Rivers and Engineering

Rivers and Engineering:

The flow of a river brings many positive as well as negative changes on the landscape. The rivers or streams transport sediment from one location to another. We should also need to know that as a river flows and erodes sediment, gravels and silt, which changes the shape of the course of the river. The process of erosion always has been, and still is, a natural part of the rock cycle. Without erosion the existence of sediments and formation sedimentary rocks will be impossible. Erosion detaches the loose, unconsolidated soil and sediment from over the bedrock.

Streams and rivers erode and transport sediment coming across their course. They erode bedrock and sediment from one location and deposit these sediments at another location. The flowing water in rivers and streams is one of the major agents in eroding the surface of the bedrock and sediments from over the bottom of the river/stream. As a result of erosion, the rivers and streams reshape their course of flow. These changes can be positive and beneficial for mankind, as well as negative. The negative change includes flooding, land-sliding, excessive erosion, excessive deposition, and wearing and tearing of the adjacent landscapes, and geological features. Rivers and streams create many practical challenges to civil engineers, some of which are as follows.

• Rivers require construction of bridges across them for carrying highways and railways.
• Water power of rivers can be utilized to generate hydroelectricity.
• Dams are built on rivers to store water meeting the need of irrigation, and floor control.
• Regulation of river channels is done for navigation and flood control.
•  River-deposits are the important sources of the construction material.
• The life of some artificial reservoirs is reduced considerably by river deposits.

(1). Flood Control:

During floods, the rivers cause destruction of life and property and therefore, flood control is a very important problem for a civil engineer. The various methods which are used to control floods are as follows:

1. Construction of Levees: The levees are longitudinal embankments that are built along the river banks to check the overflow of the excess water during floods. The levees not only confine the river water into its channel but they also increase bed erosion and keep the channel clean.
2. Dredging: It is the process of removing the sediment deposited at the bottom of the river channel. Dredging is a costly affair as it has to be carried out all the time.
3. Construction of Check Dams: The Construction of check dams for controlling floods is a very useful method. The check dams are usually built on small tributary streams that regulate the flow of the main river.
4. Diversion of River Water: During floods, a part of the river water is diverted and made to flow through a newly constructed channel. Thus the river water gets divided and the effect of flood reduces.
5. Shortening Course of Meandering Rivers: In meandering rivers, artificial cut-offs are made to straighten the course of the river/ stream. This tool increases the efficiency of the river.

(2). River Training:

The river training is mainly connected with the improvement of the river channel for navigation. The various river training measures are as follows.

1. Dredging is done to remove sand, mud, and silt from the bottom of the river. Another objective of the dredging is to deepen the deck of the river to accommodate much water. The large deck of the river will prevent the overflow of the water beyond the banks of the river. Dredging also saves the cost of levees. The dredged material can be deposited along the river banks.
2. Training walls are constructed which restrict the flow of the water to a given channel. It enhances the scouring effect of the water currents and keeps the channel clean.
3. Low groynes (underwater barriers) are constructed in the course of the river in order to check the erosion caused by the flow of the river at a steep surface.