Image of House Under Water - Flood

What are Floods?

Floods generally result from excessive precipitation, and the severity of a flooding event is typically determined by a combination of several major factors, including:

  • Stream and river basin topography and physiography
  • Precipitation and weather patterns
  • Recent soil moisture conditions
  • Degree of vegetative clearing and impervious surface

Generally, floods are long-term events that may last for several days.

Flooding Types

The primary types of general flooding are inland and coastal flooding. Due to The City of San Antonio’s inland location, only inland flooding is profiled in this section.

Inland or riverine flooding is a function of excessive precipitation levels and water runoff volumes within the watershed of a stream or river. It is natural and inevitable as it is the overbank flooding of rivers and streams, typically resulting from large-scale weather systems that generate prolonged rainfall over a wide geographic area.

Some river floods occur seasonally when winter or spring rainfalls fill river basins with too much water, too quickly. Torrential rains from decaying hurricanes or tropical systems can also produce river flooding.

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