If rivers overflow &flood during heavy rain &snow melts why don't canals?

Question

It'sjust that i've never seen a canal overflow

Answer 1

In extreme cases it is possible for a canal to overflow.

Rivers occur naturally and the water that flows in them is the run-off from large areas of land. When it rains some of the water soaks into the ground and some of it makes it's way into the rivers. In very heavy rain nearly all the water flows straight into the rivers and very little disappears underground.

Canals on the other hand are man made and don't drain water from the land. In instances of very heavy rain water can make it's own streams and run into the canals, plus of course there's the rain that actually falls on the canal itself.

Canals do flow like a river but on a much smaller scale. If you toss a leaf onto a canal you'll notice it floats slowly away and you've probably seen the water flowing down the channels alongside locks. The opening and closing of locks also relaeases some of the water and there are overflows as well which usually empty into a nearby river.

Canals have plugs just like a sink. Several years ago when they were dredging the local canal they accidentally pulled the plug and all the water drained away.

Answer 2

The section of a canal between locks is technically known as a Pound (whatever its length or shape). All Pounds have overflow points.

These may be visible as small 'spillways' alongside longer pounds which empty into adjoining rivers or streams.

Sometimes the overflows are visible at locks where surplus water from the higher Pound is ducted down (by-passing the lock itself) to to drain into the lower Pound.

Water passing down a 'healthy' Pound to a spillway will create a weak current in the canal water. Sometimes it's noticeable if there's a lot a water about.
If a lot of rain falls (snow melt or whatever) the spillways sometimes can't cope and the canal will overflow or burst at the weakest point of its bank.

The locks themselves are used to raise and lower boats. It is not their primary purpose to control Pound water level.

Answer 3

Rivers form from many many small sources, creating a funnel type effect.. so when there is very heavy rain fall the river is overwhelmed because its not just the rain falling on the river that is making it rise, it's the rain from a very large area flowing into it.

Canals are man-made and don't have this same source. Canals also don't have the same kind of flow characteristics. The water is often still and separated by locks.

Answer 4

They do. I saw this in New Orleans back in the late 70's, it rained 9 or 10 inches in about 12 hours or so and guess what? - the dang canals were flooding into the streets.

Answer 5

My yard does sometimes after heavy rain. We're in a newer development and the grading is horrible. We put sod in the backyard and that has helped a lot. We also have a sump pump in our basement...THANK GOD! We had a lot of rain today and that has been running all day. I'm afraid of what my basement might look like if we didn't.

Answer 6

Rivers form where natural drainage concentrates runoff. Canals occasionally do overflow but are less likely to since they are (almost by definition) not in places runoff water naturally flows to.

Answer 7

Canals generally have locks which are used to control the water level.

Answer 8

Im not positive but are canals not usually between two large bodies of water? If im correct on that well the answer is simply this becuase it takes so much water to raise the entire body of water level that it would have to rain for weeks. ..Lets

Answer 9

Canals cannot overflow. They have an effective sluice system that takes away excessive water (Rather like the overflow in your bath)
Moral. LIve by a canal!

Answer 10

Where i used to live the cannal overflowed on a reasonably annual basis. Most water activities were posponed for this reason.