Aging levee systems, particularly those under private ownership. Silt deposits in rivers and streams have reduce capacity and demand higher levees to contain flows. Increase in paved surfacing. Over the last few decades development has encroached into flood plains resulting in a greater number of homes in high risk areas.
Population increase demands more land be turned to development.
Most of our most common flood events are classified as riverine . This means that rainfall or snowmelt occurring at any point in a watershed will have an impact on waterways and communities located down stream. The further down stream you go, the more water there is pouring into the main river from its many tributaries. This is why flooding in coastal areas, particularly when coupled with storm tides and high winds can be so devastating as the greatest volumes are concentrated there. Authorities measure flood events by their rate of rise .