GALL

Gullies are forms of soil erosion that occur when the rainwaterinstead of infiltrating the earth or flowing gently through the surface, it begins to concentrate on certain points already Drain strongly. This process drags soil particles, creating small grooves that, with time and continuity of the flow of water, they become deep channels and well defined. In other words, a gullity is a type of eroded channel that is formed by the action of water on unprotected or degraded soils.

They usually appear on land with little vegetation, in earrings or slopes, where the ground is exposed directly to rainfall. Vegetation normally acts as a natural barrier that reduces water speed and helps maintain soil structure. However, when the land has been deforested, cultivated without control or urbanized without planning, the loss of vegetation coverage facilitates the beginning of the erosive process that leads to the formation of gullies.

Cacavas not only represent a visual alteration of the landscape, but also imply important ecological and economic consequences. On the environment, they cause the fertile soil losswhich affects the agricultural productivity and biodiversity of the place. In addition, they can Alter the natural course of water currents, favor floods and contribute to sedimentation of rivers, reservoirs or irrigation channels. From a social and economic perspective, gullies can damage infrastructure, such as rural roads, homes or crops, and generate high costs for rehabilitation or control.

An important characteristic of the gullies is that, once they begin to develop, they tend to advance and deepen if no measures are taken to stop the process. The water that runs through a gullity can increase its volume and speed with each rain, eroding further the margins of the channel and making it extend both in depth and in length. Therefore, in many rural areas, gullies control is a key aspect in soil conservation plans.

The formation of Cárcavas is a gradual, but persistent process, which develops in several stages that mainly driven by the action of water and by terrain conditions that favor erosion. These are the formation stages of the gullies:

1. Start of erosion: It all starts with superficial runoff. The water begins to form small grooves called microsurks or microchannels, which are very narrow and shallow. Although they seem harmless, these channels mark the beginning of the linear erosion process.
2. Groove Development: With repeated rains and continuous runoff, these microsurks are enlarged and becomes more defined grooves. At this stage, water gains speed and volume, which increases its ability to drag soil particles. As erosion intensifies, grooves become deeper and more wide, marking the passage towards a more severe erosion.
3. Formation of galls themselves: When the grooves exceed a certain threshold in depth and width, they transform into gullies. This point is critical, since gullies are not only more visible and destructive, but they are also more difficult to stop.
4. Retrievers and expansion: A typical characteristic of gullies is its setback to the upper part of the slope. This means that, as the water continues to drain, the head of the gullies (the highest part of the channel) is moving uphill. This setback can lead to gullies increasingly affecting the area of land, damaging cultivable land, roads or nearby infrastructure.

The formation of gullies does not occur in isolation, but depends on a combination of natural and human factors:

• PENDING OF THE LAND: Inclined areas favor the increase in water speed, which increases its erosive capacity.
• Type of soil: Sandy or very erodable soils are more likely to be dragged by water. It also influences soil compaction, which reduces infiltration. Here you can know the types of soils and their main characteristics.
• Vegetable coverage: The absence of vegetation leaves the soil unprotected, facilitating the beginning of erosion.
• Soil use: Activities such as intensive agriculture, overparation, deforestation or construction without conservation measures contribute to the formation of gullies.
• Rain intensity: Strong and sudden rains generate greater runoff, especially in climates with intense seasonal rainfall.

We recommend you read these other ecology articles about what is the erosion of the soil: causes and consequences and water erosion: definition, types, causes and consequences.

The gullies can be found in many parts of the world and under different geographical and climatic contexts. Although they usually appear in rural areas, they can also be formed in peri -urban or even urban areas if the conditions allow it. Let’s see some examples:

• Galls in agricultural areas: One of the most common examples occurs in poorly managed agricultural land. When a field is plowed on the slope without following level curves, and trees or bushes are also eliminated that acted as natural barriers, rainwater flows with force on the ground, starting the formation of gullies.
• Galls in Spain: In Spain, especially in the Aragon region, Castilla-La Mancha and the peninsular southeast, there are gullies that have been developed very visible due to the combination of clayey soils, steep slopes and little vegetation. These gullies have formed very eroded landscapes known as “Badlands”, a term that means “bad lands” for their low productivity and difficult access.
• Urban or peri -urban gullies: Although less frequent, gullies can also be formed in urban environments, especially in neighborhoods built on slopes without adequate drainage planning.
• Gullies as natural attraction or scientific study: In some places, gullies have become an object of study or even tourist attraction, thanks to their geomorphological forms. An interesting example is the Natural Park of Las Cárcavas in Madrid, near the municipality of Patones.

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