Can waterways which are prone to flooding be dug deeper to help prevent flooding? Like just digging big trenches through the bed of the waterway?
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Generally it’s easier to make them wider, or to make a sort of buffer zone for the flooding. The dutch have entire systems for this.
They can reduce the risk of flooding, but not prevent flooding. It all depends where the water is coming from that causes the flooding.
Digging trenches in the bed of a waterway won’t accomplish anything. Imagine you have a stream. Dig a hole in the bottom of the stream bed. The hole immediately fills with water from upstream as the stream continues to flow. The level of the stream doesn’t drop. Now a flood comes along. The hole you dug is already full of water, so no more will go in there. The stream rises just like it would have if the hole had never been there.
The level of water in a river cannot be dictated locally. Where a river crests is dictated by start and finish elevations and flow rates, to name a couple variables. Digging the riverbed deeper would only serve to slow the flow down. You would end up with a deep pool and a calm flow at the same elevation it was before.
No. It doesn’t work. Rivera are kept clear, there’s digging involved, but mostly to move the sediments and vegetation away from critical areas.
The control is done by controlling the amount of water. You chose an area like a lake or valley or farmland, you build earthworks like a dam but with a narrow exit, and keep that place low level the entire year. If a flood comes, that designed area get flooded while the narrow exit fills the river with a controlled rate. That’s the best flood control. If properly done, you can even store some flood water and use it later to fight a draught.
Digging the river would just create a deeper valley, with stagnant water in the new trench, that trench you made would quickly get filled by sediments, so you spend a lot for little benefit.
You mean dig trenches locally, or through the whole river system? If the whole system, that’s a lot of work to do and maintain, and ultimately you’d have to deal with the ocean coming in to backfill the trench you dig. And then you’d have to deal with sediment, etc…
If you mean locally, that wouldn’t work either because the flow would simply adjust to re-attain an equilibrium between the upstream and downstream flows. There wouldn’t be *no* change but you may actually end up with faster flows that do more damage.
Finally, why is this different from a dyke? Because a dyke only kicks in when the water level reaches it. It’s no interfering with the flow as it currently stands. A trench would change the flow conditions of the river under normal conditions, and then you’d have to think about how upstream and downstream conditions affect your trench, and vice versa.
These videos give you a sense of some of the flow changes that might happen if you dug out a trench. It also gives you some search terms if you’re still interested!
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