Floodplain Analysis and Flood Zones

With the latest technology associated with flood analysis and hydrologic software, D.L. Howell can very efficiently help a property owner determine whether or not their property or home is located within the flood zones or floodplain. As it seems that FEMA is constantly updating its maps and more and more property owners are required to pay expensive flood insurance premiums. For this reason, it is important for D.L. Howell to stay on pace with the changes and maintain the ability to accurately determine the actual flood zones elevation where FEMA has not. Many communities located in southeastern Pennsylvania are within areas designated as Zone A.

In these Zone A areas, flood delineations are “estimated” by FEMA and can vary by up to as much as 100 feet in some instances from the actual calculated or “modeled” flood zone boundary. In addition to requiring flood insurance, most municipalities have specific standards for building or developing in an approximate flood area. This is where D.L. Howell can help. Our project experience ranges from analysis for a single-family house to large-scale community planning.


Utilizing the U.S. Army Corps of Engineers HEC-RAS River Analysis Program in conjunction with AutoCAD Civil 3D, D.L. Howell and Associates can now determine flood levels more quickly and accurately than ever before. HEC-RAS is a computer program that models the hydraulics of water flow through natural rivers and other channels.  Then the modeling program is used with a three-dimensional surface in AutoCAD Civil 3D, cross-sections and base plan data can be entered in a fraction of the time with much greater accuracy.

Another time-saving tool is the ability to export the calculated flood water surface right from HEC-RAS back into the site plan for quick and easy display of the flood limits. From this, we can develop a more accurate flood map.

Services provided by D.L. Howell are listed below:

  • Floodway Modeling
  • Flood Insurance Elevation Determinations
  • Parking Lots in Flood Hazard Areas
  • Elevation Certificates
  • FEMA Letter of Map Amendments (LOMA)
  • Letter of Map Revisions (LOMR)
  • Local permitting assistance.

If you would like to discuss your specific project or have any other flood zone-related questions, please contact Andrew DeFonzo or Dave Gibbons at our West Chester Office (610-918-9002).


Previous Floodplain Analysis and Flood Zone Projects

Crystal Springs
A 130 Unit Townhouse Subdivision where the site entrance from Route 10, in Parkesburg Borough, crossed through a stream. Our analysis concluded the minimum possible concrete box culvert to safely convey the 100-year flow under the proposed roadway, without passing over the road.

Lafayette Square
A 125 Unit Apartment Building Development where the site entrance encroached within the 100-year flood zone of the upstream side of an existing culvert under Business Route 30 in Sadsbury Township, Chester County.  Our analysis concluded that the minor grading involved with the site entrance construction will satisfactorily separate the proposed roadway from the 100-year flood without causing an unsafe condition along the existing highway.

The Sands Property
The Sands Property was a private, residential property bisected by a stream and floodplain.  We provided analysis of the limiting nature of the floodplain and associated riparian buffers and designed a residential subdivision and road system around those limiting areas.