Impacts Of Channelisation

Question 1

What are the four impacts of channelisation?

Answer 1

Instability
Increased blood hazard
Aesthetic
River ecology

Question 2

Instability (what are natural channels constantly doing and how, what does channelisation immediately change, what is also created downstream, example of levees)

Answer 2

Natural River channels are constantly adjusting their shape and form through processes of erosion and deposition. engineering schemes of channelisation can immediately change the channels characteristics and the rivers response to this unnatural change often leads to instability this change to the channel shape along section of a river not only alters its characteristics but also create a new regime further downstream beyond the change section For example levees are natural/ man made raisings of the riverbank to increase river capacity and flooding but raising rivers above floodplain makes it difficult for water to drain back into river e.g floods in Bangladesh designed to reduce seasonal monsoon floods but prolonged the floods from six weeks to 4 months

Question 3

Increased flood hazard (what does moving more water at quick speeds cause the risk of, what areas do this and how, what is ultimately created downstream)

Answer 3

Moving a greater amount of water more quickly to an untainted section in the river is inevitably going to increase the risk of river flooding downstream many urban areas attempt to reduce flooding through resectioning and alignment but ultimately this creates a blood hazard downstream to the unchanged part of the channel where there is a lower river carrying capacity

Question 4

Aesthetic (what is the river course to the local community? What is it used for? What is the objection to what is lost and what is produced?)

Answer 4

The river course is valued as a amenities by the local community. It is used for sport, walks on banks and scenic environment. There is objection to the canal look appearance. channelisation results in the loss of the rivers riffles and pills and progresses a wider variation in discharge with low flow levels which exposed the bed becoming common.

Question 5

River ecology (what do rivers provide for biotic and abiotic elements of an ecosystem? What do rifles and pills provide ,how? How does channelisation impact the reparian environment? What happens the floodplains and what suffers from this? What happens when the river banks are modified and why is this bad?)

Answer 5

Rivers provide a diversity of habitats and environments for animals and plants to interact riffles and pills in the river provides habitats for plant and animals. in rifles the course gravel beds are for fish laying eggs. Pills provide habitat and shelter for fish and low flow. channelisation can impact the riverbed and environments. The reparian environment is directly impacted under channelisation. AG floodplain drainage makes it drier so the flora and fauna of marshes and wetland suffer, channelisation modifies the riverbanks through recreating their profile and clearance of vegetation however vegetation provides food and shelter for animals and this is lost.