Also found in: Dictionary, Thesaurus, Medical, Financial, Wikipedia.


a. an extra race to decide the winner after a tie
b. a contest or election held after a previous one has failed to produce a clear victory for any one person
2. that portion of rainfall that runs into streams as surface water rather than being absorbed into ground water or evaporating
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


When soil is infiltrated to full capacity with excess water from rain, snowmelt, or other sources. This is a major component of the water cycle. When runoff flows along the ground, it can pick up soil contaminants such as petroleum, pesticides, herbicides and insecticides, and fertilizers that pollute water sources.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



in hydrology, the flow of rain and meltwater into seas and low-lying areas. Runoff occurs along the earth’s surface, in which case it is called surface flow, and in the layer of soils and rocks, in which case it is called subsurface flow. The process is a constituent part of the earth’s water cycle. Thus, runoff, which is primarily a product of climate, influences the shaping of the relief, geochemical processes in the earth’s crust, the development of the soil cover, and the distribution of vegetation. In turn, the quantity and regime of runoff depend on the amount and regime of precipitation, evaporation, and temperature conditions, as well as on the nature of the region’s relief and geological structure, soil cover, and vegetation. Erosion, natural drainage and irrigation, and the transport and deposition of products of denudation are associated with runoff.

The proportion of atmospheric precipitation that does not evaporate and is not consumed by plants but forms runoff is inversely related to the average air temperature. On plains maximum runoff is usually observed in the wettest forest zone on the western and eastern coasts of the continents, and in mountains the amount of runoff increases up to a certain elevation, primarily on the slopes of mountain ranges facing humid airstreams. The typical periods in formation of runoff are high water, freshet, and low water (summer and winter).

The amount of runoff in any period of time (year, season, month) is expressed by the depth (in mm or cm), total volume, average discharge, modulus of runoff, and modular coefficient of runoff. The total volume of runoff (in cu m or cu km) is the amount of water that flows through the hydrometrically closed segment of a drainage basin. The total volume of runoff is usually determined graphically by constructing a hydrograph, that is, a diagram of change over time (t) of discharge (Q) for a year. Using the hydrograph it is possible to construct the integral curve of runoff, which gives a representation of the progressive accumulation of water volume (in a reservoir) with the passage of time. The modulus of runoff is the volume of runoff in a unit of time per unit of area of the watershed; it is usually expressed in //sec-km2 or //sec-hectare. The modular coefficient of runoff is the ratio of the quantity of runoff changing in time to its average value. The coefficient of runoff shows the ratio of the amount of runoff to the amount of precipitation that has fallen on the area for the same period of time; in other words, it specifies what proportion of precipitation goes into runoff. In addition to water (liquid) runoff, the runoff of suspended sediment and sediment drawn along the bottom (solid runoff) as well as dissolved mineral substances are also determined.

Observations are made at hydrologic posts and stations, and experimental investigations are conducted at runoff sites and in laboratories to study the runoff process and make a quantitative determination of all the factors that affect it. The determination of the numerical parameters of runoff, including where it is a regulated flow, can be done at reservoirs by means of hydrologic calculations and forecasts.

The total volume of annual river runoff into the world ocean is 35,000–40,000 cu km; of this volume roughly one-third is formed by subterranean waters drained by river valleys (a certain part of the subterannean runoff enters the ocean directly). The volume of annual river runoff into enclosed interior basins on land is roughly 750 cu km, of which 320 cu km goes to Middle Asia and the Caspian Sea basin. The total annual runoff of rivers in the USSR is about 4,700 cu km. Runoff from the rivers of Brazil (3,200 cu km), China (2,600 cu km), and the United States (2,100 cu km) is also significant.


Poliakov, B. V. Gidrologicheskiianaliz i raschety. Leningrad, 1946.
Muraveiskii, S. D. Rekiiozera: Gidrobiologiia, Stok. Moscow, 1960.
Zhelezniakov, G. V., and B. B. Danilevich. Tochnost’ gidrologichesakikh izmerenii i raschetov. Leningrad, 1966.
Sokolovskii, D. L. Rechnoistok. Leningrad, 1968.
Rukovodstvo po opredeleniiu raschetnykh gidrologicheskikh kharakteristik. Leningrad, 1973.
Mirovoi vodnyi balans i vodnye resursy Zemli. Leningrad, 1974.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


Surface streams that appear after precipitation.
The flow of water in a stream, usually expressed in cubic feet per second; the net effect of storms, accumulation, transpiration, meltage, seepage, evaporation, and percolation.
(mining engineering)
Collapse of a coal pillar in a mine.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


The flow of rainwater away from the area on which it has fallen.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
References in periodicals archive ?
"We were trying to find the physical mechanisms behind why precipitation and runoff extremes are increasing all over the globe," said the study's lead author Jiabo Yin, a visiting student from Wuhan University working in Gentine's group.
* In the Ninth Circuit, Group 41, Laura Shaffer with 42 percent and Dean Mosley with 30.5 percent made the runoff, while Lorraine Elizabeth DeYoung with 27.3 percent was eliminated.
The destruction of soil particles will cause macro soil pore blockage to inhibit soil water infiltration, consequently increase of surface runoff (Van Noordwijk et al., 2004).
The data used in this study were (a) land-use data (2014) from the Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences; (b) daily precipitation data of the 756 meteorological stations in a 51-year period (from 1961 to 2011) from the China Meteorological Data Sharing Service System (Figure 1(b)); and (c) annual runoff coefficient, which is obtained from digitizing to Hydrological Atlas of China by ArcGIS.
Daily rainfall data, land use map, hydrological soil group, and infiltration study were used to arrive at runoff curve numbers for NRCS model.
But the party says NEC has failed to react to the recommendation allegedly submitted by the two parties due to meet in the runoff and did not call them into a meeting to discuss it.
In order to determine the trend of runoff and SL, samples were collected in time steps of 2, 4, 6, 9, 12, 15, 20, 25, 30 min after the beginning of rainfall, and the volume of runoff was measured for each interval.
In order to investigate the changing trends of runoff and sediment transport in the Han River basin, five-year moving average method, rank-based Mann-Kendall method, and slope change ratio of cumulative quantity method were used in this study to test the evolutionary trend of runoff and sediment transport in the past decades.
where wi indicates different watershed number, [R.sub.wi]--Runoff (mm), P--Precipitation (mm), [S.sub.wi]--Potential maximum retention after runoff begins (mm) and [([I.sub.a]).sub.wi]--Initial abstraction which is the water losses before surface runoff begins.
In November of this year, legislators from the conservative Partido Accion Nacional (PAN) introduced an initiative to reform Article 88 of the Mexican Constitution to allow a runoff election in the presidential vote if the front-runner in the first round does not receive 50% or more of the vote.
Physically based and spatially distributed hydrologic computer models are in existence to calculate the phases of runoff generation for a given rainfall event (Beven and Kirkby 1979, Murari Paudel et al 2006, Ratika et al.2010, Jaehak et al 2010).