Master Drainage Planning Challenges of a Large Coastal Plain Watershed in Virginia Using 1D-SWMM
The City of Chesapeake (City) has systematically studied major watersheds throughout the locality. In doing so, the Southern Chesapeake – 5 (SC5 or SC-5) watershed was identified as an area that has not yet been modeled or studied. On April 9th, 2021, a storm caused significant flooding of the Northwest River Water Treatment Plan (NRWTP), a critical infrastructure facility within the SC-5 watershed. According to anecdotal information from the city public works personnel, the significant storm recorded around ten inches of rainfall within six hours during this event in or near the NRWTP. This rainfall event prompted the City to pursue developing a Master Drainage Plan (MDP) for the SC-5 watershed. The City was awarded a 2021 (Round 1) grant from the Virginia Community Flood Preparedness Fund (CFPF) to develop the SC-5 MDP. The City contracted GKY & Associates, Inc. (GKY) to develop the SC-5 MDP. SC-5 watershed receives inflows from its upstream contributory watersheds, including SC-1, SC-2&3, and SC-4. About 33,060 acres (or 51.66 sq. miles) contribute to SC-5 from these four upstream watersheds. The SC-5 watershed extends slightly to the south of the city line to the City of Moyock, NC, and to the east of the city line to the City of Virginia Beach, VA, with a total drainage area comprising 34,131 acres (or 53.33 sq. miles). The total contributory drainage area at its outfall is 105 sq. miles. Previously, in 2012, MDP was developed for the four upstream watersheds, including SC-1, SC-2&3, and SC-4, and their SWMM models were updated to reflect 2024 existing conditions. This paper presents master drainage planning challenges of this large coastal plain watershed using 1D-SWMM. The goals of the MDP development are: a. To develop an existing conditions model using PCSWMM for various design storms including 2-, 5-, 10-, 50, 100-, and 500-yr. to investigate flooding. b. Perform an event simulation analysis of the April 9th, 2021, storm event and check if the existing model reflects the extent of flooding caused at the NRWTP complex. c. Identify potential improvements for further consideration in the areas of flood concerns and those considered as master drainage facilities (MDFs). under specific design storms. d. Develop the improved conditions model and run it for all the design storms to analyze improvement effectiveness. e. To develop a master drainage plan and discuss the potential improvements in a report based on the model results.
Author Bio
Dr. Iyer is a Senior Water Resources Engineer with GKY and Associates in their Newport News, Virginia, office. He has over 40 years of professional and research experience in the field of water resources planning, development, management, and engineering. Dr. Iyer’s experience spans natural water system modeling; watershed management; hydrologic, hydraulic, and bridge scour analysis; and stormwater management. Dr. Iyer is a PE, Certified Floodplain Manager (CFM), and Fellow of ASCE (F.ASCE). He is currently serving as a board of directors for the Virginia Lakes and Watershed Association (VLWA). He is also active participant of ASCE EWRI Task Committees.
