Strategy of Channelization in River Systems
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The purpose of this essay is to analyze the strategy of channelization in river systems in order to reduce flooding, and other purposes such as navigation. Also the importance of channel forms and the value of the systems approach are evaluated within this essay when considering the pros and cons of restoration activities and whether these schemes are beneficial to the environment. Overall this essay will look at the environmental degradation caused by channelization and determine whether channelization is the most beneficial strategy in reducing flooding or are there alternatives that lead to less environmental degradation.
Channel forms help humans comprehend the behaviour of rivers. This is vital as one can foresee how rivers may be affected by various changes and restoration schemes. Thus, the ability to protect and restore river health is enhanced. Channel forms are regulated by convoluted interactions between profuse environmental variables. This is why the systems approach is a useful method when analysing channel systems, as it does not just look at one variable but all of the linked variables involved. Even with this system shaping channel forms is highly dependent on geology; directly and indirectly over a prolonged period. Human interactions have also had an impact on the change of channel form for instance channelization (Water and river commissions, 2002).
Channelization and its implementation:
Human interaction with river systems is both the reason why channelization was implemented for example as a result of flooding and the cause of environmental degradation of the river systems. Humans interact with river systems in many ways and have impacted flooding of river channels due to increased population pressure, which has put a growing demand on water supply systems leading to environmental degradation. Deforestation around river channels have also increased flooding as deforestation impacts the interaction between precipitation and the drainage basin response.
Due to increased awareness of river behaviour and dynamics new strategies were implemented and overtime humans modernised engineering structures and built broad structures to control and regulate river flows, such as channelization.
Channelization according to Brookes is a type of “river engineering whereby the natural river channels are modified to control flooding, drain wetlands, and improve river channels for navigation, control stream-bank erosion and to improve river alignment” (Brookes, 1988). River channelization has seven types of alterations (Gregory, 2006). These are “(1) re-sectioning and realignment, (2) Dredging, (3) Snagging and clearing, (4) Levees or artificial embankments, (5) Bank protection, (6) Bed protection and (7) River training” (Charlton, 2008). An example where these alterations have been implemented is during the channelization of the River Raba in Carpathians, Poland (Wyzga, 1993).
However, these engineering structures tend to have a large impact on river and the natural ecology and hydrology of the channel system. For years humans have interacted with channels and altered the natural geology of the systems and thus have lead to severe impacts on the “physical, chemical and ecological condition of the channel systems” (Brookes, 1988). The impacts of channelization usually involve the alteration of river hydraulics and the decrease of instream habitat. Other impacts discovered as a result of these alterations include increased water temp, erosion, elimination of bankside habitat. These impacts can cause severe environmental degradation (Gregory, 2006).
The deterioration of systems within the environment by either natural or human influence is considered environmental degradation and as channelization alters the natural river system it leads to extreme environmental degradation. Impacts on the environment associated with human interference are usually quite complex and are mostly long term effects. Nevertheless, few studies have been conducted on the long term effects of channelization (Brooker, 1985). Swales (1982a) however inspected several environmental effects on channel engineering systems, in particular the impact on stream habitat and discovered that channelization has a major impact on instream and bankside habitat (Brooker, 1985), as well as the hydrology, aspects of flow and suspended sediment within river systems (Wilcock, 1991). Effects of channelization can also occur downstream in a channel system which broadens the extent of ecological disturbance (Brooker, 1985).
The increase of flow velocity and its carrying capacity as a result of shortening and straightening the channels has an immediate ecological effect on instream habitat as many ecosystems need particular conditions in terms water velocity (Gore, 1978). This destruction within the channel systems leads to erosion of bankside vegetation which increases sediment loads in the channel (Keller, 1976; Karr and Schlosser, 1978). Sediment loads in channel systems are usually low (Lewin, 1981), however, in channelized rivers se the loads are increased as bed/channel wall sediments are scraped up. This release of sediment has major effects on the ecology of the river (Wilcock, 1991) as removal of bankside vegetation leads to temp changes and in results affects the ecosystem as well as reducing energy flow (Brooker, 1985). In some cases channel slopes have also seen as increase whilst channel roughness is seen to reduce.
An example of environmental degradation was shown in Gregory (2006) which involved the Channelization of the Blackwater River in Johnson County, Missouri. This channel was shortened in 1910 in order to reduce flooding by deepening and widening the channel by “up to four times its original size” (Emerson, 1971). This subsequent lowering and increase of channel width lead to increased erosion in the river system, also bridge repairs have had to be carried out and there has been a severe loss of farmland. “Downstream reduction in channel capacity has caused suspended sediment in turn increased flooding rather than reducing it due to termination of dredging” (Emerson, 1971).
Channelization was initially implemented to straighten and shorten river channels to reduce flooding. It was also implemented to decrease flow velocity and prevent flooding, however, this lead to environmental degradation which resulted in the depletion of instream habitats and depleted drainage function. As channelization has had problems leading to environmental degradation, alternative channel schemes have been developed to enhance water quality functions whilst preserving drainage function and lessening environmental degradation (Evans, Bass, Burchell, Hinson, Johnson and Doxey, 2007). There are many alternatives to channelization that environmentalists could install; one such method is stream renovation which has been implemented on “streams in Charlotte, North Carolina” (Nunnally, 1978). Unlike channelization stream restoration aims to decrease the risk of flooding and drainage problems “by employing channel design guidelines that do not destroy the hydraulic and morphologic equilibria that natural streams possess” (Nunnally, 1978). Minimal straightening which promotes bank stability by leaving trees is employed in this scheme. Also the reduction of channel reshaping and the use of bank stabilization techniques are used here to reduce flooding and control erosion as well as sedimentation problems (Nunnally, 1879). Other alternatives involve the formation of in-stream wetlands and “lowering of the floodplain to reconnect the channel with the floodplain, redesign of channels using natural channel design principles, and establishment of conservation easements” (Evans, Bass, Burchell, Hinson, Johnson and Doxey, 2007).
Recognising channel forms and understanding how they behave and change is crucial for managing and protecting channel systems, especially for river restoration activities. Due to severe environmental degradation restoration schemes have been implemented. Though, it is not known whether these schemes are beneficial.
Restoration activities generally improve bank stabilization (Florsheim, Mount, and Chin, 2008) and have positively increased depth and flow variety and velocity as well as increasing habitat diversity in channel systems (Pretty, Harrison, Shepherd, Smith, Hildrew and Hey, 2003). Other benefits include the protection of infrastructure around river channels, and in relation to instream habitat it guarantees overall ecological system. Restoration schemes allow the natural process in the channel systems to redevelop and surrounding landscapes to restore.
Restoration schemes are constructive in counteracting the environmental degradation caused by channelization; yet there are a few cons. For instance natural processes may not necessarily be enhanced. Also a clear understanding of channel process is important in implementing these schemes, as they may sacrifice natural conditions in order to protect infrastructure. Restoration schemes are extremely expensive and very complicated therefore it is generally impossible to remove all human influences meaning restoration may not lead to higher biological diversity.
Channelization is commonly used to prevent flooding of channel systems; however, it has been found that the adverse impacts created by channelization projects far outweigh the benefits they intend to create. It is for this reason that alternative strategies are being developed so that in the long run creates less environmental degradation. The use of the systems approach is important as the use of all variables regulated by channel forms is necessary in making the new strategies environmentally acceptable. Also increased knowledge of channel systems and its dynamics have helped better restoration schemes and thus leading to the recuperation of many already channelized systems.
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