When basements flood, it is usually from ground water.
Most of the soils in our area are very poorly draining soils with seasonal high water table levels.
Due to these issues, it is common for basements in our area to flood when the soil becomes saturated during periods of high rain.
In rare occurrences, a flooded basement may be the result of surface flooding. All of the storm sewer systems throughout the city are designed to carry the 10 year storm event. Detention ponds are designed and constructed to detain overflows above the 10-year storm, up to the 100 year flood level. However, these ponds become overwhelmed when (a) we have beyond the 100 year storm; and (b) circumstances occur such as back-to-back storm events, higher intensity storms than the 100 year event (this is a “flash flood” type of occurrence), or blockages of any storm sewer pipes, inlets, and/or pond outlets.
Generally, in addition to requiring engineers to design for the 10 year storm and requiring all home pads be constructed high enough to be protected from the 100 year flood event, we require engineers show us what happens during the 100 year storm event. We expect much of the water to run over the streets, etc. in order to get to the detention ponds. Ditches will run over into yards, but surface water should not be getting into homes – that is, unless they have built walk-out basement levels or windows exposing themselves to these lower elevations. When basements flood, it is usually from groundwater, and that is something we just can’t help.