Abstract

The Alton Mill is located in Caledon, Canada, on a tributary of the Credit River that discharges into Lake Ontario. The Alton Mill initiative is aimed at converting a century-old plus heritage stone mill and pond complex into an artisan oriented tourism destination. A stormwater management servicing plan was developed to lessen the impact of this development on adjacent properties and on the receiving watercourse. The servicing plan featured a storm sewer and swale collection system along with an infiltration gallery designed to temporarily store surface runoff for subsequent percolation and groundwater recharge. Runoff is discharged evenly through a manifold perforated pipe system into the gallery, which is filled with continuous clear stone and covered with native soil material. Runoff exceeding the capacity of the collection system or gallery is designed to discharge via overland sheet flow into the receiving watercourse.

Construction of the stormwater facilities was completed in September 2008. While no formal post-construction monitoring was required as part of the permitting process, additional analysis was undertaken in January 2010. Continuous hydrologic simulation was used to evaluate the long term water balance and to verify the system’s hydraulic performance under a full range of storm events, using a wider array of risk based indicators including the depth and velocity of infiltration gallery overflows during extreme rainfall events.

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