Hjulström curve

Hjulströms diagram en

Hjulström curve is a graph that illustrates the relationship between the velocity of a river or stream and the size of sediments (particles of sand, gravel, and boulders) that can be transported, deposited, or eroded by the flow of water. The curve was developed by Swedish geologist Filip Hjulström in 1935, making it an essential concept in the fields of geology, geomorphology, and hydrology.

Overview

The Hjulström curve shows on the vertical axis the velocity of the flowing water in meters per second and on the horizontal axis the diameter of the sediment particles in millimeters. The curve is divided into three main areas: erosion, transportation, and deposition.

• Erosion: This area of the curve indicates the minimum velocity required to erode and lift particles of different sizes from the river bed. It shows that fine particles like clay require higher velocities to be eroded than sand or gravel because of the cohesive forces between the fine particles.
• Transportation: Once particles are lifted into the flow of the river, they can be transported. This part of the curve demonstrates that a wide range of velocities can transport particles, and it varies significantly with the size of the sediment.
• Deposition: This area illustrates the velocities at which different sizes of particles will settle and be deposited from the water. Larger particles require higher velocities to remain in suspension and are therefore deposited first as the velocity decreases, followed by smaller particles.

Significance

The Hjulström curve is significant in understanding the dynamics of river systems and the processes of erosion, transportation, and deposition. It helps in predicting how changes in river velocity can affect the landscape, influencing river management and restoration projects. For example, it can aid in determining the conditions under which a river might erode its banks or deposit sediment, leading to the formation of new landforms.

Applications

The Hjulström curve is used in various applications, including:

• Predicting sediment transport in river engineering projects.
• Understanding and managing sedimentation in reservoirs and waterways.
• Analyzing past river environments in geological studies.
• Planning for flood prevention and management of sediment-related issues.

Limitations

While the Hjulström curve is a valuable tool, it has limitations. It does not account for factors such as sediment cohesion, water chemistry, or the impact of vegetation on erosion and deposition processes. Additionally, the original curve was based on laboratory experiments, which may not fully replicate natural river conditions.

Conclusion

The Hjulström curve remains a foundational concept in the study of sediment transport in river systems. Despite its limitations, it provides a basic framework for understanding how rivers interact with their sediment load, which is crucial for managing water resources and protecting riverine environments.