Report

To: Development Services Committee Item: Date of Report: DS-11-204 May 25,201 1

From: Commissioner, Development Services Department

File:

B-1100-0060

Date of Meeting:

May 30, 201 1

Subject: Flood Relief Study for the Harmony and Farewell Creeks prepared by Greck and Associates Ltd. PUBLIC REPORT

1.0 PURPOSE

The purpose of this report is to:

1. Provide an overview of the "Flood Relief Study for the Harmony and Farewell Creeks1' prepared by Greck and Associates Limited dated July 2010 ("Greck Study") and the recent Central Lake Ontario Conservation Authority's (CLOCA) position on the study.

2. Recommend that CN Rail be consulted regarding the feasibility of installing a new bridge for the creek in the CN Rail embankment located south of Highway 401, east of Farewell Street in order to reduce the flood risks and increase the amount of developable land north of the CN Rail embankment and Highway 401.

Attachment No. 1 is a map showing the location and zoning of the area.

Attachment No. 2 is a map showing the existing floodlines and the approximate new floodlines with the construction of a bridge in the railway embankment.

Attachment No. 3 is a copy of CLOCA's report dated April 6, 201 1 on the Greck Study. A copy of the Executive Summary of the Greck Study is attached to the CLOCA report.

Due to the length of the Greck Study, the entire report is not attached to this report. However copies are available for viewing in the Development Services Department (Planning Services, 8th lo or, Rundle Tower, contact Susan Ashton).

2.0 RECOMMENDATION

That the Development Services Committee recommend to City Council:

1. That the Flood Relief Study for the Harmony and Farewell Creeks prepared by Greck and Associates Limited dated July 2010 be received for information.

2. That CN Rail:

(a) Be provided a copy of Report DS-11-204 and the related Council resolution;

Report to the Development Item: DS-11-204 Services Committee (Continued) - 2 - Meeting Date: May 30, 201 1

(b) Be consulted by staff to determine the feasibility of constructing a structure in the CN embankment south of Highway 401, east of Farewell Street; and

(c) Be requested to permit a geotechnical assessment on the CN Rail embankment.

3. That, in the event CN Rail confirms items 2(b) and 2(c) above, that staff endeavour to negotiate a cost sharing agreement amongst various parties for the geotechnical assessment.

4. That staff report back to the Development Services Committee and Council as appropriate.

3.0 EXECUTIVE SUMMARY

Mario Veltri owns land on Bloor Street East that are located in the floodplain north of Highway 401 and west of the CP Railway line. A large part of this area is floodplain because the CN Rail embankment south of the Highway 401 acts like a man-made dam for water from the Harmony and Farewell creeks under certain storm events.

In the past, Mr. Veltri has requested that the City ask the Ministry of Natural Resources and CLOCA to reduce the Regulatory Floodplain in this area from the Regional Floodline (Hurricane Hazel storm event) to the 100 year floodline in order to free up land for development.

A study recently completed by Greck and Associates Limited has confirmed that the floodplain could be reduced by approximately 44 hectares (109 ac.) with the construction of a 30 metre (100 ft.) wide x 6 metre (20 ft.) high bridge to replace an existing culvert in the CN Rail embankment. This would free up land for development and provide some flood relief to existing flood prone structures.

The Greck Study has also noted that further work is required, including consultation with CN Rail regarding the feasibility of constructing a bridge and examining the structural integrity of the rail embankment to allow for a bridge.

The estimated cost of the bridge in 2007 was $1 0 million.

The next logical step in the process to potentially reduce the floodplain is to determine if CN Rail is willing to allow a bridge on CN Rail land in the future and to determine from a geotechnical perspective if a bridge is feasible.

This report recommends that CN Rail be requested to confirm, in principle, its willingness to consider a new bridge structure and to permit a geotechnical examination of the structural ability of the embankment to accommodate a bridge. If CN Rail confirms, staff will discuss cost sharing the geotechnical work with potential benefiting landowners and other stakeholders (e.g. MTO and GO Transit) and will report back.

Report to the Development Item: DS-11-204 Services Committee (Continued) - 3 - Meeting Date: May 30, 201 1

4.0 INPUT FROM OTHER SOURCES

4.1 Other Departments and Agencies

P Input from has been received the Central Lake Ontario Conservation Authority.

4.2 Auditor General

P The Auditor General has no comment.

5.0 BACKGROUND

9 In 2005 the Central Lake Ontario Conservation Authority and the City of Oshawa retained Greck and Associates Limited to do a study of potential flood relief measures for lands in the Harmony Creek and Farewell Creek area around Bloor Street East between the CP Rail and the CN Railway.

P The flood hazard lands in this area are caused by the natural flood plain characteristics of the Harmony and Farewell Creeks and are exacerbated by the CN Rail embankment which impedes flood flow in this area, causing an additional 45 hectares ( I I I ac.) of land to be within the floodplain in this area.

9 The modeling of the floodplain in this area also indicates that flood waters overtop Highway 401 and Bloor Street East.

9 This area of the City is predominately designated as Open Space and Recreation in the Oshawa Official Plan and zoned OSH (Hazard Lands Open Space) in Zoning By- law No. 60-94. Amendments to these planning documents would be required to allow urban development in this area.

9 A number of options were reviewed in the Greck Study, including structural and non- structural relief alternatives. Structural options included drilling and boring through the CN Rail embankment to install culverts to increase flood flow or the construction of a new bridge which would replace an existing culvert in a portion of the existing embankment. Non-structural options included using the 100-year storm event rather than the Regional Storm event, seeking new flood storage areas higher up in the HarmonyIFarewell systems and using a Two Zone approach.

9 After review, non-structural options were not considered appropriate given the recent flooding experiences in Ontario which suggest that the risk of flood damages could be greater than ever previously experienced. A more conservative approach to flood management was determined to be reasonable in this area.

9 The Greck Study concludes that the best option for reducing the floodplain is to construct a 30 metre (100 ft.) wide x 6 metre (20 ft.) high bridge in the CN Rail embankment to accommodate the creek. This bridge and its new capacity to carry flood waters would free up approximately 44 hectares (109 ac.) of land for future development and provide flood relief to existing flood prone structures.

1 4

Report to the Development Item: DS-11-204 Services Committee (Continued) - 4 - Meeting Date: May 30, 201 1

9 The bridge option would require a temporary CN Rail track diversion, embankment works and channel re-alignment works. An approximate cost to construct the bridge and any related work in 2007 was $10 million.

9 The configuration of the 44 hectares (109 ac.) of potential new developable land could be altered and further rationalized through a possible cut and fill exercise.

P This area of Oshawa is the eastern approach to the City via Highway 401. Byremoving lands [approximately 44 hectares (109 ac.)] from the floodplain, the City has opportunity to work with landowners to develop gateway uses critical to the City and new assessment opportunities.

P In a report to the CLOCA Board in April 201 1 (see Attachment No. 3), CLOCA staff noted that the Greck Study identified a number of issues that require further study. These include:

Potential future GO Train expansion; Consultation with CN Rail regarding the feasibility of a replacement bridge; Structural integrity of the embankment to allow for a bridge replacement; Detailed cut and fill analysis; Environmental and erosion analysis; Affected property owners and funding; and, More detailed analysis to be completed based on the most recent flood elevations based on the updated flood plain mapping for this area.

9 On April 19, 201 1 the CLOCA Board adopted the following resolution:

"THAT (CLOCA) staff Report #4953-11 be received for information;

THAT the Flood Relief Study for Harmony and Farewell Creeks (Greck 2010) be accepted as a technical guideline document;

THAT the CLOCA Board of Directors endorses the recommendation that "the use of non-structural approaches to relieve the extent of flood prone land, such as a two zone policy, Special Policy Area designation or a reduction of the regulatory flood limit from the regional storm to the 100 year storm, should not be considered. These approaches are inappropriate solutions to reducing flood hazards with the study area; and,

THAT the CLOCA Board of Directors endorses, in principle, the use of a structural method to increase additional hydraulic capacity under the CN Rail Embankment as an option that can be pursued by the City of Oshawa and applicable landowners with the understanding that CLOCA will not be responsible for any costs associated with the flood reduction measures and that subsequent detailed studies and assessments are required; and

Report to the Development Item: DS-I 1-204 Services Committee (Continued) - 5 - Meeting Date: May 30, 201 1

THAT all stakeholders, including the City of Oshawa, Region of Durham, Canadian Pacific, Canadian National, and all applicable landowners be informed of any future endeavours within the Harmony and Farewell Creeks study area."

> The next step in the process is to consult with CN Rail regarding the feasibility of constructing a bridge and examining the structural integrity of the embankment to confirm it will allow for a bridge to be constructed.

> Golder and Associates Ltd. has estimated the cost of the geotechnical analysis as $130,000. The majority of this cost is the actual drillinglborehole work required to detail the subsurface conditions and groundwater conditions in the CN Rail embankment.

> If CN Rail is willing to consider a bridge at some point in the future and also consents to the geotechnical work being undertaken on its land, the costs could be shared amongst affected property owners and other the stakeholders (including MTO, GO, Region of Durham and the City of Oshawa).

> Staff will report back to the Development Services Committee on any response received from CN Rail and any subsequent cost sharing proposal for the geotechnical work.

6.0 FINANCIAL IMPLICATIONS

> There are no financial implications at this time.

P The cost of the Greck Study was $30,000 plus tax and was shared equally by the City and CLOCA.

7.0 RESPONSE TO THE COMMUNITY STRATEGIC PLAN

P The removal of lands from the floodplain of the HarmonyIFarewell Creeks would advance Goal B (A Green and Sustainable Community) of the City's Community Strategic Plan by managing growth and using land wisely.

Paul Ralph, B.E.S., RPP, Director Planning Services

Development Services Department

Attachments

Attachment No. I

DEVELOPMENT SER VICES DEPARTMENT

Item No.: DS-11-204 Subject: Flood Relief Study for the Harmony and Farewell Creeks

prepared by Greck and Associates Ltd. File No.: B-1100-0060

Attaahment No. 2

D m P M E N T SERnCESDm-

Item No.: DS-41-204 - Flood Relief Study for the Harmmy and F dCreeks prepared by Greek and Asdates LU.

Fils Mo.: 5 1l O ( M 0 8 0

-Existing Floodlines -New Floodline if 30m span bridge amhmbd .

Potential lands above new floodline - 18

CENTRAL LAKE ONTARIO CONSERVATION AUTHORITY

DATE: April 6,201 1 FILE: IMS: PSSG224

S.R.: 4953-1 1 APPROVED BY

MEMO TO: Chair and Members, CLOCA Board of Directors

FROM: Chris Darling, Director, Development Review and Regulation Perry Sisson, Director, Engineering and Field Operations

SUBJECT: FIood Relief Studv for the Harmonv and Farewell Creeks

Purpose The purpose of this report is to seek the Board's endorsement of recommendations contained in the Hood Relief Study for the Harmony and Farwell Creeks, dated July 2010 prepared by Greck and Associates Ltd.

Backsound In 2005, CLOCA and the City of Oshawa jointly retained the services of Greck and Associates Ltd. to undertake a Flood Relief Study for the Harmony and Farewell Creeks, in the City of Oshawa, generally bounded by the Canadian Pacific Rail (CP Rail) to the north and the CN Rail to the south (see Attachment 1).

Within the study area, the Harmony and Farewell Creeks flow parallel to and in close proximity to each other until just north of Colonel Sam Drive where they merge. The flood plain for each creek merges much furthernorth, upstream of the CP Rail embankment. This combined flood plain is partly attributed to the relatively flat land and low lying topography. There are a number of transportation corridors that cross the Harmony and Farewell Creeks. For each crossing there is a culvert or bridge structure which can obstruct flood flows thereby exacerbating flood elevations within their flood plains. The most significant obstruction, the CN Rail embankment, results in a significant impediment to flood flow for both the Harmony and Farewell Creeks. As a result, the regulatory flood plain created by both watercourses encompasses a significant area including existing uses subject to flood hazards and lands that could otherwise be valuable development land.

There have been a number of past studies that examined potential flood relief measures. The most recent study completed in 2010, reassesses some of the previously identified options for flood relief solutions, examines new potential relief measures and recommends a strategy to provide flood relief and additional development opportunities for the subject area. The Study is a technical guidance document to be used as a guideline by CLOCA, City of Oshawa and development proponents wishing to proceed with development. Generally, the Study concludes that the best solution for flood relief in this area is by providiig a larger bridge under the rail embankment to improve flood passage. Attachment 2 contains the Executive Summary of the Study.

Studv Highlights The study confiied that the CN Rail embankment and the limited capacity of the existing culverts results in a significant back-up of flood flows and an increase in the floodplain area. The study indicates that the embankment results in an increase in flood eIevation upstream as high as 7 m and an additional area in the flood plain of 52 ha (see Attachment 3).

cont'd ........2

S.R. #4953-11 IMS: PSSG224

April 6,2011 Page 2

The study considered two potential approaches to flood relief solutions,one being a non-structural or policy approach and the second being the consideration of physicaYstructural improvements.

Non-Structural Approach In terms of a non-structural approach to reducing flood prone area, the study considered the use of a 100-year flood event as opposed to the HurricaneHazel standard storm event. In most areas of Ontario including CLOCA's watershed, flood plains are based on the greater of the Hurricane Hazel storm event or the 100-year return period storm. Generally, Hurricane Hazel is the greatest rain event recorded in our region. It has a great volume of rainfall over a 48-hour period and is therefore somewhat insensitive to land use (ground is completely saturated). The 100-yearstorm is a theoretic rainfall event with a 1% chance of occurring in any given year. This storm is sensitiveto land use and will produce greater flow from urban areas. Only for a few smaller watersheds within CLOCA is the 100-yearevent the greater of the two. The study concludesthat for the followingreasons a change to 100-yearflood event standard is not recommended:

The entire watershed for both the Harmony and Farewell would have to be remodeled All affected municipalities would have to endorse such a change (Oshawa, Clarington, Region of Durham) Simcant cost to undertake a new flood plain study 100-year flood event does not account for potential blockage of the existing culverts which could result in flood elevations similar to the regional storm event Recent floodingexperiences in Ontario suggest the risk to flood damages could be greater than experienced. As a result, it is prudent to utilize the greater storm event. Since much of the Farewell Creek is undeveloped at this time it is prudent to use the most conservative approach to flood plain management in order to ensure that changing conditions such as increase in impermeable surface can be mitigated.

The study also considered other potential policy approaches such as using a Two-Zone concept and Special Policy Areas as a means to maximizing developmentpotential. The Two Zone approach is only applied to areas which have extensiveflood plains with shallow depths and low velocities where some development could occur without increasing the extent of flood risks to existing or new buildings. SpecialPolicy Areas are designated by the Province and are limited to those areas which are essential for the continued viability of existing uses such as historical downtownareas built prior to flood plain policies coming into effect. The study concludes that these two approaches are not applicableand inappropriate to apply to this flood hazard area.

Structural Approach Existing bridge structures for the crossing of Farewell and Harmony Creeks are approximately 5 m X 6 m and 5 m X 4 m respectively. A cost benefit comparison was carried out for various culvert and bridge improvements/replacement options in order to increase flood flows through the embankment. The study concludes that the option of replacing the existing culvert at the CN Rail embankment with a 30 m wide by 6 m high bridge resulted in the greatest reduction in flood plain area and the best benefitkost analysis. Modelling indicates that the flood plain would be reduced by approximately45 ha with the 30 m bridge option thereby freeing up land for development and providing some flood relief to existing flood-prone structures. Such an option would require a temporary track diversion, embankmentworks and channel realignment works. An approximatecost of $10 million was provided.

cont'd......3

S.R. #4953-11 IMS: PSSG224

April 6,2011 Page 3

Two additional options were also considered, modelling upstream storage and cut and fill. To date flood flow conditions have been modelled in accordance with provincial policy and are based on steady flow techniques. Steady flow models do not account for the storage of flood flows caused by obstructions such as road and railway embankments. This is largely due to these structuresnot being suitableto hold flood flows during a large storm event. However, the use of non-steady flow method is allowed for by the province. Accounting for flood storage upstream of CN Rail embankmentreduces the flood elevation by 0.92 m and reduces the current defined flood hazard by 9 ha. The additional area gained is relatively minor and distributed around the perimeter of the flood hazard area. The study concluded that the use of factoring in storage of flood waters should only be used if suitablerelief is provided by means of additional flow capacity through the embankment. The potential for iceldebrisjamming at the existing undersized culverts creates too great a risk for the implementation of this option. If a large opening is created in the CN Embankment, then the flood storage analysis could be revisited. Similarly, the study concludes that the option of cut and fill would have little merit as a single method of flood relief. However, if additional hydrologic capacity wasmade possible by way of a replacement bridge, it may become a more viable option to consider.

Study Recommendations

Based on the analysis of these considerationsthe study concluded with 6 recommendations (see Attachment 2 -Executive Summary).

The recommendationscan be summarized as follows: That the study be shared with the proponents for development within the study area; That the benefits of reducing flood elevation by using storage capacity should only be consideredif additional flow is achieved through the embankment; That CLOCA and the City of Oshawa encourage development proponents wishing to achieve flood relief in this area to support the implementation of the replacement bridge; If suitableflow conveyance improvements are implemented, the benefits of flood storage and cut and fill opportunities could be considered; That the use of non-structural approaches to relieve the extent of flood prone land not be considered.

Conclusion

The study makes two key conclusions. The fmt is that a non-structural approach to reducing flood plain area is not recommended. The second is that the best structural approach is a replacement bridge with a greater capacity to allow flood flows.

Staff concurs with the study conclusion that a non-structural approach aimed at reducing flood plain area is not recommended. The application of a storm event less than the regional event can have simcant adverse effects on the Authority's ability to effectivelyreduce potential for injury, loss of life and property damage resulting from flooding. Other non-structuralpolicy approaches such as the Two-Zoneconcept or SpecialPolicy Area are simply not meant to address areas such as this which are largely undeveloped and subject to signif~cantflood elevations. As a result, is recommended that the Board endorsethe recommendationof the Study that a non-structural approach not be pursued.

cont'd ......4

April 6,2011 Page 4

The studyclearly indicates that the most viable option for flood relief in this area is by way of a new bridge structurewhich will allow for increased flow through the embankment. A new bridge in this location would not only reduce the area subject to flooding but would also reduce the risk of flood hazard on several existing structures within the floodplain. Staff also concurs that if a new bridge structure can be implementedthat the consideration of furtherreduction of flood plain area could be considered through potential flood storageor cut and fill measures. As a result, staff recommends that the Board endorse this approach in principle with the understanding that CLOCA will not be responsiblefor any costs associated with the flood reduction measures and that subsequent detailed studies and assessments are required.

The study identified a number of issues that require further study: Potential future Go Train expansion on the CN Rail corridor; Consultation with CN Rail regarding the feasibilityof a replacement bridge; Structuralintegrity of the embankmentto allow for a bridge replacement; Detailed cut and fill analysis; Environmental and erosion analysis; Affected property owners and funding.

Furthermore, CLOCA has recently updated the flood plain mapping for this area, resulting in a slight increase in flood elevations. Although the conclusions of the Studyremain valid, more detailed analysis should be carried out based on the most recent flood elevations.

Staff from the City of Oshawa Engineering Division have reviewed the Flood Relief Studyand this report and indicated that they concur with the recommendations.

RECOMMENDATZON:

THAT Staff Report #4953-11 be receivedfor information;

THAT the Flood Relief Studyfor Harmony and Farewell Creeks (Greck2010)be accepted as a technical guideline document;

THAT the CWCA Board of Directors endorsesthe recommendationthat "the use of non-structural approaches to relieve the extent of flood prone land, such as a two zone policy, Special Policy Area designation or a reduction of the regulatoryjbod limitfiom the regional storm to the 100year storm, should not be considered. Theseapproachesare inappropriate solutions to reducingjlood hazards within the study area.'); and,

THAT the CLOCABoard of Directors endorses, inprinciple, the use of a structural method to increase additional hydraulic capacity under the CN Rail embankmentas an option that can bepursued by the City of Oshawa and applicable landowners with the understanding that CLOCA will not be responsiblefor any costs associated with theflood reduction measures and that subsequent detailed studies and assessmentsare required.

CDMt Attach. s:\reportsY2Ollbr4953-11.doex

=;=hi-

--

HARMONY CREEKSAND FAREWELL FLOOD RELIEF STUDY

EXECUTIVE SUMMARY ATTACHMENT 2 -PAGE 1OF 11

INTRODUCTION

For several years there has been an interest to develop lands east of Harmony Road South which are bounded by the Canadian Pacific Rail to the north and the Canadian National Railway (CN Rail) to the south, see Figure I . This area is viewed as the eastern gateway into the City of Oshawa along Highway 401. A significant portion of this area is designated as flood hazard lands under current provincial flood hazard policies. The CN Rail embankment is a significant impediment to flood flow for both Harmony and Farewell Creeks which flow through this embankment. As a result, the regulatory floodplain created by both watercourses encompasses a significant area including existing urban areas and lands that could otherwise be valuable development land. This flooding issue not only raises concerns with respect to the potential for loss of public property and safety within this large flood damage centre, but it also is a concern regarding social and economic hardship for several owners of property within this area.

The purpose of this study was to bring to a conclusion for the City of Oshawa, CLOCA and development proponents issues related to the opportunities and constraints for land development as they pertain to the flood hazards associated within the study area. This report provides a basic understanding of the potential benefits with structural and non- structural flood relief methods or concepts. The information presented may be used by CLOCA, the City of Oshawa and proponents for development within the study area to prepare plans which fall within the opportunities and constraints presented in this report. This study does not present in detail any specific or preferred flood relief solution.

STUDY AREA

The study area location is illustrated in Figure 1. This figure illustrates the location of the regional and 100 year storm floodlines prior to 2010. Regulatory floodlines were recently updated by CLOCA. This updated has resulted in 23 percent increase in peak flow and a 0.22m increase in the regulatory flood elevation at the CN Rail embankment. While this update was not available at the time this report was prepared the flood relief concepts presented in this document may still apply or be considered.

Within this study area the lower reaches of Harmony Creek and the Farewell Creek flow parallel to and in close proximity to each other from approximately Bloor Street to Colonel Sam Drive. Although the confluence for these two watercourses occurs just

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HARMONYAND FAREWELL FLOODCREEKS RELIEF STUDY

AlTACHMENT 2-PAGE 2OF 114 - 9 upstream of Colonel Sam Drive, their regional storm flood plains begin to merge just upstream of the CP Rail embankment. This combining of the flood plains is partly attributed to the relatively flat land and low lying topography of the study area.

Portions of the study area are also identified as Environmentally Significant Areas. Figure 2 illustrates the location of Environmentally Significant Areas (ESAs), Provincially Significant Wetlands (PSWs), and a 30 m stream buffer zone. These areas have been defined by CLOCA and the Ontario Ministry of Natural Resources and present development constraints within the study area.

A few residential lots on Armada Court, the Harmony Creek Golf Course Club House and the Holiday Inn Hotel on Bloor Street, are identified within the bounds of the regulatory storm flood plain. Each of the major transportation corridors including Colonel Sam Drive, CN Rail, Highway 401 and Bloor Street are overtopped by flood waters. While a number of buildings and roads are at some risk of flooding the focus of this study was to examine flood reduction measures to increase development opportunities for land immediately north of the CN Rail embankment.

PREVIOUS STUDIES

Since 1981 three previous studies of the same area have concluded that increasing the opening under the CN Rail embankment is the preferred structural approach to reducing upstream flood risks.

FLOOD HAZARDS CAUSED BY THE CN RAIL EMBANKMENT

To place into perspective the flood impact created by the CN Rail embankment, an analysis was completed to determine the regional storm flood elevation, floodline and area removed from the currently defined flood hazard area as if the CN Rail embankment did not exist. This analysis represents the natural flood plain area or the maximum potential area from which new development could occur outside of the flood hazard area. The existing regulatory flood elevation upstream of the CN Rail embankment is at 86.2 m and the flood hazard area is approximately 94 ha. Excluding the CN Rail embankment, results in a flood elevation of 79.5 m downstream of Highway 401. The area removed from the current flood hazard area would be approximately 52 ha, see Figure 7. This indicates that the CN Rail embankment is responsible for approximately 55 percent of the regional storm flood hazard area.

The results of this analysis indicate that if the impacts of the CN Rail embankment could be completely removed or significantly reduced, then there is the potential to free up

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+-/o ATTACHMENT 2-PAGE 3OF 11

lands which may be suitable for devolvement. Flood hazards will still exist but to a lower extent on a number of private lots, and across Bloor Street and Highway 401.

FLOOD STORAGE CONSIDERATIONS UPSTREAM OF THE CN RAIL EMBANKMENT

Flow conditions are dynamic and traditional flood hazard analyses, including those for the subject study area, have been based upon steady flow modelling techniques. Furthermore, the full flood storage potential immediately upstream of the CN Rail embankment has not been considered in previous studies. While most flood hazard analyses completed in Ontario are based on gradually varied steady flow analytical methods, the use of non-steady flow methods is allowed for and described in the Ministry of Natural Resources Flood Plain Management in Ontario Technical Guidelines (MNR 1987). Results of the non-steady flow and flood storage analysis completed in this study show the maximum flood elevation upstream of the CN Rail embankment would reduce to 85.3m. This elevation is 0.92 m less than the current regulatory flood elevation of 86.2m. The flood hazard area would reduce to approximately 85 ha at an elevation of 85.3m. This is a reduction in the currently defined flood hazard area of 9 ha. This additional area is gained primarily as a narrow band along the outer limits of the current flood hazard boundary, and a knoll of land between Harmony and Farewell Creek on the downstream side of the CP Rail embankment see Figure 15.

There are three ways in which the benefits of flood storage can be considered.

1. The reduced flood elevation could be used to establish new regulatory floodlines for the study area and possibly further upstream.

2. The existing regulatory flood elevation can be maintained knowing that there is some buffer capacity within the flood prone area.

3. The current regulatory flood elevation could be maintained and the buffering capacity is used by allowing for cut and fill within the floodplain thereby consolidating the developable area.

STRUCTURAL FLOOD RELIEF ALTERNATIVES

Past studies have examined a number of solutions to reduce flood hazards including increased conveyance with larger bridges or multiple culverts, channelization, upstream detention storage (within the watersheds), use of a two zone flood plain management

GRECKAND ASSOCIATES Page vLIMITED

HARMONYAND FAREWELLCREEKSFLOODRELIEFSTUDY

ATTACHMENT 2 - PAGE 4 OF 11dy// policy and changing the regulatory storm used to define the flood hazard. Table 4 provides a summary of the previous alternatives considered and the conclusions drawn on the suitability of their implementation.

The performance of a 30 m wide by 6m high bridge replacement, recommended in previous studies, was re-examined in this study using the unsteady flow and flood storage model. The resulting flood elevation upstream of the CN Rail embankment for the regional storm would be 81.21m. This elevation is slightly lower than the estimated flood elevation of 81.68 m determined in earlier studies. While the benefits of the 30 m bridge appear to significant in terms of the flood relief, a significant portion (45%) of this area is still flooded by the natural topography of the area, and hydrologic conditions caused by the convergence of flows from Harmony and Farewell Creeks. Previous cost estimated for the 30 m bridge were $4.7 million in 1982, $6.7 million in 1990 and $7.5million in 2001. These costs included considerations for temporary track diversions, embankment works and channel realignment works. Track diversion costs were 37 percent of the total cost. In 2007 the cost of the 30 m bridge would be approximately $10 million.

Considering the significant cost associated with a bridge structure an alternative flow conveyance approach was considered. Modern tunnelling techniques were considered as an alternative as it may reduce construction costs associated with temporary track diversions. These methodologies can minimize risks to the rail line provided a suitable depth of cover is available over the proposed culvert(s). Culvert pipes of various sizes are possible. Larger tunnels cost more as they are less commonly installed, require steel case linings and require contractors with more specialized experience, qualifications and equipment. Large pipes also reduce the depth of cover and could add risks to the rail line. Larger pipes, on the other hand, have less potential for becoming clogged or obstructed by debris during large storm events.

The use of six 3 m diameter pipes can reduce the regulatory flood elevation to 83.lm. This flood elevation is 3.1 m lower than the current regulatory flood elevation. The resulting flood elevation however remains 3.5 m higher than if no CN Rail embankment existed. Preparation of detailed cost estimates for micro tunnelling, or tunnelling and jacking methodologies is beyond the scope of this project. Because of the uncertainty associated with which technology would be the most appropriate for this site, an average cost $19/mmlm pipe length was used. The cost for six 3 m diameter pipes, each 28 m long, would cost approximately $9.6 million. Figure 24 shows the relative costs for flood hazard area removed for various culvert and bridge options. It also illustrates the benefits cost ratio of these alternatives.

Not included in Figure 24 are the flood relief benefits provided to existing buildings. While all options do not entirely remove flooding to existing structures they do reduce

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/ ATTACHMENT 2-PAGE 5OF I I

both the depth and duration of flooding. For example the use of six 3m diameter culverts could reduce the duration of flood hazard at the Holiday Inn from an excess of 18 hour to 6 hours, and the depth of flooding from 4.3 m to 2 m. Although damages from such flooding may not be proportionally reduced these are flood reduction benefits which are obtained in addition to the gain in developable land.

Due to the natural topography of the land, the area freed from the flood hazard designation through the implementation of culverts or bridges is located along the perimeter of this area. This may limit the direct use of this potential gain in developable land. It may be possible however to make better use of this area by considering a cut and fill approach to relocate or concentrate the area removed from flood hazard designation. This approach however must be implemented such that they meet the following technical criteria.

1. Flood depths for all return period storms must be maintained to existing conditions, this includes events for the 2 through 100 year design storms as well as the regional storm event.

2. The cumulative flood storage volume must be maintained for all flood elevations. This is particularly important for the study area if the benefits of storage upstream of the CN Rail are to be considered in reducing current regulatory flood elevations.

3. Designated environmental features must be protected from the impacts of cut and fill locations and operations.

The potential for implementing cut and fill operations in this area may be constrained by the diversity of land ownership.

NONSTRUCTURAL FLOOD RELIEF ALTERNATIVES

In addition to considering structural solution to resolving development constraints imposed by the flood hazard lands, non structural solutions were considered. Specific consideration was given to a request made to the City of Oshawa by a development proponent to revising the regulatory flood standard from the regional storm event to the 100 year storm.

The current, 2005 Provincial Policy states that development shall generally be directed to areas outside of hazardous lands adjacent to rivers and streams which are impacted by flooding hazards (MAH 2005). The minimum acceptable regulatory flood standard in Ontario is the 100 year flood. In small watersheds the 100 year storm may produce flood flows which are greater than the regional storm, due to the rapid response of the

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watershed and the high intensity of the 100 year event. An example of this is Branch 6 which flows into the study area.

CLOCA has implemented 100 year flood policies within two of the fifteen watersheds within their jurisdiction, Pringle Creek and Darlington Creek. Both of these watersheds are relatively small, 28.5 km2 and 16.0 km2 compared to the total watershed area of 82 km2 for the Harmony and Farewell watersheds. Implementation of this policy has created a number of administrative challenges for CLOCA. The challenges lie in the inherent variability with assessing and defining flood hazard areas between pre and post developed conditions.

The Ministry of Natural Resources can also modify the regulatory flood standard to reflect observed flood events. As such, for most of southern Ontario the flood event which occurred when Hurricane Hazel passed in 1954 was adopted by the Ministry of Natural Resources as the regional storm to which regulatory flood hazard must be defined. Although the path of the hurricane was located to the west of Toronto it was felt it could have occurred anywhere within the southern Ontario area (MNR Flood Plain Management Technical Guidelines (1987).

The regional storm provides a "buffer" in which to managing developing lands. This would be particularly important when considering the future development of the Farewell Creek watershed. Most of this watershed is currently undeveloped and future urban development will likely occur over many years. This situation has the potential to create greater variability in peak flow estimates due to the greater amount of land use change to occur. Alternatively a Two-zone flood plan management approach may be used in selected areas.

The Two-zone concept identifies the floodway and the flood fringe. The floodway refers to that portion of the floodplain which is required for the safe passage of flood water. No development is allowed within the floodway. The flood fringe is the portion of the floodplain where development may be permitted subject to certain established standards and procedures. These standards are typically based on limitations to flood proofing buildings, flow depths and velocities, or a combination there of, which does not present a significant risk to public safety. Possible delineations of the floodway within the study area were determined to be unsuitable for flood proofing or provided limited additional area for development. As such, application of a Two Zone floodplain management policy within the study area was determined to be an inappropriate means for providing additional lands for development.

In some unique or exceptional situations, communities are allowed to continue uses in a flood plain if the area is officially designated as a Special Policy Area (SPA). The application of the SPA concept is limited to those areas which are essential for the

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continued viability of existing uses; e.g., historical sites or old neighbourhoods built before flood plain policies came into effect. Once again, the extent to which development may take place in a SPA may be based with the adequate use of flood proofing measures. This study concluded that it would be inappropriate to knowingly develop open land within a currently designated flood hazard area and then apply a Special Policy Area designation.

A municipality may apply to the Ministry of Natural Resources for a reduction in the regulatory flood standard from the regional storm to the 1:100 year storm floodline under specific circumstances. This is possible where there is no record of occurrence of a regional storm and where the 1:100 year storm has not been exceeded historically. In 1990 a request came to the City of Oshawa to initiate the process with the Ministry of Natural Resources to reduce the regulatory flood standard from the Regional flood standard to a 1:100 year flood standard. In 1994 the Public Works Department responded with the following recommendations:

1. That the City of Oshawa request the Municipality of Clarington to give consideration to approval, in principle, of the reduction of the regulatory flood plain on the Harmony and Farewell creek watersheds from the regional storm to a 100 year storm.

2. That a copy of the Director of Public Works' report dated 1994/01/11 be forwarded to CLOCA and the proponent for the change in Regulation.

The City of Oshawa and CLOCA at that time had agreed in principle to proceed with the application to change the flood hazard standard. CLOCA however had additional consideration associated with their approval. To proceed with the application for the change in regulation a number of flood reduction measures, particularly the enlargement of the bridge at Farewell Creek to a 30 m (100 feet) span bridge was required. CLOCA also required the Town of Newcastle to be an equal partner and that floodline mapping be completed or updated for each of the Harmony and Farewell Creek watersheds. Environmental considerations were not raised as an important issue at that time with respect to changes in the regulation by either the City of Oshawa or CLOCA.

City of Oshawa staff held a number of additional meetings over the years to further understand the request by the proponent(s). As a consequence of these meetings, it has become apparent that no financial commitment for the enlargement of the structure under the CN Rail embankment is being offered. As such, City of Oshawa staffs have recommended not approving the request until such financial commitment is provided.

There are other issues that must be considered if flood regulations are to be changed.

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Changing the policy from the regional storm to the 100 year storm must be a policy which is applied watershed wide. As such, the potential impact to Farewell Creek watershed would have to be reviewed in detail. Completion of this task requires floodline mapping be prepared for the entire Farewell Creek watershed. This would require detailed hydrologic and hydraulic analyses be completed for existing and future land use scenarios. This could put restrictions or delay proposed development projects within the watershed until such work is completed. The result of this assessment may be the requirement for a greater level of stormwater management in the entire Farewell Creek watershed.

Furthermore, the impact of such a policy change is not limited to those of the study area. Applying a 100 year storm policy would likely upset others who have complied withwthe current policy. There may be implications with respect to obtaining suitable flood protection insurance if infill development occurs in a previously designated flood hazard area. While the change may be acceptable from a regulatory perspective, the perceived risks may not change fbm an insurance perspective.

RECENT FLOODING EXPERIENCE IN ONTARIO

The people of Ontario have experienced extreme weather events in the past, such as the Hurricane Hazel Storm. This storm event was the largest 12-hour rainstorm ever recorded in Ontario up until 1954. The storm was centred over the Humber River in Toronto and affected a 30,000 square kilometre area, dumping over 280 mm of rain in a two day period, resulting in the loss of 81 lives and incredible damages to property and infrastructure.

Since Hurricane Hazel, more extreme events have occurred. Presented below is a summary of a few of these events.

The Harrow Storm occurred in 1989 over the Town of Harrow in Essex County in south- western Ontario with a total recorded amount of 450 mm of rain that fell in less than 36 hours. The rainfall event exceeded the Hurricane Hazel Storm, and resulted in close to 100 million dollars of damage (MNR Understanding Natural Hazards 2001).

On June 8-11 2002 a storm referred to as the 4gth ~arallel storm a storm in Manitoba spilled into northern Ontario dropping over 360 mm of rainfall in two days. This volume was 2 to 3 times greater than the current Timmins Regulatory storm for this area of Ontario. Over $31 million in damages were incurred in Ontario alone (Environment Canada 2002 and J. Klaassen 2005).

The Peterborough flood in 2004, located north of Oshawa, occurred when 240 mm of

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rainfall fell in less than five hours. Cost estimates included an excess of $88 million in insured losses, $25 million for emergency repairs, and upwards of $30 million for possible sanitary and storm sewer improvements (Environment Canada 2004).

Remnants of Hurricane Frances in September 9, 2004 had peak rainfall intensities of 150 mm in 12 hours exceeding, 6,12 and 24 hour 100 year rainfall intensities in the Ottawa area. Over $54 million insurance claims were made in Canada for this event (3. Klaassen 2005).

The summer storm of 19 August 2005 was Ontario's most expensive storm. On this day a trail of storms from Kitchener to Oshawa left a trail of damages which exceeded $500 million. This was the second largest loss event in Canadian history. A flash flood in Toronto resulted in the washing out Finch Avenue. This storm dropped 103 mm of rain in one hour. This roadway was closed for several months. The event exceeds that of the 100 year storm and had a peak intensity greater than that of Hurricane Hazel. A private rain gauge recorded as much as 175 mm of rainfall, (Environment Canada 2005). '

A 2004 the Ministry of Natural Resources reported that in Ontario a state of emergencylmunicipal disaster has been declared virtually every year since 1995. Disaster relief assistance to municipalities has been provided by the province at an increasing rate since that time (MNR 2004).

It is difficult to know exactly what the future holds, as the actual impacts of climate changes are unknown. It may be safe to say however that currently we are going through a period of uncertainty. It will be difficult to get regulators to lower flood hazard standards with this uncertainty, particularly when it results in potentially greater risks to life and property damages, and as the number of insurance clams dramatically increases. If changes are to be made, it is more likely that the standards will become more stringent than they are today.

FLOOD RELIEF IMPLEMENTATION CONSIDERATIONS

This study has focussed on conducting technical analyses related to reassessing existing flood hazards and alterative flood relief solutions at the CN Rail embankment previously not considered. This work was completed to define in general the opportunities and constraints from a flood hazard management perspective. This study could be used as a guide by CLOCA, the City of Oshawa and development proponents wishing to proceed with development within the flood regulated area.

Since development planning, engineering design and the logistics for implementing

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flood relief works can become complex, it is beyond the scope of this study to provide details for one specific solution. Further detailed assessment of a preferred flood relief approach is one which would typically be completed by the development proponent(s). This study does provide however information from which a development plan can be formulated which is within the constraints of flood hazard management policy and opportunities which may exist to provide flood relief.

A few specific issues were identified during the course of this study which may influence the planning and design process. While detailed assessments of these issues were beyond the scope of this study, because of their importance they are listed below:

1. Potential future Go Train expansion particularly on the CN Rail corridor:

2. Consultation with CN Rail regarding the feasibility or opportunities for installation of multiple culverts or a replacement bridge.

3. Materials used to construct the CN Rail embankment may significantly influence the feasibility and costs associated with implementing micro tunnelling or bore and jack type works.

4. Several public and private land owners may be affected by the type of flood relief works selected. This may influence the selection and funding for a preferred flood relief solution.

5. Analyses completed in this study have not considered the potential flood relief benefits with possible upgrade to structures on Highway 401, Bloor Street East andlor the CP Rail embankment in association with flood relief works at the CN Rail embankment. The potential benefits resulting from improvements to the structures can only occur if flood relief measures are implemented at the CN Rail embankment.

RECOMMENDATIONS

The following recommendations have been prepared based on the findings of this study.

1. The findings of this study should be shared with the proponents for development within the study area and with CN Rail.

2. The benefits of a reduced flood elevation, brought about by consideration of the storage capacity upstream of the CN Rail embankment, should only be used to establish a buffering capacity for the area and not to maximize urban development opportunities.

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3. Notwithstanding item 2, the benefits of the storage capacity should be considered if suitable flood relief is provided by means of additional flow capacity through the CN Rail embankment. To be cost effective this flood relief should be provided in the form of a large 30 m wide by 6 m high replacement bridge structure. While the total cost of this option may be greater than that provided by the installation of several large flood relief culverts, for example six 3m diameter culverts, it has better cost benefits. The additional flood relief benefits of maintaining the existing culvert and adding a 30 m wide by 6 m high bridge are minor.

4. CLOCA and the City of Oshawa should encourage efforts to provide the greatest additional hydraulic capacity under the CN Rail embankment possible. This not only provides opportunities for urban deployment but as a priority reduces potential flood damages to existing structures including bridges, residential and commercial buildings and the operation and integrity of the CN Rail embankment. As such, they should encourage development proponents to support the implementation of the replacement bridge flood relief option. In doing so however they should also consider the possibility of contributing to the overall cost of providing flood relief to this area.

5. If suitable flow conveyance improvements are implemented, the benefits of flood storage should be considered as well as the possibility for implementing cut and fill within the flood hazard area to maximize opportunities for development. Cut and fill applications must provide appropriate information to demonstrate that

a. Flood elevations are maintained to existing conditions for all return period storms including the 2 through 100 year design storm events and regional storm event,

b. The cumulative flood storage volume is maintained for all flood elevations and

c. Designated environmental features are protected from the impacts of cut and fill locations and operations.

6. The use of non-structural approaches to relieve the extent of flood prone land, such as a two -zone policy, Special Policy Area designation or a reduction of the regulatory flood limit from the regional storm to the 100 year storm, should not be considered. These approaches are inappropriate solutions to reducing the flood hazards within the study area.

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