Basin runoff generation is the first link of runoff formation.Compared with the traditional concept, runoff generation is not only a static concept of water production, but a dynamic concept with temporal and spatial changes.It includes the spatial development of runoff producing area at different times and the time history change of runoff producing intensity with rainfall process.At the same time, runoff generation is not just a concept of water volume, but a formation process of multiphase flow including water production, sediment production and solute transport. In addition, runoff generation mainly occurs on the slope of the watershed. For different size watersheds, the proportion of slope area is different, and various factors affecting runoff generation on the slope, including vegetation, soil, slopeLand use status, slope area and location are different in different watersheds.
basinOfprecipitationThe water flowing from the surface and underground into the river network and out of the outlet section of the basin is called runoff.Liquid precipitationformationRainfall runoff，Solid precipitationIce and snowMeltwaterRunoff.fromprecipitationFrom reaching the ground to the whole section where the water flows through the outletPhysicsProcess, called runoffFormation process。precipitationThe formation process of runoff varies with the form of runoff.China's riversRainfall runoffMainly,Snow melt runoffIt only occurs in local sections of rivers in western high mountains and high latitudes.According to different formation processes and runoff paths,River runoffIt can also be controlled by surface runoffUnderground runoffandInterflow(Surface flow) Three runoff components.
Runoff isAtmospheric precipitationFormed and passed throughbasinThe flow of water into a river, lake or ocean through different paths.It is also used to mean the amount of water that passes through a certain section of the river in a certain period of time, namely runoff.PressprecipitationMorphology is divided intoRainfall runoffandSnowmelt runoff。According to the formation and flow path, it can be divided into surface runoff generated on the ground and flowing along the ground;staysoilThe surface flow formed in the soil surface and flowing along the relatively impermeable layer interface, also known asInterflow；The underground water flows from high water head to low water head after the formation of underground water.In a broad sense, runoff also includesSolid runoffandChemical runoff。Runoff causes rivers, lakes, groundwater, etcWater bodyWater regimeDirect factors of change.Its formation process is a process fromprecipitationTo where the water flows intobasinThe whole process of exit section.Rainfall runoffThe formation process ofrainfall, retention, infiltrationFilling depression、basinEvapotranspiration, slope confluence and channel confluence.Snowmelt runoffThe formation of requires a certain amount of heat to convert snow intoliquid。Occurs during snowmeltrainfallWill formMixed runoff of rain and snow。Factors affecting runoff includeprecipitation, temperature, terraingeology、soil、vegetationandhuman activityEtc.
precipitationyesRunoff formationOfPrimary link。Fall into a channelsurface of the waterThe rainwater on the surface can directly form runoff.basinInrainfallIn case ofvegetation, some will be intercepted.Fall onbasinInfiltration of rainwater on the groundsoil, whenrainfall intensity When the soil infiltration strength is exceeded, the ground surface is generatedPondingAnd filled in large and small potholes, and the water stored in the potholes seeps into the soil or is evaporated.When the potholes are filled, they flow from high to lowOverland flow。Overland flowMany of them are different in size and timeTrickle(channel）Flow to the foot of slope whenrainfall intensity Under the condition of large and flat slope, it can flow in sheets.fromOverland flowThe process from the beginning to flowing into the channel is called overtopping process.The river channel gathers the water flow on the slope along the bankLongitudinal flowThe process to control section isRiver channel concentrationProcess.sincerainfallFrom beginning to formationOverland flowInfiltrationsoilWater insoil moisture content Increase and generateFree gravity waterWhen encountering relatively small permeabilitySoil layerOr impervious parent rock, it will accumulate on this interface and flow along the interface slope direction, formingUnderground runoff(surface flow and deep underground flow), and finally flows into river channels or lakes and seas.The flow in the channel is called channel flow, and it passes throughFlow hydrograph segmentationSurface runoff andUnderground runoff。
The formation of runoff is a very complex process. In order to have a certain understanding of the concept, it can be generalized into two stages, namelyEffluxPhase andConfluence stage。
Flow generation stage
WhenrainfallSatisfiedBotanyInterceptiondepressionStorage and surfacesoilAfter storagerainfall intensity When the rainfall exceeds the infiltration intensity, it begins to move along the surfaceOverland flowMoving, called slope overflow, is the beginning of runoff generation.If the rainfall continues to increase, the range of overtopping will also increase, forming a comprehensive overtoppingOverland flowDynamic flow into river channel is called slope runoff.The process of overland flow is called runoff generation stage.
Confluence stage
rainfallThe generated runoff is collected into the nearby river network, and thenupper reachesFlow downstream, and finally all flow throughbasinThe exit section is called river network confluence, and this process of river network confluence is called confluence stage.
influence factor
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Runoff isbasinMedium climate andUnderlying surfaceAll kinds of natureGeographyThe product of comprehensive action of factors.The distribution characteristics of runoff first depend onclimateConditions.In the sameClimatic zone, mountainous areabasinRunoff is generally greater thanplain；geology、soilUnder different conditions, the drainage basin has different water permeability. The drainage basin with strong water permeability produces less runoff, and vice versa.Influenced by elevation, the runoff hasVertical differenceCharacteristics of.basinThe scale of area determines the size of runoff,vegetation、lake、swampIt has the function of regulating runoff.The temporal and spatial variation characteristics of runoff are also deeply affectedhuman activityImpact: Deforestation will aggravate soil erosion,flood peakRunoff surge;reservoirThe construction of water storage projects will increasebasinTo regulate runoff;IndustryfarmlandA large amount of water will be reducedRiver runoff；Inter basin water diversion can reduce the runoff of the diverted basin and increase the runoff of the introduced basin.Runoff is the surface of the earthwater cycleThe important link in the processChemistry、PhysicsProperty pairgeographical environmentAnd ecosystem play an important role.
Climatic factors
Underground runoff
It is the influenceRiver runoffThe most basic and important factors.Climatic elementsInprecipitationAnd evaporationRiver runoffThe formation and change of.In terms of precipitation, precipitation form, total amount, intensity, process and spatial distribution will all affectRiver runoffChanges.For example,precipitationThe larger,River runoffThe greater;Precipitation intensityThe larger, the shorter the timefloodThe more likely it is.Evaporation is mainly restricted by airSaturation differenceandwind speed。The greater the saturation difference, the greater the wind speed, the stronger the evaporation.Other elements of the climate, such as temperature, wind and humidity, often pass throughprecipitationAnd evaporation effectsRiver runoff。
Underlying surface factors of watershed
Underlying surface factorMainly including landformgeology、vegetation, lakes and marshes, etc.landformsZhongshanInfluence of ground elevation and slope aspectprecipitationThe amount of rain, such as windward slope more rain, leeward slope less rain.Hillside impactbasinInternal confluence andInfiltrationThe water like mountain and stream is easy to rise and fall steeply.basinwithingeologyandsoilThe conditions often determine the infiltration, evaporation and maximum underground water storage of the basin, such asfault, where joints and fractures are developed,groundwaterRich,River runoffIt is greatly affected by groundwater.vegetation, especially forest vegetation, can play the role of water storage, water and soil conservationPeak discharge, addLow waterFlow, makingRiver runoffThe annual distribution tends to be uniform.
human activity
For example, by manualrainfall, artificial melting of ice and snowbasinWater diversion increases river runoff;Regulate runoff changes by planting trees, building terraces, ditches and canals;The temporal and spatial distribution of runoff is changed by building reservoirs and flood storage, flood diversion, flood discharge and other projects.
Runoff is the surface of the earthwater cycleIt is an important link in the process. Its chemical and physical characteristics play an important role in the geographical environment and ecosystem.
metering method
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Related formula
The data required for runoff study are provided by the hydrological stationExperimental basinOr runoff station, laboratory and field investigation.Runoff is mainly studied through observation, experiment, analysis and calculation.The measured values of runoff include flow, runoff, runoff modulus, modulus coefficient, runoff depthRunoff coefficientEtc.
Flow（Q）Yes means passing within unit timeOverflow sectionIn cubic meters per second.
Q=VA
WhereVAverage flowCurrent Speed；AIs the area of water discharge section.
Runoff（W）Is a certain period of time (△T）The volume of water passing through the discharge section in cubic meters.
W=Q△T
Runoff modulus(M）Is the runoff (water yield) per unit area, in liters/(seconds · km2).
analysis
WhereFIs the drainage area, in square kilometers.Modulus ratio coefficient（K）, also called flow variability, is the runoff modulus of each period（Mi) And normal runoff modulus（M0), i.e
Runoff depth（R）Is the inner diameter flow within a certain period of timeDrainage areaDepth value in mm on.
Runoff coefficient(C）Refers to the relationship between the inner diameter flow depth or runoff in a certain period andprecipitationDeep（P）Or total precipitation（Wp) Ratio of.
research meaning
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Runoff is formed by landformExternal forceAnd participate in theearthChemistryProcess, which also affectssoilThe growth of plants and the formation of lakes and marshes.Runoff is of great significance in the national economy.Runoff is an important condition for regional industrial and agricultural water supply, and also a constraint factor for regional socio-economic development scale.The ability of manual control and regulation of natural runoff is closely related to whether industrial and agricultural production and people's lives are endangered by floods and droughts.Therefore, the measurement, calculation and prediction of runoff are all important tasks of water conservancy construction.
