To provide you information in advance of our July CAC meeting, in which we will hear a presentation on the TOAG,  please find attached the following documents:

1.  TOAG Response to Stormwater Model Calibration Tech Memo - dated April 28, 2014

2.  The Aug 2012 Intro to the Modeling Project to the Stormwater Advisory Group

Also, please find below a description of the project from the City Library website.

Phase 1 of the stormwater model development process was completed from 2006-2008 and included a detailed inventory of all stormwater drainage system features. These included pipes, manholes, catch basins, open channel cross-sections, and detention basins. The feature inventory was provided to the City as part of a geographic information system (GIS) and was also used to build a stormwater model framework. This base model is functional but has not been calibrated based on actual storm data.

The purpose of the 2012-2015 Stormwater Model Calibration and Analysis Project (commonly referred to as the SWMM project, which stands for Stormwater Management Model) is to refine the model that was developed in 2008.  The current model describes an informed idea of how stormwater will behave in the City; however, additional data are needed to validate whether the assumptions used in the previous model remain accurate.  This project will deploy flow monitors, rain gauges, and collection of visual stormwater observations in order to generate the needed data, and then the model will be fine-tuned – or calibrated – to reflect these real-world conditions. 

Once the model is calibrated, it will enable the City of Ann Arbor to review a realistic picture of how stormwater behaves – which will help us identify potential improvements to the stormwater system that would yield the highest return on investment.  These improvements could be as low-tech as concentrating a cluster of rain gardens in certain areas to retain stormwater and allow it to infiltrate the soil slowly rather than rushing into the underground stormwater pipes; in some areas, it is possible that up-sizing the stormwater conduits could be indicated in some areas where the system is not equipped to handle the flows it is receiving.

In support of the technical aspects of the project, Ann Arbor residents will be invited to contribute by collecting project data and sharing anecdotal information about the areas of greatest concern when it comes to stormwater in their neighborhoods.  These activities are intended to help develop a shared understanding of stormwater behavior in general, with specific emphasis on the engineering aspects of stormwater conveyance and what expectations citizens may have regarding stormwater behavior in their neighborhoods.

The City of Ann Arbor is partnering with CDM Smith, an engineering firm that will perform the technical aspects of the stormwater modeling and calibration project. As part of the CDM Smith team, Alexander Resources Consulting, LLC, will lead a public engagement process designed to embrace citizens as valuable sources of relevant project information, as well as share findings at logical intervals throughout the project.

Timeline

Fall 2012 – Model Updates

Winter 2012-2013 – Neighborhood meetings, Preliminary Calibration

Spring – Fall 2013 – Data Collection

Winter 2013-2014 – Final Calibration

Summer 2014 – Model Analysis