DHI Water & Environment

Associated Engineering uses MIKE URBAN to complete a complex dual drainage model for the City of Calgary to identify urban drainage problems and evaluate capital improvement alternatives

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Source: DHI Water & Environment

The City of Calgary experienced significant flooding and overland flow during a severe thunderstorm on June 6, 2007. Significant damage occurred to 14th Street NW along a steep hill; sealed manholes failed causing extensive road damage and overland flows. The City of Calgary recognized the importance of the overland system as part of the drainage evaluation of this area as well as for future flood protection. Much of this area consists of older neighborhoods which were not designed using the major-minor system concept (i.e. roadways and pipes).

The City of Calgary engaged Associated Engineering to prepare a detailed dual drainage hydraulic model using MIKE URBAN. The 1450 ha watershed consists of a fully developed urban area with an extensive drainage system that discharges to the Bow River. The City requested that the model include the major overland flow system (roadways), the minor system (pipe network) and a dynamic connection between the major-minor system using the hydraulic capacity of all the catchbasins as well as the non-pressurized manholes.

The objective for this detailed approach was to understand the available conveyance and storage capacity within the overland system and thereby develop more cost-effective infrastructure upgrades for these areas. A secondary objective was to develop a clear understanding of the flooding locations and problematic surface flows. This would allow for the development of more effective solutions that would limit damage to private property owners from future storm events.

Due to the size of the model, the required detailed representation of the drainage system, and the complexity of the hydraulics in the combined major and minor drainage conduits, the MIKE URBAN MOUSE numerical engine and GIS-based modeling environment was selected to complete the study.

As part of this project, Associated Engineering developed sophisticated, GIS-based, analysis routines to expedite the development of the one dimensional dual drainage model. Nearly 4200 overland flow channels, primarily consisting of urban roadways, were developed by analyzing various client supplied data, including the DEM. The finished model included over 5100 conduits, of which about 900 conduits represent the storm drain system. The remaining 4200 links represent the overland flow linkages. The model included over 3100 nodes.

One catchment was delineated for each of the nearly 3000 catchbasins using spatial analysis routines and digital topographic information. These catchments were assigned to the major system network node which connects the CB to the pipe network. As a result, flows from each catchment were evaluated against the capture capacity of every CB. This approach allows uncaptured flows to continue downstream in the major system, potentially combining with other uncaptured flows, and provides an opportunity for capture at other downstream CB's as determined by available capacity.

With the high resolution of data and explicit representation of all relevant drainage elements, effective data management proved to be a critical factor in successful execution of this study. Since MIKE URBAN stores all of the model data in a standard geodatabase format with an open architecture, it was possible to write the data from the working GIS environment directly into the associated tables in MIKE URBAN using standard querying and read/write commands.

The finished model was successfully analyzed using MIKE URBAN 2008. Calibration of the model was completed using observed rain and flow data collected during the summer of 2008. The calibrated model accurately replicated the estimated pressures along 14th Street NW manholes as well as observed flood depths during the June 6, 2007 event. Failure of the sealed manholes was modeled using ‘Real-Time-Control’.

The City of Calgary is presently reviewing the results of the final report and considering the development of a capital works program. The recommended improvements include nearly 2000 m of storm drain upgrades and 25,000 m3 of underground storage at an estimated cost in excess of $30 million (CDN).

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