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What Is a Meander - Characteristics, Formation and Types

 
Andrea Márquez
By Andrea Márquez, Environmentalist specialized in marine and costal environments. July 25, 2023
What Is a Meander - Characteristics, Formation and Types

Meanders are natural formations found in rivers across the globe. These sinuous, winding curves give rivers a unique and visually striking appearance, creating ever-changing landscapes. Meandering rivers are a testament to the dynamic forces of erosion and sedimentation that shape our planet's geography.

In this article, we will explain what meanders are, explore how they are formed, their characteristics, and ecological significance.

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Contents
  1. What is a meander and what are its defining characteristics?
  2. How is a meander formed?
  3. Types of meanders
  4. Ecological significance of meanders

What is a meander and what are its defining characteristics?

A meander is a distinctive geological feature found in river systems. It refers to the sinuous, winding curves that rivers create as they flow through alluvial plains with gentle slopes. Meanders are a result of the dynamic interplay between erosion and sedimentation processes within the river.

  • Meanders display a pronounced sinuosity, making them easily recognizable on the landscape.

  • They typically originate in rivers situated on gently sloping alluvial plains.

  • Meanders have a greater capacity to drag and transport sediments compared to straight rivers.

  • Final deposition of sediments results in the formation of lobes or point bars.

  • Meandering rivers' behavior is shaped by the combined erosive and sedimentary actions of freshwater.

  • Their course is unstable, which may lead to the creation of horseshoe or bull's-eye lake formations.

  • The creation of meanders varies across different rivers due to factors like flow, current speed, and channel material composition.

  • Meanders contribute to increasing the length of the river.

  • Meanders consist of an external erosive zone with higher speed and turbulence, and an internal sedimentation zone.

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What Is a Meander - Characteristics, Formation and Types - What is a meander and what are its defining characteristics?

How is a meander formed?

After understanding the definition and characteristics of meanders, you might be curious about how they are formed. Meanders typically take shape in alluvial plains with gentle slopes, driven by changes in water current.

The section with the highest water speed experiences heightened erosive processes, resulting in the excavation of the shore and giving rise to a concave terrain. Conversely, in the areas where water flows more slowly, sedimentation processes dominate, shaping the meander's features.

As the flow of a river increases, its ability to carry sediment also grows. This increased sediment transport can lead to a process known as meander strangulation. During meander strangulation, the higher water flow erodes the outer bank of the meander, causing it to cut through the neck of the bend. As a result, the river starts following a more direct and straighter path.

During this process, the meander is effectively "strangled" as the river carves a new, shorter route. The connection points between the old meander and the new course experience sediment accumulation due to decreased water flow in those areas. This sediment deposition eventually forms what is known as an abandoned meander, leaving behind a horseshoe-shaped lake or oxbow lake. These abandoned meanders are fascinating remnants of the river's previous course and showcase the ever-changing nature of river landscapes.

Types of meanders

Indeed, meanders can be classified into two main types:

Divergent meanders

Diverging meanders form on alluvial plains with a low slope. In these areas, the river's flow encounters sections with varying water speeds. As the river flows around a curve, it experiences greater resistance on the outer bank, leading to erosion. This erosion contributes to the formation of divergent meanders, where the river creates pronounced curves and bends in its path.

Embedded meanders

Embedded meanders are shaped by changes in the base level of the river. When the base level drops or lowers, the water flows in a downward direction, causing the river to cut deeper into the terrain. Embedded meanders are typically found in narrow and steep valleys.

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Ecological significance of meanders

The ecological significance of meanders extends far beyond their visually captivating appearance. These sinuous bends play a vital role in shaping river ecosystems and supporting a diverse range of plant and animal life. Here are some key aspects of their ecological importance:

  • Meanders provide a variety of habitats, such as slow-flowing sections on the inner banks and faster-moving sections on the outer banks. These diverse microhabitats support a wide array of plant and animal species, contributing to overall biodiversity in river systems.

  • The sheltered areas and calm waters of meanders offer important habitats for aquatic and semiaquatic wildlife. Fish, amphibians, reptiles, and various invertebrates thrive in these sheltered zones.

  • The slower flow of water in the inner curve promotes the deposition of sediments and organic matter. This accumulation of nutrients supports the growth of aquatic vegetation and provides a rich food source for aquatic organisms.

  • Meanders help regulate sediment transport in rivers. They trap and retain sediments, preventing excessive erosion downstream and aiding in flood control.

  • Over time, sediment deposition in meanders contributes to the development of floodplains. These fertile areas are essential for nutrient cycling, groundwater recharge, and providing habitats for various terrestrial species.
  • The presence of meanders creates diverse riparian zones along riverbanks. These areas are often rich in vegetation and serve as critical corridors for wildlife movement, enhancing ecological connectivity.

  • The slow flow and sediment deposition in meanders facilitate the infiltration of water into the ground, contributing to groundwater recharge and maintaining healthy aquifers.

  • Meanders and the associated vegetation play a role in carbon storage. The plants within riparian zones sequester carbon, helping to mitigate the impacts of climate change.

  • The bends of meanders help to dissipate the energy of the flowing water, reducing erosion along the riverbank and stabilizing the surrounding landscape.

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What Is a Meander - Characteristics, Formation and Types - Ecological significance of meanders

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What Is a Meander - Characteristics, Formation and Types