Today, all over the world and including in Iran, all kinds of river materials, including sand, rubble, and fine-grained materials, have found various uses in human life, especially in construction and industrial activities, and thousands of tons of all kinds are used daily. These materials are dug and harvested from the bed and banks of different rivers in the country. Different fields of use can be mentioned for river materials, among them is the production of concrete, and it can be said that approximately 75 percent of concrete is sand. Nowadays, concrete is widely used in the construction of buildings, dams, bridges and roads. In road construction, from its substructure to the asphalt of the road surface, sand is known as the main building blocks. In the construction of embankments, filters and industries such as glass making, mosaic making, etc., the use of sand is also widely used. River sands that have been subjected to continuous transport in water are particularly desirable sources of materials because their weak and loose materials have been removed by abrasion, leaving behind durable, well-circulated, well-graded sands. This has caused that these resources need less exploitation, and on the other hand, its easy access and proximity to transportation roads and the place of consumption, which ultimately increases its economic value, are among the reasons for its increasing use. He has been looking for mountain materials.
● Sand segmentation places in rivers
After the stone particles are separated from the parent rock due to weathering, they are transported downstream by various factors, the most important of which is water, increasing the amount of water and the speed of the flow are two important factors in increasing the carrying capacity of the river. Wherever the energy of the river is reduced, it will precipitate what it is no longer able to carry. In such a situation, first coarser particles and then gradually finer particles will settle. and in the end parts of the river due to low water energy, it is mostly silt and clay, so usually the middle parts of the river contain suitable places of sand. The old river, which is completely dry today, and you can also find streams. In the places where the river meets the natural or artificial lake such as dams, or at the intersection of the main and side rivers, you can generally find rich sources of sand. Another suitable place is the alluvial cone, which is the place where the river enters the plain from the mountains. Also, on the convex side of the inner arches, due to the low speed of the water, sand is easily deposited in them.
● Effects of proper harvesting of sand from rivers
Applying correct and appropriate management in removing sand from the rivers can have many positive effects on the revitalization of the river, the most important of which are mentioned below. The side of the inner arch is inclined to prevent the steepening of the arch of the openings. In addition, although the capacity of the flood has increased and there will be no lateral displacement, and finally we will have the stability of the bed.
Sand extraction from small sedimentary islands, which mainly happens in arterial rivers or behind diversion dams, eventually removing these islands. It aims to reduce the roughness coefficient and increase the cross-sectional area and increase the capacity of the flood. . The removal of materials from the upstream of bridges and sometimes their opening is one of the things that seems necessary to protect the bridges. When managing the removal of construction materials, in addition to keeping in mind the method of removal that brings the least changes to the river and its surroundings, it is necessary to organize We should also consider the suitable harvesting points in the river.