i3D Antecedent Moisture Model-An Advanced Method for Sewer System Rehabilitation and Sizing
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http://www.ohm-advisors.com. An American Council of Engineering Companies National Finalist project, this presentation features a breakthrough new hydrologic model for sanitary collection systems. The i3D model more accurately accounts for the antecedent moisture that enters a sewer system through inflow and infiltration. The outcome? Using i3D, engineers can determine the right system size, without overbuilding or risking unhealthy SSOs and CSOs.
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i3D Antecedent Moisture Model-An Advanced Method for Sewer System Rehabilitation and Sizing
- 1. Innovative Model Creates Breakthrough Solution in the North Huron Valley / Rouge Valley (NHV/RV) System
Editor's Notes
- 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 retained 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 a new methodology called the i3D Antecedent Moisture (AM) Model to perform the hydrologic modeling. The i3D model 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 system resulted in large capital improvement estimates needed 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 – the 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 sizing from 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.