Storm Water Management: From Design to Disaster

On the Scene E-Newsletter, Edition 117, June 8, 2010

Hurricanes, El Niño, and excessive rain or snowmelt typically lead to excessive rainfall that ultimately collects and pools and contributes to flooding. Storm water is a term used to describe water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt or runoff water from overwatering that enters the storm water system. Storm water that does not soak into the ground becomes surface runoff, which either flows directly into surface waterways or is channeled into storm sewers, which eventually discharge to surface waters. The proactive side of these types of disasters is the engineering discipline of storm water management.

Take for example a case involving a community maintained storm water management pond adjacent to a claimant homeowner's property. The case involved the role of the storm water pond in basement flooding, commencing more than 10 years after construction of the pond and the community homes.

One of CED’s civil engineers with experience in home construction/maintenance, storm water management, and flood damage/mitigation, investigated the matter.  Of particular concern was the fact that the client’s basement was flooding, while an adjacent homeowner’s basement was not.  CED inspected the site and evaluated the as built drawings.  Also evaluated, were the vertical separation between the pond and the two homes in light of local standards for storm water management design.  The engineer concluded that while both homes were designed with the same basement finished floor elevation, the as-built condition of the basement floor of the non-flooding property was one foot higher than the flooding property.  In addition, the weir (overflow-type dam commonly used to raise the level of a pond) elevation of the pond was level with the finished floor elevation of the flooding basement.  As the stone weir of the pond silted up over the years, storm water was held up to the elevation of the homeowner’s basement floor, leading to flooding.

Engineers with storm water management expertise are trained in managing the following aspects of its effects;  control of flooding and erosion, managing and controlling hazardous materials to prevent release of pollutants into the environment, building 'soft' structures such as ponds, swales, or wetland to work with existing 'hard' drainage structures, such as pipes and concrete channels, planning and constructing storm water systems so contaminants are removed before they pollute surface waters or groundwater resources. CED's Construction group investigates claims and litigation stemming from flooding resulting from all of the above.