What are river bars, how do they form and why are they so important

Observation of a river everyone noticed particular formations of sand or gravel emerging from the water as if they were “little islands”. Have you ever wondered what it is? It is about river bars and is one of the typical elements that we can find in a river bed riverbed (or bed) – i.e. the “furrow” in which water flows. You may have even seen them, and when you returned to the same place after some time, you noticed that they had moved, changed, or even disappeared.

River bars are very dynamic and constantly evolving and play a very important role in the river ecosystem: they form exceptional habitats for plants and animals and have a significant influence on the morphology of the river and its behavior. Therefore, let’s try to better understand what they are, how they are formed, and what their meaning is.

Definition of a river bar

The PUSH bar it is a typical trough shape and is a bearing surface composed of deposits similar to those at the bottom of the channel. It is a part of the trough that has emerged, as a kind of island and is affected by the passage of river water only in the event of a flood. Usually, the rods consist only of sediments (such as sand or gravel) but sometimes the bar may be partially covered vegetation which, however, is always low and disjointed, like grasses or bushes.

If the bar is completely covered with low vegetation and trees, it turns into Rathni Island. Unlike gratings, it is more stable: even during flood events, it can stay above the water level, which is why vegetation can grow on it.

How rods are formed

Very simply, rivers can do three things: erode the material, transport it, or save it. The water flowing in the river has great erosive power, and therefore it can use its energy to erode the fragments of rock it encounters on its way. In addition, if the energy is sufficient, the river transports eroded debris: as the water flows, debris materials such as boulders, pebbles, and rocks move and rub against each other. This movement causes breaking and smoothing, making the boulders smaller and more rounded.

When the flow of water slows down the energy of the river decreases and the material settles. Just in these areas river bars are created: where the watercourse is no longer able to carry the debris it has eroded, it settles and accumulates, growing more and more until it emerges from the water, creating river dams.

Sidebars, meander bars, and other types

River bars do not appear randomly, but they follow the energy of the river and emerge when the flow slows. They can be distinguished by their shape and position in the trough different types see also in the picture below the list:

1. Side panels: formed parallel to the main flow of water along the banks of the river; in fact, water flows more slowly on the sides than in the middle. They are specific to straight rivers or rivers with low sinuosity and can be elongated or smaller and isolated. Gravel and cobblestones are types of coarse material common in siding.
2. Meander bars: typical of rivers with more pronounced sinuosity, they develop in meanders, i.e. such zigzag curves that are often observed along the course of the river, especially in plains. In the inner part of the curve, the speed of the water is lower, as well as its energy, and for this reason the material settles. Meander bars are often long and narrow, following the profile of a meander curve.
3. Confluence rods: they are formed in places where two rivers or streams meet and mix, that is, they converge. When two rivers meet, the flows merge and the velocity of the water decreases, causing a drop in energy. The material usually settles on the sides of the confluence and forms river bars.
4. Longitudinal bars: they develop along the main course of the river, in the middle, follow a direction parallel to the water course, and have a linear and elongated shape. These streaks form in the center and not on the sides, because in some cases the water velocity can be slower than the center of the channel, causing settling. This can be caused, for example, by the presence of obstacles at the bottom of the river that slow down the flow.
5. Diamond bars: they are diamond-shaped and are typical of rivers with braided channels, i.e. watercourses that have multiple channels that flow and intertwine with each other. In these cases, when the water flow encounters obstacles and changes direction, turbulence and areas of slower flow occur in which the material settles and forms an elongated diamond structure;
6. Diagonal bars: Unlike the previous ones, these partitions are created against the direction of the main flow of the river. They are often found in curved sections and are derived from the lateral extension of longitudinal bars that are placed close to the banks.
7. Bars on the dunes: due to the complicated interactions between the water and the river bed, these bars can also form in the center of the channel, with a crescent shape with the apex facing the direction of the current.

Importance in the river ecosystem

River bars are mobile, unstable elements, precisely because it varies according to the behavior and energy of the river. They usually emerge from the water but may be submerged, destroyed, or migrate further downstream in the event of a flood. Especially in these moments, the poles are very important: indeed they increase the width of the river bed so that it can be vented without overflowing during flood events. Additionally, in low flow stages, they offer one very important area for river biodiversity: Grids form a basic habitat both for river animal species that find shelter here and for plant species.