Flooding at Dulles: A Thorough Drainage Investigation

James Dishner, EIT, Design Engineer, JMT

Due to frequent flooding, erosion, and debris collection at two stream crossings through a perimeter security road at Washington Dulles International Airport (IAD), the Metropolitan Washington Airports Authority (Authority) contacted JMT to identify the cause(s) of excessive stormwater discharge. Existing conditions on the site were posing critical environmental and safety concerns to IAD, and the study developed by JMT would address these issues and provide recommended improvements for a future design task. Although the crossings were located on Authority property, various scenarios were proposed using combinations of on-site modifications and upstream drainage improvements. Review and examination of historical and aerial mapping, construction and as-built plans (going as far back as the 1980s), adjacent project drainage reports, and drainage features supplemented through survey and a field visit, were part of the analysis. The investigation identified several issues associated with the drainage conditions in the area including uncontrolled discharges from adjoining projects, security measures that reduced maintenance of the drainage structures, water quantity waivers associated with upstream development, and hydrological discrepancies of adjacent developments. All of these factors contributed to the aggravated flooding and erosion conditions along the perimeter road. There were several challenges on this project that required creative modeling approaches and techniques. Challenges included an aggressive schedule with a short turnaround time and the need to incorporate security measures with the drainage structures without compromising their hydraulic efficiency. Considerable effort and re-evaluation of the hydrology of the watershed was done in conjunction with innovative BMP routing to determine the actual results and come up with creative solutions. Six different scenarios for the two crossings were produced to ultimately resolve the concerns of excessive discharges, overtopping, and erosion on the Authority’s property.

Author Bio

Mr. James Dishner is a design engineer for JMT working in their water resources department. Originally from West Virginia, he moved to Richmond after graduating from Marshall University in 2020. Mr. Dishner primarily focuses on developing site drainage plans and water quality and quantity BMP's for linear development projects as well as the occasional floodplain study. He enlisted in the Marine Corps in 2018 and is currently serving in the reserves as a squad leader. He spends his free time travelling and backpacking across the country.