Shoreplan Engineering Limited 55 Eglinton Avenue E., Suite 800 Toronto, ON Canada M4P 1G8 T) 416.487.4756 F) 416.487.5129 E) mail@shoreplan.com March 31, 2016 Mr. Ed English Senior Project Manager Waterfront Development Office City of Hamilton 77 James Street North, Suite 400 Hamilton, Ontario L8P 4Y5 Dear Sir: Re: Pier 8 Wave Overtopping Analysis (65 Guise Street East) Our File: 16-2377 We have completed our wave overtopping analysis for Pier 8 in Hamilton Harbour and have concluded that the overtopping that will occur during design conditions is significant, but manageable. We carried out separate analyses for the western, northern, and eastern pier walls, as described below. Figures 1 and 2, respectively, show a location plan and a site plan for Pier 8. The pier is exposed to waves generated with Hamilton Harbour. Shoreplan Engineering Limited was retained to complete a wave overtopping analysis for the western, northern, and eastern facing pier walls. The walls are constructed of steel-sheet piles with either a concrete or steel cap. Figure 3 shows current typical conditions along the east, west and north walls. The area landward of the walls can be generally characterized as hard paved and sloped to provide drainage back towards the harbour. Overtopping rates are related to the type of shore structure and the top elevation of the structure being overtopped. The site plan of Figure 2 shows elevations from two OLS surveys provided either by you or by the City of Hamilton on other recent projects. The wall caps are relatively flat but there is some variation in top elevation that is not visually obvious due to the length and overall uniform appearance of the paved areas landward of the walls. The top elevation along the west wall varies between 76.40 and 76.63 metres. The top elevation along the north wall varies between 76.46 and 76.67 metres, with lower area near the northwest corner of the pier. Elevations along the top of the east wall vary between 76.05 metres and 76.34 metres with the exception of the northeast corner of the pier where the elevation is 76.61 metres.
Our overtopping analysis was undertaken to define the extent of the flood hazard at this site, as required by the Hamilton Conservation Authority (HCA). HCA regulates development along the shoreline of their watershed through the administration of Ontario Regulation 161/06. Under provincial procedures flooding hazards along the shoreline of the Great Lakes should be assessed for wave uprush and overtopping associated with an approximately 20-year return period storm event occurring at the 100-year instantaneous water level. We also examined the 100-year storm event occurring at the 100-year water level as a design condition for the pier surface adjacent to the walls. Under their planning and regulation policies and guidelines, HCA has adopted a water level of 76.0 m IGLD for the flood level, which is the 100- year instantaneous water level. Design wave conditions were determined using the CMS-Wave spectral wave numerical model developed by the U.S. Army Corps of Engineers. An extreme value analysis of annual maxima wind speeds measured at Hamilton Airport provided input wind conditions to the CMS-Wave model. Design wave conditions along the western and northern wall were uniform along the length of the wall. Conditions varied along the eastern wall due to the sheltering provided by the entrance to Haida basin. Waves diffract into the basin after passing through the narrower entrance and the diffraction effect produces lower wave heights along the eastern wall of Pier 8. Table 1 Design Wave Heights for Overtopping Analysis Design Wave Height (m) 25 yr 100 yr west wall 0.76 0.80 north wall, oblique waves 1.15 1.25 north wall, perpendicular waves 0.91 0.98 east wall 0.78 1.15 0.83 1.25 Two different wave conditions were considered for the north wall as the highest waves, which originate from a north-easterly direction, strike the wall at an angle of approximately 30 degrees. Waves striking perpendicular to a wall produce higher overtopping flows for a given wave height, so the smaller perpendicular waves were also examined in case they produced more overtopping than the bigger oblique waves.. Figure 4 is a wave height contour and vector plot showing design wave conditions during a File 2377, 2016-03-31 2
northeasterly wind. The diffraction effect that produces varying wave heights along the east pier wall can be seen in Figure 4. Under the conditions described above, significant wave overtopping will occur. The overtopping waves will flood some distance inland due to the very gently sloped, paved backshore. There are no accurate and practical means of estimating the extent of inland flooding when this level of overtopping occurs on such a flat backshore. Overtopping rates for the three walls were estimated using the methods described in the Overtopping Manual (EurOtop, Wave Overtopping of Sea Defences and Related Structures: Assessment Manual, Environmental Agency UK, Expertise Netwerk Waterkeren, NL, KFKI, DE, August 2007.). This manual is considered to represent state-of-the-art procedures for estimating overtopping of coastal structures. Figure 5 shows mean overtopping rates in litres per second per metre length of wall, for the west and north walls which have uniform wave conditions along the length of the walls. That figure shows the overtopping rate as a function of the top of wall elevation, which varies slightly along the walls. Assuming an average top elevation of 76.5 metres for the west wall and 76.6 metres for the north wall would give mean overtopping rates of 23 and 50 l/s/s during the 20-year event, and 27 and 60 l/s/m during the 100-year event, for the west and north walls, respectively. Figure 6 shows overtopping rates for the 20-year and 100-year wave condition for the east face of Pier 8. That figure shows the mean overtopping rate as a function of the distance along the wall, measured from the northeast corner of the pier. There is a much greater variation in overtopping rates along the length of the wall due to both the greater differences in elevation along the top of the wall and the change in design wave height along the wall associated with the greater sheltering at the south end of the wall. One section, approximately 45 to 60m south of the north face of the pier, has a top of wall elevation of approximately 76.05m, which is only 0.05m above the design water level for this analysis. Overtopping rates at that location will be approximately 125 and 140 l/s/m during the 20-year and 100-year conditions, respectively. As noted above, the 20-year event is considered when assessing the flood hazard. Overtopping rates of 20 to 125 l/s/m are significant and extensive flooding of the areas immediately adjacent to the walls should be expected. Although it is not certain to what extent that overtopping water will flow inland under existing conditions, it can be reasonably concluded that it will flow into areas where development will be proposed. Therefore, the solution is to manage the overtopping flow as part of the site design. File 2377, 2016-03-31 3
The most practical means of managing the overtopping flow is through the use of a low secondary wall located back from the water s edge, combined with site grading. The wall would have to be at least 6 metres back from the edge of the pier to allow maintenance access to the face of the pier walls. The secondary wall location and height are subject to detailed design, but as general guidance, on the north pier face we would expect that a wall located 6m back from the face would need to be in the order of 0.4 to 0.5m high to manage the mean overtopping rate of 40 to 60 l/s/m. A secondary wall located 6m back from the west pier face would be expected to be in the order of 0.2 to 0.3m high to manage the 20 to 30 l/s/m mean overtopping rate that would be expected there. If a uniform height wall were to be constructed 6m back from the east pier face it would probably need to be in the order of 0.6m high to deal with the 125 l/s/m overtopping rate where the wall is lowest. Each of those wall heights could be reduced somewhat by locating them further back from the pier face. The area between the pier face and the secondary wall should be hard paved in order to withstand the overtopping that occurs during the 100-year event. The overtopping manual notes that mean overtopping rates in the order of 50 l/s/m will damage vegetated or lightly protected surfaces One alternative to a secondary wall would be to construct a low berm as part of a landscaping feature, but that berm would likely need to be constructed more than 6m back from the north pier face in order to withstand the forces of the overtopping water. The location and shape/composition of the berm is a design detail, but as general guidance we would expect that a berm would have to be at least 10m back from the north wall. A berm 6m back from the west wall might be feasible. A berm is not likely to be practical or feasible for the higher overtopping areas on the east wall. Another alternative would be to modify the crest of the concrete cap when maintenance or replacement of the seawalls is undertaken in the future. Increasing the wall crest elevation and possibly also incorporating a wave return or bullnose could significantly reduce overtopping volumes. Such modifications would need to be associated with appropriate drainage design in the back shore. Even small crest elevation changes in the order of 0.2 to 0.3 m can notably reduce the wave overtopping rate. To summarize the above, Figures 5 and 6 show mean overtopping rates under design conditions for the west, north, and east faces of Pier 8. Due to the flat nature of the hard-paved top of the pier, there are no means of accurately and practically estimating how far inland that overtopping water will flow. Instead, the overtopping water should be managed, most practically File 2377, 2016-03-31 4
with the use of secondary walls located some distance back from the face of the pier, combined with site grading. The location and height of those walls is subject to detailed design but we have provided some estimated wall heights for general guidance. Landscaped berms located further back from the wall face or modifications to the wall crest during future maintenance could also be considered. We trust that this letter provides a sufficient description of the overtopping related flood risks at this site. Please feel free to contact us if you have any questions. Yours truly, Shoreplan Engineering Limited Bruce Pinchin, P. Eng. File 2377, 2016-03-31 5
Scale 1:5000 Hamilton Harbour Pier 8 Figure 1 Location Plan
Legend: Elevations based on survey by MacKay, MacKay & Peters Limited (November 5, 2013) Elevations by on drawings by S. Llewellyn & Associates Limited Figure 2 Scale 1:1500 Hamilton Harbour Pier 8 Site Plan
Figure 3 Existing Conditions (March 2016) File 2377, 2016-03-31 8
Figure 4 20-Year Return Period Wave Height Contours and Vectors, Northeast Winds File 2377, 2016-03-31 9
Figure 5 80 Wave Overtopping Rates for the North and West Walls Mean Overtopping Rate (l/s/m) 70 60 50 40 30 20 10 0 76.35 76.40 76.45 76.50 76.55 76.60 76.65 76.70 76.75 Top of Wall Elevation (m) north wall (100yr) north wall (20 yr) west wall (100yr) west wall (20yr) Figure 6 160 Wave Overtopping Rates for the East Wall Mean Overtopping Rate (l/s/m) 140 120 100 80 60 40 20 0 0 25 50 75 100 125 150 Distance Along the Wall, Measured from Northeast Corner (m) 20 yr wave 100 yr wave File 2377, 2016-03-31 10