What is the difference between runoff and discharge

Spatially, precipitation is particularly variable in mountain regions. In general, higher amounts fall on high altitudes and large differences exist between slopes. Topographic depressions and deep valleys are precipitation shadow areas, many of which are semi-arid. Similarly, considerable quantities of snow and rain are frequently deposited on high altitudes of the Cordilleras of MRB, sufficient at places to nourish some glaciers; but precipitation diminishes greatly in the precipitation shadow areas at the eastern foothills downwind of the mountain chains Hydrological Atlas of Canada The least amount of precipitation reaches the lowlands and low plateaus.

Annual precipitation of MRB and YRB, with hyetographs for selected stations to show contrasts in magnitude and timing of monthly precipitation in different parts of the basins. Storage modifies the timing of river flow response to water inputs in liquid and solid phases. Situated at continental high latitudes, the storage of snow and ice is an important consideration. Snowfall accumulates in winter to build up a seasonal snow cover that undergoes re-distribution, mainly through drifting by wind and interception by vegetation.

For both basins, snowmelt and associated runoff is a major event in the spring, and streamflow is often accompanied by the breakup of river ice to generate annual peak flows. Rivers and lakes usually acquire an ice cover in the winter. This feature, commonly revealed as an abrupt drop in the winter hydrograph, is insignificant in magnitude compared with the storage of winter snow.

In the thaw season, wetlands provide summer storage through their numerous hollows that retain water and their vegetation that impedes water movement. The rates of groundwater recharge and storage in large northern basins are poorly known, although the mechanisms are understood. Groundwater sustains base flow of large rivers such as those cited in this paper, but most smaller ones would cease to flow.

Karst terrains in limestone areas are especially favourable for groundwater discharge, sometimes maintaining perennial springs to feed the river system. Ground ice in permafrost is a long-term storage but a warming climate and disturbance resulting from geomorphic processes or human activities lead to permafrost thaw and the release of water from ground ice storage to affect river flow e.

Lakes and wetlands are particularly effective for surface water storage. Water influx is first retained and then released gradually as relatively more uniform and delayed outflow. Runoff generated from the drainage areas is controlled by water gains from precipitation and losses to evapotranspiration, while land storage through surface detention and groundwater exchange governs the timing of water release to the rivers. The discharge for sub-basins of such size is not easily obtainable for YRB and therefore runoff is calculated using the discharge of headwater catchments or by considering the difference in discharge for the inter-station area between two adjacent stations along a river Figure 5.

Stations that lie immediately below reservoirs are excluded because their flows strongly reflect the influence of storage rather than runoff contribution from the land area of the basin. We used two different periods — for Angara and — for upper Yenisei that have more data available to us. Discrepancies in dates are expected to affect the mean runoff values, yet the averages thus obtained give a general picture of runoff contribution from various parts of the basin.

Monthly runoff from inter-station areas strongly affected by reservoirs is not shown. Within this region, the southern zone usually has the largest runoff; it exceeds mm, supported by rainfall, snowmelt and glacier melt at high altitudes. The Shield region has — mm of annual runoff, values that are intermediate between the mountains and the plains.

Regarding the YRB, large annual runoff comes from the western uplands and from the southern mountains, but the latter area has a complex relationship with topography. Large contrasts exist between the rivers fed by high rainfall and ample snowmelt water e. Nizhnyaya Tunguska and Yenisei above Nikitino and those in the rain shadow areas e.

Seasonally, winter is the period of low runoff, as indicated by the November to March values Figures 4 and 5. Air temperatures are exceedingly low e. At low temperatures, winter precipitation is stored and does not melt until spring. Snowmelt first comes in late April or May in the southern parts of both basins and on slopes below the high plateau in YRB, then proceeds to other basin areas in June and July.

Meltwater is responsible for generating high runoff in most areas, but summer rainfall and glacier melt in restricted localities also augment runoff. They found that for —89, large amounts of runoff come from mountainous areas in Siberia and the Canadian Rockies, and in areas with frequent cyclonic activities. Low runoff occurs on continental areas leeward of mountain ranges, including the Selenga basin and the western Canadian Arctic drainage. The seasonal rhythm, or the regime, of flow at a particular station along the main river is largely controlled by two water sources: the discharge coming from the upstream station and the contribution from tributaries that enter the main river below the upstream station.

The flow is also modified by channel storage along the drainage network. For both MRB and YRB, the most common natural flow rhythm is the nival regime in which the melting of winter snow in conjunction with river ice breakup gives rise to annual high flow, usually starting in the southern regions where the snow melts early e.

Snowmelt high flow is followed by a general recession in the summer, ending with low flow in the winter. Glaciers and late-lying snow in northern MRB prolongs high flow. Although southern YRB has glaciers that would continue to yield melt runoff in the summer, the storage function of a series of reservoirs downstream of Tannu Ola and Sayan mountains mutes the hydrograph rises produced by glacier melt discharge and summer rain.

Where both winter snow storage and summer rain are important water sources, river flow exhibits a pluvio-nival regime with mixed or dual peak periods e. Where rainfall becomes increasingly dominant, the pluvial regime prevails, with high flows responding to summer rain. On a local scale, flow regimes can be modified by other considerations such as glacier melt or substantial evapotranspiration loss from wetlands that draws down the water level to dampen the flow response to summer rain events Woo Lake storage can have pronounced effect on river flow.

For large natural lakes including the Athabasca, Great Slave and Great Bear in MRB and Lake Baikal in YRB, the retention and subsequent release functions significantly impact the timing and magnitude of their outflow, producing a prolacustrine flow regime. Reservoirs as artificial lakes significantly modify the natural flow regime of a river Vyruchalkina ; Stuefer et al. This study concerns only the operational excluding the construction and filling phase when discharge fluctuates from day to day to suit the need for power production.

Since water is not for consumptive use, flow regulation alters the seasonal rhythm of flow Yang et al. Along the main trunks of Mackenzie and Yenisei rivers, there is a downstream amalgamation of flow regimes and an integration of flow volume, as their tributaries enter the main stems. Figure 6 a traces the downstream integration of flow along these mega-rivers.

Williston Reservoir on Peace River in MRB distorts the original pre-dammed nival regime, which is restored by the natural inflow downstream. The river that flows out from this lake is the Mackenzie River, which displays a prolacustrine regime as shown at Strong Point. However, in meeting the Liard River, the pronounced nival flow regimen of this tributary overwhelms the lake effect on Mackenzie flow.

This flow pattern is conveyed all the way downstream to Arctic Red River station before the Mackenzie branches into its delta. In a similar fashion Figure 6 b , the pluvio-nival flow regime found at Kyzyl is altered by reservoir operation downstream and is changed again at Yeniseysk where it is joined by the Angara River, itself having a combination of flows from such unregulated rivers as the Taseeva and the highly regulated Angara above Boguchany.

Further downstream, the Yenisei receives natural inflows from the Podkamennaya Tunguska and Nizhnyaya Tunguska rivers, which further adjusts the regime of the Yenisei River at Igarka.

As a consequence of the merging of flows in the drainage networks, the regime of Mackenzie and Yenisei rivers at their mouths is an amalgamation of different flow patterns. Superficially, the resulting configuration of seasonal flow takes on the appearance of a nival regime despite the mixed origins of the flow i. Downstream transformation of regime for a mega-river depends on the hydrograph shape of the main stem, which usually has larger flow than its tributaries; and the strength of the signal conveyed by the incoming tributaries that reinforces or weakens the flow rhythm of the main trunk.

One measure to assess similarity of flow regimes is to correlate the hydrographs between two stations. In this, we correlate monthly flow of individual years at the lowest stations in the basins i. For each year of record, 12 pairs of monthly values are used and the correlation coefficients r values are plotted in Figure 7 note that depending on the years of record available, the number of r values differs for different stations.

Tight clustering of high r values for many years indicates similarity of flow regimes, but wide scattering of r values suggests inconsistency in the influence of a tributary on the flow regime of the main river. Anomalously high and low r values occur in some years. These are attributable to departures of seasonal precipitation from its normal pattern or human modification of the natural regime. Correlation of the tributaries with the main station generally increases for stations further downstream, and that is due to similarity between the natural nival regimes of these northern tributaries and the apparent nival regime exhibited at the main river outlets.

For MRB, significant correlations are found between the flow at Arctic Red River station and its three principal tributaries Slave, Liard and Mackenzie at Strong Point , with the correlation increasing downstream except for Great Bear River with prolacustrine regime, and Peace River where the flow is human-modified. The high correlation between Athabasca River in the south and Arctic Red River station in the north results from the glacial flow regime of Athabasca River with late-season high flow imitating the large flow in northern rivers sustained by late-lying snowmelt.

In the YRB, correlation also increases downstream, but to a lesser extent and significance. Here, the flow in the southern portion of the basin Selegna, Angara, and Yenesei Rivers , where several of the major reservoirs in the YRB are situated McClelland et al. However, correlations improve for the northern portion of the basin below Yeniseysk where there is less human interference with the natural flow rhythm.

Correlation coefficients of monthly flows for a Mackenzie at Arctic Red River and b Yenisei at Igarka, with their contributing tributaries. In order to compare the flows of the Mackenzie at Arctic Red River and Yenisei at Igarka rivers, Figure 8 presents their monthly means as well as the contribution from their major sub-basins and inter-station sections along the main trunks. Note that these are averages for the periods after major dams were built and the flow of individual years can depart substantially from these values.

On an annual basis, the mean flow of the Mackenzie at Arctic Red River is km 3 and for the Yenisei at Igarka it is km 3. Monthly flow contribution from major tributaries or inter-station areas to the total flow of the Mackenzie and Yenisei rivers. For convenience of discussion, flow condition is partitioned into three seasons Table 1 : winter November to April of low flow; snowmelt period May to July with high flow; and summer August to October when the flow generally recedes from the spring high.

A steep post-winter hydrograph rise comes in May for both basins when snowmelt commences, and the flow peaks in June. Flow contribution from sub-basins and inter-station areas to seasonal flow of Mackenzie and Yenisei rivers. However, their absolute magnitudes are modest and stable. Outside of the winter season, other basin areas yield much higher runoff so that the lake and reservoir contributions become proportionally overwhelmed.

This is especially notable in the principal snowmelt period. The flow produced by snowmelt runoff takes time to travel down river, frequently detained by river ice blockage. A flood profile may be drawn to show elevation at a given time, crests during a particular flood, or to show stages of concordant flows.

Flood routing. The process of determining progressively the timing and shape of a flood wave at successive points along a river. See Carter and Godfrey , Floods above a base. See Partial-duration flood series. Flood stage.

The gage height of the lowest bank of the reach in which the gage is situated. The term "lowest bank" is, however, not to be taken to mean an unusually low place or break in the natural bank through which the water inundates an unimportant and small area.

Linsley , , p. The stage at which overflow of the natural banks of a stream begins to cause damage in the reach in which the elevation is measured. Weather Bur. See also Bankfull stage. Flood wave. A distinct rise in stage culminating in a crest and followed by recession to lower stages. A part of the flood plain otherwise leveed, reserved for emergency diversion of water during floods.

A part of the flood plain which, to facilitate the passage of floodwater, is kept clear of encumbrances. The channel of a river or stream and those parts of the flood plains adjoining the channel, which are reasonably required to carry and discharge the floodwater or floodflow of any river or stream Erbe and Flores , , p.

Flood zone. The land bordering a stream which is subject to floods of about equal frequency; for example, a strip of the flood plain subject to flooding more often that once but not as frequently as twice in a century. See White , , p. Flow-duration curve. A cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded. See Searcy , Effects resultingfrom the presence of forest or brush upon climate , soil water , runoff , streamflow , floods, erosion, and soil productivity.

Kittredge , , p. Frazil frazil ice. A French-Canadian term for fine spicular ice, derived from the French for cinders which this variety of ice most resembles. When formed in salt water, it is known as lolly ice. It is composed of fine particles which, when first formed, are colloidal and not seen in the water in which they are floating. Barnes , , p. The water-surface elevation referred to some arbitrary gage datum. Gage height is often used interchangeably with the more general term stage although gage height is more appropriate when used with a reading on a gage.

Gaging station. A particular site on a stream, canal, lake, or reservoir where systematic observations of gage height or discharge are obtained. See also Stream-gaging station. Bodies of land ice that consist of recrystallized snow accumulated on the surface of the ground Matthes , , p. Ground water. Water in the ground that is in the zone of saturation , from which wells, springs, and ground-water runoff are supplied.

After Meinzer , , p. Ground-water outflow. That part of the discharge from a drainage basin that occurs through the ground water. The term "underflow" is often used to describe the ground-water outflow that takes place in valley alluvium instead of the surface channel and thus is not measured at a gaging station. Ground-water runoff. That part of the runoff which has passed into the ground, has become ground water, and has been discharged into a stream channel as spring or seepage water.

See also Base runoff and Direct runoff. The loss of water in liquid form from the uninjured leaf or stem of the plant, principally through water stomata. Lee , , p. The amount of heat necessary to raise the water from the minimum temperature of winter to the maximum temperature of summer. Welch , , p. A graph showing stage , flow, velocity, or other property of water with respect to time.

An accounting of the inflow to, outflow from, and storage in, a hydrologic unit, such as a drainage basin , aquifer, soil zone, lake, reservoir, or irrigation project.

Hydrologic cycle. A convenient term to denote the circulation of water from the sea, through the atmosphere, to the land; and thence, with many delays, back to the sea by overland and subterranean routes, and in part by way of the atmosphere; also the many short circuits of the water that is returned to the atmosphere without reaching the sea. Hydrologic equation. The equation balancing the hydrologic budget.

The science encompassing the behavior of water as it occurs in the atmosphere, on the surface of the ground, and underground. Civil Engineers , , p. The science that relates to the water of the earth.

The science treating of the waters of the earth, their occurrence, distribution, and movements. In practice the study of the water of the oceans and the atmosphere is considered part of the sciences of oceanography and meteorology. Graphical representation of rainfall intensity against time. See Thermal stratification. The flow of a fluid into a substance through pores or small openings. It connotes flow into a substance in contradistinction to the word percolation , which connotes flow through a porous substance.

See also Schiff and Dreibelbis , p. Infiltration capacity. The maximum rate at which the soil, when in a given condition, can absorb falling rain or melting snow. Infiltration index. An average rate of infiltration, in inches per hour, equal to the average rate of rainfall such that the volume of rain fall at greater rates equals the total direct runoff.

Langbein and others , , p. The process and the amountof rain or snow stored on leaves and branches and eventually evaporated back to the air. Interception equals the precipitation on the vegetation minus stem flow and throughfall after Hoover , , p. Irrigated area. The gross farm area upon which water is artificially applied for the production of crops, with no reduction for access roads, canals, or farm buildings. The controlled application of water to arable lands to supply water requirements not satisfied by rainfall.

Irrigation Efficiency. The percentage of water applied that can be accounted for in soil-moisture increase. Pillsbury, Compton, and Picker , , p. Irrigation requirement. The quantity of water, exclusive of precipitation, that is required for crop production. It includes surface evaporation and other economically unavoidable wastes. Blaney , a, p. Irrigation, supplemental. See Supplemental irrigation.

See Isohyetal line. Isohyetal line isohyet. A line drawn on a map or chart joining points that receive the same amount of precipitation. Variously defined as time from beginning or center of mass of rainfall to peak or center of mass of runoff.

After Am. That branch of hydrology pertaining to the study of lakes. Long-period variations. Secular when a cycle or a change in trend is completed within a century; climatic when the period of change runs through centuries or a few millenia; geologic when the period runs into geological time.

Willett , , p. See Trend. Low-flow frequency curve. A graph showing the magnitude and frequency of minimum flows for a period of given length. Frequency is usually expressed as the average interval, in years, between recurrences of an annual minimum flow equal to or less than that shown by the magnitude scale. Structure containing a mass of soil, and designed to permit the measurement of water draining through the soil.

Harrold and Dreibelbis , , p. See also Kohnke, Dreibelbis, and Davidson , , p. A graph of the cumulative values of a hydrologic quantity such as precipitation or runoff , generally as ordinate, plotted against time or date as abscissa.

See Double-mass curve , and Residual-mass curve. Maximum probable flood. See Flood, maximum probable. The winding of a stream channel. Distance between points of maximum curvature of successive meanders of opposite phase in a direction normal to the general course of the meander belt, measured between centerlines of channels.

Meander belt. Area between lines drawn tangential to the extreme limits of fully developed meanders. Meander breadth.

The distance between the lines used to define the meander belt. Meander length. Distance in the general course of the meanders between corresponding points of successive meanders of the same phase. Twice the distance between successive points of inflection of the meander wave. Leopold and Wolman, , p. Meromictic lake.

A lake in which some water remains partly or wholly unmixed with the main water mass at circulation periods is said to be meromictic. The process leading to a meromictic state is termed meromixis The perennially stagnant deep layer of a meromictic lake is called the monimolimnion.

The part of a meromictic lake in which free circulation can occur is called the mixolimnion. The boundary between the monimolimnion and the mixolimnion is called thechemocline. Hutchinson, , p. Water diffused in the atmosphere or the ground. Moisture equivalent. The ratio of a the weight of water which the soil, after saturation, will retain against a centrifugal force 1, times the force of gravity, to b the weight of the soil when dry.

The ratio is stated as a percentage. Meinzer, , p. A well-mixed mass of water and alluvium which, because of its high viscosity and low fluidity as compared with water, moves at a much slower rate, usually piling up and spreading over the fan like a sheet of wet mortar or concrete. Woolley, , p.

A central value such as arithmetic average or median of annual quantities for a year period ending with an even year, thus ; , and so forth. The flow of rainwater or snowmelt over the land surface toward stream channels. After it enters a stream, it becomes runoff.

A list of all flood peaks that exceed a chosen base stage or discharge, regardless of the number of peaks occurring in a year. Also called basic-stage flood series , or floods above a base. The movement, under hydrostatic pressure, of water through the interstices of a rock or soil, except the movement through large openings such as caves. Percolation, deep. In irrigation or farming practice, the amount of water that passes below the root zone of the crop or vegetation.

Barrett and Milligan, , p. Small-scale storage at a waterpower plant to equalize daily or weekly fluctuations in riverflow or to permit irregular hourly use of the water for power generation to accord with fluctuations in load.

After Barrows, , p. A deep reach of a stream. The reach of a stream between two riffles. Natural streams often consist of a succession of pools and riffles.

Water loss that will occur if at no time there is a deficiency of water in the soil for use of vegetation. Thornthwaite, , p. Potential natural water loss. The water loss during years when the annual precipitation greatly exceeds the average water loss. It represents the approximate upper limit to water loss under the type and density of vegetation native to a basin, actual conditions of moisture supply, and other basin characteristics, whereas potential evapotranspiration represents the hypothetical condition of no deficiency of water in the soil at any time for use of the type and density of vegetation that would develop.

After Troxell and others, , pl. Potential rate of evaporation. See Evaporativity. As used in hydrology, precipitation is the discharge of water, in liquid or solid state, out of the atmosphere, generally upon a land or water surface. The term "precipitation" is also commonly used to designate the quantity of water that is precipitated. Precipitation includes rainfall, snow, hail, and sleet, and is therefore a more general term than rainfall. Liquid precipitation. The quantity of water that falls as rain only.

Not synonymous with precipitation. Rainfall excess. The volume of rainfall available for direct runoff. It is equal to the total rainfall minus interception , depression storage , and absorption.

See Am. Civil Engineers, , p. Rainfall, excessive. Rainfall in which the rate of fall is greater than certain adopted limits, chosen with regard to the normal precipitation excluding snow of a given place or area. In the U. Weather Bureau, it is defined, for States along the southern Atlantic coast and the Gulf coast, as rainfall in which the depth of precipitation is 0.

The length of channel uniform with respect to discharge, depth, area, and slope. The length of a channel for which a single gage affords a satisfactory measure of the stage and discharge. The length of a river between two gaging stations.

More generally, any length of a river. Recession curve. A hydrograph showing the decreasing rate of runoff following a period of rain or snowmelt. Since direct runoff and base runoff recede at different rates, separate curves, called direct runoff recession curves or base runoff recession curves, are generally drawn.

The term "depletion curve" in the sense of base runoff recession is not recommended. Recurrence interval return period. The average interval of time within which the given flood will be equaled or exceeded once. As used in this sense, the word "regime" applies only to streams that make at least part of their boundaries from their transported load and part of their transported load from their boundaries, carrying out the process at different places and times in any one stream in a balanced or alternating manner that prevents unlimited growth or removal of boundaries.

A stream, river, or canal of this type is called a "regime stream, river, or canal. In unspecialized use "regime" and "regimen" are synonyms. After Blench, , p. Regimen of a stream. The system or order characteristic of a stream; in other words, its habits with respect to velocity and volume, form of and changes in channel, capacity to transport sediment, and amount of material supplied for transportation.

The term is also applied to a stream which has reached an equilibrium between corrosion and deposition or, in other words, to a graded stream. Bryan, The artificial manipulation of the flow of a stream. Re-regulating reservoirs. A reservoir for reducing diurnal fluctuations resulting from the operation of an upstream reservoir for power production.

A pond, lake, or basin, either natural or artificial, for the storage, regulation, and control of water. Residual-mass curve. A graph of the cumulative departures from a given reference such as the arithmetic average, generally as ordinate, plotted against time or date, as abscissa. See Mass curve.

Retarding reservoir. Ungated reservoir for temporary storage of flood water. Sometimes called detention reservoir. Return flow. That part of irrigation water that is not consumed by evapotranspiration and that returns to its source or another body of water.

The term is also applied to the water that is discharged from industrial plants. Also called return water. A rapid in a stream. Pertaining to the banks of a stream. That part of the precipitation that appears in surface streams.

It is the same as streamflow unaffected by artificial diversions , storage , or other works of man in or on the stream channels. Runoff may be classified as follows: Classification as to speed of appearance after rainfall or snow melting: Direct runoff Base runoff Classification as to source: Surface runoff see Overland flow Storm seepage Ground-water runoff see Stream, gaining Runout. See Water yield. Same as cfs. This term is no longer used in published reports of the U.

Geological Survey. Fragmental material that originates from weathering of rocks and is transported by, suspended in, or deposited by water or air or is accumulated in beds by other natural agencies. Colby, Hembree, and Jochens, , p. Sediment discharge. The rate at which dry weight of sediment passes a section of a stream or is the quantity of sediment, as measured by dry weight, or by volume, that is discharged in a given time.

The free oscillation of the bulk of water in a lake and the motion caused by it on the surface of the lake. Bergsten, , p. Shifting control. See Control. The diversion of water from a stream or conduit by a shallow overflow used to avoid diversion of sand, silt, or other debris carried as bottom load. A form of precipitation composed of ice crystals.

Snow course. A line or series of connecting lines along which snow samples are taken at regularly spaced points. Agriculture, Soil Conserv. Service and Nevada State Engineer, , p. Snow density. Ratio between the volume of melt water derived from a sample of snow and the initial volume of the sample. This is numerically equal to the specific gravity of the snow. Linsley, Kohler, and Paulhus, , p. The general altitude to which the continuous snow cover of high mountains retreats in summer, chiefly controlled by the depth of the winter snowfall and by the temperature of the summer.

Snowline, temporary. A line sometimes drawn on a weather map during the winter showing the southern limit of the snow cover. Snow, quality of. The ratio of heat of melting of snow, in calories per gram to the 80 calories per gram for melting pure ice at 0 degrees C. Bernard and Wilson, , p. See also Wilson, b, p. Percentage by weight which is ice Linsley, Kohler, and Paulhus, , p. Soil moisture Soil water. Water diffused in the soil, the upper part of the zone of aeration from which water is discharged by the transpiration of plants or by soil evaporation.

See Field-moisture capacity and Field-moisture deficiency. The height of a water surface above an established datum plane; also gage height.

Stage-capacity curve. A graph showing the relation between the surface elevation of the water in a reservoir, usually plotted as ordinate, against the volume below that elevation, plotted as abscissa.

Stage-discharge curve rating curve. A graph showing the relation between the gage height, usually plotted as ordinate, and the amount of water flowing in a channel, expressed as volume per unit of time, plotted as abscissa.

Stage-discharge relation. The relation expressed by the stage-discharge curve. Stage, flood. See Flood stage. Rainfall or snowmelt led to the ground down the trunks or stems of plants. Hoover, , p. Water artificially impounded in surface or underground reservoirs, for future use.

The term regulation refers to the action of this storage in modifying streamflow. See also Conservation storage , Total storage , Dead storage , and Usable storage. Water naturally detained in a drainage basin, such as ground water , channel storage , and depression storage. The term "drainage basin storage" or simply "basin storage" is sometimes used to refer collectively to the amount of water in natural storage in a drainage basin.

Storage, bank. See Bank storage. Storage, conservation. See Conservation storage. Storage, dead. See Dead storage. Storage, depression. See Depression storage. Storage ratio. The net available storage divided by the mean flow for 1 year. Hazen, , p. See also Thomas and Harbeck, , p. Storage-required frequency curve. A graph showing the frequency with which storage equal to or greater than selected amounts will be required to maintain selected rates of regulated flow.

Storage, total. See Total storage. Storage, usable. See Usable Storage. A disturbance of the ordinary average conditions of the atmosphere which, unless specifically qualified, may include any or all meteorological disturbances, such as wind, rain, snow, hail, or thunder. See Direct runoff. Storm seepage. That part of precipitation which infiltrates the surface soil, and moves toward the streams as ephemeral, shallow, perched ground water above the main ground-water level.

Storm seepage is usually part of the direct runoff. A general term for a body of flowing water. In hydrology the term is generally applied to the water flowing in a natural channel as distinct from a canal.

More generally as in the term stream gaging , it is applied to the water flowing in any channel, natural or artificial. Streams in natural channels may be classified as follows after Meinzer, , p. One which flows continuously.

Intermittent or seasonal. One which flows only at certain times of the year when it receives water from springs or from some surface source such as melting snow in mountainous areas. One that flows only in direct response to precipitation, and whose channel is at all times above the water table. Relation to space. One that does not have interruptions in space. One which contains alternating reaches, that are either perennial, intermittent, or ephemeral.

Relation to ground water. A stream or reach of a stream that receives water from the zone of saturation. A stream or reach of a stream that contributes water to the zone of saturation. A stream or reach of a stream that neither contributes water to the zone of saturation nor receives water from it.

It is separated from the zones of saturation by an impermeable bed. A perched stream is either a losing stream or an insulated stream that is separated from the underlying ground water by a zone of aeration. The discharge that occurs in a natural channel.

Although the term discharge can be applied to the flow of a canal, the word streamflow uniquely describes the discharge in a surface stream course. The term "streamflow" is more general than runoff , as streamflow may be applied to discharge whether or not it is affected by diversion or regulation.

Streamflow depletion. The amount of water that flows into a valley, or onto a particular land area, minus the water that flows out the valley or off from the particular land area. Blaney, a, p. What do you mean by runoff? What is the difference between runoff and discharge? What is a runoff in writing? What is a runoff in a sentence?

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