Baird. North Bay Waterfront Assessment Final Report. September 18, Navigating New Horizons. oceans. engineering.

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1 Baird oceans engineering lakes design rivers science watersheds construction North Bay Waterfront Assessment September 18, 2009 Navigating New Horizons

2 North Bay Waterfront Assessment Prepared for North Bay Mattawa Conservation Authority Prepared by Baird W.F. Baird & Associates Coastal Engineers Ltd. For further information please contact Derek Williamson at (613) Or This report was prepared by W.F. Baird & Associates Coastal Engineers Ltd. for the North Bay Mattawa Conservation Authority. The material in it reflects the judgment of Baird & Associates in light of the information available to them at the time of preparation. Any use which a Third Party makes of this report, or any reliance on decisions to be made based on it, are the responsibility of such Third Parties. Baird & Associates accepts no responsibility for damages, if any, suffered by any Third Party as a result of decisions made or actions based on this report. Navigating New Horizons

3 TABLE OF CONTENTS 1.0 INTRODUCTION DATA SOURCES Early Surveys Aerial Photography CHS Field Sheets Baird Survey, ENVIRONMENTAL CONDITIONS Water Levels Wave Conditions Erosion and Accretion Events SHORELINE COMPARISONS Methodology South of First Rocky Point Reach C First Rocky Point to Treatment Plant Reach B South of Marina Reach A North of Marina PROFILE COMPARIONS Methodology Reach D South of First Rocky Point Reach C Campbell Avenue Area Reach A Marathon Beach SEDIMENT MOVEMENT AND BALANCE Historical Evidence Sediment Transport Direction Shoreline Structures from Typical Beach Profiles Sediment Transport at the Government Wharf Marina Effects Retreat of a Profile Mitigation of Erosion North Bay Waterfront Assessment Table of Contents

4 7.0 CONCLUSIONS AND RECOMMENDATIONS Probable Causes of Erosion Recommended Approach REFERENCES Appendix A 1916 Shoreline Survey North Bay Waterfront Assessment Table of Contents

5 1.0 INTRODUCTION The waterfront of North Bay has undergone many changes over the years, with the most significant change taking place in the region of the City Marina and the lakefill to the south of this area. Development has taken place since the region was first settled in the late 1800 s and involved the construction of many homes and cottages along the lakeshore. The development of residential and commercial interests along the lakeshore transformed the previously dynamic shore of Lake Nipissing into a shoreline that can no longer adjust to storm events without some serious consequences to stakeholders. Figure 1.1 shows an example of limited beach width and various structures along the waterfront. Figure 1.1 Example Shoreline Conditions Along North Bay Waterfront (July, 2007) In the summer of 2007, Baird & Associates was asked to visit the waterfront and comment on the erosion that was occurring in some areas. The conclusion from this site visit was that some regions were experiencing persistent erosion, as was observed in an earlier study by Baird (1992). In order to better quantify the changes that have occurred to the area, Baird & Associates was retained to complete a more quantitative assessment of the changes that have occurred to the North Bay Waterfront. This comparison will be based on historic data from the region, in addition to a new survey of the waterfront. These data, combined with recent and historical aerial photographs will be used to better understand the condition of the North Bay waterfront. This report provides a brief history of the changes that have occurred along the waterfront, followed by comparisons of beach profile data and shoreline positions. A discussion of sediment transport along the shoreline is also provided, followed by a discussion of possible approaches to mitigate some of the problems that are occurring. North Bay Waterfront Assessment Page 1

6 This report uses a description of different shoreline reaches along the North Bay waterfront that are consistent with those that were used in the 1992 Baird report. These reaches were selected based on similar shoreline conditions and challenges faced by the stakeholders. Figure 1.2 shows the delineation of the different shoreline reaches. Figure 1.2 Definition of Shoreline Reaches A through F North Bay Waterfront Assessment Page 2

7 2.0 DATA SOURCES 2.1 Early Surveys The earliest surveys that we have obtained of the waterfront are from 1905 and were completed (presumably) to support the construction of the government wharf. Prior to this construction, there was a railway wharf that was built to the south of the present marina, as shown in Figure 2.1. This survey provides water depths in the region, although the vertical control for the survey is uncertain and requires some assumptions. Figure Survey of North Bay Waterfront (Public Works) One interesting fact is that this wharf had a large amount of sand accumulated around the structure, particularly on the south side of the structure. The next available survey was completed in October 1916 and covers the region from First Rocky Point to 1.5 Miles West of the Government Wharf. By this date, the CPR wharf is noted as abandoned, and the government wharf is shown in its initial state. Again, there is evidence of sand being moved from south by virtue of the accumulation to the south of the structure. A section of this survey is shown in Figure 2.2, while the complete survey is provided in Appendix A. North Bay Waterfront Assessment Page 3

8 N Figure 2.2 Part of Survey from 1916 (Public Works) This 1916 survey was used as one of the primary sources of data for comparisons. Two of the surveyor s benchmarks from 1916 (one on an island 650 m NW of the government wharf, and one at First Rocky Point) were located and used to determine a relationship between the vertical datum used in the 1916 survey and present benchmarks. 2.2 Aerial Photography Starting in 1928, there are a number of different sets of aerial photography available. These photographs are at different scales and cover different areas. A summary of the available aerial photographs is presented in Table 2.1. In order to make shoreline comparisons, it is necessary to spatially reference the images and then digitize a shoreline position. Some complicating factors include poor photograph scale, poor spatial reference opportunities (landmarks), different water levels, ice cover and different lighting conditions. Due to these challenges, the photographs were first screened to determine their usefulness, and then selected photographs were selected for further investigation. Table 2.1 Aerial Photograph Availability Date Image Type Scale Coverage Comment July 25, 1928 Aerial Photo 1:15, km of shore Lower quality than 1929 July 20, 1929 Aerial Photo 1:15,000 Full site Good shoreline definition but fewer landmarks for alignment Sept 25, 1948 Aerial Photo 1:24,000 Full site Poor scale, but good sandbar visibility Sept 11, 1950 Aerial Photo 1:12,000 Reach C to F Good scale, good shoreline def. Aug 23, 1952 Aerial Photo 1:18,600 Full site Poor scale, shoreline in shadow North Bay Waterfront Assessment Page 4

9 Aug 15, 1962 Aerial Photo 1:14,000 North of gov. wharf Limited area, otherwise good Apr 1, 1966 (?) Aerial Photo 1:18,000 Full Site Poor scale, some ice near shore June 2, 1967 Aerial Photo 1:22,200 Missing south end Good shore def., scale poor Apr. 26, 1974 Aerial Photo N/A Full Site Lake still frozen, not useful May 1980 Aerial Photo 1:22,000 Reach A to C Good shore def., scale poor Sept 19, 1994 Aerial Photo 1:20,000 Full Site Good shore def., scale poor May 9, 2008 Satellite Img. 0.7 m pixel Full Site QuickBird Satellite image 2.3 CHS Field Sheets Another primary source of data is bathymetric information from the Canadian Hydrographic Service (CHS). The CHS produces the navigation charts for the lake, and in support of these products, produces more detailed field sheets. Field sheets of Lake Nipissing are available from 1979, and cover the entire waterfront area. A greater level of detail is available in the region close to the government wharf, while the amount of data available further south becomes much less. Figure 2.3 shows an example of the some of the more detailed information in the region of the government wharf, while Figure 2.4 shows the lesser amount of detail available in regions further to the south. Figure 2.3 Detailed Field Sheet 8028 from 1979 Near Government Wharf (5 to 8 m between soundings) North Bay Waterfront Assessment Page 5

10 Figure 2.4 Field Sheet 8015 from 1979 Near Reach C (approx. 50+ m between soundings) Data collected for the field sheets is typically going to be biased towards the shallows in a region since the focus of these sheets is for navigation. For instance, if the field crew completing the survey locate a shoal or bar that could be dangerous to navigation, they are more likely to measure this feature than a deeper area. Therefore, one expects to see the top of bars appearing in surveys, rather than many measurements in the trough between bars. 2.4 Baird Survey, 2008 With the relatively complete survey information from the 1979 field sheets, particularly near the Government Wharf, the opportunity for more detailed comparisons exists in this area. To facilitate this, a hydrographic survey was completed in the summer of This provides a comparison over a period of 29 years and allows for some more quantitative results to be produced. The survey was completed by Baird staff in July/August 2008 using a single beam Knudsen 320B echosounder. Horizontal positioning was completed using a Trimble Pro XRS GPS system (using WAAS correction), which was linked into a laptop computer running the Hypack hydrographic surveying software. This survey involved the collection of data over the full study area, although with much greater surveying density in regions where quality historical data were present, or where persistent problems occur. Persistent higher winds towards the end of the survey period North Bay Waterfront Assessment Page 6

11 limited the amount of data that could be collected near the south end of the study area. However, the lower erosion rates and limited historical data made surveys in this area a lower priority. The hydrographic survey coverage was extended to the shoreline in regions that were too shallow for the echosounder, using land-based survey methods. Surveys were also completed using landbased survey equipment to define the elevations in regions such as Marathon beach. The coverage from the Baird survey is shown in Figure 2.5, while a close-up of the region near Reach C and Marathon Beach is provided in Figure 2.6. North Bay Waterfront Assessment Page 7

12 Figure 2.5 Baird Survey Coverage North Bay Waterfront Assessment Page 8

13 Figure 2.6 Close-up of Survey Coverage in Reach C and Marathon Beach Area North Bay Waterfront Assessment Page 9

14 3.0 ENVIRONMENTAL CONDITIONS 3.1 Water Levels Water levels are typically reported as an elevation above mean sea level, which can be a complicated measurement when considering historical data. Postglacial rebound of about 0.3 m per century means that a water level from one hundred years ago needs to be moved upwards by about 0.3 m to be representative of the water level today with respect to shoreline features around the lake (which would have moved up a similar amount). Early reports of water levels in Lake Nipissing must be treated cautiously since the accuracy of the vertical elevations was poor at this time. Reports from 1860 list the water level as perhaps a few feet lower than it is today, although this seems unlikely since the outflow from the lake is through rocky channels that are probably very stable. Better water level information starts to become available when the vertical datum was more accurately established to support the studies for the Georgian Bay Ship Canal in about Sparse information from Publics Works (1908) indicates water levels in the lake at m (about m in today's datum) in October This is lower than any other post 1933 October water level by about 0.4 m. Water levels in Lake Nipissing were uncontrolled until the first structures were built on the French River in 1907 (Landriault, 1980). Two timber crib dams (at Big Chaudiere and Little French) were soon found to be ineffective and by some reports had to be destroyed in 1909 to reduce flooding. These were replaced by larger structures with more capacity in 1916, which were built specifically to control the summer lake level. A third dam was built in 1950 for the purpose of further control on lake levels. Modifications were then made to the dam structures in 1962 to 1967 in order to allow greater flows to pass through the dams, likely as a result of flooding in The Landriault (1980) report proceeds to list a number of significant flood events that occurred along the North Bay waterfront, with two of the largest events being m in 1898 and in 1929 at m. Water levels on Lake Nipissing have been gauged since 1933 and were examined to look at the variability of the month means. Figure 3.1 shows the water levels from 1933 to The water level from August 1916 ( m) was obtained from the 1916 Public Works survey data. It is interesting to note that this water level is lower than any of the monthly mean water level from 1933 to 2005, with the lowest during this time being m. While this is only a comparison of a single daily water level with monthly means, but it does suggest that the water level is managed today to be somewhat higher in the late summer and fall in comparison to the past. The goal of control structures on water bodies such as Lake Nipissing is typically to reduce the overall range in the water levels by reducing the flood levels in the spring and preventing lows that are a problem for navigation. It is likely that the water levels that are presently maintained in late summer are higher then they would have been historically. The implications of this management approach is discussed later in this report. The average monthly water levels from 1933 to 2005 are shown in Figure 3.2. North Bay Waterfront Assessment Page 10

15 Water Level (m GSC +190) Max Mean Min Figure 3.1 Monthly Mean Water Levels from 1933 to 2005 Average Water Level (m GSC +190) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 3.2 Average Monthly Water Level from 1933 to 2005 There is evidence from historical records that lake levels prior to regulation may have been lower throughout much of the year and would have resulted in wider sandy beaches during this time. Supporting evidence for this hypothesis came from historical records and archaeological sites in the area. The wide sandy beaches from the 1905 survey also support this hypothesis. Furthermore, the dunes that are present along Reach C (presently with houses on top of them) must have been built by the wind at a time when there was more beach in front of the dunes. Exposed beach is required for the wind to be able to starting moving the sand landward and deposit it in the dunes. This could not have occurred with today s shoreline conditions. It is possible anthropogenic factors, North Bay Waterfront Assessment Page 11

16 such as shoreline hardening and sand mining have also reduced the amount of sand along the shoreline to build beaches. 3.2 Wave Conditions Waves on the lake are most severe during westerly winds although the erosive potential of these waves is greatly dependent on the water level at the time of the storm. There is no evidence that wave conditions over the past decades have changed substantially and therefore any erosion patterns are not likely due to changes in the wave conditions. 3.3 Erosion and Accretion Events The lakefront of North Bay features a fairly shallow sandy bottom that causes waves to break before they impact the shoreline. The amount of damage that occurs at the shoreline is therefore closely linked to the combined occurrence of waves and water levels. For this reason, high winds during the spring months are far more likely to create shoreline erosion than during the late fall when lake levels are lower. Long term erosion of the nearshore area must affect both the nearshore area, and the region further offshore. Large wave events during periods of low water may cause adjustments to the deeper sections of the shoreline profile, but have limited influence near the shoreline. During a high water level storm, the shoreline may be more seriously eroded, while the offshore regions are less affected. Accretion can occur as gentle waves tend to move the sand shoreward. However, if the water level is too high, this recovery process may not be able to move the sand that lies in deeper water. Accretion is typically associated with gentle swell waves, where the onshore component of the wave induced current is greater in magnitude than the offshore current. Falling lake levels, such as the annual drop from June to March, can also result in cross-shore profile adjustments and the onshore transport of sand (Baird, 2003; Hands, 1979). A preliminary site-specific investigation of sediment transport along the waterfront was completed using the sediment transport model COSMOS. COSMOS is a profile model that simulates the wave dynamics as they approach the shore, and determines the wave heights and sediment transport rates that occur over the various features in the profile. Site specific results from the COSMOS modeling are discussed in section 5 of this report. North Bay Waterfront Assessment Page 12

17 4.0 SHORELINE COMPARISONS 4.1 Methodology Shoreline comparisons were undertaken by importing historic and recent data into GIS. The most recent image was obtained from the QuickBird Satellite from 2008 and was received in a georeferenced format. Ground truthing was then completed to verify the position of various landmarks so that this image could serve as the primary position data source. Aerial photographs, surveys and CHS Field Sheets were then imported into GIS and aligned with the QuickBird image. This is relatively straight forward for the CHS Field sheets since latitude and longitude are marked on the sheets; however, for the early photographs and surveys, this is much more challenging. Landmarks such as the government wharf, streets, buildings and railways are used to align these images. One of the main challenges lies in the fact that good landmarks may be difficult to precisely define due to poor photograph scale, tree cover, deep shadows and numerous other factors. For the early surveys (1905 and 1916) the positions can be fairly accurately defined close to the government wharf, and are probably within two meters in this area. Further to the south, away from these more precise landmarks, the accuracy of the survey is likely within about 5 m, although it may locally exceed this. Aerial photographs are generally registered to an accuracy of about 3 to 5 meters. Again, accuracy is better in areas close to more defined landmarks such as the government wharf. An important question when evaluating shoreline change measurements is whether the erosion/accretion trend is greater than the combined positional accuracy of the historical and recent imagery (Zuzek et al, 2003). CHS Field Sheets are easily registered into the system, but suffer somewhat in certain areas since the scale is so large. The lines on the field sheets that depict the shoreline can be the equivalent of 3 m wide or more, so determining very precise shoreline positions can be a challenge. An additional complication in making shoreline comparisons is the varying water level during different surveys and photographs. A review of the aerial photographs revealed that all the useful images had water levels that were at m (CD +0.5) ±0.03 m. Therefore, the horizontal position of the shoreline was not adjusted to account for differences in lake levels. The 1916 survey had a much lower water level, noted as ft (in a different datum), which translates to m. Therefore, in addition to digitizing the waterline from the 1916 image, the 642 ft contour ( m in today s datum) was used to represent an equivalent shoreline. 4.2 South of First Rocky Point The region south of First Rocky Point, described as Reaches D through F in this report was assessed based on aerial photographs from 1929, 1950, 2008 and the CHS Field Sheet from Shoreline changes in this area were not significant and were within the range of the accuracy of the photograph. It is also important to consider that the photograph represents only one position in time as the beach responds to different wave events and continually moves back and forth. North Bay Waterfront Assessment Page 13

18 Additional survey data from 1916 did not cover this region. A plot of one section of the shoreline is provided in Figure 4.1. The stability at First Rocky Point is attributed to the exposed bedrock at the waterline and also re-affirms the accuracy of the shorelines in this region. In other words, large changes in shoreline position would not be expected. North Bay Waterfront Assessment Page 14

19 Figure 4.1 Limited Shoreline Changes in Reach D North Bay Waterfront Assessment Page 15

20 4.3 Reach C First Rocky Point to Treatment Plant Shoreline changes in the southern part of this area show a gradual recession of the shoreline over the past 92 years, as shown in Figure 4.2. The 1916 waterline is significantly further lakeward; however, this is partially due to the lower water at the time of this survey. If a water level equivalent with those that occur today is used, the resulting shoreline position differences are less. In some parts of this reach, the shoreline has changed by about 15 m since The majority of this change (about 10 m) appears to have taken place between the years of 1916 and 1929, with only a few meters change in the past 80 years. This translates into only a few centimetres a year, although with the uncertainty in the beach position from photographs, precise erosion rates cannot be stated. In the northern section of Reach C, as shown in Figure 4.3, the amount of shoreline change is much less. With the accuracy of the shoreline from old photographs and surveys, a definitive answer about continued shoreline erosion cannot be stated. However, given the degree of development along the shoreline and the elimination of the backbeach/dune environment due to home construction, it is seems unlikely this beach will recover or grow in the future. It appears that a narrow beach (at best) has existed for many decades at this site. North Bay Waterfront Assessment Page 16

21 Figure 4.2 South End of Reach C North Bay Waterfront Assessment Page 17

22 Figure 4.3 North End of Reach C North Bay Waterfront Assessment Page 18

23 4.4 Reach B South of Marina In the region south of the marina to the mouth of Chippewa Creek, there have been numerous manmade changes. These include the realignment of the creek mouth, the construction of the outfall from the treatment plant, and various adjustments to the shoreline in the form of lake fills. With all the man-made changes in this area, it is impossible to define natural changes to the shoreline or to establish if an erosion trend is present. Shoreline changes in this area are provided in Figure 4.4. North Bay Waterfront Assessment Page 19

24 Figure 4.4 Shoreline Changes in Reach B North Bay Waterfront Assessment Page 20

25 4.5 Reach A North of Marina The region of Marathon Beach has changed significantly over the years, with some erosion and accretion taking place. Figure 4.5 shows the shoreline changes in this area. The 1905 shoreline is similar to that which exists today, although this may have occurred at a lower water level, meaning that the effective regulated water level shoreline may have been further shoreward. The shoreline appeared to recede from 1916 to 1929 when the first aerial photograph is available. The severity of the erosion that appears to have taken place from 1916 to 1929 prompted a review of any specific events that could have contributed to this. Landriault (1980) makes reference to severe flooding in both 1928 and 1929 and shoreline property damage. In 1928 the flood level reached almost 197 m (possibly requiring adjustment upward for today s datum) and 1929 was only 30 cm below this. It is likely that these events may have caused some serious shoreline erosion, and resulted in the transport and deposition of sand in the offshore region. Furthermore, water levels from the time of the 1929 photograph are unknown since published monthly data did not start until This particular example of possible shoreline adjustment highlights some of the difficulties in making generalized conclusions from a snapshot of the shoreline position. Information about changes to the full beach profile (from back-beach to offshore depths) is often more useful for ascertaining long-term shoreline trends. By 1952, the shoreline has moved lakeward somewhat, but does not move more substantially lakeward until the 1979 survey. Additional beach width accreted from 1979 until 1992, with a slight increase from 1992 to Comparisons of the profiles in this area are discussed in Section 5. North Bay Waterfront Assessment Page 21

26 Figure 4.5 Shoreline Changes in Reach B North Bay Waterfront Assessment Page 22

27 5.0 PROFILE COMPARISONS 5.1 Methodology Profiles are used to make comparisons in regions where there is offshore data in addition to (or instead of) shoreline data. Profile comparisons can be more useful than comparing waterline positions from historical aerial photographs because they give an indication of changes to the full profile and provide more information about the overall sand balance in the region. Profiles were extracted in a number of locations according to where past and present information was available, as shown in Figure 5.1. The data in the profile includes the distance from an arbitrary start point, and the corresponding elevation relative to Chart Datum (195.4 m). Data sources from 1905 and 1916 were adjusted to today s datum to provide more appropriate comparisons. North Bay Waterfront Assessment Page 23

28 Figure 5.1 Locations of Profile Extraction Since the spacing of points in the area of interest can be very random and not co-linear, nearby points are applied to the profile line, provided that they are within a user-defined swath. For some data sets such as the 1979 field sheets (away from the Government Wharf), the sparse data can lead to some irregular looking profiles. Figure 5.2 shows an example of two 1979 field sheets and the 2008 survey data. In general, these profiles are similar; however, field sheet 3998 has more sparse data and has a more irregular looking profile. Factors such as the amount of detail in the data and horizontal positional error must be considered when drawing conclusions from the data. North Bay Waterfront Assessment Page 24

29 Figure 5.2 Comparison of Profile Through Sparse Data Sets Profile comparisons were completed in reaches A through D and are presented in the following sections. Many regions have a lack of good historical data, which makes reliable profile comparisons impossible. 5.2 Reach D South of First Rocky Point The region south of First Rocky Point has gentler slopes and a greater distance from the shore to the outer sand bar. Comparisons from 1979 and 2008 show similar profiles. In this instance we are assuming that the surveyors in 1979 measured the tops of the sand bars rather than the troughs. Given the variability in profiles extracted from the 1979 data set, we can only conclude that the profiles are similar from 1979 to North Bay Waterfront Assessment Page 25

30 Elevation (m CD) July Field Data 1979 (map 3998) Horizontal Distance (m) 5.3 Reach C Campbell Avenue Area Figure 5.3 Profile Comparison at Location 12 Profile 11 is in a location that has data from 2008, 1979 (two field sheets) and The 1979 information is extremely variable and is not included in Figure 5.4, which shows the 2008 and 1916 profiles. It appears that the 2008 profile may be slightly landward, with the location of the bars about 10 m further east. Exact positions are still questionable due to horizontal positioning error in the 1916 survey, but it appears there may be a slight shoreward migration of the bars. Bar elevations appear to be slightly higher today, which may be consistent with regulated, slightly higher lake levels. Profile 9, shown in Figure 5.5 also shows the 2008 profile being slightly further to the east. Elevations of the bars are very similar. North Bay Waterfront Assessment Page 26

31 Elevation (m CD) Field Data Horizontal Distance (m) Figure 5.4 Profile Comparison at Location and Elevation (m CD) Field Data Horizontal Distance (m) Figure 5.5 Profile Comparison at Location and North Bay Waterfront Assessment Page 27

32 5.4 Reach A Marathon Beach Profile 3a provided the best alignment between data sets in this area for making a comparison. The 1905 data seems to indicate the presence of some bars that are more pronounced in the pre-wharf survey than after construction of the wharf. The profile shows a general loss in volume from 1979 to 1992, although a slight gain in the profile from 1992 to These comparisons must be treated cautiously since they represent the volume of material at the south end of Reach A, but may not be indicative of the full length of the reach Elevation (m CD) Oct Field Data 1992 May Field Data 1979 (map 8028) Horizontal Distance (m) Figure 5.6 Profile Comparison at Location 3b 1905, 1979, 1992 and North Bay Waterfront Assessment Page 28

33 6.0 SEDIMENT MOVEMENT AND BALANCE 6.1 Historical Evidence The sandy shoreline that exists along the southern North Bay waterfront is a result of the glacial melt that moved through the Lake Nipissing region and into the Ottawa River about 7000 years ago. Throughout the North Bay and Ottawa River region, there are numerous sand and gravel deposits from large flows, deeper water and a great deal of sediment that was associated with glacial retreat. As water levels dropped and flows decreased, the sand deposits along the shore of Lake Nipissing were worked into dunes that are still evident today in regions such as Reach C. The important distinction is that the sand along the lake shore is primarily a historical deposit, and is not being continuously delivered in any significant quantity from rivers, streams, or erosion of the updrift shoreline, as is typical in the Great Lakes (Baird, 2007). The homes that exist throughout much of Reach C are built on what appears, based on our site observations, to be a sand dune. In many places there is evidence of the trough between the first line of dunes (with the beachfront homes) and the second row of dunes (with the homes on the street) Sediment Transport Direction Hydrographic surveys from 1905 and 1916 both indicate that there is some sediment transport from south to north at the site, based on the accumulated sand to the south of the structures and by the orientation of the mouth of Chippewa Creek (Figure 6.1). However, if there were some net movement from the south to the north, there would likely be larger beaches and some large depositional feature at the north end of the North Bay Waterfront. These features are not evident at the site. It is more likely that the sand accumulation shown in the surveys is a result of the local effect of the orientation of the CPR railway wharf and the protection offered by the southward extension of the government wharf. Both of these surveys were also carried out in August (from what we can determine) and thus the sand patterns may also be indicative of the wind and wave conditions during the summer months which are typically more southerly. Examination of aerial photographs from (for example) 1950, do not reveal any large sedimentation features that indicate a significant net transport of sand. Instead, much as we see today, the site consists of a series of pocket beaches that are separated by headlands near the shore. Further offshore, the sand is continuous and provides some linkage between the beaches, so that they are not completely independent of each other. Sediment transport clearly does occur at the site, but historical evidence and recent observations do not support a large net movement in either direction, as is typical on larger lakes or ocean beaches. North Bay Waterfront Assessment Page 29

34 Figure 6.1 Northward Orientation of Chippewa Creek Mouth (from 1916 survey) Shoreline Structures from 1916 Examination of the 1916 survey shows some interesting features in the region from Chippewa Creek to Charles Street. This stretch of shoreline has many shoreline defence structures such as concrete walls, timber walls, stone and wire breakwaters, groynes, and erosion areas noted between these features. Figure 6.2 shows selected parts of the 1916 survey that demonstrate these features. Figure 6.2A shows many small buildings close to the shore, fronted by timber walls. Figure 6.2B shows concrete walls that are lakeward of the eroding shore on either side, and possibly a damaged structure (dashed line). Figure 6.2C shows a schematic of the waterfront with seven 100 ft long groynes along the waterfront in addition to a brush breakwater. Figures 6.2 D and E show cross sections of various shore defence structures such as a groyne profile, a brush + wire breakwater and a stone + wire breakwater. This is clearly a region that is suffering from some severe erosion issues in A further consideration is that at this time, the lake levels were not regulated and were lower in the late summer and fall. Despite these unregulated lake levels, erosion still persisted and the residential properties were already at the waters edge versus well setback from the shoreline. North Bay Waterfront Assessment Page 30

35 Figure 6.2 Sections of the 1916 Shoreline Survey North Bay Waterfront Assessment Page 31

36 6.2 Typical Beach Profiles The beach profiles from different sections of the waterfront have a number of similarities. In most locations there are very distinct bar patterns that are evident from aerial photography. These bars are smaller and closer together close to the shore, while in an offshore direction culminate in a final bar that exists at an elevation of about 0.9 to 1.2 m relative to Chart Datum (CD, or m). From the 2008 survey completed by Baird, the position of the outer sandbar was identified through reaches C and D. The location of this bar, shown in Figure 6.3, is much closer to the shore throughout reach C, as compared to reach D. The bar alignment is essentially unchanged as it passes the feature at First Rocky Point, indicating that although First Rocky Point affects the beaches very close to the shore, the offshore sediment transport is unaffected by this shoreline feature. Figure 6.3 Location of Outer Bar from 2008 Survey Figure 6.4 shows two lakebed profiles from Reach C and Reach D, with the horizontal positions aligned to match the position of the first bar. Both profiles have very similar slopes in the deeper North Bay Waterfront Assessment Page 32

37 water and have the first offshore bar at an elevation of 1.15 m CD. However the barred profile in Reach C (where erosion is more persistent) has bars that are closer together and at a slightly steeper slope from one crest to the next. The steeper nearshore will allow more wave energy to approach the shoreline and may result in more erosion in an area such as this, especially during high lake levels. Figure 6.4 Comparison of Two Barred Beach Profiles A preliminary comparison of the level of protection offered by these two nearshore profiles was completed using the numerical model COSMOS. An eighteen hour storm was simulated over these two profiles and the change in the beach profile was documented. Figures 6.5 and 6.6 show the greater level of protection offered by Reach D s profile than that of Reach C. The total erosion on the beach was found to be many times higher on Reach C compared to Reach D. Note that these results are provided for comparison purposes only, and do not consider variables such as varied sand grain size along the profile, or longshore movement of the sand that could cause a readjustment of the profile. The important fact to note from this comparison is the greater level of erosion that takes place in the steeper nearshore profile compared to the flatter one. North Bay Waterfront Assessment Page 33

38 Line 12 Cross-shore Profile Adjustment for 18 Hour Storm from the West (max Hs=1.4 m, Tp=4.6s, wl=0.7m, profile=238 deg, 0.4 mm sand) Pre-storm Profile 3.0 Post-storm Profile 0.10 Depth below CD (m) Erosion/Accretion Trend Erosion (pos) / Accretion (neg) Trend (m) Distance (m) Figure 6.5 Erosion and Accretion from Sample Storm in Reach D Line 8 Cross-shore Profile Adjustment for 18 Hour Storm from the West (max Hs=1.4 m, Tp=4.6s, wl=0.7m, profile=238 deg, 0.4 mm sand) Pre-storm Profile 3.0 Post-storm Profile 0.10 Depth below CD (m) Erosion/Accretion Trend Erosion (pos) / Accretion (neg) Trend (m) Distance (m) Figure 6.6 Erosion and Accretion from Sample Storm in Reach C North Bay Waterfront Assessment Page 34

39 6.3 Sediment Transport at the Government Wharf The government wharf is a porous structure and therefore some sand moves through the structure today, and did so in the past before the marina was built. To examine the sediment transport patterns in this area, a sample storm was run along the profile (3b) to the north of the wharf for two different water levels. The resulting sediment transport patterns are shown in Figure 6.7. The wharf extends from approximately the 600 m to the 925 m mark the x-axis of Figure 6.7. Figure 6.7 Longshore Sediment Transport North of the Government Wharf The sediment transport patterns that are reflected in this figure are consistent with the pattern of sand deposition into the marina. The greatest amount of sediment transport is occurring in a water depth of about 1.5 meters. This information was compiled in a different manner in order to assess the percentage of sediment transport that occurs along the profile relative to water depth. Figure 6.8 shows the cumulative sediment transport, and indicates that only about 10 per cent of the sediment transport (for the fairly severe sample storm) occurs at depths deeper than 2.8 m. It should also be noted that the COSMOS model provides a 2D assessment of currents and sediment transport. In other words, the model assumes the updrift and downdrift shoreline feature a similar shoreline configuration. Locations that feature abrupt changes in shoreline orientation or a man-made structures, such as the wharf, can cause a difference in the sediment transport patterns. Therefore these results are only an approximation to the conditions at the site. North Bay Waterfront Assessment Page 35

40 Cum. Longshore Sed. Trans. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Water Depth (m) Figure 6.8 Cumulative Longshore Sediment Transport versus Water Depth for Sample Storm 6.4 Marina Effects When the marina was built in the early 1980 s, it created a barrier to sediment transport that did not exist in the past. The preliminary COSMOS sediment transport modeling north of the Government Wharf suggest that the majority of longshore sediment transport occurs between the 2.8 m depth contour and the shoreline for the beach slopes in the area and a severe storm event. For smaller storm events, the zone of sediment transport would be even closer to the shoreline. The outer limits of the wharf extend to a depth of approximately 3.7 m and has effectively sub-divided the shoreline into two sediment cells. To evaluate the degree of sediment exchange between these two cells requires the application of a 3D hydrodynamic model, which was beyond the scope of this investigation. However, the results presented in Figure 6.7 and 6.8 suggest the degree of sediment exchange is considerably less than the historical condition prior to the construction of the marina. When the marina was built, the dredging of the main basin resulted in a localized loss of material from within the confines of the marina basin. The porous structure (the Government Wharf) on the north side of the marina has subsequently allowed sand to migrate through the wharf and into the marina basin, where it was unable to escape. This resulted in a sediment sink, and periodic maintenance dredging to provide adequate navigation depths in the marina. The net effect of the porous structure on the north side of the marina has been the gradual loss of sediment into the marina basin from the adjacent beach and nearshore zone, which was observed by making comparisons of the 1979 and 1992 surveys of Marathon Beach. To the south of the marina, the sand was unable to be transported to the north due to the marina structures. Unlike the north side, the south structures are not porous to sand movement and there North Bay Waterfront Assessment Page 36

41 has not been a net loss of sand into the marina. To our knowledge there has been no maintenance dredging near the south side of the marina, which supports our conclusion that there is not a dominant northward transport of sediment along the North Bay waterfront. Therefore, the largest impact of the deposition and subsequent dredging of sand from the marina basin is the loss of material from Marathon Beach. Prior to the development of this shoreline, under natural conditions some of this material may have been transported further to the south and spread over a very large area. However, this small movement of sand of (for example) 6,000 m 2 spread over the nearshore of reaches C and D (Area = 150 X 4600 m) results in only about 1 cm in vertical bed change. Recent dredging operations in February 2007 along the northwest edge of the marina removed about 2060 m 3 of sand (2701 yds 3 ) since the previous dredging seven years earlier. Dredging previous to this took place in about 2000 and 1994, although records from these dredging operations are not readily available. Data from the period of 1979 to 1992 were obtained in the early 1990 s and were analysed to assess the amount of sand that was dredged from the marina. The conclusion from this study that a total of 2387 m 3 was dredged, over a duration of 8 years. These two data sources indicate that recent and earlier rates of sedimentation are 295 and 298 m 3 /yr respectively. These two estimates are in very close agreement and therefore, approximately of 300 m 3 /yr appears to be passing through the Government Wharf into the marina. A comparison of the profiles along Marathon Beach from this same period suggest that from 1979 to 1992 there was a loss of material of 4200 m 3 /yr, or about 320 m 3 /yr. Therefore this evidence supports the hypothesis that the sand moving into the marina and being removed is coming from Marathon Beach, and that the sand on Marathon Beach is not being replenished by some other natural source. Comparisons of profiles from 1992 to 2008 does not show the same decrease in the volume of material that is on Marathon Beach. The volume of material in 2008 was similar or slightly greater than that which was present in However, during the 1990 s the program of dredging that took place in the marina placed the sand back onto Marathon Beach, rather than removing it from the site. This practice was subsequently stopped due to concerns from the M.O.E. about taking material from the marina, which contained some organics, and placing it back on the beach. Therefore, a decrease of the amount of material on Marathon Beach during this time period is not expected. The recent dredging of material from the marina in the winter of 2007 hauled the material off-site. Therefore, a continuation of the loss of material from Marathon Beach may be anticipated, unless it is replaced naturally. 6.5 Retreat of a Profile Profile adjustments take place on a regular basis with each storm event. These adjustments could take place as sand moves along the shore in a more north-south direction, or in a cross-shore direction. Cross-shore profile adjustments could be changes in the position of bars, or localized erosion at the shoreline or against a seawall that deposits the sand just offshore. These fluctuations are normal and are different than a long-term erosion process which involves retreat of the nearshore profile. North Bay Waterfront Assessment Page 37

42 Long term erosion of a shoreline is typically a result of erosion of the entire profile, rather than just an adjustment of the more visible portion of the beach. Therefore, for a beach to complete a longterm adjustment in its position due to erosion, the entire profile must be moved shoreward by a similar amount. Based on the profiles that were measured in the area, the COSMOS simulations and other statistical relationships, the point of closure (depth to which sediment transport occurs) is estimated to be to about 1.7 m, although other methods may support a depth of closure much deeper than this. Therefore erosion of the shoreline would involve a change from about +1.0 m (assumed elevation of a revetment or seawall) to a depth of 1.7 m or deeper. Thus the volume of sand required to increase the width of beach by 1 m is 2.7 m 3, or perhaps double that value. With the very gentle average nearshore slopes in the range of 200:1, this extra 1 m of beach would be associated with less than 1 cm of sand, spread over 150 m or more. Due to the strong linkage between the different reaches of the lake, recession or accretion of the nearshore profile will be spread over a wide area, rather than affecting only one isolated area. It is reasonable to assume that if the marina were causing a loss of sand to the system, recession would take place in reaches C and D, totalling 4.6 km of shoreline. Therefore, it would take a loss of about m 3 of sand to change the nearshore beach position by 1 m in the horizontal. Note that this refers to a long-term trend in the erosion, rather than a longshore or cross-shore profile readjustment in response to one event. Prior to settlement of this shoreline, it is quite possible this portion of Lake Nipissing featured a small long term recession rate. The underlying bedrock would have been largely stable but the consolidated glacial material on top of the bedrock and the mobile sand deposits would erode under wave action, particularly during storms at high lake levels. Based on our experience with similar shorelines in the Great Lakes watershed, when residential properties and commercial development is constructed along an eroding shoreline, a collision between natural shore processes and a desire to sustain our economic investments occurs. This generally leads to the construction of shoreline protection structures, which further degrades the dynamic nature of the nearshore and beach zone. At North Bay, homes and shore protection structures are now constructed in the former dynamic beach environment and this profile cannot respond dynamically to erosion and accretion events. The shoreline protection structures also further starve the shoreline of new sediment through natural background erosion. The cumulative impact of all the development and structures is the disruption of natural shoreline processes and erosion will continue indefinitely. 6.6 Mitigation of Erosion Since the erosion taking place at the site is due to processes that will likely continue into the future, engineered approaches to reducing the effects of long term erosion may be considered. Note that these measures will not halt the long-term erosion processes, but will mitigate the effects. Typical coastal engineering approaches to protecting a shoreline are listed below, along with a discussion of the implications. North Bay Waterfront Assessment Page 38

43 Shoreline Armouring: Building revetments and seawalls has been done in many areas of the study area, and particularly in Reach C. These structures can be effective locally but are typically not what most homeowners want along their waterfront, since they inevitably result in the loss of a dynamic beach. Further, by reducing the long-term erosion rate and thus the delivery of new sand and gravel to the nearshore zone, the construction of a revetment will have negative impacts on the adjacent beaches. Costs are variable depending on the type of structure that is built. These structures should also be constructed to withstand the future erosion that may occur at the site (a deeper nearshore). Summary: Somewhat effective, but not aesthetically pleasing. Groynes: Groynes are shore perpendicular structures that trap sand that is moving along the shoreline, when the wind and waves are oblique to the shore. Figure 6.9 shows how groynes work in a region with a net sediment transport direction, which is not the case in North Bay. Examination of these structures along the waterfront demonstrates that in a region with little net longshore transport, these structures have limited effect. They may trap sand on one side, but at the same time result in a loss on the opposite side. Changing wave directions will alternate which side has the improvement versus the deterioration. They can sometimes be functional with specific other options (below). Also, unless these structures are pre-filled, they will trap nearshore sediment and have a negative impact on the overall regional sediment budget. Summary: Limited usefulness and may lead to downdrift impacts at the edge of the groyne field. Figure 6.9 Schematic Diagram of Groynes Beach Fill: Placing sand on the beach is commonly completed, but has a number of challenges. The amount of sand that would be required to change the shoreline position is prohibitive. Furthermore, the sand can be moved along the shoreline such that fill in one area could quickly be spread over several kilometres and have limited value where it was originally placed. This can somewhat overcome by placing sand that is much coarser (perhaps 1 to 3 mm in size) than the native sand, so that it is stable and will remain near the shore. Structures (such as groynes) may also be required to keep the larger material from distributing along the shoreline. Summary: Need coarser sand and structures. Offshore Breakwaters: Offshore breakwaters are shore parallel and reduce the amount of energy approaching the shore. Depending on the spacing of the breakwaters relative to their length, and their distance from the shore, different shoreline features may result. Figure North Bay Waterfront Assessment Page 39

44 6.10 shows a schematic of these structures. Their design is site specific and subtle differences in design can result in very different levels of protection. Along the North Bay waterfront these structures may be viable since the lakebed is gently sloped and the structures would be in shallow water (and less expensive). These structures should be combined with beach fill to create the beaches that are desired. Summary: Complex, but possibly successful. Navigation concerns would have to be mitigated. Figure 6.10 Schematic Diagram of Offshore Breakwaters T-Headed Groynes: These are a combination of groynes and offshore breakwaters, as shown in Figure 6.11, and combine some of the functionality of these two structures. The groyne component prevents movement of material along the shore, while the outer section provides added protection to the filled sand and the shoreline. These are typically more expensive structures and provide somewhat more protection than either groynes or offshore breakwaters alone. Summary: Need sand fill in combination with structures. Figure 6.11 Schematic Diagram of T-Headed Groynes North Bay Waterfront Assessment Page 40

45 Beach Widening: The large amount of sand in the offshore area may present the opportunity to dredge sand from the offshore and pump it onto the beach to widen the beach. Further study would have to be completed to evaluate this option. This is probably less expensive than trucking sand in from a more distant location. The drawback with this alternative is that the sand will have a tendency to erode back to its original profile. The rate at which this erosion takes place will be dependent on the combined occurrence of high water levels and high winds. The Department of Fisheries and Oceans (DFO) may also have concerns with this approach if there is seen to be a large amount of siltation or disturbance to the aquatic environment. The potential also exists to pump in some native sand and then cap it with coarser sand so as to extend the length of time that the beach remains in place. Summary: Probably also requires coarser sand for long term benefit. Remove the Hazard: Shoreline erosion is a natural process and contributes to the dynamic nature of the Lake Nipissing shoreline. If the erosion becomes too severe in the future or the cost to protect the residential properties too great, then the shoreline could be naturalized by removing the development and returning the riparian zone to public lands. North Bay is not in such a dire situation today to warrant these actions; however, options like this are considered and acted upon in more extreme cases such as some places on the Great Lakes. Summary: Not appropriate for North Bay waterfront. Considering the options for this site leads to the conclusions that beach fill would be required regardless of the structural approach (e.g. offshore breakwaters) to minimize downdrift impacts and maintain local beaches. Native sand could only be used if offshore structures were also placed; however, larger diameter sand and pebbles/cobbles would be more stable and possibly more successful. Groins could only be successful at this site if they were placed in combination with coarser sand than what is presently at the site. These groins would not work as conventional groynes that trap a net longshore transport of sand. They would effectively become ends to the beachfill and prevent migration of the coarser fill along the shoreline to other reaches. All of the options presented would result in significant alteration of the nearshore and beach zone of the North Bay waterfront. An extensive environmental assessment would be required to first consider all options and complete preliminary engineering designs. Then comprehensive environmental impact evaluations would be required for all options that altered the shoreline and nearshore below the high water mark. The implications of the following policies and legislation would have to be evaluated: Section 3.1 of the Provincial Policy Statement (Natural Hazards Section), MNR Public Lands Act, the Federal Fisheries Act and the Navigable Waters Protection Act. In particular, some of the works described in this section could involve a Harmful Alteration, Disruption of Destruction (HADD) of fish habitat (Federal Fisheries Act), and could involve additional studies and mitigation efforts. Furthermore, Ontario s Endanger Species Act (ESA, 2007) would have to be considered as there are presently 11 species, which could be impacted by some proposed works, that reside either in or along the shore of Lake Nipissing. In summary, extensive permitting would be required prior to construction of most types of engineered solutions. North Bay Waterfront Assessment Page 41

46 7.0 CONCLUSIONS AND RECOMMENDATIONS 7.1 Probable Causes of Erosion Erosion occurs along the waterfront of North Bay in both short term events related to major storms, and through long term processes. Long term erosion is visible through a comparison over many years or decades, and is difficult to accurately define due to data uncertainties from historical data. The most probable causes of erosion are as follows: Naturally occurring processes: The sediment along the waterfront of North Bay is mostly of glacial origin and was redistributed in the area as the lake was formed. There are no major sources of sediment at present. Some losses of sediment (offshore, onshore, etc.) occur in any system and it is possible that these sediments are not being replaced at the same rate. Bathymetric influences: The distance between the outer bar and the shoreline is much less in the region of Reach C, thereby offering Reach C less protection from waves. Without shore protection and without features such as First Rocky Point the shoreline would eventually move towards an alignment of Reaches C and D. In other words, erosion of Reach C and perhaps accretion of Reach D would result in a continuous shoreline. This would be a very long-term process, and would also be classified under the naturally occurring process item listed above. Armouring of the dunes and residential buildings: Along Reach C, the houses are built on what were once dunes along the lake. When natural erosion occurred in the past, these dunes would have provided sediment to the system, helping to reduce the erosion response. During calm periods, the dunes and beach could recover from erosion. Seawalls, riprap and houses have essentially replaced the dynamic beach and eliminated the potential for the profile to recover from erosion events. Changes in the lake levels: The lower late summer and fall water levels prior to regulation of Lake Nipissing would have had beneficial effects on the nearshore profile. Greater protection to the shore (from wider beaches) would occur at lower lake levels, and the lower lake levels may have allowed sediment to move onshore towards to the beach. Higher late-season water levels have reduced the potential for onshore sediment transport and may have increased the long term erosion rate. Losses to the marina: Sand dredged from the marina and disposed off-site is a net loss to the system in the region of Marathon Beach. However, the isolation of this sediment cell from the remainder of the North Bay waterfront (south of the marina) mean that potential impacts to the south are extremely limited. Even if this isolation did not exist, the shoreline recession due to the marina losses would be extremely small due to the length and width over which the change would have to take place (about one square kilometre or more). In summary, the construction of the marina probably has limited, if any impact on the erosion processes that are occurring in Reach C. A more significant problem has been the construction of residential and commercial/industrial developments in the dynamic beach zone along a shoreline that features a slow long-term recession rate. North Bay Waterfront Assessment Page 42

47 7.2 Recommended Approach Mitigation of the erosion problem along the waterfront does not involve changes to the marina or the manner in which material is removed from this location. This may eventually become a problem for Marathon Beach; however, this does not appear to be an imminent problem. The most likely method of implementing a successful shoreline stabilization program is through the placement of coarse sand, in addition to a number of coastal structures to help keep this sand in place. Solutions to the erosion problem along North Bay s waterfront would ideally be dealt with through a more regionally implemented solution rather than in a piece-by-piece approach by various property owners. For individual property owners, the only feasible solution is to construct revetments or seawalls that protect their property. However, this does not provide the type of waterfront that most property owners desire. Implementation of more complex schemes should be completed over a larger area, and it may also be cost prohibitive to complete the analyses and design for smaller projects. When considering a wider scale solution to the problem, an impact/cost/benefit analysis needs to be completed. The impacts of large scale engineering structures and a beach nourishment project would require an extensive environmental evaluation. While the benefits of a wider beach for residents to enjoy are difficult to quantify, this is an important part of the equation. Other benefits would include reducing the cost for future shore protection works and reduced damage to nearshore infrastructure. In some cases, it is also possible to incorporate habitat enhancements in the engineering structures. On a shoreline improvement project, the recipient of the benefit would include the waterfront home owner, but potentially also a much broader section of the population if a newly created public beach is used by nearby residents or people that may travel by car to get there. All of these benefits need to be assessed, in addition to how the cost may be distributed to different residents or stakeholders. If the impacts of the project cannot be mitigated, or the cost for implementing a wider scale solution is greater than the benefits, then the status quo of a problematic lakeshore with property-byproperty defences may be the only solution. In other words, there are solutions to the erosion problem at this site; however, the cost for these solutions may be beyond what most individual property owners would be willing to pay. In the future, a more holistic long-term planning approach for the North Bay waterfront should be adopted by all stakeholders to maximize the benefits of this resource. A long-term approach may include naturalizing the shoreline when it is too costly to protect the existing development from the erosion hazards. In the future, new shoreline development should be regulated away from the waters edge to avoid the development of similar problems. North Bay Waterfront Assessment Page 43

48 8.0 REFERENCES Baird, Fiscal Year 2001/2002, Flood and Erosion Prediction System for the Lake Michigan Potential Damages Study. Report Prepared for the U.S. Army Corps of Engineers Detroit District. Baird, Sustainable Management Strategy for Southeast Leamington. Report Prepared for the Essex Region Conservation Authority. Landriault, Joanne Past Flooding Occurrences in North Bay Lake Nipissing and Chippewa Creek. Report Prepared for the North Bay Mattawa Conservation Authority, May, Hands, E.B., Changes in Rates of Shore Retreat, Lake Michigan, USACE Coastal Engineering Research Center, Technical Paper No Zuzek, P.J., Nairn, R.B., and Thieme, S.J.., Spatial and Temporal Considerations for Calculating Shoreline Change Rates in the Great Lakes Basin. Journal of Coastal Research Special Edition 38, p North Bay Waterfront Assessment Page 44

49 APPENDIX A 1916 SHORELINE SURVEY North Bay Waterfront Assessment Page 45

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