Streambank Erosion Control Stream Restoration

Streambank Erosion and Restoration

Streambank erosion is one of the important and often neglected environmental problems. If not properly maintained the river and the stream banks can be easily eroded by the sheer force of the flowing water during the heavy raining season. The precarious situation, which results as a consequence of erosion, cannot be taken lightly. It is these stream and rivers, which replenish the water needs of the people. Conservation of this vital natural source is an important task and the responsibility lies with man. Let us now briefly analyze the problem of Streambank erosion and the remedial solution.

Factors causing Erosion

Stream bank erosion is a common natural phenomenon, which occurs during the heavy flow of water. While erosion to a certain extent is natural and cannot be avoided what is disconcerting is the uncontrolled erosion. This has a disastrous effect on the water quality, soil fertility and the overall Eco system. The banks along the stream are rather delicate in that any change in them will have adverse implications. There are many reasons, which contribute to the uncontrolled erosion of streambanks. First and foremost is the sheer speed of the water flow. The main cause for this is that the rapid urbanization has drastically limited the water permeable surface of the land. This consequently increases the amount of water joining the stream and hence the velocity of water flowing in the stream. Changing the course of a stream by straightening the natural curves also results in increasing the velocity of water flow, which in turn results in greater erosion. Another major cause is the construction of dams. Water that comes inside the dam is full of sediments but the water which leaves the dam is relatively sediment free (due to filtering and deposition) and this adds to the velocity of stream water. (Sediment free water travels faster and this implies increased erosion)[SWCD]

Impact of Erosion

The main impact of erosion is the loss of fertility of the soil and the result is uncultivable land along the streambanks. Increased sedimentation also affects the quality of water. Due to construction of dams the productivity of lands downstream is greatly affected. Above and all these is the impact on the ecological system. Excessive sedimentation makes the water unsuitable for variety of fishes and other aquatic species. Indifferent attitude in this regard will ultimately lead to the extinction of these local species. Finally we should not underestimate the dangers to property due to the uncontrolled flow of the stream. [Cullen Gunn]

Remedy for Erosion

Soil Bioengineering is the best solution for preventing streambank erosion. This is a collective term for a wide variety of techniques that use a combination of plants and other materials to hold the banks of the stream together. Obviously plants hold the key to natural restoration as their roots can hold the soil firmly. Instead of growing vegetation if we simply place boulders alongside the banks it would only result in an increased resistance downstream. So a permanent solution would be to grow vegetation around the streambanks and in places where the slope of the stream is too steep, structures can also be built. Any of the several Bio engineering techniques like live staking, conventional plantings, live fascines, branchpacking, brushlayering, and brushmattressing can be used to prevent erosion. The choice between these techniques is made with respect to the topography of the stream (its slope gradient, speed etc.). Let us look at one of these solutions.

Bankside Plantings

One of the several soil Bioengineering techniques, Bankside planting is a natural and best solution to safeguard against soil erosion. The technique is to grow vegetation alongside the banks of the river. We can choose from a wide variety of native plants. This may include herbs, shrubs, and even some varieties of grasses. Plants that grow well in the native conditions and have a well-developed root system are to be preferred for this purpose. These plants can be appropriately spaced out so as to effect a combined binding force on the soil. Plants are excellent in slowing the run off. These plants not only stabilize the erosion by means of their soil binding power but also improve the greenery of the region and thereby assist in the prospering of a wide variety of local species. This is not a quick fix solution like barbing and using boulders but it is a long-term plan. It may even take a few years for the plants to grow well and get firmly rooted. This method is a little costly, as we need to procure the plants and it involves significant labor. [Bob Tjaden, Glenda M. Weber]

The advantages and disadvantages of these different methods are to be weighed carefully before implementing them. For example replanting vegetation alongside the banks simultaneously involves a need for change in cattle gracing habits. This method can take a long time to take effect but would be a natural solution and increase the chances of flourishing of wildlife habitat. On the other hand using rocks and boulders would prevent erosion on the spot but they will increase it downstream.