Canals and Irrigation Canals

I currently have no canals but would like to build some. However, I dont have the spoon dredger technology so is it worth it? How long will it take them to silt up? and what happens whe they do silt up? I assume that, in the absence of the spoon dredger, I have to spant the same amount to clean them as to bring them up a leel.

I am thinking I may also construct irrigation canals, I dont see any mention of needing spoon dredgers for these so I assume I dont need them.

Anyone have any experirence of these issues? Thanks

You can start building canals without spoon dredgers but the canals will eventually collapse, this is the whole basis for the war in game 7 as France claim that England promised him spoon dredgers. They never arrived and the new French canals collapsed.
You will probably need spoon dredgers or all the money invested can disappear very quickly. The canals will give a significant boost to trade but price is high, a long term project to say the least.
No need for spoon dredgers to maintain irrigation canals.

I've built canals in a few games now and agree with Ardagor. They are well worth the money unless you live in a very hilly country. I don't think paying extra for tunnels has much impact.
Dredgers seem to be essential unless you can find another way of maintaining them, perhaps like roads?
I've had mixed experience with irrigation canals. In one position they did nothing at all, but in another they did increase the chance of improved harvest.
I guess the results depend on the geography of the country concerned.

Canals and roads will up your economy no end russia makes great profit from them