River Modification

A major threat to the environmental health of a freshwater ecosystem comes from the anthropogenic modification of fluvial systems. River modification is a practice that humans have employed for thousands of years in order to obtain the largest benefits from the river systems improving the availability and accessibility to freshwater resources, with the earliest known implementation of a largescale dam occurring in around 3000 BCE with the Jawa Dam situated in modern day Jordan. These practices have developed over the centuries improving as engineering has advanced allowing for the scale of the modification efforts to drastically increase.

Many of the modifications seen to river systems have been completed to aid in the development of human settlements throughout the world. These range from diverting flow for use in agricultural practices to canalisation and the damming of many river systems across the world. These practices were often undertaken to improve the quality of life of the people within the river system as well as improving the ease of use of natural resources. A prime example of this is the canalisation of many river systems within the U.K. which were often undertaken during the industrial revolution. The modification of natural meandering river systems to a series of canals and lock systems allowed for the further industrialisation of the country as it improved transportation links for both the import and export of goods for manufacturing, with many of these systems leading to the development of urban settlements.

Another example of the modification of rivers comes from dams, these structures have a large number of uses with the main three being for the generation of hydroelectric energy, control over flooding and the preservation of freshwater resources for potable use throughout nearby regions. As such there are many benefits to the humans within the region, with the better management of freshwater resources as well as the generation of cleaner energy. It should also be noted that the number of these structures has greatly improved across the globe since the industrial revolution as construction techniques and the technology available has developed, as such a larger amount of the world's freshwater resources are being impounded affecting the natural function of fluvial systems across the world.

However, many of the practices that have been employed in the process of river modification have adverse effects on the natural environment leading to the deterioration of ecosystems and ecology.

Environmental Impact

Through the processes of River modification there are major impacts on the natural habitats that are located within these modified systems. These include the use of Dams, Canal systems and river straightening.

Dams

Processes such as damming freshwater resources can impact the natural environment in a multitude of ways, namely through habitat loss as a result of the flooding of the area behind a reservoir. The damming of a river system also impacts the overall regime of a river system with these structures obstructing the natural flow of a river system as the discharge of freshwater resources is controlled by the operation of the dam. This can greatly impact ecosystems downstream with the loss of flow to areas leading to the collapse of ecosystems, as well as impacting any migratory species within the modified river system preventing the travel upstream often to spawning grounds which can lead to species loss. The damming of a river system can also greatly impact the overall function of a river system through the loss of transport for sediments, which have the potential to accumulate behind the dam preventing the sustained health of a fluvial system as well as the transportation of nutrients within the river downs stream.

Canal systems

The production of canal systems diverts the natural flow of a river system into a system that was created more for its usage as a transportation route rather than for the natural function of the environment. Canal systems often contain biota within them however there is a severe loss of natural habitats within these systems as the banks are often constructed with a mixture of sand, clay and slate originally with modern systems being constructed through the use of concrete and plastic sheeting. Lock and canal systems throughout the world can negatively impact the migration of fish species upstream with the inability to bypass these structures and move upstream. These systems are often seen as a suitable setting for the expansion of non-native invasive species that can lead to the further deterioration of the fluvial environment.

Mitigation

In order to reduce the overall impact of the river modifications, multiple strategies are implemented from largescale processes to smaller modifications to the systems that are inplace. In terms of the mitigation of largescale river modifications such as dams that impact the natural regimes of rivers not only in terms of fresh water resources but also the sediment transportation of a river system, the use of improved management strategies of these structures not only improves the freshwater availability to ecosystems downstream improving environmental health but also increases the sustainable use of the resources. Other strategies are also implemented such as the flushing of dams in order to remove the sediments that build up within the reservoirs allowing for these sediments to travel downstream aiding in the continued maintenance of the natural fluvial regime.

A major impact originating from river modification is the loss of species namely migratory fish species that have been prevented from traveling to their spawning grounds as a result of structures impeding their way. As such in the case of Canal and Lock systems Fish ladders are often implemented allowing for the species to bypass the obstruction in the flow in order to continue with the natural migration of the species.