Flooding actually occurs from a range of causes and conditions not always the ones that first come to mind. For example, few people appreciate that inland flooding has been the cause of more than half the deaths arising from hurricanes in the last three decades. Torrential rains can accumulate when a storm becomes stalled in a certain location, even hundreds of miles from the coast. Of course, river flooding is the kind we think of most commonly. Heavy rains or rapid snowmelt on upstream watersheds cause rivers to rise more so at chokepoints or where tributaries converge.
Coastal flooding is also very common.
In many places, coastal land is very close to sea level, and therefore vulnerable. When violent surf and storm surge coincide with normal high tides, the results can be catastrophic. Less often thought of are the floods that can result from the failure of dams, impoundments, or other regulatory systems. The Johnstown flood is an example. There are more than 76,000 dams in the National Inventory of Dams, and probably others uncounted.