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HomeMy WebLinkAboutHK - 2012-05-01 - Environmental Assessment (EA) - Huron Rd Bridge/~ ~~~~ Page 1 /"1~ Memorandum April 24, 2012 To Kevin Mick P.Eng Page 1 cc Steve Allen P.Eng Subject EA Evaluation Criteria From Scott Davis P.Eng date April 24, 2012 Project Number 60237716 Further to our discussion please find below the proposed Environmental Assessment Evaluation Criteria and limited background information. 1. Background The Huron Road Bridge Structure is a 9.6 metre single span, concrete on steel beam girder bridge over the Schneider Creek with a single load posting of 18 tonnes. The bridge was constructed in approximately 1930, and has been modified and rehabilitated several times since. The bridge is located on Huron Road, 200m east of Homer Watson Boulevard in the City of Kitchener. Originally constructed with six steel girders, five more girders were added at an unknown date. The bridge was rehabilitated in 2000; the rehabilitation work included: • Deck repairs and a concrete overlay; • The replacement of two original girders and two replacement girders; • The replacement of a section of the original railing. The bridge received a Mike Wagner Heritage Award for the repair work completed to the bridge in 2001. Full depth deck repairs were again required in the spring of 2011. The Schneider Creek watershed (65km2, upstream of the study area) is located within the Grand River Watershed. The predominant land use in Schneider Creek is urban. 1.1 Problem Statement The City of Kitchener has identified the need to address the structural deterioration and the substandard load posting of the Huron Road Bridge Structure. In addition, the existing structure does not meet current design standards for roadway width and is deficient with respect to its physical condition and road side safety. M 2012-04-23 Draft Prelim Evaluation Criteria 60237716.Doc ~~~~ Page 2 Memorandum April 24, 2012 2. Alternative Solutions The following alternatives were developed to address, in whole or in part, the identified issues with the Huron Road Bridge as expressed in the study Problem Statement. 2.1 Alternative 1- Do Nothing In this alternative, no work would be done to the bridge. The bridge will continue to have load restrictions and will gradually deteriorate until it can no longer carry traffic. The bridge will require regular inspection to monitor the continuing structural deterioration and to ensure safety of the public. Figure 1 displays the existing configuration of the bridge, which would be maintained under this alternative. Figure ~ -Alternative 1- Do Nothing 2.2 Alternative 2 -Rehabilitate the Bridge In this alternative, repairs will be undertaken to the existing structure to rectify any deterioration, strengthen the bridge, and remove the load posting at the bridge. As the corrosion potential survey in 2011 indicated reinforcing steel corrosion over 80°/0, and the deck chloride contamination was identified as significant in the 2010 condition report, the deck will be replaced. The existing railings are located directly on top of the deteriorating deck and are integral with the deck. As a result the railings will be removed and replaced. 2.3 Alternative 3 -Replace the Bridge on a new Alignment In this alternative, the existing bridge will remain and a new structure will be constructed on a new alignment. The existing structure will remain in place, but be closed to vehicular traffic. The new structure will be capable of carrying full highway loading, and will also be widened to comply with current design standards. ~~~~ Page 3 Memorandum April 24, 2012 3. Bridge Heritage Constructed in approximately 1930 the Huron Road Bridge was reviewed as a part of the Region of Waterloo 2004 study "Spanning the Generations, A study of old bridges in Waterloo Region Phase 1 Inventory". The bridge was identified as the earliest example of a bridge with a visible I-Beam in Waterloo Region. The heritage assessment gave the bridge a score of 60. According to Phase 2 of this report heritage bridges usually achieve a score in the range of 50 to 80 points. The Region of Waterloo Heritage Planning Advisory Committee has indicated strong support for the preservation of the heritage and character defining features of the bridge, notably the railings and the visible I-Beams. Although the bridge is a modest structure, it contributes to the ambience and character of the area. The bridge is adjacent to the Waterloo Region Museum and the view from the museum property is impacted by the aesthetics of the bridge. Based on this information a heritage character statement has been developed for the bridge: The heritage character of the existing bridge resides in ifs rural modest simplicity with steel visible 1-Beams supporting a single lane deck and rural fence style barrier. The original site relationship between the railing and the creek has remained intact with the creek as a highly visible component of the bridge crossing. The interplay between the concrete barrier material and reveal inset details which face traffic are important to the character of the barrier. The Ontario Ministry of Transportation Heritage Bridge Guidelines (HBG) for Provincially Owned Bridges suggests conservation options for bridges such as the Huron Road Bridge. The eight conservation options from the HBG are listed in order of least intervention. Option 1 is to be shown as non-viable before Option 2 is considered and soon. The eight conservation options are: 1. Retention of existing bridge with no major modifications. 2. Restoration of missing or deteriorated elements where physical documentation exists. 3. Retention of existing bridge with sympathetic modification. 4. Retention of existing bridge with sympathetically designed new structure in proximity. 5. Retention of existing bridge adapted for new use. 6. Retention of bridge as a heritage monument only. 7. Relocation of bridge. 8. Bridge removal and replacement with sympathetically designed structure (salvage elements, undertake full recording and documentation of existing structure). The HBG guidelines recommend demonstrating that prior to replacing a bridgelelement one of the following conditions be demonstrated: 1. The safety of the existing bridge or element is compromised and cannot be rehabilitated. 2. The cost of rehabilitation is prohibitive compared to replacement (by more than 10%). 3. The bridge has been severely altered from its original form. 4. Replacement is required to meet demand requirements that are not achievable through rehabilitation or upgrading. The Canadian Highway Bridge Design Code (CHBDC) recognizes the value of the aesthetics of a bridge, and recommends that bridge structures be designed so that they are perceived to bean enhancement to the natural surroundings. The Ontario Ministry of Transportation's Structure ~~~~ Page 4 Memorandum April 24, 2012 Rehabilitation Manual (SRM) further emphasizes the importance of preserving the integrity and original appearance of a heritage bridge wherever possible. In 1994 the Grand River, along with its tributaries were declared a Canadian Heritage River. As a component of the cultural landscape, bridges have contributed to the development of Ontario. The Huron Road Bridge is an important part of the built heritage in the Doon Valley area. 3.1 Traffic Safety In the vicinity of the bridge Huron Road has an Average Annual Daily Traffic (AADT) of 2047 as calculated in 2002 with a speed limit of 50km/hr. The road forms an important link between Homer Watson Boulevard and residential neighbourhoods along Green Valley Drive. The detour distance around the bridge is 1 km. The existing bridge has an average road width of 5.36 metres. The Ontario Ministry of Transportation's Structural Manual (OSM) includes exceptions to the Canadian Highway Bridge Design Code (CHBDC) which provides for guidelines in the design of bridges on low volume roads. The guidelines apply to bridges with an AADT in both directions of 400 or less. The guidelines may also be used by the City of Kitchener where operational issues such as traffic delays and collisions over a bridge are minimal. The OSM includes the following considerations: • The MTO guidelines discourage single lane bridges with road widths greater than 4.9 metres as bridges wider than 4.9 metres may appear to be two-lane bridges; • Adequate warning to traffic is required on single lane bridges; • For AADT> 400 traffic control measures such as yield signs and traffic signals should be considered; • Speed limits should be less than 50kmlh where the road width is less than 7 metres; and • Horizontal and vertical alignment should be determined using existing roadway design criteria. The geometry of the road isdeficient incross-section, horizontal and vertical alignment. These deficiencies may impact the safety of roadway users. The road over the bridge measures more than a single lane and less than is recommended by the Transportation Association of Canada (TAC) for two lanes. There is a potential for drivers to be confused and perceive the bridge as a two-lane bridge. Due to the potential for flooding over Huron Road it is recommended that drivers be able to see the road surface for a sufficient time to be able to stop their vehicle safely. The sightlines along Huron Road to the bridge are disrupted by overhanging branches from trees, a horizontal curve in the southwest quadrant, and by rolling terrain in the vertical alignment of the road. Furthermore, the existing railing over the river has a substandard height, gaps and crash rating. The minimum vehicle, pedestrian and cyclist railing heights, as well as maximum gaps are indicated in Figure 2. AECOM 4. Evaluation Criteria Page 5 Memorandum April 24, 2012 Each alternative needs to be evaluated with a consistent methodology, the goal of which is to identify potential challenges and opportunities within the options. Table ~ describes the evaluation criteria used to assess the bridge alternatives. Table ~ -Criteria for the Evaluation of Alternatives Criteria Description Hydraulics, Construction, and Potential to implement project with conventional methods and to obtain agency Approvals approval for implementation. Effectiveness to mitigate, manage or reduce floodin Impact to Public Safety Impact to the safety of road users including vehicles, pedestrians, cyclists. Construction Costs Relative measure of the initial costs to instalUconstruct the proposed works Service Life Costs Relative measure of the ongoing maintenance costs and risks following implementation ronmental Construction Impacts The impact of construction activities to the surrounding natural environment Impact to Private Property Impact to adjacent private property (i.e. loss of property, access to property) Impact to Heritage value Impact to the heritage value of the structure 5. Evaluation of Alternatives 5.1 Alternative 1- Do Nothing This alternative includes taking no action to repair or replace the bridge, and does not address the identified structural deterioration or load posting issues. Ongoing maintenance to the bridge will be required. 5.1.1 Technical Criteria Due to the deteriorating condition of the bridge the Do Nothing alternative may eventually lead to a closure of the bridge. In the Do Nothing alternative the current single load posting would remain, and eventually as deterioration occurs it will continue to be reduced until the bridge has no remaining Figure 2: Existing Railing AECOM Page 6 Memorandum April 24, 2012 capacity and is not suitable for traffic loading. Further there will be no opportunity to improve the safety of pedestrian, cyclist, and vehicle traffic through improvements to the roadway and the railing. 5.1.2 Economic Criteria The cost of maintenance will continue to increase as the structure continues to deteriorate. 5.1.3 Environmental Criteria The "Do Nothing" alternative has the lowest impact to the environment, as there will be no adverse impacts due to construction activities. 5.1.4 Social Criteria The 18 tonne load limit reduces access to property for heavier vehicles. Eventually the bridge may close, which will result in a 1 km detour, reduced access to property, and time lost. The heritage components of the bridge will continue to deteriorate. 5.2 Alternative 2 -Rehabilitate the Bridge This alternative includes a deck replacement and the strengthening and repairing of existing steel girders to address issues of structural deterioration and to remove the load posting on the bridge. 5.2.1 Railing Options The necessity to replace the bridge deck as part of the bridge rehabilitation means that the existing concrete railings also need to be replaced. In considering the multiple replacement railing options available for the Huron Road Bridge the heritage character of the bridge and the existing railing was defined: The heritage character of the existing railing resides in its simplicity as a rural rectangular fence style barrier. The original site relationship between the railing and the creek has remained intact with the creek as a highly visible component of the bridge crossing. The interplay between the concrete barrier material and reveal inset details which face traffic are important to the characterof the barrier. The review of preliminary railing options including the development of criteria for a railing to be considered further: 1. The barrier should be constructed from concrete and include reveal details facing traffic to match the original construction material and reveal inset details of the existing rail; 2. Only railings which include heritage characteristics of the existing rail, such as potential for reveal details, posts, and concrete rails will be considered. AECOM Page 7 Memorandum April 24, 2012 Examples of railings which were reviewed and rejected based on the above criteria are included in Figure 3. The four options which were evaluated are represented in Figure 4, Figure 5, Figure 6, and Figure 7. The railing replacement options were evaluated in accordance with Table 2. ~' • k~ d' ~ . ~~ B ~ , A4. MCI li ~ ~:.~~ +~t"~ _ J 5+ e ~ ,~ Y # '~+, es 6jC R ~+~. '^ * ~.' •~ ~ ~ ~~ ~~ ~y .~~ ~. A f I .~u ,. ~:~ ~~~ Figure 3: Rejected Railing Options ~ "~'~~~ -, - ~ rn ~~ ~ y_~. -_.~'" ~~ a ~- Table 2. Criteria for the Evaluation of Railing Replacement Options ~ Criteria Description Technical Impact to public safety for road users including pedestrians, traffic, and Impact to Public Safety cyclists Economic Construction Costs Relative measure of the initial costs to construct the proposed railing. ~ Service Life Costs Measure of the ongoing maintenance and risk associated with an option. Social ~ Impact to Heritage value Impact to the heritage value of the structure Figure 4: Railing Option 1 AECOM Figure 5: Railing Option 2 t. ~ i~r ~~ ~~, ~~~:. ~~: ~~_ ~~ ~, 1{. ~. ~~~ , ,~ '~ _ ~ __ -~~ ~ a _ J - ~ ~ ~~ ~{{ M'TF~ 'a~ ~ ~~~ 5 ~st"' i -! ' q~. ~ ,~ ~~; , Figure 6: Railing Option 3 Figure 7: Railing Option 4 ~w~ ~,. ~`~ r ~. , ~~ ~;~x. ~ ~+y ,.,. 5.2.1.1 Technical Criteria -Railing Options Page 8 Memorandum April 24, 2012 Formwork for concrete is typically constructed for a specific job. The easiest forms to build are for parapets that are constructed most often. In Ontario the option 2 parapet will be the most common type of parapet, and hence the most constructible of the options. Where specialized formwork is required for detailed reveals or separated railings additional effort will be required for the manufacturing of the formwork. /~ ~~~~ Page 9 /"1~ Memorandum April 24, 2012 In accordance with the Canadian Highway Bridge Design Code (CHBDC) bridge railings need to withstand crash testing for specific performance levels in accordance with American Association of State Highway and Transportation Officials (AASHTO) requirements. In Ontario there are a handful of designs accepted by the Ontario Ministry of Transportation (MTO) which are typically used for most bridges. However, bridge railings have been crash tested across North America which meet the requirements of the CHBDC. Crash testing for railings is a time consuming and expensive endeavour. The Huron Road Bridge requires railings which meet the Performance Level 1 (PL-1) which is the lowest performance level accepted in Canada. In addition to requiring railings to be crash tested, different requirements are specified by the CHBDC depending on the road usage. On Huron Road it is expected that pedestrians, cyclists and vehicular traffic will continue to use the bridge. As a result the CHBDC indicates that the railing is required to meet the standards of a combination railing for crash testing, height, and openings between railing elements. The code requirements are established to protect the safety of the general public. The four proposed railing options vary significantly in their ability to meet the CHBDC safety requirements. A comparison of the ability of each railing option to meet the CHBDC safety requirements is included in Table 3. Table 3 -Comparison of Safety and Railing Replacement Options Option Comments Option 1 Does not meet crash testing, height or maximum opening requirements Option 2 Meets all requirements Option 3 Meets all requirements Option 4 Does not meet overall height requirement for cyclists. 5.2.1.2 Economic Criteria -Railing Options All of the proposed bridge railings will be above the average costs for barriers. Every detail added above the typically constructed railings will result in additional labour, material and effort on the part of the contractor which will result in additional costs. A barrier designed in accordance with the CHBDC has a lower the risk of incurring service life costs over the next 40 years, such as railing reconstruction. 5.2.1.3 Social Criteria -Railing Options Cultural heritage contributes significantly to what makes a community unique. Heritage bridges form an integral link between local heritage and the utilitarian purpose they were created to serve. The heritage value of a structure is based on several key criteria including DesignlPhysical value, Contextual value, and Historicl Associative value. The railing option which has the greatest value to the heritage of the bridge is the railing which retains the most heritage character of the original railing. ~~~~ Page 10 Memorandum April 24, 2012 5.2.1.4 Evaluation of Railing Options Four railing options have been identified to address the rehabilitation needs of the Huron Road Bridge. The railing options were evaluated according to criteria that examine economic, technical and social impacts of the options. A qualitative rating scale is used to assess each of the evaluation criteria. An overall rating is then given to each category to allow an alternative-to-alternative comparison of how well the criteria, and therefore the identified issues, are addressed. Table 4 contains a breakdown of the evaluation where each of the three criteria is given an equal weighting to determine the overall rating as in Evaluation level 1 of the sensitivity analysis. Table 4 -Evaluation of Railing Options Evaluation Least Preferred Symbol ~~ Points ~ 2 Most Preferred 4 6 8 Criteria Description Option 1 Option 2 Option 3 Option 4 Technical (33%) ~ Impact to Public Safety Safetyfor road users including pedestrians, 0 ~ 0 (33 /o) traffic, and cyclists Economic (33%) Construction Costs (16 6%) Relative measure of the initial costs to construct 0 . the proposed railing. Service Life Costs (16.6%) Measure of the risk to install a railing which is 0 non-compliant to the CHBDC Social (33%) ~ Impact to Heritage Value Impact to the heritage value of the structure ~ O ~ o (33 /o) Overall Rating (Max 24) 8 15 20 13 A sensitivity analysis of the evaluation is useful to determine if the anticipated evaluation recommendation will be consistent, when emphasis on an individual criterion is altered. The sensitivity analysis considered 4 scenarios: • Evaluation Level 1-the technical, economic and social criteria are weighted equally; • Evaluation Level 2 -the technical criterion (Public Safety) is weighted to be twice as important as the economic and social criteria; • Evaluation Level 3 -the economic criteria (Construction and Service Life costs) are weighted to be twice as important as the technical and social criteria; and • Evaluation Level 4 -the social criterion (Heritage value) is weighted to be twice as important as the economic and technical criteria. A detailed breakdown of the evaluation levels is include in Table 5 and reviewed in Figure 8. In all of the scenarios the Option 3 railing scores the highest number of points. AECOM Table 5 -Sensitivity Analysis Evaluation -Railing Options Weightings (%) Technical Economic Social Evaluation 1 33% 33% 33% Evaluation 2 50% 25% 25% Evaluation 3 25% 50% 25% Evaluation 4 25% 25% 50% 5 ~5 10 5 Page 11 Memorandum April 24, 2012 ^ lailn option I~aMlin ptioi~ l~ilinption3 ^It~ilinpton~ Evaluation Level Figure 8: Railing Option Evaluation- Sensitivity Analysis 5.2.2 Technical Criteria There is no change to the cross-sectional opening of the structure in this alternative, and thus no change to the effectiveness of the bridge to manage, mitigate or reduce flooding. The rehabilitation of the bridge will include: • Deck and railing replacement; • Steel girder painting and repairs; • Abutment and wi ngwal I concrete repairs; and • Approach guiderail improvements. In the rehabilitated bridge, the barrier system and guiderails will be improved. The deck will be replaced and the load posting removed. The width of the travelled portion of the road over the bridge will not increase to accommodate two lanes, thus maintaining difficulty of use for multi-vehicle and pedestrian traffic. As the bridge will remain a single lane structure, road alignment and traffic challenges will require modifications to the bridge approaches. These may include reduced speeds, additional signage, and increased visibility to improve the overall safety of the road. ~ 4 ~~~~ Page 12 Memorandum April 24, 2012 In the event that in-water works are required to complete the construction of the bridge, a Fisheries Act Authorization will need to be obtained from the GRCA which has a Level III agreement with DFO. As well, approval under the GRCA Conservation Authority Act 0. Reg 150106 Regulation of Development, Interference with wetlands and Alterations to Shorelines and Watercourses will be required as works will be conducted within the GRCA Regulated Area. 5.2.3 Economic Criteria Maintenance costs for a rehabilitated structure are typically greater than for a new structure. Life cycle cost analysis (LCCA) is a means of analyzing the expense relating to a structure over its lifetime. These costs include capital costs, rehabilitation costs, maintenance costs, and disposal costs for a structure. LCCA considers more than initial construction costs; the goal of LCCA is to find the most cost effective approach over the lifespan of the structure. In order to perform an LCCA, rehabilitation and maintenance alternatives are developed, and the timing of improvements is considered. Costs for construction, rehabilitation and maintenance including engineering and administrative costs are estimated. Costs for structure users have not been considered as part of the analyses. User costs may include detour time, increased fuel costs, or other qualitative considerations. Alternatives are considered over a 40 year period of time, and the present value of the alternative is calculated. The results of the present value costs are analyzed and further rehabilitation and maintenance strategies may be considered as needed. The analysis period considered for the purpose of this study is 40 years which is within the typical service life for a structure. Required maintenance costs beyond 40 years generally have little effect on the LCCA. Predicting future costs can be complex. Inflation and discount rates are applied to come up with the present values fora 40 year cycle on the structure. However, in the selection of a discount and inflation rate the analysis may be skewed towards a particular result (replacement or rehabilitation). As such a sensitivity analysis is conducted on several combined discount and inflation rates. For this study inflation rates of 2% and 4% and discount rates between 2% and 8% were considered. Based on a Present Value and Sensitivity Analyses life cycle costs are indicated in Figure 9. AECOM Page 13 Memorandum April 24, 2012 ~~cfccc ~c~~ct~c ~o,~oo ~a,cca ~cc,cc~a ~, 4of~oo ~~~,~t~~ 1~~f~0~ I ^ Inflation ~~~ _ ~ ~n~l~ti~n ~~~~ = 4 ~is~o~int Rats Figure 9: 40 Year Lifecycle Costs Alternative 2-Sensitivity Analysis 5.2.4 Environmental Criteria The rehabilitation alternative will have a minor environmental impact from construction activities (e.g., access routes, sedimentation in the creek, etc.) which can be mitigated through construction best management practices and limiting the construction footprint. 5.2.5 Social Criteria During rehabilitation the road will be closed, resulting in traffic disruption to road users. As no widening will occur, there will be limited improvement in the accommodation ofmulti-vehicle traffic, pedestrians or cyclists The heritage aspects of the bridge will be reflected in the rehabilitated bridge. The original steel girders will be repaired, protected, and reinstated. 5.3 Alternative 3 -Replace the Bridge The bridge replacement alternative is anticipated to include a single span concrete deck on steel girder structure on a new road alignment. The existing bridge will remain without any improvements, but will be closed to vehicle traffic. 5.3.1 Technical Considerations This alternative will include the replacement of the Huron Road Bridge with a new girder structure. The new structure will provide an opportunity to increase the hydraulic capacity of the bridge to accommodate the upstream or downstream hydraulic conditions, and improve the road safety by including sidewalks, two vehicle lanes and bike lanes. ~~~~ Page 14 Memorandum April 24, 2012 The proposed structure is of standard construction. This alternative represents a solution which improves the safety of the structure to meet current standards. A new structure will accommodate full CHBDC vehicle loads, and will meet current Ontario Highway Design cross-section widths or better. The lifespan of a new structure is typically 75+ years with regular maintenance. The replacement of the bridge will be a more significant undertaking than rehabilitation, and may require additional agency approval review. In the event that in-water works are required to complete the construction of the bridge, a Fisheries ActAuthorization will need to be obtained from the GRCA which has a Level II agreement with DFO. As well, approval under the GRCA Conservation Authority Act 0. Reg 150106 Regulation of Development, Interference with Wetlands and Alterations to Shorelines and Watercourses will be required as works will be conducted within the GRCA Regulated Area. A Canadian Environmental Assessment Act screening report will likely be required as part of the Transport Canada Navigable Waters Permit. 5.3.2 Economic Considerations In the short term the cost for a structure replacement is the most expensive of the three alternatives presented in this study. However, maintenance costs for a rehabilitated structure are typically greater than for a new structure. Life cycle cost analysis (LCCA) is a means of analyzing the expense relating to a structure over its lifetime. These costs include capital costs, rehabilitation costs, maintenance costs, and disposal costs for a structure. LCCA considers more than initial construction costs, the goal of LCCA is to find the most cost effective approach over the lifespan of the structure. ,~r~. ~~~c,~. ~,~ac~a~.oo ~~ac~ao. ~„~~~.c ~,~o~~o ^ lr~fla~i~n Rte = ° Di~coun~ ate Figure 10: 40 Year Lifecycle Costs Alternative 3-Sensitivity Analysis As indicated in Figure 10 the bridge replacement alternative is less cost effective in all of the financial scenarios considered when compared to the rehabilitation alternative (Figure 9) over a 40 year LCCA. ~~~~ Page 15 Memorandum April 24, 2012 5.3.3 Environmental Considerations The following is a preliminary assessment of potential impacts from the preferred alternative Terrestrial impacts will be largely related to the replacement of the bridge structure, staging areas as well as associated clearing and grubbing activities. Potential construction-related impacts that are of particular relevance to the proposed bridge replacement are: ~ Construction-related runoff contributing to erosion of soils, siltation, etc. and subsequent deposition within the wetland communities; • Loss of trees within the replacement area; Compaction of soils within tree rooting zones along vegetation community edges; • Impact of materials in staging areas, as well as construction access routes; ~ Scarring and decreased health of adjacent trees damaged by machinery or affected by construction related dust and sedimentation; • Disturbance to wetland community vegetation; • Disturbance to wildlife caused by increased noise, lighting, and construction traffic; and • Introduction of aggressive non-native plant species into the adjacent wetland communities, reducing the natural integrity of the area. To avoid impacts to the warm water fishery within the study area, appropriate warm water timing windows as set by local MNRICA between March 15t" and July 15t" should be adhered to for any construction activities. Bridge design should also give consideration to the value of the habitat within the immediate area of the bridge. Risks to aquatic habitat and fish can be considered to be one of two types: a) Potential impacts related to the design or layout of the new water crossing structure, and; b) Potential impacts related to construction activities occurring in or near a watercourse. Potential impacts that are generally associated with the replacement of a water crossing structure include: • Loss of natural substrates; • Loss of in-stream habitat • Loss of riparian habitat (reduced bank stability, change to in-stream shading); ~ Change in stream hydrology; and • Temporary displacement offish communities. Impacts from the construction in and around aquatic habitat are generally associated with the length of the construction window. Potential impacts to fish and fish habitat from construction related activities i ncl ude: • Impacts to water quality from the release of a deleterious substance (i.e. sediment, oil and grease). Changes in water quality may impose significant behavioural and physiological stress on fish species, resulting in impaired spawning or feeding. AECOM Page 16 Memorandum April 24, 2012 • Temporary disruption of substrateslhabitat is likely to occur at locations where in-water work is required. Disruption of fish habitat has the potential to impair spawning, feeding and rearing of the resident fish community. Fish passage within the channel may also become temporarily restricted as a result of construction activities, disrupting migration patterns. • Short term, isolated dewatering to remove surface water from excavation areas may be necessary during the construction phase. If surface water dewatering is not managed properly, there is potential for impacts to occur to the associated watercourse. While many of the potential impacts are avoidable, if they are not managed through proper installation and by monitoring of mitigation measures, they may lead to significant damage to ecological features and consequently functions. 5.3.4 Social Considerations The replacement of the bridge would mean that Huron Road would be open on its existing alignment for the duration of construction. This would result in minimal disruption to roadway users. The original heritage Huron Road Bridge would be protected from any modifications, but will no longer act in its intended capacity as a part of the roadway system, and will gradually deteriorate and lose its heritage features. 6. Preliminary Preferred Alternative Three alternative scenarios have been identified to address issues related to the structural integrity of the Huron Road Bridge and four railing options. Each of the alternatives and railing options were evaluated according to criteria that examine economic, technical, environmental and social impacts of the alternatives. A qualitative rating scale is used to assess each of the evaluation criteria. An overall rating is then given to each criteria category to allow an alternative-to-alternative comparison of how well the criteria, and therefore the identified issues, are addressed. Table 6 contains a summary of the alternatives evaluated where the technical, economic, environmental and social criteria are weighted equally. Based on the evaluation the preferred alternative is the rehabilitation of the bridge structure with replacement railing option 3. Comparing alternative scenarios can be complex since the variation between alternatives and options may appear to be small, a sensitivity analysis of the evaluation is useful to determine if the anticipated evaluation recommendation will be consistent when emphasis on the individual criteria is altered. A sensitivity analysis of the evaluation is useful to determine if the anticipated evaluation recommendation will be consistent, when emphasis on an individual criteria is altered. The sensitivity analysis considered 5 scenarios: Evaluation Level 1-the technical, economic, environmental and social criterion are weighted equally; Evaluation Level 2 -the technical criterion for public safety is weighted to be twice as important as the hydraulic technical criteria and is equal to the economic, environmental and social criteria; Evaluation Level 3 -the economic criteria (Construction and Service Life costs) are weighted to be twice as important as the technical, environmental and social criteria; f~ ~ N N ~ N ~ ~ a O N ~ '~ Q 'a N i y e ~ ~ ~~ ~ L ,Y L L i ~_ a o Q ~ 0 J I o ~ ~ W ~ `~ 3 ; ~ +~+ ~ W vii a° ~ ~ L r ~~ >~ ~~ i I I~ I I~ ~ I~ ~ L ~ a~ ~~ ~~ .o ~ M ~ Q O C 0 ~ ±= ~M ~ ~ 0 N~ L ~ ~ N ~ >_ '' 6 N C C 0 ~~ +, 00 M i ~ O a ~~ C ~ 0 Q ~ N O ~ ~ > ~ L ~ G L Z M ~ 0 a° Y ~ I I I I ~ I ~ ~ ~ ~ ~ ~ o ~ ~ ~ N ~ O L N ~ o ~ ~ ~ 3 U m ~ ~ o a o _ ~ o ~ ~ c ~ ~ '~ a ~ U o > > ~ o > ~ ~ U ~ ~= ~ o Q . ~ c ~ O ~ ~ •L Q m ~ - C ~ ~ ~ O Q N ~= ~ N ~ U ~ C L '- ~. '~ ~ C ~ i= L ~ ~ > 0 ~ (B 0 U ~' ~ ~ N U m O ~_ 'L _ U U N Q N C N ~ U ~ ~~ ~ (a ~ N ~ ~~ N O N ~ O O O O ~ ~ ~ ~ +r C U U O U ~ p U +r +r N c6 N t6 ~ ~ ~ N }, to Q N Q EQ`~ O O W ~ (6 N N ~ (ate O ma c (~ p ~ ~ N ~ O ~ ~ N ~ ` W ~ •N ~ N U . N . L N ~ ~ o.~ ~ m ~ ~ O ~ ~ ~ ~ ~ ~ o~ s ~ ~~ ~ U _ ~ ~ m ~ (0 C O O L ~ C O ~ +r U N O ~ O ~ ~ N ~ N ~ +r ~ N ~ N p U ~ ~ ~ N Q ~ N ~ N ~ ~ ~ O ~ ~ ~ ~ 0 0 ~~ O ~ ~' ~, . ~ ~ ~ O ~ ~ • O (Q N ~ (~ N O 0 ~ ~ ~ .~ ~ ~ cn ~ p p J ~ U L[ ~ N ~ x ~ N ~ o ~ 0 C N ~ O ~ N ~, o ++ o U ~ c r .. N ~ ~ N ~, N ~ ~ ~ *'' N N ^ O N v *N'' ~ ~ .~ O ~ Ul ~ ~ ..., Nr ~ V p ~ Q ~ ~, o ~? N . . V ~ ~ ~ = V ~ ~ ,.~ ~ ~ N U ~ v G ~ ,~ ~ ;~ ~ ~ ~ ~ ~ N rv' _ N , ~ L ~ ~ L `/ a ~- ~ Q ~ Q ,U 0 ++ U , 0 L ++ ~ a.d ~ ~ 2 a U L ,~ ~ U , ~ L 2 A A ~ v N p a Y/ U O 0 U 0 w E .~ a` l0 D M N a N O N AECOM • Evaluation Level 4 -the environmental criterion is weighted to be twice as important as the economic, social and technical criteria; • Evaluation Level 5 -the social criteria (Property and Heritage impacts) is weighted to be twice as important as the economic, environmental and technical criteria; and • Evaluation Level 6 -the social criterion for heritage is weighted to be twice as important as the property technical criterion and is equal to the economic, environmental and technical criteria. 6.1 Preferred Alternative A sensitivity analysis comparing different value weightings considered 6 scenarios as indicated in Table 7 and reviewed in Figure 11. Each scenario compared Alternative 1, Alternative 2 with 4 different railing options and Alternative 3 for their technical, economic, environmental and social value. In all of the evaluations Alternative 2 -Railing Option 3 scores highest. Table 7 -Sensitivity Analysis Evaluation of Alternatives Weightings (%) Technical Economic Environmental Social Hydraulics Safety Property Heritage Evaluation 1 25% 25% 25% 25% Evaluation 2 11 % 22% 22% 22% 22% Evaluation 3 20% 40% 20% 20% Evaluation 4 20% 20% 40% 20% Evaluation 5 20% 20% 20% 40% Evaluation 6 22% 22% 22% 11 % 22% 5~ 4~] c ~ p 10 0 , ^ ~4it~rn~#lv~ 1 ^ iternat~r R~ilin~ ~pti~n ~ ~ ~il~ pti~n ~ter~~tiv~e - ~nlir~ Option 4 ~ ~ Ev~lu~tion Figure 1~: Alternative Evaluation- Sensitivity Analysis M 2012-04-23 Draft Prelim Evaluation Criteria 60237716.Doc AECOM 7. Conclusion Page 19 Memorandum April 24, 2012 The Huron Road Bridge has continued to deteriorate in recent years. A total of three alternatives including four railing options were evaluated against technical, economic, environmental and social criteria. Regardless of the importance weighting of the various criteria, rehabilitation of the structure is the preferred alternative to address the structures ongoing deterioration. In the evaluation of the railings, option 3 scores highest.