how can we strenghten natural levees?

Answer 1

By definition, a levee is a man-made structure. There is no such thing as a "natural levee."

In fact, they could be said to be highly un-natural structures, as they exist to artificially restrain the flow of rivers. Restraining nature on such a scale is always risky, and even levees that have been built of the most durable materials and by the most resistant structural methods known to man have failed miserably in the face of nature's power.

The best solution is to resettle people out of the flood plains and let the rivers flow naturally.

Answer 2

Levees can be natural or man-made. A natural levee is formed when sediment settles on the river bank, raising the level of the land around the river.

One way to strengthen a natural levee could be to excavate a deep trench through the levee, parallel to the river, and fill it with an impermeable material, clay, plastic liner, or concrete.

Answer 3

Shelly - to quote the US Army Corps of Engineers...

ALL LEVEES FAIL.

The assorted governments in flood plains and mountain valleys refuse to believe this.

There is one subdivision in the California(?) mountains that has a levee over 7 metres tall...it overtops EVERY building in the division by over a metre. WHEN (not if) this particular levee fails, everyone will die, and every structure in the valley will be gone. If I'm recalling correctly, we're talking several hundreds of homes pricing at over $200,000US each.

As for strengthening the banks of a river (to prevent erosion), there are several different ways, but many of them have a negative impact on the esthetics of the area (heavy bags of gravel, concrete, etc). Others can increase the esthetics of the area (trees, etc), but they slow, not stop erosion.