Flooding and Groundwater Seepage Evaluations

Summary

Flooding is one of the most unpredictable aspects of hydrology and can cause the greatest impacts. Proper planning can minimize impacts but often results in mitigation measures that are costly and thus not popular. Federal and State flood regulations have helped reduce impacts from many flood events through detailed floodplain mapping, requirements for building construction, and flood insurance. We are seeing an increase in the number and intensity of storms that produce flooding, so current floodplain regulations that are designed for the 100-year flood event (meaning a 1% probability of occurring in any year) may prove to be inadequate in the future.


Less dramatic but still damaging is flooding caused by a rise in groundwater levels. This can be caused by infiltration of rainfall, increased irrigation, leakage from ponds or canals, and even a decrease  in nearby pumping. These groundwater-related flood events are generally not covered by flood insurance policies but can be very costly to mitigate. And unlike surface water floods, groundwater-related flooding is often very slow to end since aquifer water levels change slowly.

Approach

We have been involved with a wide variety of flooding and seepage evaluations so each site warrants a unique approach.  Our technical evaluations have included the following items:

  • Obtaining and reviewing floodplain maps from FEMA and any local agencies
  • Examining maps of site topography, utilities and site soils for characteristics of flooding potential, infiltration, runoff, compaction and moisture retention
  • Site walk-throughs to identify nearby surface water features and uses
  • Examining basements, crawl spaces and other impacted areas 
  • Assessing existing perimeter drain and sump pump systems

With this information we evaluate the likely sources and causes of flooding, and make recommendations to reduce the flooding or seepage impacts.