Runoff is the term used for describe the movement of water through the ground, either as a result of rain, melting snow, or other sources of water. It is a natural process and essential to life on Earth, helping to provide water for plants and animals, as well as replenishing freshwater supplies in bodies of water.
Concept and definition of water runoff
Water runoff refers to the movement of water through the ground surface or in the subsurface, into bodies of water or drainage systems, as a result of precipitation, melting snow or snowmelt. Runoff occurs when the amount of water reaching the ground is greater than the soil’s ability to absorb and retain it.
Runoff is an important natural process in the water cycle that helps maintain water quality and also allows provide water to ecosystems and human communities. However, when the amount of runoff is too large, can cause damage and problems such as flooding, soil erosion and water pollution. Therefore, proper runoff management is essential to minimize risks and maximize benefits.
What is meant by runoff?
Runoff refers to the movement of water over or through the ground, into rivers, streams, lakes, or other bodies of water. This occurs when the amount of water reaching the ground, whether as a result of rain, snowmelt or snowmelt, is greater than the capacity of the soil to retain and absorb water. Runoff can be:
- Superficialmoving on the surface of the soil.
- undergroundmoving through the subsoil layers.
It is an important natural process in the hydrological cycle, which helps maintain water qualityprovides water to ecosystems and human communities.
What are the causes of runoff?
Runoff can be caused by various reasons. The most common causes include:
- Precipitation: Rain, snow and hail are the main causes of runoff. When the amount of water that falls to the ground is greater than the capacity of the ground to absorb it, the excess water flows over the surface ground.
- Topography: Land topography can also contribute to runoff. In mountainous areas, for example, rainwater or melted snow can flow into the valleys and rivers through streams and waterfalls.
- ground cover: The amount of vegetation and the quality of the soil can influence the amount of runoff that occurs. If the soil is covered by a thick layer of vegetation, it can absorb more water, thus reducing runoff. If the ground is covered by a layer of asphalt or cement, runoff will be higher.
- land use: The way the land is used can also affect the amount of runoff that occurs. For example, urbanization and the construction of buildings and roads can increase the number of impervious surfaceswhich in turn increases the amount of runoff.
- soil type: The type of soil can also influence the amount of runoff. The more sandy and permeable soils they absorb less water than clayey and heavy soils.
- Soil saturation degree: If the ground is already saturated with water, such as after a prolonged rain, the amount of runoff will increase.
- evapotranspiration: The amount of water that evaporates or is transpired from the soil surface and from vegetation can also influence the amount of runoff that occurs. The higher the rate of evapotranspiration, the lesser the amount of water available for runoff.
What are the characteristics of the runoff?
Runoff characteristics may vary depending on various factors such as climate, topography, soil cover, among others. Now they present some of the most common features from runoff:
- Amount: The amount of water flowing in runoff can vary from small amounts, such as morning dew, to large amounts, such as the floods caused by torrential rains.
- Speed: The rate at which runoff flows can vary from slow and steady to fast and turbulentdepending on the slope of the land and the amount of water that flows.
- concentration time: The time it takes for water to reach a certain point in the watershed is known as concentration time. This time can be short or longdepending on the slope of the land and the distance that the water has to travel.
- Water quality: The quality of runoff water can be affected by various factors, such as the presence of contaminants in the soil and in rainwater.
- Erosion: Runoff can cause soil and rock erosion, which can affect soil stability and water quality.
- sediment transport: Runoff can carry sediment, like sand, silt and clayfrom the upper parts of the hydrographic basin to the rivers and lakes.
- Water temperature: The runoff water temperature may vary depending on the time of year and the water source. In general, runoff water tends to be cooler than the water in the rivers and lakes into which it flows.
What are the types of runoff?
There are several types of runoff, each with its own characteristics and processes. Below are some of the more common types of runoff:
- surface runoff: It is the type of runoff that occurs on the earth’s surface above the ground and flows over the ground into streams, rivers and lakes. This runoff is common in urban and agricultural areas where the ground is covered with impervious surfaces such as asphalt or cement.
- interrupted runoff: Occurs when the flow of water in a stream stops temporarily, such as in a temporary puddle, swamp, or wetland area. This type of runoff is important for groundwater recharge and for regulation of water flow in streams.
- subsurface runoff: This type of runoff occurs when water flows through the pores and cracks from the soil basally, but below the soil surface. This runoff is important for the recharge of aquifers and for the supply of groundwater to wells and springs.
- channel runoff: This type of runoff occurs when water flows through artificial channels, such as sewers and drainage systems. This type of runoff is common in urban areas and is important for prevent flooding and property damage.
- infiltration runoff: This type of runoff occurs when water flows through the soil and infiltrates into the subsoil. This type of runoff is important for the recharge of aquifers and for regulating the flow of water in streams.
- deferred runoff: It is important because it can contribute to the recharge of aquifers, maintain the flow of rivers and streams during periods of drought, and reduce soil erosion and water pollution. Also, deferred runoff can be a water source for irrigation crops and human consumption in some areas.
It is important to note that these types of runoff are not mutually exclusive and can occur simultaneously in different parts of a watershed.
Groundwater runoff is a type of runoff that occurs when the water flows below the surface of the ground, through aquifers and areas saturated with water. This process occurs when water infiltrates the ground and moves through the underground layers until it finds an impermeable layer that prevents it from continuing its way down, so flow horizontally.
What are the consequences of runoff?
The runoff can have various consequences both positive and negative. Below are some of the more common consequences of runoff:
- soil erosion: The flow of water from surface runoff can cause soil erosion and lead to nutrient loss and soil organic matter. Soil erosion can also negatively affect water quality by carrying sediment and pollutants into streams and bodies of water.
- floods: Runoff can cause flooding in low-lying areas and urban areas with impervious surfaces. Floods can cause property damage, loss of human and animal life, and affect water quality by carrying pollutants into streams and bodies of water.
- Alteration of the hydrological regime: Runoff can alter the natural hydrological regime of a watershed, which can have negative consequences on flora and fauna of aquatic ecosystems. The alteration of the hydrological regime and also of the soil humidity can affect the supply of water for human consumption or agriculture.
- increased salinity: Runoff can carry salts and other minerals into bodies of water, which can increase salinity and affect the physicochemical quality of water and aquatic life.
- aquifer recharge: Groundwater runoff can recharge aquifers and supply water for human consumption and agriculture.
It is important to note that the consequences of runoff may vary depending on the amount of water, the intensity of the rain, the type of soil and the topography of the hydrographic basin. Therefore, it is important to properly manage water and minimize the negative impacts of runoff on the environment and on society.
Examples of a runoff in the water
A common example of water runoff is when it rains heavily in an urban area and the water flows rapidly through the streets and accumulates in drainage systems and nearby rivers. Water can carry sediment, trash, and other contaminants along its path, which can have a negative impact on water quality and aquatic life.
Another example of runoff into water can be when the snow melts in a mountainous area and the water flows into nearby rivers and streams. Runoff can carry sediment and nutrients along its path, which can affect water quality and aquatic life.