Streambank erosion causes, impacts, and bioengineering solutions

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]

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.

For example the Soque River in Georgia continued to inundate the farmlands and left severe sedimentation problem in the reservoirs that supplied water to Atlanta. This destroyed a variety of aquatic species and involved huge water treatment costs. The problem was identified to be the failure of years of government-aided methods of placing boulders, and other temporary methods of altering the course of the river. Instead of going in for a long-term solution they went in for an instant fix. Dani Wise-Frederick, watershed hydrologist and director of Stream Restoration Institute, North Carolina State University says, "Obviously we've been messing with streams for ages. What's new is our understanding that rivers are self-forming and self- maintaining. If you relocate, straighten or otherwise alter a river, it's going to try to carve its way back to its natural position." [Jessica Snyder Sachs] So it is necessary to have a futuristic perspective before we agree upon a remedial solution for streambank erosion problems.

Conclusion

Left unattended Streambank erosion will have an adverse effect on the ecological balance. Streambank erosion not only affects the soil fertility and the quality of the drinking water but also seriously endangers the survival of many forms of aquatic species. Growing vegetation alongside the banks seems to offer the best and Eco friendly solution of preventing erosion. These streams and rivers, which are the lifeline for many different species have to be better preserved so that they can continue to support and sustain all the different forms of life.