Briefly describe the formation process of river runoff?

Precipitation is the first link in the formation of runoff.

Rainwater that falls on the surface of the river channel can directly form runoff. Rainfall in the watershed is partially retained if it hits vegetation. Rainwater that falls on the ground of the basin seeps into the soil when the rainfall intensifies.

When the intensity of soil infiltration is exceeded, water on the surface is generated and filled in large and small potholes, and the water trapped in the potholes seeps into the soil or is evaporated.

When the potholes are filled, a slope flow from high to low is formed. In the slope flow, many small streams (gully flows) of different sizes flow to the foot of the slope, and can flow in sheets when the rainfall intensity is high and the slope is flat.

The process from the beginning of the slope flow to the flow into the river channel is called the flow process. The process of collecting the water flow of the coastal slope and making it flow longitudinally to the control section is the process of the channel catchment. From the onset of rainfall to the formation of slope currents and trough catchments, water seeping into the soil increases the soil moisture content and produces free gravity water.

In the encounter permeability.

When a relatively small soil layer or impervious parent rock is deposited, it accumulates on this interface and flows along the interface slope to form underground runoff (surface flow and deep underground flow), and finally flows into river troughs, lakes and seas. The flow of water in a river channel is called channel flow, and surface runoff and underground runoff can be separated by the flow process line segmentation.

The valley is eroded by glaciers on the top of the mountain, and the valley is formed by the erosion of the ice and snow meltwater, which is then fed by the meltwater and the topographic rain formed by the uplift of the terrain. This creates river runoff.

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The formation process of runoff is the whole physical process from the rainfall to the surface of the watershed to the collection of water flow to the river outlet section.

The entire process from the arrival of rainfall to the ground to the collection of water flow and the flow through the outlet section of the watershed is called the runoff formation process. The formation of runoff is an extremely complex process, and for the sake of conceptual understanding, it can be generalized into two stages, namely the runoff phase and the confluence phase.

Abortion stage. When the rainfall satisfies the plant interception, the water storage of the depression and the storage of the surface soil, the subsequent rainfall intensity exceeds the infiltration intensity, and the rainfall exceeds the infiltration intensity and the base, and after it falls to the ground, it begins to flow along the surface slope called slope diffuse which is the beginning of runoff. If the rainfall continues to increase, the scope of the diffuse flow will also increase, forming a comprehensive diffuse, and this super-permeable rain flows along the slope surface into the river channel, which is called slope runoff.

The process of surface flow is called the runoff stage.

Confluence phase. The runoff generated by rainfall is collected into the nearby river network, and then flows from the upstream to the downstream, and finally all flows through the outlet section of the river basin, which is called the confluence of the river network, and the confluence process of the river network is the confluence stage.

Runoff Profile:

Runoff is the flow of water that is formed by atmospheric precipitation and enters rivers, lakes or oceans through different paths within a basin. It is also customary to indicate the amount of water passing through a certain section of a river in a certain period of time, that is, the amount of runoff. According to the precipitation pattern, it can be divided into rainfall runoff and snowmelt runoff.

According to the formation and flow path, it is divided into surface runoff that is generated on the ground and flows along the ground.

The surface flow that forms in the soil and flows along the interface of the relatively impervious layer of the soil surface layer is also called the soil middle flow; A flow of groundwater that flows from a high head to a low head after groundwater is formed. Broadly speaking, runoff also includes solid runoff and chemical runoff.

Runoff is a direct factor that causes changes in the water conditions of rivers, lakes, groundwater and other water bodies. The formation process is a whole process from precipitation to the convergence of water flow in the outlet section of the watershed.

The formation process of rainfall runoff includes rainfall, interception, infiltration, depression filling, evapotranspiration in watersheds, slope confluence and river channel confluence. The formation of snowmelt runoff requires a certain amount of heat to convert the snow into liquid. When rainfall occurs during snowmelt, mixed rain-snow runoff is formed.

Factors that affect runoff include precipitation, temperature, topography, geology, soil, vegetation, and human activities.

Influencing factors.

Runoff is the product of the comprehensive effect of various natural and geographical factors of climate and underlying surface in the basin.

a Climatic factors. It is the most basic and important factor affecting river runoff. Precipitation and evaporation in climate factors directly affect the formation and change of river runoff.

In terms of precipitation, the form, amount, intensity, process and spatial distribution of precipitation will affect the changes in river runoff. For example, the greater the precipitation, the greater the river runoff; The greater the intensity of precipitation, the more likely it is that floods will form in a short period of time. In terms of evaporation, it is mainly affected by the difference in air saturation and wind speed.

The greater the saturation difference and the greater the wind speed, the stronger the evaporation. Other elements of climate, such as temperature, wind, humidity, etc., often also affect river runoff through precipitation and evaporation.

b Underlying surface factors of the watershed. The underlying surface factors mainly include geomorphology, geology, vegetation, lakes and swamps. The elevation and slope aspect of the mountainous areas in the landform affect the amount of precipitation, such as more rain on the windward side and less rain on the leeward side.

Slopes affect the confluence and infiltration in the basin, such as the water of mountain streams is prone to rise and fall steeply. The geological and soil conditions in the basin often determine the infiltration, evaporation and maximum underground water storage in the basin, for example, in areas where faults, joints and fissures are developed, groundwater is abundant, and river runoff is greatly affected by groundwater. Vegetation, especially forest vegetation, can play a role in water storage, water retention and soil conservation, reduce peak flood flow, increase dry water flow, and make the annual distribution of river runoff tend to be even.

c Human activities. For example, river runoff can be increased through artificial rainfall, artificial melting of ice and snow, and cross-basin water transfer; Regulate runoff changes through afforestation, terraces, ditches and canals; The temporal and spatial distribution of runoff will be changed through the construction of reservoirs and flood storage, flood distribution, and flood discharge projects.

Runoff is an important link in the process of water circulation on the earth's surface, and its chemical and physical properties play an important role in the geographical environment and ecosystem.

The variation characteristics of river runoff are generally answered from the annual runoff [fine] flow and seasonal changes of runoff. And the reason is related to the way of supply. For example, the runoff changes and causes of the Yangtze River in China and the Rhine River in Europe are compared

Yangtze River: The annual runoff is large, and the runoff season [sharp] changes greatly. Reason: The main recharge mode is precipitation recharge, which belongs to the monsoon climate in the basin and has a large amount of precipitation; The monsoon climate has more precipitation in summer and less precipitation in winter, so river runoff varies greatly from season to season.

Rhine River: The annual runoff is large, and the runoff season changes little. Reason: The main recharge mode is precipitation recharge, and the basin is a temperate marine climate, with abundant and uniform precipitation throughout the year, so the annual runoff is large and the seasonal variation is small.

The influencing factors of river runoff are:

1. River recharge (climate: precipitation);

2. Topography (plains, basins);

3. The size of the basin area;

4. How many tributaries;

5. The size of the evaporation amount;

6. Degree of vegetation coverage.