How does modifying a river by channeling impact a river or stream ecosystem?

Question

Channel straightening, bank raising or removal of connections to the rest of the flood plain all have an impact on the ecosystem of the river. In particular I am interested in New Zealand river and stream systems but I imagine the basic impact of this is the same anywhere.

Answer 1

yeah, of course it does, cananalising a river will casue major loss, from the construction work, loss of the bank area of the stream/river, sediment being lost in the river, normally when rivers are canalised they are dug deeper into the surrounding area meaning that you loose bankside enviroments

hope this helps

Answer 2

Best example.
The Corp of Engineers, US, decided that they could shorten the travel time on the Mississippi River, by straightening out all the curves in the river.

They accomplished this over several years, shortening the distance by approximately 800+ miles.

RESULT.
The flow speed and erosion is so bad that the mouth of the river at the Gulf of Mexico has to be dredged on a regular basis because of the erosion/buildup.

Where did the erosion come from?
The banks of the Mississippi!
What did the Corp do to stop it?
No plants would grow fast enough to overcome the speed of erosion.
SO! They discovered a vine plant in China that grows 1" every 24 hours.
Wholla! The "Cud Plant".

They planted it along the river.
ALAS! The roots are so shallow it didn't stop the erosion.
BUT! It did grow like hell. All over the place.
It covers the landscape, it covers the trees, anywhere it can take hold. And kills everything, blocking the sun.

If one were to drive through the states of Alabama, Mississiippi, Louisana, parts of Western Georgia, and Southern Arkansas, you can't see the forest for the "Cud".

The Corp tried to cut it down, but, it was discovered that the damn plant doesn't die. All the cuttings, tiniest pieces, take root on their own.

Several years ago I had heard that the Chinese could kill it with "acpuncture", feeding poison into the vines. Don't think that ever was tried. Wonder what the result of that might be? Hmm

The Corp has been working about 20 years or so, trying to re-route the river by cutting new curves back into the flow. I heard that they may have lengthened the bed by 100-200 miles.

And the beat, erraah, the flow goes on!

You might like this too.
There is an animal in Florida, called "Nutria", that eats "Water Lilies", and very nicely keeps the lakes free of excessive lilies.
WELL! Texas had a similar problem with water lilies clogging the lakes.

SO! They imported "Nutria" to Texas lakes.

In Texas, the "Nutria" DO NOT EAT water lilies. They eat game fish.
They multiply faster than they can be eradicated. ARRRGGGHHHH!
They resemble large rodents.

Answer 3

By not letting the seddiment go where its been building allready such as the barrier islands from the Mississippi river in Louisiana.Good food for thought.