Revision history [back]

FEMA (Federal Emergency Management Agency) deals with flooding issues in the U.S. They have some online documentations that can be helpful. Usually, for a residential structure, they mandate the lowest floor of the structure to be built abover the base food elevation (BFE), which is the rise of floodwaters during a 100-year storm event, a rainfall that has a 1% chance of occurring per year. This can be the 1% rain event during a six-hour storm, e.g. 4.5 inches, etc., that will go into estimating/calculating the amount of flow at a specific discharge point in the watershed. Thereupon, they use the flow value in hydraulic calculation to estimate the rise of floodwaters under such severe (1%) circumstances. There are two (2) freewares that can help you with ths: HEC-HMS for flow computation and HEC-RAS for the floodplain/hydraulics; both are reliable softwares overseen but the U.S. Corps of Engineers (USACE). You will need some topographical maps of the location. If no such information available, you can guestimate the height of floodwaters by observing previous flooding events. Regardless, build above the BFE, then the foundations must withstand the flow that goes at it; the practice that FEMA had was one square-inch opening per square-foot of floor area. Thus, no hydrostatic pressure will be built against the foundation. The FEMA guidelines are written for the homeowners and explains it to anyone from any educational background.

FEMA (Federal Emergency Management Agency) deals with flooding issues in the U.S. They have some online documentations that can be helpful. Usually, for a residential structure, they mandate the lowest floor of the structure to be built abover above the base food elevation (BFE), which is the rise of floodwaters during a 100-year storm event, a rainfall that has a 1% chance of occurring per year. This can be the 1% rain event during a six-hour storm, e.g. 4.5 inches, etc., that will go into estimating/calculating the amount of flow at a specific discharge point in the watershed. Thereupon, they use the flow value in hydraulic calculation to estimate the rise of floodwaters under such severe (1%) circumstances. There are two (2) freewares that can help you with ths: HEC-HMS for flow computation and HEC-RAS for the floodplain/hydraulics; both are reliable softwares overseen but the U.S. Corps of Engineers (USACE). You will need some topographical maps of the location. If no such information available, you can guestimate the height of floodwaters by observing previous flooding events. Regardless, build above the BFE, then the foundations must withstand the flow that goes at it; the practice that FEMA had was one square-inch opening per square-foot of floor area. Thus, no hydrostatic pressure will be built against the foundation. The FEMA guidelines are written for the homeowners and explains it to anyone from any educational background.