Appendix B. Surface Water Hydrology

Transcription

1 Appendix B Surface Water Hydrology

2 Memo To: From: Muneef Ahmad, City of Mississauga Aaron Farrell/Ron Scheckenberger Date: May 20, 2016 File: Re: TP Ninth Line Lands Scoped Subwatershed Study Hydrologic Model Development Summary Further to our discussion, and in order to address key matters requested by Conservation Halton, the following has been prepared to summarize the background and the refinements to the VisualOTTHYMO hydrologic model, which have been completed for the Ninth Line Lands Scoped Subwatershed Study. PREVIOUS MODELLING Hydrologic analyses specific to the Ninth Line Lands have been completed as part of the Toll Highway 407 Sixteen Mile Creek Stormwater Management Study Phase 1 Report (M.M. Dillon Ltd., April 1996 Draft). The analyses completed for that study have applied the OTTHYMO methodology, and have incorporated the stormwater management and drainage system proposed for the Highway 407 through the area. As such, the OTTHYMO modelling completed for the study incorporated the most detailed information for the drainage systems and stormwater management within the area. In 2003, the City of Mississauga initiated the North Sixteen District Scoped Subwatershed Study and Ninth Line District Floodline Mapping (Philips Engineering Ltd., December 2004). The hydrologic modelling completed for that study applied the SWMHYMO methodology, and built upon the previous hydrologic modelling completed for the Toll Highway 407 Sixteen Mile Creek Stormwater Management Strategy Study Phase 1 Report (Draft) (M.M. Dillon Ltd., April 1996). The hydrologic model was updated to incorporate the existing and approved conditions as per the 401 Corridor Integrated Planning Project and Scoped Subwatershed Plan (Dillon Consulting, March 2000). The hydrologic modelling applied the 12 hour SCS design storm distribution to generate peak flow rates corresponding to the 2 year through 100 year return period, as well as peak flows for the Regional Storm (Regulatory) event North Service Road Burlington, Ontario L7N 3G2 Tel Fax amecfw.com Amec Foster Wheeler Environment & Infrastructure Registered office: 2020 Winston Park Drive, Suite 700, Oakville, Ontario L6H 6X7 Registered in Canada No ; GST: RT0008; DUNS: P:\Work\TP114008\Corr\Memo\ Miss-MAhmad.docx

3 2 City of Mississauga May 20, 2016 HYDROLOGIC MODEL UPDATES Model Import Into VisualOTTHYMO Format The hydrologic modelling for the Ninth Line Lands Scoped Subwatershed Study built upon the hydrologic modelling completed for the December 2004 Scoped Subwatershed Study. As part of the current study, the SWMHYMO hydrologic model which was developed for December 2004 Scoped Subwatershed Study has been imported into the VisualOTTHYMO Version 2.4 hydrologic model for application in this assessment. The VisualOTTHYMO hydrologic model methodology and the SWMHYMO model methodology are both based upon the OTTHYMO89 modelling platform, however not all of the operational commands and corresponding algorithms from the SWMHYMO model are applicable for the VisualOTTHYMO Version 2.4 modelling methodology. The following modifications to the SWMHYMO model have been required for the import and execution using the VisualOTTHYMO Version 2.4 methodology: Urban runoff responses using the COMPUTE URBHYD command have been converted to the CALIB STANDHYD command; the drainage areas and impervious coverages have been retained from the original COMPUTE URBHYD command, however it is recognized that the CALIB STANDHYD command applies different equations to determine the runoff response. Channel routing using the COMPUTE RATING CURVE, COMPUTE TRAVEL TIME, and ROUTE commands have been replaced with the ROUTE CHANNEL command; the roughness coefficients, channel slopes, cross-sections, and reach lengths have been retained from the original routing commands. Rural runoff responses using the COMPUTE NASHYD command were replaced with the CALIB NASHYD command which uses some, but not all, of the parameters required of the COMPUTE NASHYD command. The subcatchment identifiers were modified by the VisualOTTHYMO model as a result of the importing process, to apply numerical identifiers rather than the combination of numerical and alphabetic identifiers applied in the previous modelling. The subcatchment numbering in the under the VisualOTTHYMO model and the previous SWMHYMO compilation are provided in the attached table for reference. Following the import of the SWMHYMO model, the model schematic of the VisualOTTHYMO model was reviewed and adjusted as required in order to correspond to the current land use conditions and to match the schematic of the original SWMHYMO model. Following the import, the VisualOTTHYMO model has been executed for the Regional Storm event, and the peak flows at key locations compared to the results of the original SWMHYMO hydrologic model, in order to verify the performance of the converted VisualOTTHYMO model. The results of this assessment are presented in Table 1. P:\Work\TP114008\Corr\Memo\ Miss-MAhmad.docx

4 3 City of Mississauga May 20, 2016 Table 1: Comparison of Simulated Regional Storm Peak Flows From Original SWMHYMO Model and Imported VisualOTTHYMO Model (m 3 /s) Hydrograph Number (SWMHYMO/ VisualOTTHYMO) 1. Location SWMHYMO (2004) VisualOTTHYMO (2015) Difference (%) 802/79 Hwy /82 C.P.R /85 6/70 9/104 Derry Rd. Inlet to Osprey Marsh Brittannia Rd /134 Upstream of Park /136 Proposed Park /137 Downstream of Park /145 8th Line /148 Trafalgar Rd /151 Outlet to Sixteen Mile Creek NOTE: 1. The hydrograph numbering for the VisualOTTHYMO model corresponds to the re-numbering automatically developed by the VisualOTTHYMO model following the import of the SWMHYMO model. The results in Table 1 indicate that the simulated peak flow rates for the Regional Storm event are comparable between the original SWMHYMO model and the imported VisualOTTHYMO model (i.e. less than 2.8% difference). The minor differences between the two models are considered attributable to the different commands which have been used to generate runoff from the urban catchments and the rural catchments as discussed previously. Given the comparable results between the two models, the imported VisualOTTHYMO model is considered to be consistent with the previously approved SWMHYMO hydrologic model for the study area, and the current VisualOTTHYMO model is considered to be appropriate for refinement and use in this assessment. P:\Work\TP114008\Corr\Memo\ Miss-MAhmad.docx

5 4 City of Mississauga May 20, 2016 Model Refinement The VisualOTTHYMO model which has been developed based upon the original SWMHYMO hydrologic model for the study area has been used in order to determine the peak flows at key locations within the Ninth Line Lands and downstream for the 2 year through 100 year storm events, as well as for the Regional Storm event. The subcatchments along the Ninth Line Lands have been refined based upon the base mapping provided for the Ninth Line Lands Planning Study, in order to provide a higher level of resolution (i.e. number of subcatchments) and more consistency among the catchment sizes compared to the previous modelling. Subcatchment Parameterization The subcatchment parameters along the Ninth Line Lands have been determined for the existing land use and soils within the area. The SCS Curve Numbers have been established using Chart 1.09 of the MTO Drainage Management Manual (Ministry of Transportation, 1997). The time-topeak for the subcatchments has been calculated using the Airport Equation. The parameters for the subcatchments within the Ninth Line Lands are summarized in Table 2. Table 2: Subcatchment Parameterization for Ninth Line Lands Existing Land Use Conditions Catchment ID Area (ha) CN AMC II CN AMC III Slope (%) Tp (hrs) The updated VisualOTTHYMO hydrologic model has been used to determine the peak flow rates for the 2 year through 100 year return period storm events as well as for the Regional Storm event at key locations within and downstream of the Ninth Line Lands under existing land use conditions, in order to establish a baseline for future land use impact assessment and development of management strategies. Consistent with the approach applied for the North Sixteen District Scoped Subwatershed Study (Philips Engineering Ltd., December 2004), the 12 hour SCS distribution has been applied to generate the synthetic design storms for the return period storm events. Soil conditions corresponding to AMC II conditions have been used for the 2 year through 100 year storm events, and all existing and approved stormwater management facilities have been represented within the model. For the Regional Storm event, soil conditions corresponding to AMCIII conditions have been simulated, and all stormwater management facilities have been removed from the hydrologic model. The simulated peak flow rates for existing land use conditions are summarized in Table 3. P:\Work\TP114008\Corr\Memo\ Miss-MAhmad.docx

6 5 City of Mississauga May 20, 2016 Table 3: Simulated Peak Flow Rates for Return Period and Regional Storm Event Under Existing Land Use Conditions for Ninth Line Lands (m 3 /s) Node/Hydrograph Number Location Return Period (Years) Regional 79 Hwy C.P.R Derry Rd Outlet from Osprey Marsh Britannia Rd. Eighth Line Trafalgar Rd. Outlet to Sixteen Mile Creek Model Validation Unitary flow rates have been calculated based upon the catchment boundaries and simulated peak flows generated by the updated Visual OTTHYMO model for the 2 year through Regional Storm Events, and the results have been compared to the unitary flow rates generated by the 2004 SWMHYMO model, in order to validate the simulated peak flows generated by the updated Visual OTTHYMO model. The results of this assessment are attached for reference. The results indicate that the unitary flow rates generated by the updated Visual OTTHYMO model are comparable to those generated by the original SWMHYMO model. Differences between the results generated by each model are considered to be attributed to the different commands and algorithms applied in the updated Visual OTTHYMO model for generating and ranking the hydrograph from various urban and rural subcatchments within the model, as previously noted. Recognizing the differences between the methodologies used in the model, as well as the comparable unitary flows generated by the updated and original model, the updated Visual OTTHYMO model is considered to reasonably represent the hydrologic conditions within the study area and is suitable for the hydrologic analysis of the Ninth Line Lands. CONCLUSION The VisualOTTHYMO hydrologic model for the Ninth Line Lands Scoped Subwatershed Study has been developed, based upon the currently approved SWMHYMO hydrologic model for the study area. The SWMHYMO hydrologic model has been imported into the VisualOTTHYMO format, and the routing and runoff commands have been revised as appropriate to conform to the P:\Work\TP114008\Corr\Memo\ Miss-MAhmad.docx

7 6 City of Mississauga May 20, 2016 VisualOTTHYMO methodology. The imported hydrologic model has been validated based upon a comparison of Regional Storm event peak flow rates, as well as a review and verification of the model schematic. The VisualOTTHYMO hydrologic model has been refined within the limits of the Ninth Line Lands based upon the detailed topographic (i.e. LiDAR) mapping provided for use in the study. The simulated peak flows generated by the refined and updated VisualOTTHYMO hydrologic model have been verified based upon a comparison of simulated unitary peak flow rates generated from the original SWMHYMO model and the updated VisualOTTHYMO hydrologic model. We trust that the foregoing adequately addresses Conservation Halton s questions and requirements regarding the development of the VisualOTTHYMO hydrologic model. AF/RBS/af Attach. P:\Work\TP114008\Corr\Memo\ Miss-MAhmad.docx

8 Ninth Line Area Hydrologic Model Subcatchment ID s SWMHYMO VisualOTTHYMO 303A B C 78 8C 182 8D A E 187 9A 94 9C 96 9B B D E F B A C H G I K 1 304J A 41 5B 44 6A 47 6B2 49 6B1 51 6C 56 6D 59

9 6E 62 6F 64 6G 66 6H 69 7A 189 7B A A B B C 121 9D B B

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11 VisualOTTHYMO EXISTING CONDITIONS MODEL SCHEMATIC

12 HWY 401 N HUDSO AY RAILW D WEST TENTH LINE WEST NINTH LINE HWY 407 DERRY R BRITANNIA T ROAD WES NINTH LINE ET THOMAS STRE. TRE BLVD HWY 407 ERIN CEN E WEST N AVENU EGLINTO LEGEND 3 HWY 40