infiltration capacity is reduced because of surface sealing, or in paved areas; this occurs in city areas where pavements prevent water from flooding. When the soil is saturated and the depression storage filled, rain continues to fall, the rainfall will produce surface runoff; the level of antecedent soil moisture is one factor affecting the time. This runoff is called saturated overland flow or Dunne runoff. Soil retains a degree of moisture after a rainfall; this residual water moisture affects the soil's infiltration capacity. During the next rainfall event, the infiltration capacity will cause the soil to be saturated at a different rate; the higher the level of antecedent soil moisture, the more the soil becomes saturated. Once the soil is saturated, runoff occurs. After water infiltrates the soil on an up-slope portion of a hill, the water may flow laterally through the soil, exfiltrate closer to a channel.
This is called throughflow. As it flows, the amount of runoff may be reduced in a number of possible ways: a small portion of it may evapotranspire. Any remaining surface water flows into a receiving water body such as a river, estuary or ocean. Urbanization increases surface runoff by creating more impervious surfaces such as pavement and buildings that do not allow percolation of the water down through the soil to the aquifer, it is instead forced directly into streams or storm water runoff drains, where erosion and siltation can be major problems when flooding is not. Increased runoff reduces groundwater recharge, thus lowering the water table and making droughts worse for agricultural farmers and others who depend on the water wells; when anthropogenic contaminants are dissolved or suspended in runoff, the human impact is expanded to create water pollution. This pollutant load can reach various receiving waters such as streams, lakes and oceans with resultant water chemistry changes to these water systems and their related ecosystems.
A 2008 report by the United States National Research Council identified urban stormwater as a leading source of water quality problems in the U. S; as humans continue to alter the climate through the addition of greenhouse gases to the atmosphere, precipitation patterns are expected to change as the atmospheric capacity for water vapor increases. This will have direct consequences on runoff amounts. Surface runoff can cause erosion of the Earth's surface. There are four main types of soil erosion by water: splash erosion, sheet erosion, rill erosion and gully erosion. Splash erosion is the result of mechanical collision of raindrops with the soil surface: soil particles which are dislodged by the impact move with the surface runoff. Sheet erosion is the overland transport of sediment by runoff without a well d