i3D is the marriage of traditional hydrologic modeling with technology borrowed from aerospace engineering. The idea was sparked when Robert Czachorski, a civil engineer, and his college roommate, Tobin Van Pelt, an aerospace engineer, were talking about the challenges of predicting how sewer systems would function in wet weather situations. The result was like the old Reese's Peanut Butter cup commercial - two great ideas that worked great together.
Fast forward nearly ten years and the i3D modeling method is helping to save communities hundreds of millions of dollars. In one project alone, the director of Wayne County's Department of Environment credited i3D with saving Michigan taxpayers $170 million dollars. Here's more of that story, which also turned into an American Council of Engineering Companies (ACEC) National Finalist Project. Take a look at a short slidedeck on the project.
i3D Antecedent Moisture Model-An Advanced Method for Sewer System Rehabilitation and Sizing
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Wayne County, Michigan was faced with the challenge of complying with a new, stricter Michigan Department of Environmental Quality (MDEQ) policy to control sanitary sewer overflows (SSOs) in its North Huron Valley/Rouge Valley (NHV/RV) interceptor system. The County hired Orchard, Hiltz & McCliment, Inc. (OHM) to develop an antecedent moisture model of the Middle Rouge Branch of the NHV/RV system, demonstrate that the model accurately reflects observed flows in the system based on historic rainfall records, and then use the model to perform a frequency analysis to size a regional transport/storage tunnel.
OHM used the i3D Antecedent Moisture (AM) Model to perform the hydrologic modeling. i3D is a continuous model developed from system identification theory from aerospace engineering that closely matches observed flow data over time. The accuracy of the model created a high level of confidence in the frequency analysis for SSOs and served as the basis for recommending improvements to control wet weather SSOs. The use of the AM model, combined with a frequency analysis for sizing improvements, eliminated the need to select a design storm event based on “average” conditions, reducing many of the conservatisms that are frequently included in event models such as the capture coefficient and seasonal effects.
Previous modeling of the NHV/RV system recommended large capital improvement costs to make the system compliant with the MDEQ SSO Policy. Using the new technologies, including the i3D AM model and frequency analysis, OHM determined that the required system improvements – a relief/storage tunnel – could be scaled down significantly. The Final Engineering Report recommended an effective tunnel size of 6.4 MG, at an anticipated cost of $95 million – a savings of $175 million over the size recommended by the previous event model. This created a breakthrough between the local communities and the MDEQ who were in conflict over the sizing. Most importantly, the public health of more than 500,000 people will be protected while simultaneously cost-effectively decreasing sanitary sewer overflows in the system.
