Understanding Water Erosion And Its Global Impact

The world is losing a football pitch of soil to erosion every five seconds, according to FAO. Soil erosion is a naturally occurring process, in which the topsoil (the most fertile layer) is carried away by water, wind, or ice. It is, however, fast-tracked 100 to 1,000 times by such human activities as intensive farming, overgrazing, and deforestation, which decreases soil fertility and cropland productivity, endangering global food security in the long run. 

Water Erosion

A chisel in the hands of Mother Nature, water has been sculpting its way through lands and rocks for eons to create intricately beautiful landforms. Grand Canyon, Niagara Falls, and Mexican cenotes are all stunning examples of water erosion. At the same time, this natural phenomenon is accountable for about 72% of the world’s eroded soils. And, given the effects of climate change in some regions, this figure is likely to increase as the amount of precipitation grows. As a result, farmers are losing the most significant resource for growing crops – topsoil – which directly affects soil’s fertility and its potential to produce abundant yield.

What causes erosion by water

Water erosion involves several processes: detachment, transportation, and deposition of soil material. It is primarily triggered by several forces: rainfall and flowing water. Depending on the intensity of rainfall, raindrops can splash soil particles away at various, yet small distances, while runoff water further moves them downslope. Finally, the resulting sediments are deposited in streams, ponds, and reservoirs, where they build up over time.

Another point to consider while looking for the roots of erosion by water is human activities that directly and indirectly contribute to this phenomenon. Improper irrigation of cultivated lands results in degradation of soil, which erodes away and becomes vulnerable to flooding or waterlogging. Farmlands left bare after intensive tillage are especially prone to erosion; such soils lose structure and ability to properly hold plants. These are direct causes of water erosion. Whereas glacier melt exacerbated by greenhouse gas emissions that are massively produced by industry, transport, fossil fuel burning, and human-induced deforestation are indirect causes.

Improper Irrigation Methods: A leading cause of soil erosion

There are a multitude of factors that determine how badly water affects soil, causing it to erode away. These are typically related to soil type (structure, porosity, water infiltration capacity, etc.), land topography (grade of slope), and climate (rainfall intensity and duration). It is considered that most often water erosion occurs in regions with steep slopes, soils having low water infiltration rates, and poor (or no) vegetation cover. 

Water-induced erosion: types and scale

Erosion by water manifests itself in various forms depending on the magnitude and damage extent. The most widespread types are interlinked with each other and can be best described as several stages of a single process.

1. Splash erosion

Rain provides crops with water, which is essential for proper plant development. Raindrops, however, have an adverse effect on soil, slowly ruining its top layer. Raindrops hitting bare ground create “mini-explosions” that move soil particles away and leave tiny craters behind them. The detached soil dissolves in water and continues its way down the slope as a mud. Finally, soil gets covered with a crust and its ability to infiltrate water reduces. That’s how splash erosion occurs. 

Bare farmlands typically become an easy prey to this least impactful, yet dangerous type of water damage since it paves way for other, more detrimental eroding processes. 

2. Sheet erosion

This water erosion type occurs whenever rainfall is so intense that soil can’t fully absorb the incoming water. The finest light particles of soil’s top layer are carried away by the sheet of excess water overflowing above the ground and further down the hill. With it, the most nutrient-rich part of soil is lost. 

Water erosion

In most cases, sheet erosion hits badly crusted soils.

3. Rill erosion

If left unattended, sheet erosion can progress to form finger-shaped channels or rills that are usually up to 30 cm deep. More soil particles are carried away with the water flow, intensifying damage done to soil, and eventually gullies are formed. 

4. Gully erosion

Gullies are wide and deep trenches that develop as a result of the increased water runoff, both in volume and speed. They typically originate from cattle burrows and bullock cart tracks. At times, gullies can grow up to a scale where they impede farm machinery passes or even make cropland unusable for farming. Being one of the most advanced types of water erosion, gullies require serious interventions in terms of restoration. Aside from soil degradation, gully erosion also affects water quality due to high concentration of sediments that end up in streams and larger water bodies.

5. Tunnel erosion

Also called “hidden”, this type of water-induced soil damage erodes the subsurface, creating underground cavities that may remain unnoticed for a long time. It happens when water moves down through a structurally unsound soil into a hollow space below where it keeps washing away the soil to form water-flowing tunnels. Dispersive soils like sodosols and sodic soils that have unstable subsoil are especially prone to tunnel erosion and eventual collapse.

Impacts of water erosion on ecosystems 

Accelerated water erosion that by far exceeds the land’s natural erosion rate leaves its mark on both nature and human well-being. 

Loss of topsoil layer, which is most rich in organic matter, nutrients, and microorganisms, directly affects flora. Plants growing in eroded soils with diminished water infiltration can’t get the required amount of water and nutrients for proper development. As a result, soil grows infertile and croplands underproductive, affecting the income and livelihoods of farmers that live off crops.

Another major problem resulting from erosion by water is flooding. Compared to healthy soils, eroded soils have reduced ability to absorb water, which increases the risks of flooding after storms and intense rainfalls. Flood-prone regions, such as low-lying landscapes or areas with poor soil drainage, are hit the worst. In extreme cases, floods can sweep away roads and other infrastructure objects disrupting transportation, supply chains, and even causing fatalities.

Water supply itself is badly affected by water erosion. The nutrient-rich topsoil is washed away to rivers, lakes, and reservoirs, increasing the presence of nitrogen and phosphorus in the water (a process known as eutrophication) and reducing its oxygen levels. Moreover, harmful pesticides from farmlands get washed away from agricultural fields and reach neighboring bodies. This causes pollution and further decreases water quality. Modified chemical composition of water and presence of agrochemicals also have adverse effects on aquatic wildlife, leading to over-the-top algae bloom and fish kill.  

Keeping water erosion at bay with EOSDA Crop Monitoring

Knowing how to prevent water erosion – for example, by maintaining proper vegetation cover and leaving a protective layer of crop residue on top of the ground – can help preserve soil fertility and cropland productivity. Today, the implementation of beneficial soil conservation practices is simplified through the use of digital precision agriculture tools. EOSDA Crop Monitoring, an online satellite data-based tool developed by EOS Data Analytics, delivers actionable information about fields and vegetation that helps spot and address various types of water erosion in croplands, large and small. 

An array of vegetation indices has proven instrumental in distinguishing between vegetated areas and bare soil, which is vulnerable to splash erosion. The combination of Productivity maps and Scouting feature allow for precise detection of field areas that consistently underperform over seasons and dispatching professional scouts to check for any signs of sheet erosion, which might be causing it. 

Additionally, EOSDA Crop Monitoring can provide a strong basis for rehabilitating farmlands damaged by tunnel erosion. The repair requires a combined set of techniques, including chemical amelioration and subsequent fertilizer application to restore productivity in affected areas. The platform’s Zoning feature may add precision and simplify the respective soil testing for chemical analysis and variable-rate application of nutritive agents.

Water is a powerful force that may be both beneficial and harmful to one of the planet’s most precious and finite resources – soil. Water erosion destroys arable lands at alarming rate and is projected to increase by 30 to 66% by 2070, exacerbated by human activities. To keep it at bay, it is necessary to implement soil conservation practices preventing the water-induced damage. Modern data-rich precision agriculture tools are designed to improve soil-preserving strategies and make the implementation as simple and effective as possible.