National Weather Service United States Department of Commerce

Flood Infographics

 

SCIENCE OF RIVER FLOODING -
Water is essential for life on Earth. But in large enough quantities, the very substance we drink and use to grow crops can destroy homes, businesses and cause fatalities.

River flooding occurs when river levels rise & overflow their banks or the edges of their main channel and inundate normally dry areas.

River flooding can be caused by heavy rainfall, dam failures, rapid snowmelt and ice jams.

Six Steps to Create a River Model
Hydrologic Cycle: Hydrologists try to understand and simulate the natural hydrologic cycle, which is the intricate combination of many processes such as evaporation, transpiration, precipitation, infiltration, interflow, groundwater storage, and runoff.

Precipitation: Precipitation is the primary input to basin hydrologic processes and serves as the primary driver of hydrologic models. Accurate representation of precipitation input is an important intial step. Small river channel systems are very sensitive to rainfall.

Runoff: The next step is to compute the amount of precipitation that appears in surface water within a relatively short time from the onset of a storm event. This is runoff. Runoff consists of 3 components: 
overland flow, rain falling directly on surface water bodies, and interflow.

Unit Hydrograph: After computing basin runoff, the next step is to calculate a forecast hydrograph in units
of discharge. A hydrograph is a plot of the change of stage or discharge with respect to time. Discharge is the volume of water flowing past a location per unit time and is usually expressed in cubic feet per second (cfs).

Streamflow Data: Scientists use streamflow measurements to capture the vital relationship between discharge (volume flow rate) and stage (height) for a given location. This can only be done by taking streamflow measurements at different river levels and noting the corresponding stages. This relation is called a rating curve.

Routing: Hydrologists analyze and interpret how the water moves once it’s in the river and how a flood wave is modified due to the effects of storage and friction as it moves downstream. So, what happens upstream affects the entire downstream community.
Don't underestimate the power of water! 6 inches of fast-moving water can knock over and carry away an adult. 12 inches of fast-moving water can carry away a small car. 18-24 inches of fast-moving water can carry away most large SUVs, vans and trucks.
Do you really know how deep the water is?  6 inches of fast-moving water can knock over and carry away an adult.  12 inches of fast-moving water can carry away a small car.  18-24 inches of fast-moving water can carry away most large SUVs, vans and trucks.
Flood Warning: A Flood Warning is issued when flooding is happening or will happen soon.  Move to higher ground.  Never drive through flooded roads.  Flood Watch: A Flood Watch is issued when flooding is possible.  Stay tuned to radio/TV, follow weather.gov and be ready to seek higher ground.  Learn more at weather.gov/flood
Flooding At Night - Sometimes difficult to see during the day. Impossible to see at night.