These images of floods in Lima, Peru show the power of fast-moving water. It becomes much more dangerous when the river is pushing huge piles of debris.https://m.youtube.com/watch?v=iy6LHR4FdCA
These latest pix were taken in Peru in 2017.
I am just wrapping up a 16-month trip in S. America. We visited Peru and Chile. We were in Santiago during heavy rains and floods in April, 2016. We were astonished to discover that the street in front of our hotel, which was in the center of the downtown area, actually turned into a river. The water was 6-12 inches deep. But really, we were lucky. At the edges of actual riverbeds, the effects of the currents are very strong. Some parts of these cities can go underwater.
The basic problem is that the western side of the Andes mountains is very steep. So when these mtns get hit by torrential rain, huge volumes of water start gushing towards the ocean. Peru and Chile just do not have the resources to build engineered-water channels. So the results are chaos.