Ineffectiveness on river management?

Question

I wanna know what is the disadvantage or ineffectiveness of river channel realignment, resectioning, bank protection ( building artificial levees, gabions), and planting vegetation )

Answer 1

Channelisation is changing the natural course of river to reduce the possibility of flooding.

Advantage

Re-alignment- straightening of river channel to increase speed of river to wash away localised flooding to reduce occurrence of floods

Re-sectioning- Widening and deepening of river to increase river's ability to hold water and replace soil with cement and granite to reduce friction to increase speed of river.

Bank protection-Building levees to increase the capacity of river to hold water. Orotects river banks from being eroded.

Planting vegetation- Hold soil firmly together and prevent large amount of water entering the water at one time and slows down surface runoff, reducing chance of flooding.

Disadvantages

Flooding downstream- re-sectioning will cause volume of water to increase upstream and the channel downstream may not be able to hold it, thus channelisation may cuase flloding at another part of the river.

Accumulation of sediments

Higher speed of river upstream may cause more sediments to be washed downstream into sea or ocean resulting in lesser sunlight reaching seabed, affecting growth of marine life. Construction of dykes also causes sediments to accumulate behind these structures, causing river channel to be shallower, thus still leading to flloding.

Higher dykes have to be built regularly and sediments have to be dug up.

Loss of marine life and wetlands

Ecosystem may be destroyed as too little sunlight reaching the river bed, affecting aquatic plant growth, thus affecting the food chain. Natural habitats of these marine lives are also destroyed and leading to disappearance of wetlands by shortening the course. 'no nett loss in wetlands' is a policy that ensures plants and animals to have wetlands to live in.

Hope I helped!

Answer 2

River channel reallignment can lead to increases in channel speed, therefore more erosion. Artificial levees can cause more severe flooding (ie Mississippi).