Read the following passage and answer the questions. Floods are normal events…

Read the following passage and answer the questions.

Floods are normal events that cause damage. As rivers carve and shape the landscape, they build broad floodplains, level expanses that are periodically inundated. A "10-year flood" would be expected to occur once in every ten years; a "100-year flood" would be expected to occur once every century. The biggest economic loss from floods is usually not the buildings and property they carry away but rather, the contamination they cause. Many human activities like paving roads and parking lots reduces water infiltration into the soil and speeds the rate of runoff into streams and lakes. Even more than development, though, flood-control structures have seperated floodplains from rivers. Levees and flood walls are built to contain water within river banks, and river channels are dredged and deepened to allow water to recede faster. Every flood-control structure simply transfers the problem down-stream. However, the water has to go somewhere. If it doesn't soak into the ground upstream, it will simply exacerbate floods somewhere downstream-leading to more levee development, and then to more flooding farther downstream, and so on.

What is the biggest economic loss from floods typically due to ?