Hampton Roads Sanitation District (HRSD) owns and operates an interceptor sewer system consisting of both gravity and force mains, and nine sewage treatment plants (STPs) servicing the Hampton Roads area. The HRSD system is interconnected with, and serves, surrounding Localities, including the cities of Chesapeake, Hampton, Newport News, Poquoson, Portsmouth, Suffolk, Virginia Beach and Williamsburg; the counties of Gloucester, Isle of Wright, and York; the James City Service Authority; and the town of Smithfield. The regional system formed by these inter-connected systems consists of approximately 450,000 connections, 5,819 miles of gravity sewers, 1,577 pumping stations, and 1,121 miles of force mains. The regional system covers an area of 2,000 square miles, serves a population of over 1.6 million, and conveys and treats an average of more than 165 million gallons of sewage each day.
Due to a combination of aging infrastructure and a continually growing population HRSD and the localities have entered into a State Order by Consent (Consent Order) to evaluate the existing collection and conveyance systems and to develop a Regional Wet Weather Management Plan to minimize sanitary sewer overflows.
HRSD committed to providing the Hampton Roads localities with a regionally integrated, calibrated dynamic Regional Hydraulic Model. In addition, each of the Hampton Road Localities will be developing a model of their sanitary sewer system to be used in conjunction with Regional Hydraulic Model being developed by HRSD.
These models will be key element for the development of the Regional Wet Weather Management Plan, and for design, testing and optimization of infrastructure improvement plans. HRSD and the Hampton Roads Localities worked together with their consultant, CDM, to undertake an extensive evaluation of the commercially available sewer modeling software.
Hydraulic Model Selection
The model requirements for the Regional Hydraulic Model are:
- Fully dynamic hydraulic solution
- Minimal volume balance errors and numerical instabilities
- Model both gravity and pressurized flows, simultaneously including the measurement of negative pressures and siphons
- Stable and robust solution for transitions between gravity and pressure flows
- Stable pump controls including pump curves, switch on/off controls, variable speed pumps, and real-time control capabilities
- Model surcharge manholes with either storage of surcharged volume out of manhole lids and/or flow depth in excess of manhole depth predicted to overflow the manholes
- Capable of accepting diurinal curves and hydrographs as flow input
The model evaluation and selection process involved a comprehensive review of the key features, functionality and performance of each product, as well as a demonstration of each product using data provided by the selection committee. At the conclusion of the evaluation process, the selection committee chose DHI’s MIKE URBAN modeling platform as the product best suited for this project.
MIKE URBAN met all of the technical requirements in terms of simulation processes and system performance, particularly with respect to the way it handles combined gravity main and force main systems with complex real-time operation of pumps and valves for controlling inflow rates and pressures. These were key considerations because these are the key processes influencing the behavior and responses of the HRSD system.
For more information on this project, or to see how MIKE URBAN can help you to meet your collection system modeling needs, please contact Patrick Delaney, Vice President of Software for North America, DHI Water & Environment, Inc. (pad@dhigroup.com)