City of Morgan Hill Sewer System Master Plan 2017

influenced by the severity and length of storm events. Table ES.3 shows the City flows recorded at the SCRWA WWTP have decreased from 2.85 mgd in 2010 to 2.37 mgd in 2015. In addition to listing the 2010-2015 flows, and for comparison purposes, the table calculates the peaking factors applied to the corresponding average annual flows for each year. The land use methodology was used to estimate the buildout flow s from the City’s Planning Area and to be consistent with the General Plan. Table ES.4 documents the total acreages for residential and non-residential land use categories, and the undeveloped lands designated for urbanization. The undeveloped lands were multiplied by the corresponding unit flow factor to estimate the wastewater flows. The existing sewer flows were increased to 2.7 mgd to account for 100% occupancy, and the ultimate buildout flows were calculated at 4.2 mgd. ES.7 HYDRAULIC MODEL DEVELOPMENT AND CALIBRATION The City’s hydraulic model combines information on the physical characteristics of the sanitary sewer system (pipelines, lift stations, force mains) and operational characteristics (how they operate). The hydraulic model then performs calculations and solves series of equations to simulate flows in pipes, including backwater calculations for surcharged conditions. Computer modeling requires the compilation of large numerical databases that enable data input into the model. Detailed physical aspects, such as pipe size, ground elevation, invert elevations, and pipe lengths contribute to the accuracy of the model. The hydraulic modeling software used for evaluating the capacity adequacy of the Morgan Hill sewer system, InfoSWMM by Innovyze Inc., utilizes the fully dynamic St. Venant’s equation which has a more accurate engine for simulating backwater and surcharge conditions, in addition to having the capability for simulating manifolded force mains. The software also incorporates the use of the Manning Equation in other calculations including upstream pipe flow conditions. Model Development The City of Morgan Hill’s sanitary sewer system was skeletonized to reduce the model from approximately 156 miles of pipeline extracted from the GIS to 44 miles of pipeline modeled. Skeletonizing the model is useful in creating a system that accurately reflects the hydraulics of the pipes within the system while reducing the complexities of large models. This process reduces the time of analysis while maintaining accuracy, but will also comply with the limitations imposed by the computer program. The modeled pipes generally include pipes 10-inches in diameter and larger, and critical smaller diameter lines, as well as force mains. The modeled sewer system is shown on Figure ES.2 . Model Calibration Calibration is intended to instill a level of confidence in the flows that are simulated in the hydraulic model. The calibration process was iterative as it involved calibrating each of the flow monitored sites in the 2014 V&A flow monitoring program and for the following three calibration conditions: 1)

August 2017

ES-8

City of Morgan Hill Sewer System Master Plan