The impact of dams and sand-gravel extractions on the downstream channel deformations (in the example of the Goychay River)

What are the consequences of building dams on rivers with a high gradient and removing sand and gravel from the channels? The main purpose of this article is to study the channel deformations that occurred because of sand-gravel extraction and dam construction. Gravel extraction from river channels not only causes channel deformations, but also seriously affects hydraulic infrastructure. Our study found that along with sand-gravel removal, flow regulation leads to the entry of clearer water into the lower basin, and as a result, erosion processes are accelerated. In recent decades, intensive extraction of sand and gravel from the channel of the Goychay river, as well as dam construction, has led to the erosion of the downstream channel. To study these effects, using satellite images and energy and mass conservation equations, all the factors that can affect the channel deformations were analyzed. The study confirms that excavations in different areas of open channels create various hydraulic jumps along the riverbed, which accelerates the washing capacity potential of the flow. Excavations at various sites often result in the conversion of potential flow energy into kinetic energy and the continuation of this process eventually leads to the erosion of the channel. In addition, the construction of a dam on the channel and the regulation of the flow increases the washing capacity of the downstream water. The study also found that the regulation of small streams decreases sediment transport capacity in downstream parts. The flow discharged downstream is not saturated with sediments and has a velocity equal to or close to the scouring one. As a result, an intense deep erosion process takes place in the lower banks of the dams built on rivers with a high gradient, and a deepening of the channel occurs, which results in collapse of coastal buildings and hydraulic construction.