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09 - Port Burwell Coastal Processes Sedimentation & Dredging Review
Final Report Port Burwell Coastal Processes, Sedimentation and Dredging Review Municipality of Bayham prepared by Shoreplan Engineering Limited March 2010 SHnREPLAN March 31, 2010 Mr. Kyle Kruger Administrator Municipality of Bayham 92344 Plank Road, Box 160 Straffordville ON NOJ 1 YO Dear Sir: RE: Port Burwell Harbour Sedimentation Our File: 09 - 1250 We are pleased to provide this final report presenting our review of the coastal processes, sedimentation patterns and dredging options at Port Burwell Harbour. We thank you for the opportunity to work on this project and would be pleased to provide any further services that you may require. Yours truly, Shoreplan Engineering Limited e. PJ �. d�' -'� Bruce Pinchin, P.Eng. PA. PINChIIN ,rye Mar 31, 2010 q k;*4,,, �I6NFOIE OF O Shoreplan Engineering Limited 55 Eglinton Avenue E., Suite 800 Toronto, ON Canada M4P 1 G8 T) 416.487.4756 F) 416.487.5129 E) mail@shoreplan.com SHnREPLAN Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 EXECUTIVE SUMMARY Port Burwell has been experiencing an ongoing sedimentation problem since its original construction in the 1830's. The original east and west pier extensions, the west extension wall and the armour stone breakwater were all constructed to mitigate the sedimentation problem. There are two primary causes: the sediment load coming down Big Otter Creek and the coastal processes acting on the nearshore deposit of sand immediately in front of the entrance piers. Structural solutions were considered as a means of reducing the annual dredging requirements. We determined that there are no practical structural solutions to the portion of sedimentation at the harbour entrance that is due to coastal processes. Extending the armour stone breakwater will not affect the processes acting on the existing harbour deposit. The cost of extending the entrance piers and the likelihood of obtaining approvals for the required volume of infill makes that solution impractical. A potential structural solution for sedimentation within the creek and the portion of the harbour not affected by wave action would be to narrow the channel width by filling. Decreasing the channel cross section will increase the flow velocities, causing a greater amount of the sand to be transported through the harbour. In order for this solution to be effective the channel would have to be narrowed over the entire length of the creek and harbour wherever an increased depth is required. Sand that passes through the narrowed channel will still have to be managed as it exits the harbour. An appropriate channel width or volume fill required cannot be estimated without more detailed analyses. For comparative purposes we estimated that a 20 metre wide channel would require filling in approximately 56% of the existing area. Obtaining approvals for this amount of infilling could be a significant obstacle to overcome. Potential impacts such as potential upstream flooding, ice jams and environmental concerns would need to be studied in greater detail before this type of solution could be seriously considered. An alternative structural solution for the inner harbour would be to construct a sediment trap. This would reduce the dredging area by increasing the channel depth over the area of the trap. The trap must be regularly emptied of sediment to be effective. A sediment trap could potentially be located in the vicinity of the turning basin but the location and size of the sediment trap are dependent on the characteristics of the sediment to be trapped and would require further analysis. Due to the limitations of the structural solutions the best solution to the sedimentation problem at Port Burwell is going to require some type of an on-going dredging operation. To assess the dredging alternatives we have assumed that the average annual dredging requirements will be in the order of 15,000 to 30,000 cubic metres. The uncertainty of that estimate has not been quantified. Sand within Big Otter Creek and the harbour must be removed as part of the dredging operation. Propeller wash dredging could be used to push a channel through the bar outside the entrance piers without actually removing that sand. Hydraulic dredging is generally the most cost effective method when sand must be removed from a problem SmnR _ Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 area. If open water disposal near the harbour is an option, then hydraulic dredging of the bar outside the entrance might be cost effective compared to propeller washing. Two types of small hydraulic dredges might be suitable for use at Port Burwell; a small manned cutter section dredge and a remotely controlled agitation dredge. The remotely controlled agitation dredge requires a cable stayed system to operate and that could be a significant disadvantage here. If open water disposal is not permitted then de -watering the dredgate in a land based settling basin will probably be required. That is not expected to be cost effective compared to propeller washing the bar outside the entrance, but it may still be effective for dredging within the harbour as that material must be removed, not just pushed aside. The size of the settling basin required to accomplish hydraulic dredging of the harbour area is related to the physical characteristics of the dredged material as well as the flow rate of the dredged slurry. That information is not available at this time. While it is generally preferred that dredged material be returned to the littoral cell due to the importance of its role in coastal processes that may not be the case at Port Burwell. If the sand causing the sedimentation problem is the size of sub -littoral drift it can probably be removed from the littoral system without impacting downdrift coastal processes. From an operational point of view, the beach updrift of the armour stone breakwater could be a good location for disposing of hydraulically dredged sand. The technical feasibility of placing the dredgate there would need to be confirmed with a detailed sediment transport pathways analysis. The potential environmental and sociological impacts of this type of operation would need to be studied in detail and negotiated with affected stakeholders and approving agencies. The timing that dredging can actually take place will play a major role in determining whether or not a long-term dredging program is feasible for Port Burwell. In -water work is typically restricted from mid March until early to mid July but approximately 45% of the Big Otter Creek sediment load occurs, on average, during March and April. The use of a sediment trap and over -dredging during the allowable working window could be one possible solution to a timing conflict. This report presents a qualitative assessment of the sedimentation problem and possible mitigation measures. It does not include an assessment of potential impacts or necessary approvals. Quantified information has been included only to provide order of magnitude information. It is based on rough assumptions and should be confirmed before any critical decisions are made. The measures discussed in this report will cost more than has been spent on dredging in recent years and likely cost more than has been budgeted for future dredging. Notwithstanding budgetary considerations, this report presents an assessment of long- term maintenance dredging needs at Port Burwell that is as realistic as possible given the limited data available. Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 TABLE OF CONTENTS TRANSMITTAL EXECUTIVE SUMMARY................................................................................................... i TABLE OF CONTENTS....................................................................................................iii LISTOF TABLES............................................................................................................. iv LISTOF FIGURES........................................................................................................... iv 1. INTRODUCTION...................................................................................................1 2. PORT BURWELL SEDIMENTATION AND DREDGING HISTORY......................2 2.1. Harbour Expansion and Sedimentation History.........................................2 2.2. Dredging History........................................................................................5 3. OVERVIEW OF THE SEDIMENTATION PROBLEM at PORT BURWELL ..........7 4. MITIGATION ALTERNATIVES...........................................................................10 4.1. Structural Solutions.................................................................................10 4.1.1. Big Otter Creek Modifications.....................................................10 4.1.2. Entrance Structure Modifications................................................13 4.1.3. Existing Breakwater Modifications..............................................14 4.2. Dredging Considerations.........................................................................14 4.2.1. Small Manned Dredges..............................................................16 4.2.2. Remote Controlled Mini Dredges................................................17 4.2.3. Discharge Options......................................................................18 4.2.4. Timing......................................................................................... 20 4.3. Potential Impacts..................................................................................... 20 4.4. Financial Implications..............................................................................20 5. FURTHER ANALYSIS.........................................................................................21 6. SUMMARY..........................................................................................................22 7. CONCLUSIONS.................................................................................................. 26 References...................................................................................................................... 27 SbCIRE , Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 LIST OF TABLES Table 3.1 Entrance Channel Volumes..............................................................................9 LIST OF FIGURES Figure1 Site Plan............................................................................................................29 Figure 2 Contours from June 1999 Sounding Survey....................................................30 Figure 3 Contours from August 2003 Sounding Survey ................................................. 31 Figure 4 Location of WSC Calton Gauge....................................................................... 32 Figure 5 Big Otter Creek Total Daily Sediment Load at WSC Calton Gauge ................ 32 Figure 6 Daily Distribution of Total Sediment Load........................................................33 Figure 7 Turning Basin Area Filled in 1992.................................................................... 33 Figure 8 Outline of 2000 Proposed Dredge Area........................................................... 34 Figure 9 1999 and 2003 Profiles at Harbour Entrance...................................................35 Figure 10 Possible Sediment Trap Locations................................................................ 36 Figure 11 Concept Design for Wheatley Harbour..........................................................37 Figure 12 Rotomoite 6000 Hydraulic Dredge................................................................. 38 Figure 13 Piranha Pumps Mini-Dredge..........................................................................38 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 1. INTRODUCTION Shoreplan Engineering Limited was retained by the Municipality of Bayham to carry out a review of siltation patterns and dredging options at the Port Burwell harbour. The purpose of this study was to conduct a qualitative assessment of the existing sedimentation problem and to investigate potential structural modifications to the harbour entrance to alleviate the high maintenance dredging requirements. Our assessment is based on existing information collected from local accounts, government records and past studies. We did not carry out any new analyses of the coastal conditions or river hydraulics and sediment loads. Port Burwell is located on the north central shore of Lake Erie at the outlet of the Big Otter Creek. The harbour area was originally developed in the mid 1800's and various expansions took place until the early 1930's. Figure 1 presents a site plan of the harbour area as depicted on the 1983 Ontario Base Maps. Site conditions have changed somewhat since 1983 with the biggest differences being the position of the beach east of the harbour and partial filling of the turning basin of the inner harbour. SHnREPILAN Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 2. PORT BURWELL SEDIMENTATION AND DREDGING HISTORY Port Burwell has experienced an ongoing sedimentation problem since its original construction. This section provides a brief history of the sedimentation and past dredging activities at the harbour. The information presented here was obtained from a combination of sources including maintenance files kept by Small Craft Harbours Branch; discussions held with Mr. Larry Martin, a retired commercial fisherman with knowledge of the local history; and reports prepared as part of a major study of coastal processes at Port Burwell. The coastal processes studies were carried out in support of the defense of a legal claim initiated by a group of landowners to the east. 2.1. Harbour Expansion and Sedimentation History It has been recognized since 1830 that the projection of piers from the north -central shoreline of Lake Erie results in the rapid accretion of beaches and shoals and sedimentation of the entrance. Furthermore, the response of harbour engineers to this phenomenon has, from the beginning, been to extend the jetties, from time to time, to prevent the harbour entrances from being engulfed. Each such extension increased the capacity of the structure to accumulate sediment. The fillet beach updrift of the pier and the bypassing shoal that forms along and beyond the end of the pier are collectively referred to as the harbour deposit. The original harbour structures at Port Burwell were constructed in the 1830's and until 1903 they were approximately the size of the structures currently found at Port Bruce, a community approximately 17 kilometers west of Port Burwell. A major expansion of the harbour structures was initiated in 1911 and progressed as a series of extensions. The last extension was the construction of the armourstone breakwater as it is found today. That work was completed in 1930. As part of his analysis of the harbour deposits at Ports Bruce, Stanley, and Burwell, Philpott (1983a) concluded that the Port Burwell structures were fully bypassing littoral sediments in 1896. It was found that although piers had been present since about 1830, relatively little deposition had occurred up to 1896. The harbour deposit at Port Burwell was relatively small prior to the 1911 pier extensions. It was estimated that by 1979, which was the end year of the harbour deposit analysis period, the total volume of the harbour deposit at Port Burwell was in the order of 44 million cubic metres. The submerged part of the deposit extended over 3 km out from the shore and about 8 km alongshore. The alongshore distance includes a tongue which projected to the southeast about 3.5 km beyond the end of the breakwater. Of the total volume of the deposit 40%, nearly 17 million cubic metres, was in the tongue to the east of the line of the breakwater. Philpott (1983a) concluded that the littoral sediment was bypassing the harbour but it was not possible to determine what percentage was bypassing and what percentage was adding to the harbour deposit. Local accounts note that while there used to be deep water east of the pier that area has now shallowed significantly for a distance in the order of 1 mile (1.6 km). During Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 westerly and southwesterly storms a large gyre forms to the east side of the harbour due to the alongshore current deflection caused by the armour stone breakwater. The gyre extends more than a kilometer to the east and deposition is still taking place within the area covered by the gyre. It was also noted than when the harbour entrance was dredged to the seaway depth in the 1960's, freighters used to turn around in the area adjacent to and east of the west extension wall (see Figure 1). That area has now filled such that the depth is less than 1 metre. At the same time there was approximately 2 metres of water on the west side of the west extension wall. That area is now part of the subaerial beach fronting the Provincial Park. Alongshore sediment transport rates on the north shore of Lake Erie are supply limited. The supply of sediment to the nearshore zone is less than that which could be transported by the available wave energy. When this is the case, alongshore transport rates are estimated through a sediment budget, an accounting of the sediment sources and sinks within the nearshore zone. Philpott (1983b) prepared a very detailed sediment budget covering the north central shore of Lake Erie, from Rondeau to Long Point, as part of the 1983 Port Burwell shoreline damage litigation. For a sediment budget the shoreline is divided into a number of segments or reaches and the sediment sources and sinks of each segment are determined. The volumetric differences between these sources and sinks are assumed to be transported alongshore. The net alongshore sediment transport rate at any point is found by summing the alongshore transport rates from all shoreline segments updrift of that point The Philpott (1983b) sediment budget grouped all grain sizes of sediment entering the nearshore zone into one of four size categories; shingle, littoral drift, sub -littoral drift, and washload. The grain size categories were determined on the basis of the behaviour of that size of material once it enters the nearshore zone. Shingle consists of gravel and pebble which, under most conditions, remain close to the toe of the bluff or to the face of a beach. Littoral drift consists of coarse to medium sand which generally remains within or close to the normal breaker zone. This is the main beach building material for the beaches found on Lake Erie. Sub -littoral drift consists of fine and very fine sand which is transported beyond the normal breaker zone. It is deposited during periods of high lake level and transported alongshore at lower lake levels. This material may contribute to, but does not alone form, beaches. Washload consists of silt and clay particles which are too fine to remain permanently in the nearshore zone and are eventually lost to deep water at the centre of the lake. Reviewing the Philpott (1983b) sediment budget data for 1936 to 1977, we estimated the average annual alongshore supply of littoral and sub -littoral sediments at Port Burwell to be approximately 450,000 cubic metres per year. That assumes that the Port Stanley breakwater is essentially bypassing littoral and sub -littoral sediments. Philpott (1983a) estimated that the Port Burwell harbour deposit volume was increasing at an average annual rate of approximately 700,000 cubic metres per year from 1941 to 1979. That rate is about 50 % higher than the estimated alongshore supply rate for littoral and sub- littoral sediment, indicating that there are other sediment sources. The Big Otter Creek sediment load accounts for some of that. As part of a Levels of Service Review carried out in 2006, the Canadian Coast Guard noted "The deepest known draft of vessels using this harbour is between five and six SmnP t. Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 feet. These vessels literally plough and dredge their way through the sand bottom in the approach area to get in and out of the harbour. The deepest draft that can safely navigate in the entrance of this harbour on a calm day in early summer is about two feet. Area boaters with local knowledge and taking extra cautions may be able to transit with deeper draft vessels safely. Later in the season when water levels fall or when wind negatively affects the water levels, even these vessels may have trouble." During the late 1970's and early 1980's the Village of Port Burwell operated a hydraulic dredge as part of an entrance dredging program. During one operation sand was removed from the entrance and placed on the shoreline east of the east pier in order to increase the size of the beach. It is reported that shortly after the beach nourishment was finished, a southeasterly storm moved most of the sand back in front of the harbour entrance, essentially undoing the dredging work. Figures 2 and 3 show contour plots developed from 1999 and 2003 sounding surveys of the entrance area superimposed on 2006 aerial photographs supplied by the Municipality. The surveys were undertaken by the Canadian Hydrographic Service. The areas contoured on Figures 2 and 3 are limited to the areas covered by the respective sounding surveys. The 1993 survey only extended as far north as the south end of the turning basin. The 2003 survey extended beyond the harbour area, to a point just north of the bridge. The contours show bottom elevations at or near chart datum adjacent to the harbour entrance. The deposition is so severe that the littoral sediment transport processes near the harbour entrance are similar to those on a fully developed beach. While the piers were originally extended out to a depth of almost 8 metres the system now responds as if they had been extended just beyond the waterline on a beach. A significant proportion of the sedimentation that takes places within the harbour itself is due to sand transported down Big Otter Creek. The Long Point Region Conservation Authority reports that the Big Otter Creek is the biggest source of fluvial sediment on the north shore of Lake Erie. Almost half of the annual sediment load occurs during March and April. It was noted that after last year's spring freshet, deposits of sand 6 to 8 inches deep could be observed on top of the grass within the creek's floodplain south of the bridge where the normal bank had been overtopped Historical suspended sediment concentration and total load data was obtained for Big Otter Creek from the Water Survey of Canada (WSC) station upstream at Calton. Figure 4 shows the location of the WSC Calton gauge relative to Port Burwell. The gauge site is approximately 17 kilometers upstream of Port Burwell so the WSC sediment data will underestimate the actual sediment loads that reach the harbour area. For the period of available data (1976 to 1996) it was found that the long-term average daily load was 410 tonnes. Annual loads ranged from a minimum of 35,000 tonnes in 1989 to a maximum of 258,000 tonnes in 1982, with a mean of 149,000 tonnes. Figure 5 shows a plot of the daily total load values from 1976 to 1996. It can be seen that the loading is very episodic and not evenly distributed throughout the year. Figure 6 shows the daily distribution of the total sediment load for the data available. This plot shows that the highest loading occurs in March and April (approximately 45% of the annual total). The base loading is relatively low from May to October with about 25% of the total load occurring during that 6 month period. It then increases during November and SbnQE . ", 4 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 December with about 10% of the annual load occurring in each of those months. Individual peaks are likely associated with distinct rainfall events. Aquafor Beech (1996) reviewed available sediment distribution data from the WSC Calton station and estimated that approximately 25-30% of the suspended sediment being transported down Big Otter Creek was sand and the remaining 70-75% was composed of fine silts and clays. For a rough approximation it is not unreasonable to estimate that most of the sand but only a small amount of the silt and clay transported to Port Burwell will contribute to the sedimentation problem. If we account for 75 to 95% of the sand and 5 to 20% of the silt and clay load measured at Calton, Ignore the contribution of sediment eroded between Calton and Port Burwell and neglect possible bedload, that gives approximately 30,000 to 60,000 tonnes of sediment per year (15,000 to 30,000 cubic metres), over the long-term average. That could be a low range of estimates as sediment is probably also introduced downstream of the Calton gauge site. Possible contributions of bedload transport at the gauge site were not quantified. 2.2. Dredging History Dredging has been required at Port Burwell for almost as long as the harbour has operated. Small Craft Harbours' (SCH) expenditure book shows an expenditure that "includes dredging" for the 1876-1877 fiscal year. As part of his analysis of the harbour deposits, Philpott 1983a estimated that by 1979 more than six million cubic metres of sediment had been dredged from the entrance to Port Burwell. Up until the 1960's the Port Burwell was essentially a heavy duty port for industrial and commercial shipments and a "seaway" depth of 22 feet below datum (6.7 metres) was maintained at the entrance and in the harbour. By 1970 the commercial traffic had reduced to the point that a decision was made to relocate the existing commercial traffic to Port Stanley because of the high cost of the maintenance dredging. A 1977 review by Public Works Canada showed that from 1900 to 1970 an average rate in excess of 100,000 cubic metres per year of sediment had to be dredged in order to maintain the 6.7 metre seaway depth. It was also estimated that approximately 50,000 cubic metres of dredging would be required to maintain an entrance depth of 10 feet with a harbour depth of 8 feet (3.0 and 2.4 metres, respectively). Those shallower depths were based on use changes since 1970. It was estimated that the annual cost of carrying out that dredging would be $260,000. In 1977 the Village of Port Burwell agreed to take over future dredging of the harbour and entrance and was provided a grant to assist in the purchase of a 10" cutter suction dredge. By 1979 the Village had concluded that the effort required to carry out that dredging was beyond their means and they requested that the Federal Government resume responsibility for the dredging. In 1984 the Village formally notified the government that they could no longer carry out the recurring dredging. Various modest dredging efforts were undertaken in the years following with the most recent dredging taking place in 2009. Dredging was planned for 2005 but not carried out because the tendered costs were far higher than had been estimated. The last dredging prior to that was carried out 1999 and 2000. Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 In 1992 the harbour area was dredged with a dragline and dredgate was placed within the "turning basin" area of the harbour. The turning basin had already filled in significantly since the seaway depth dredging had stopped, and the area was described as marshy. Dredgate was placed up to an elevation equal to the top of the west pier wall, effectively narrowing the width of the channel past the turning basin. This was done to reduce the channel cross-section and consequently increase the natural channel depth in the absence of further dredging. When asked if it had lead to a long-term deeper channel we were told that it certainly didn't hurt, but most people believe the channel should have been narrowed further. Figure 7 shows the location of the turning basin and the narrowed channel. The outlined fill area in Figure 7 is approximately 1.3 hectares (3.2 acres) in size. The 1999 dredging was completed using propeller washing lakeward of the piers and a dragline within the harbour entrance. The area dredged by the dragline was adjacent to the west pier (as labeled on Figure 1) Approximately 6,400 cubic metres of sand were removed from an area starting at the south end of the west pier, extending approximately 130 metres northward and 15 metres out from the pier. The dredgate was initially stockpiled and dried on the land adjacent to the west pier, and then trucked away. It is our understanding that this dredging was carried out as one of the conditions of a real estate transfer and was intended to improve access into what is known as the "gas company" property. The propeller washing extended out from the ends of the piers in a southeasterly direction. An anchored work boat was used to excavate a trench with the washing action of its modified propeller. The results of the propeller wash dredging can be seen on the contour plot of Figure 2. The following year Talisman Energy Inc carried out additional dredging to improve access to the dock wall along the edge of their property. Figure 8 shows an outline of a trench where it was estimated that approximately 27,000 cubic metres would be removed by dredging to a depth of about 3 metres. We do not know the extent of the trench actually dredged but the description of what was done is consistent with the proposed program. All of the dredging was performed using a long-arm excavator. Sand excavated from between the east and west piers was stockpiled on the land adjacent to the wall, dried and removed. Excavation beyond the ends of the piers was accomplished by building a "road" out of the dredged sand and extending it along the edge of the trench as work progressed south. That sand was placed in the shallows west of the trench, between the trench and the west extension wall. This "open -water" placement is known as side casting and is no longer readily approved if it is viewed as infilling fish habitat. The trench visible in Figure 3 is probably the remains of the trench excavated in 2000. No additional formal dredging was carried out until 2009. Some propeller washing was done by the larger boats using the harbour but this was done on an informal basis. In 2009 the work boat used in the 1999 propeller washing was again used to cut a channel out beyond the east pier. The amount of dredging done was limited by budget so the sand was just pushed out of the way to make the channel. The moved sand was left in piles rather than being fanned out. SmnPE Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 3. OVERVIEW OF THE SEDIMENTATION PROBLEM at PORT BURWELL Port Burwell experiences a high sedimentation rate because of the ready supply of sand material near the harbour. Sediment is supplied by both littoral transport (Lake Erie shoreline) and Big Otter Creek. It was noted in Section 2.1 that Big Otter Creek has been cited as being the largest single source of fluvial sediment on the north shore of Lake Erie. Our rough estimates suggest that in the order of 15 to 30 thousand cubic metres per year of fine sediment (mostly sand) from the creek could be deposited in the harbour and entrance. That estimate is based on total sediment load data derived from suspended sediment concentration measurements upstream of Port Burwell. Possible contributions of bedload transport at the measurement site were not quantified. Water depths in Big Otter Creek and within the harbour, but north of the entrance, appear to be the result of equilibrium conditions for the channel cross-sections, the long- term flow rates and the sediment supply rate. Changes in the water depth can be seen in locations where those conditions have changed. For example, a depositional zone can be seen near the north end of the turning basin in Figure 3. That deposition is most likely caused by a decrease in the flow velocity associated with an increase in the channel cross-sectional area. Sand that is suspended in the water column at higher flow velocities settles out when the velocity decreases. Figure 3 also shows two locations on the creek with localized increases in depth. One is one the outer edge of the bend in the creek north of the harbour area. That increase in depth is associated with scour along the base of the steel pile wall where flow velocities are increased due to the bend. The second location is the "hole" a short distance south of the bridge. The reason for that hole is not known for certain, but there is a reasonable chance that it the result of a scour hole caused by an ice jam during the spring breakup. We were told about an ice jam that caused a 15 foot scour hole in that location. The year that occurred was not known for certain, but it was around 2003. Sedimentation between the piers but close to the entrance is likely caused by both fluvial and littoral processes. Under certain wave conditions sediment from the shoal in front of the entrance will be pushed up the entrance channel. The distance that sand will get transported is a function of water level, wave conditions and creek flow rate. The direct cause of sedimentation just outside the harbour entrance is wave induced sediment transport that occurs mostly during southerly through to easterly wind conditions. Westerly and southwesterly winds produce the waves that cause the net transport of sediment to Port Burwell but they are expected to be less significant at the actual harbour entrance due to the sheltering of the armour stone breakwater. It would take a detailed wave and sediment transport analysis to determine which wave conditions cause the greatest transport, but that knowledge is not required for this qualitative assessment. It was noted in Section 2.1 that the area offshore of the pier ends and the west extension wall has filled in significantly since dredging to the seaway depth was stopped. If dredging were to completely cease at Port Burwell the infilling would continue until the sand deposit was at equilibrium with the long-term average sediment supply rates and Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 zone of influence of the breakwater. Anecdotal evidence that the water depth east of the entrance is still shallowing suggests that equilibrium has not yet been reached. Figure 9 shows representative profiles near at the harbour entrance derived from the 1999 and 2003 sounding data presented previously (see Figures 2 and 3). The dashed line portions of the profiles represent the assumed bottom slope extrapolated from the surveyed data. The key map included in Figure 9 shows the location of the profile line at the harbour entrance. The first 130 metres of the profile are located between the east and west piers. Figure 9 also shows the range of typical mean monthly water levels and cut lines for two different dredging depths. The range of water levels represents the long-term average high and low mean monthly water levels on Lake Erie. Actual water levels at any time may be higher or lower than the range shown on Figure 9 due to annual differences from the long-term mean and due to shorter duration water level fluctuations caused by wind and waves. Dredge depths of 7 feet (2.1m) and 10 feet (3.0m) were selected for Figure 9 as those represent the typical depths considered in the most recent dredging projects. The dredge cut lines were positioned to give desired draft at the low long-term mean monthly water level of 174.0 m IGLD, which is 0.5 metres above chart datum. Approximate entrance channel volumes were calculated assuming a 15 metre wide channel and the typical cross-sections shown in Figure 9. Channel volumes for the portions of the profile between the piers and beyond the piers are shown in Table 1. These are rough approximations of the channel volume that would need to be dredged but are appropriate for a qualitative assessment of dredging requirements. We did not carry out any site specific sediment transport calculations but it is our expectation that any channel excavated through the existing sand deposit at the entrance is likely to be filled back in within a relatively short time period. Absent any flushing associated with the Big Otter Creek outflow, we would expect a 7 to 10 foot deep channel to fill back in over the course of 1 or 2 average years. A severe easterly storm with a return period in the order of 5 to 10 years could have the potential to fill the channel back in during the course of the storm. Whether creek outflow would increase a channel's sustainability because of scouring action of the flow or would decrease its sustainability because of the creek sediment load cannot be estimated without a more detailed analysis. It is known that the creek outflow can cause noticeable changes to the creek bed and to the lake bed near the harbour entrance. It is reported that noticeably deeper water can sometimes be found along the edges of the piers due to scour. An ice jam during the 2009 spring flooding caused the scouring of a hole 18 feet deep "about half way up" the west pier. The depth at that location is reported now to be about 5 feet. Figure 2.1 shows an approximately 2.5 metre deep hole near the end of the east pier in 2003. The causes of that hole are not known but outflow scour and wave reflections from the east pier are real possibilities. Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 Table 1 Entrance Channel Volumes Channel Volumes (m) 1999 survey 2003 survey average 1999 & 2003 Dredged channel for 7 foot draft between piers 1,500 700 1,100 outside piers 3,100 2,500 2,800 total volume 4,600 3,200 3,900 Dredged channel for 10 foot draft between piers 3,300 2,500 2,900 outside piers 7,800 7,000 7,400 total volume 11,100 9,400 10,200 SMnREPLAN Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 4. MITIGATION ALTERNATIVES This section of the report discusses mitigation alternatives that could be applied to the sedimentation problem at Port Burwell. We examine both dredging alternatives and possible structural modifications that could be implemented to decrease the dredging requirements. Our review of dredging alternatives is limited as the objective of our study was to consider potential modifications to the harbour entrance structures. 4.1. Structural Solutions As noted in Section 3, there are two main sources of sediment that are contributing to the problems at Port Burwell; silt and fine sand transported down the Big Otter Creek and littoral drift moved along the shore of Lake Erie. Different structural solutions would be required to deal with each sediment source. 4.1.1. Big Otter Creek Modifications In section 3 we noted that the water depths in Big Otter Creek and most of the harbour area appear to be the result of equilibrium conditions for the channel cross-sections, the long-term flow rates and the sediment supply rate. Within the context of this study we must assume that changing the long-term flow and sediment supply rates are not an option. That leaves changing the channel cross-section as the only structural solution to the sedimentation caused by Big Otter Creek. We have considered two methods for modifying the channel cross section: 1) narrowing the channel through the entire problem area, and 2) constructing a sediment trap by deepening the channel near the turning basin. Each of those methods is discussed separately below. Narrowing the Channel Narrowing a channel to increase the flow velocity and hence the sediment carrying capacity of the flow is a "standard" solution to sedimentation problems in an open channel. The purpose of narrowing the channel is to cause or maintain the transport of sand that is currently depositing on the creek bed. That sand can be transported as either bedload or suspended sediment. The flow rates required to keep the sand moving is a function of the grain size of the sand that is to be transported. That in turn will be related to both the size of the material currently on the creek bed as well as the sand supplied from upstream. It is assumed that silt and clay will mostly remain in suspension throughout the harbour area and will settle within the lake. In order for this solution to be effective the channel would have to be narrowed over the entire length of the creek and harbour where an increased depth is required. SwnF?E 10 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 Determining an appropriate channel width requires a level of analysis well beyond the scope of this study. However, as a rough approximation we can examine the channel section near the bend in the creek above the turning basin. Measuring from the 2006 orthophotos we can see that the narrowest part of the creek south of the bridge is just south of the bend and has a width of approximately 27 metres. At the middle of the bend where scouring occurs along the base of the steel pile wall, sedimentation appears to be taking place on the inside of the curve. Accounting for that sedimentation the effective channel width appears to be in the order of 20 metres. A starting point for an analysis of a reduced channel width could therefore be a width of 20 metres. This estimate is made without any actual cross-sections, flow information or site specific sediment load data. The centre line length of Big Otter Creek from the bridge to the end of the piers is approximately 1,100 metres. A 20 metre wide channel would therefore occupy a surface area of 22,000 square metres. From the 2006 orthophotos the existing creek and harbour area over that length was estimated to be approximately 50,000 square metres. Narrowing the creek to a width of 20 metres would therefore require filling approximately 28,000 square metres (2.8 hectares or 6.9 acres), or 56% of the existing area. The volume of fill required to accomplish that cannot be estimated without cross-sectional data. It is reasonable to assume a narrowed channel will have its new banks protected against erosion. The most cost effective means of doing this would be to line the bank with rip - rap. Depending upon the fill material used to narrow the creek, a geotextile material could be required beneath the rip -rap. For the purpose of this report (qualitative not quantitative assessment) we have assumed that bank protection would need to be 4 metres high, only 1 bank would require protection (due to existing walls) and could be protected with a 60 cm thick layer of rip rap with underlying geotextile. The cost of the bank protection would be in the order of $400,000 to $500,000. The cost of placing the fill required to narrow the creek would be in addition to this. It must be noted that the above discussion is provided as part of a qualitative assessment and the numbers presented can only be viewed as having order of magnitude accuracy. The quantities and costs were estimated to provide some context to the discussion but should not be relied upon for any critical decision making. A more detailed analysis with site specific data would be required to prepare proper quantity and cost estimates even at a concept level of analysis. It must also be noted that there are potential major impacts associated with this type of work including the environmental aspects of filling a creek, such as terrestrial and aquatic habitat impacts, the potential for upstream flooding and the potential for increased ice jamming. Each of these potential impacts would need to be studied in greater detail before this type of solution could be seriously considered. Obtaining approvals for this amount of infilling could be a significant obstacle to overcome. Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 Constructing a Sediment Trap A sediment trap is used to remove excess bedload from a river, stream or creek. When combined with a change in channel cross section designed to induce settlement it can also be used to remove suspended settlement. In order to function properly a sediment trap must be regularly "emptied" by removing the sediment that has accumulated. For Port Burwell we have assumed that removal would be accomplished by dredging the trap area. More complex sediment traps with diversion channels can be constructed to allow the trap to be cleaned with earth moving equipment. If a sediment trap is given serious consideration for this site then different methods of clearing the trap should be investigated. The location and dimensions of the area to be used for the trap would depend upon the size of the particles that need to be trapped and their primary mode of transport. If only bedload needs to be trapped then the sediment trap could be smaller than one designed to trap what is suspended load at the upstream end of the trap. If suspended sediment must also be trapped then the sediment trap has to have appropriate dimensions that allow the targeted grain sizes to settle out of suspension as the flow passes through the trap. Different sizes of sand have different settling velocities so the trap dimensions are dependent upon the sediment and hydraulic characteristics of the creek. A detailed flow and sediment transport analysis would be required to determine this information. The main advantage of a sediment trap at this site is that it defines a fixed area for dredging. For example, if it were to be determined that only bedload needed to be removed from the creek then it might be possible to create a sediment trap by using a crane mounted slurry pump at one or two fixed locations along the harbour wall. A settling pond would need to be constructed to deal with the slurry pumped out of the harbour. A sediment trap could be constructed by dredging within the turning basin where deposition has already been noted (see Section 3). For example we have developed two concept locations for a sediment trap, as shown in Figure 10. Each of those traps has an area of approximately 15,000 square metres (1.5 hectares). For an average annual sediment load of 15,000 to 30,000 cubic metres per year (as discussed in Section 2.1) a depth of 1 to 2 metres, respectively, would need to be removed from the trap each year. The trap at the north end of the turning basin (left side of Figure 10) is positioned over the area where it appears that sedimentation already takes place. Placing the trap here will produce greater water depths further up the channel than will be achieved by the southerly trap, but it is not expected to improve conditions as far north as the marina. It is also possible that sediment that is not trapped could still cause depositional problems downstream of the trap. That possibility cannot be assessed without additional details of the creek hydrology and sediment characteristics. The south end of the trap on the right hand side of Figure 10 is positioned at the south end of the turning basin. The "width" of the south end of the trap area shown is 20 metres, which is the same width considered for the channel narrowing option discussed above. Narrowing the entrance channel from the south end of the sediment trap to the SwnF?E RP �_.A nrl 12 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 end of the piers in conjunction with the sediment trap might provide a positive benefit in terms of extending the life of any channel dredged through the sand bar outside the ends of the pier. Again, that is something that would need to be determined as part of a more detailed analysis. 4.1.2. Entrance Structure Modifications The standard solutions for reducing sedimentation at a harbour inlet are to either mechanically bypass the sediment or to extend the entrance structures out to deeper water. Bypassing requires dredging and is therefore covered by the discussion in Section 4.2. Extending the entrance structures out to deeper water is a structural solution and is discussed here. The current breakwater configuration at Port Burwell is the end result of a number of extensions intended to deal with the sedimentation problem at the harbour entrance. However, extending a pier or breakwater on a coast with a net supply of littoral drift is neither a permanent nor sustainable solution. It is short-term solution that merely buys time as the updrift beach extends lakeward until it is feeding the harbour bypassing shoal. The history of the harbour modifications at Port Burwell demonstrates this quite effectively. It is our opinion that neither extending the armourstone breakwater nor extending the entrance piers out to deeper water is a practical solution. Extending the armourstone breakwater would alter the overall bypassing characteristics at the site for a period of time, but would have no beneficial impact on the large volume of sand that has already been deposited within the outer harbour. It is that existing deposit that is causing the sedimentation problem at the entrance to the inner harbour. Extending the entrance piers out beyond the existing sediment deposit would buy some time but the cost of that extension would be prohibitive. Both piers would have to be extended due to the volume of sand that currently exists. It can be seen from the profiles in Figure 9 that the piers would have to be extended approximately 425 metres in order to reach a water depth of 3 metres. That represents the minimum distance required to eliminate the need for dredging today if it can be assumed that the 2003 profile still applies. They would have to be extended further to achieve any future benefit. An alternative layout was also considered whereby the east pier would be extended out to near the end of the west extension wall, and then parallel piers would be extended out to the 3 metre contour. Due to the length of the parallel piers required to reach the 3 metre contour this alternative would actually require a total pier length greater than that of the first alternative considered. This alternative would also require an extensive amount of dredging between the extended east pier and the existing west extension wall. We have not carried out any concept designs or cost estimates for an extension of the Port Burwell piers, but the results of a concept design prepared for Wheatley Harbour SHnRE� l� r, ''>' 13 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 could be considered for an order of magnitude comparison. Shoreplan (2003) considered a number of structural solutions for an ongoing serious sedimentation problem at Wheatley Harbour on Lake Erie. One of those solutions was to construct a new armour stone breakwater to connect an existing offshore breakwater to one of the harbour piers. Figure 11 shows a concept plan and typical section for that solution. That breakwater section was estimated to have a unit cost of $8,300 per lineal metre in 2003. Assuming a similar unit cost would apply at Port Burwell today, extending 2 piers a distance of 425 metres each would cost in the order of $7 million. As actual costs are likely to be higher today and a 400 metre extension would not really be sufficient, this option is not considered to be realistic. It must therefore be concluded that there is no practical structural solution to the component of the Port Burwell sedimentation problem that is associated with coastal processes outside the harbour. 4.1.3. Existing Breakwater Modifications It is our understanding that a suggestion has been made that removing a portion of the existing armour stone breakwater near the shoreline would lessen the entrance sedimentation by allowing a current to flow past the entrance. This would not be an effective solution because the breakwater interrupts the alongshore transport of littoral sediments. It is true that sediment is bypassing the breakwater but a far greater volume of sand would be transported in front of the entrance if the armour stone breakwater was not present. Removing part of the breakwater would essentially allow the updrift beach to be transported into the gap in the breakwater until it was plugged. 4.2. Dredging Considerations As noted in Section 3, there are two main sources of sediment that are contributing to the problems at Port Burwell; silt and fine sand transported down the Big Otter Creek and littoral drift moved along the shore of Lake Erie. In Section 4.1 it is noted that there are no practical structural solutions to lessen the dredging requirements. Two structural solutions are presented for dealing with the creek sedimentation although the sediment trap alternative will only work as part of an ongoing dredging operation. The alternative to narrow the creek may be technically feasible with respect to sediment transport and deposition but implementing that solution has potential major implications that have not been examined as part of this study. It is therefore reasonable to conclude that the best solution to the sedimentation problem at Port Burwell will involve some sort of on-going dredging operation. Given the sedimentation and dredging history of this site it is fair to conclude that the most important consideration to any on-going dredging operation will be the financing of that operation. A key goal should be to determine the most cost effective dredging method that can be implemented here, and to then dredge a large a volume as can be �amnF?E14 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 achieved with the available funding. There are a number of dredging methods that can and have been used at Port Burwell. Each of these methods has its own pros and cons and cost is only one of those considerations. The most recent dredging practices at Port Burwell (summarized in Section 2.2) have involved the land excavation of sand from within the harbour and propeller wash dredging beyond the harbour. One of the differences in these dredging methods is that the land based dredging removes the sediment from the problem area whereas the propeller wash dredging pushes it out of the way but does not remove it. Propeller washing is a form of hydrodynamic dredging frequently used on the Great Lakes. Van Raalte and Bray (1999) define hydrodynamic dredging as the deliberate (re)suspension of the fine fraction of sediment from the lake/riverbed with the aim of removing this material from the dredging area using natural processes for transportation. The water column itself is used as the primary transport medium for the dredged material, instead of pipes, barges or hoppers, as with conventional hydraulic and mechanical dredging techniques. Propeller wash dredging typically uses a modified work boat with a spud or other anchoring system to keep the boat in place while dredging, and a modified propeller and/or an adjustable "beaver -tail" to deflect the propeller turbulence as desired. Hydrodynamic dredging is most effective when there are significant ambient currents present to remove the suspended sediment from the dredged area. When conditions are right the suspended material itself will establish a density current that transports the sediment away from the dredging site. Propeller wash dredging is used frequently at Grand Bend on Lake Huron, typically about 40 times per season. That operator reports that once he is able to get a flow going he is able to move the sand about 50 metres if he has a place to move it to. It is most easily moved "downhill" to deeper water, particularly if a there is a hole to fill. He has described his dredging operation as moving the bar offshore. One of the main advantages of propeller wash dredging is that it is a relatively low cost dredging method in terms of cost per unit volume of material moved. One of the main disadvantages is that by only moving the sediment away from the immediate area dredged it is susceptible to being moved back into the dredged channel by natural coastal processes. That in turn necessitates its repeated removal, effectively increasing the cost of dredging because the material must be handled more than once. At Grand Bend it is not uncommon to have sand that was moved out of the entrance be blown back in during the next storm. It is likely that the possibly of having to dredge the same material repeatedly would not be a major disadvantage at Port Burwell because of the volume of sand already near the entrance. Any channel dredged through the sand deposit is expected to fill in relatively quickly. Whether sand dredged from the channel is completely removed from the area or is merely pushed aside by propeller washing, the channel will still fill in. It may fill in more rapidly if the propeller washed dredgate is in close proximity to the channel, but the difference in infilling rates is not expected to be significant. Based on reviews of dredging issues at other sites on the Great Lakes it is our experience that hydraulic dredging is generally the most cost effective method, on a unit SHnQE_ 15 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 price basis, when sand must be removed from a problem area. The cheapest method of hydraulic dredging is when open water disposal of the dredgate is permitted. Whether or not open water disposal of the Port Burwell sediments might be permitted is beyond the scope of this assessment. If open water disposal near the harbour is an option, then hydraulic dredging of the bar outside the entrance might be cost effective compared to propeller washing. If open water disposal is not permitted then de -watering the dredgate in a land based settling basin will probably be required. That is not expected to be cost effective compared to propeller washing the bar outside the entrance, but it may still be effective for dredging within the harbour as that material must be removed, not just pushed aside. The size of the settling basin required to accomplish hydraulic dredging of the harbour area is related to the physical characteristics of the dredged material as well as the flow rate of the dredged slurry. That information is not available at this time. For our assessment of dredging methods we assumed that the long-term average dredging requirement for Port Burwell will be in the range of 15,000 to 30,000 cubic metres per year. That range is based on a rough approximation of the proportion of the Big Otter Creek sediment load that contributes to the sedimentation problem, as discussed in Section 2.1. There is a significant level of uncertainty with that range of volumes so we did not increase the volume to account for the sand that must be dredged from the bar just outside the entrance piers. We note, however, that our range is consistent with the 27,000 cubic metres estimated for the 2000 dredging plan depicted in Figure 8. With respect to typical hydraulic dredging projects, the need to dredge 15,000 to 30,000 cubic metres of sand annually is a relatively small requirement. We examined two types of small dredges that could be suitable for use at Port Burwell. We also examined land- based and in -water discharge options for dealing with the slurry produced by the dredges. 4.2.1. Small Manned Dredges There are a number of manufacturers of small capacity diesel -powered self-propelled hydraulic dredges that are typically used for marina, lake and lagoon clearing. An example of this type of dredge, shown in Figure 12, is the Rotomite 6000 manufactured by SRS Crisafulli in Montana, USA. The Rotomite 6000 is a cutter suction dredge with a 6 inch slurry pump. It can excavate up to 20 feet deep (6 metres) and has a discharge rate in the order of 2,500 gallons per minute (aprox 160 litres per second), depending upon the total head differential. The dredge is approximately 10 metres long and 2.5 metres wide. The dredge manufacturer claim that it is not uncommon to dredge slurries with up to 30% solids and that assuming slurry with 20% solids is relatively conservative. For our productivity analyses we considered slurries with both 20% and 30% solids. Pumping 20% solid slurry at a rate of 2,500 gallons (US) per minute corresponds to 114 cubic metres of sand per hour so it would take 132 to 264 hours or 17 to 34 working days (8 �iR� 16 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 hours/day) to dredge 15,000 to 30,000 m3 of sand. Assuming 30% solid slurry gives 11 to 22 working days to dredge 15,000 to 30,000 m3 of sand. Depending upon the dredge discharge method (discussed in Section 4.2.3) it is quite possible that limitations at the discharge site determine the overall productivity rate. It may not be physically possible to dredge 15,000 m3 of sand in 11 days without causing other problems at the dredge discharge site. This dredge is only suitable for use in calm to light wave conditions. It can be seen from Figure 12 that the dredge does not have a significant freeboard. A dredge of this type was once tried at Wheatley Harbour and it almost sank in the entrance due to wave activity. When the dredge is rocked by waves the cutter arm bangs on the bottom and can be damaged. It should not be used with wave heights in the order of 0.6 metres or higher. 4.2.2. Remote Controlled Mini Dredges Piranha Pump of New Mexico, USA, manufactures a line of remote controlled mini - dredges with reported capabilities similar to the small dredges described above. These dredges use 460v submersible electric slurry pumps with mechanical agitators. The pump is attached to a hoist mounted on 2 pontoons. Figure 13 shows an example of one of these dredges. The mini -dredges are steered with a stayed cable system. A practical system would have to be designed to allow dredging to proceed without adversely impacting navigational use of the channel. One possible solution would be to use anchored moorings that are placed and removed as required during dredging. This would require the use of a work boat or barge with a hoist and is considered to be one of the major disadvantages of this system. The dredge is not self-propelled and would need to be towed to the dredging site. The submersible pump is raised and lowered with a remotely controlled hoist and works most effectively when it can dig a cone shaped hole with material falling towards the pump. An operator's control panel must be set up near the dredging site and must have a suitable supply of electricity. A generator can be used to provide the electricity so the operator's station could be placed on a barge if desired. We examined production capabilities and costs for two of these mini -dredges: the P-30 and the P-75. The P-30 has a 30 horsepower, 4 inch pump with an average production capability of approximately 61 cubic metres of sand per hour. Dredging at that rate would take 245 to 450 hours or 31 to 62 working days to dredge 15,000 to 30,000 m3 of sand. The P-75 has a 75 horsepower, 6 or 8 inch pump with an average production capability of approximately 172 cubic metres of sand per hour. Dredging at that rate would take 87 to 174 hours or 11 to 22 working days to dredge 15,000 to 30,000 m3 of sand. Both systems are capable of dredging down to 40 feet (25m), which is far deeper than required for Port Burwell. Like the small manned dredge, these dredges are intended for calm to moderate wave conditions. However, because these dredges do not have a cutter arm they are less susceptible to damage when rocked by waves. The manufacturer recommends not SwnF?EP 17 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 operating these dredges when wave heights are in the order of 1 metre or higher. While it could be possible to design a cable stayed system for the harbour area it is questionable how suitable a mini -dredge would be for dredging outside the harbour entrance. Piranha does sell a self propelled spud -barge dredge using the same agitation and pumping system as on the P-75 mini -dredge but the cost is considerably higher than the mini -dredge and not competitive to the Rotomite 6000 cutter suction dredge. The main advantage of the Piranha mini -dredge compared to the Rotomite 6000 cutter suction dredge is the original purchase cost. The mini -dredge costs in the order of $125,000 to $150,000 with standard features. The Rotomite 6000 costs approximately $240,000 with standard features and a new model with enhanced abrasion resistance is being developed with a projected cost of $345,000. These are base costs for the dredge and additional equipment such as discharge pipe would also be required. 4.2.3. Discharge Options Each of the dredges described has a maximum discharge pipe length over which it can pump at its maximum flow rate. Pumping over longer lengths risks reducing the flow velocity to the point that sediment drops out of suspension and clogs the pipe. The Rotomite 6000 manned dredge and the Piranha P-30 mini -dredge can pump up to about 400 metres length. The Piranha P-75 mini -dredge can pump up to about 600 metres length. These are the manufactures recommended maximum discharge pipe length assuming little static head loss and the use of low -friction HDPE pipe. From an operational perspective, the preferred discharge location is typically in open water as long as the discharged sediment is not going to be transported back to the dredged area. Open water disposal is preferred as the dredgate does not need to be re - handled as part of the disposal operation. Whether or not open water disposal would be allowed is a matter to be discussed with the relevant approving agencies. However, there may not be a suitable open water discharge location within a convenient distance of all the dredging that must be performed due to the maximum discharge lengths described above. There is a high probability that if hydraulic dredging is to be used, a land based disposal area will be required. Limitations with maximum discharge lengths can be overcome by using booster pumps on land based discharge pipes. Land based discharge of slurry typically requires a settling basin to allow the finer sediments to settle out of suspension before the dredged water is returned to the receiving basin. The design and dimensions of a suitable settling basin are a function of the size of material dredged and the dredging rate. We note that small settling ponds could physically be constructed on the lands adjacent to the harbour but further analysis would be required to assess the actual suitability and feasibility of using those sites. The ultimate fate of the dredged material might also be considered when assessing possible settling basin sites. For example, if it were permitted to remove the sand and sell it, if a market exists, then the settling basin must be situated so trucks can access SHnREPL 18 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 the site and can be loaded in an efficient manner. On many projects it is preferable that dredged material be returned to the shore downdrift of the dredging site due the importance of the dredged material in the nearshore processes of the entire littoral cell containing the dredging site. It is debatable whether or not that is the case at Port Burwell due to the size of the material to be dredged. We have not found any detailed information regarding the grain size distribution of the material causing the sedimentation problem at Port Burwell but note that it frequently referred to as fine sand. If it is mostly sub -littoral drift, as discussed in Section 2.1, then it may not play a significant role in downdrift coastal processes. Further analysis would be required to make that determination. If it is dictated that material dredged from Port Burwell must be returned to the "natural system" then a suitable location must be found to do that. It is our expectation that sand placed on the beach immediately downdrift (east) of the harbour will contribute to the sedimentation of the channel outside the entrance piers. As discussed with the propeller wash dredging, however, that may be not be a significant issue as the entrance channel is likely to fill in quickly anyways. The risk and potential consequences of that happening would have to be considered as part of the detailed design required to actually implement a long-term dredging program. One idea that is worth consideration is placing the dredged material on the fillet beach on the west side of the armour stone breakwater. Under normal circumstances it would be unwise to place dredgate on the updrift side of a dredged entrance, but the circumstances at Port Burwell are not typical. As noted previously, it is the existing substantial deposit of sand at the end of the harbour piers that is believed to be causing the bulk sedimentation problem outside the entrance. The armour stone breakwater extends much farther offshore than the sand bar at the end of the piers and there is a good probability that only a portion of any dredgate placed on the updrift beach would end up on that bar. It is our expectation that only a small portion of the sediment that bypasses the armour stone breakwater actually ends up near the harbour entrance but additional analysis would be required to prove that. Furthermore, the finer the sand dredged from the creek is, when compared to the updrift littoral sediments, then the greater the probability that the majority of the material would end up either downdrift or on the harbour deposit "tongue" described in Section 2.1. One of the main advantages of placing the sand on the updrift beach is that it could be pumped there using a fixed pipe system. Connection points to the pipe system would be placed at convenient locations along the edge of that harbour. That would reduce the amount of floating pipe that would have to be managed during dredging. We acknowledge that the concept of annually placing 15,000 to 30,000 cubic metres of sand on a beach within a provincial park is unconventional, but if the dredged material must be returned to the natural system or if there is no market for the dredged material that this concept should be considered. In Section 2.1 it was noted that the Philpott (1983b) sediment budget data showed approximately 450,000 cubic metres per year of littoral and sub -littoral drift approaches the updrift beach at Port Burwell. Adding another 15,000 to 30,000 cubic metres per year would not be viewed as a major impact in terms of coastal processes. The potential environmental and sociological impacts of this type Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 of operation would need to be studied in detail and negotiated with affected stakeholders and approving agencies. 4.2.4. Timing The timing that dredging can actually take place will play a major role in determining whether or not a long-term dredging program is feasible for Port Burwell. Due to fisheries concerns, in -water work is typically restricted from mid March until early to mid July. Figure 6, which was discussed in Section 2.1, shows that approximately 45% of the Big Otter Creek sediment load occurs, on average, during March and April. Either an exemption to to the in -water work restriction will be required, and that may not be possible, or a dredging plan must be developed to deal with this limitation. The use of a sediment trap (described in Section 4.1.1) and over -dredging during the allowable working window could be one possible solution. 4.3. Potential Impacts Consideration must be given to the potential impacts associated with any solution contemplated for the sedimentation problem. We have provided brief comments on some of the major impacts that would need to be assessed, but we have not included a comprehensive list. Approvals will need to be obtained for any of the solutions we have discussed but the exact approvals required will depend upon the nature and location of the solution considered. Approvals will probably be required from DFO, MNR, LPRCA, and the Coast Guard. Formal permits are not provided by MOE but steps must be taken to ensure that all work is undertaken in accordance with their policies and regulations. 4.4. Financial Implications It was not a part of our mandate to consider how any of the solutions we have discussed might be financed. We recognize that the purpose of this study was to examine structural solutions that could reduce the dredging requirements due to the high cost of annual dredging. Within that context we acknowledge that our solutions will cost more than has been spent on dredging in recent years and likely cost more than has been budgeted for future dredging. Notwithstanding budgetary considerations, this report presents an assessment of long-term maintenance dredging needs at Port Burwell that is as realistic as possible given the limited data available. While our solutions were focused on what is technically feasible we have considered the relative cost implications of our solutions wherever possible. Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 5. FURTHER ANALYSIS This report presents a qualitative assessment of the Port Burwell sedimentation patterns and possible mitigation measures. It was noted that additional information and further analysis of a number of items would be required to confirm the precision of some of our assumptions and to quantify the level of effort likely required to deal with the sedimentation problem. This section identifies additional work that might be performed and discusses the potential benefits of doing that work. Two significant uncertainties in our assessment are the littoral sediment transport rates around Port Burwell and the sediment loading from Big Otter Creek. Of these two, the uncertainty of the creek sediment loading will have the biggest impact on our assessment and conclusions. Determining the sediment transport pathways and bypassing rates for littoral drift that passes the armour stone breakwater and determining the likely infilling rates of a channel dredged outside the entrance piers would provide valuable information for estimating long-term dredging costs, but it is not expected to change our basic conclusion for dredging outside the harbour. We do not believe that information is required at this time, but it would be useful if a long-term dredging program is implemented. If dredged material is to be placed on the beach updrift of the armour stone breakwater then a detailed sediment transport analysis will be required. More accurately quantifying the Big Otter Creek sediment load could affect the decision making process for managing sedimentation within the creek and harbour. Our dredging assessment was based on rough assumptions about both the total sediment load and the proportion of that load that is contributing to the sedimentation problem. A more detailed analysis of the fluvial processes at Port Burwell will allow for a more accurate evaluation of the different alternatives available and could affect which solution is optimal. Such an analysis should be one of the first steps in moving forward with a long- term plan. If narrowing the channel width with fill is to be seriously considered then a hydrologic analysis of the creek and harbour will required both to design the creek cross-section and to assess potential impacts. If a decision is made to move forward with a long-term dredging or sediment management plan then there would be significant benefit to conducting a field program to collect baseline data. Sediment samples should be collected from both the creek/harbour bed and the sand bar in front of the entrance piers. Grain size distribution analysis should be carried out as well as the sediment quality analyses that may be required. This was not done in the past but would have helped with our assessment if it had been done. Nearshore bathymetric soundings should also be updated as the most recent data is from 2003. SHnREr� 1�.,.: , 21 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 6. SUMMARY Port Burwell has been experiencing an ongoing sedimentation problem since its original construction in the 1830's. The original east and west pier extensions, the west extension wall and the armour stone breakwater were all constructed to mitigate the sedimentation problem. There are two primary causes of the sedimentation problem at Port Burwell; the sediment load coming down Big Otter Creek and the coastal processes acting on the nearshore deposit of sand immediately in front of the east and west piers. The sand in front of the piers is part of the Port Burwell harbour deposit. Sediment budget estimates show that approximately 450,000 cubic metres per year of littoral and sub -littoral drift is transported to the fillet beach updrift of the armour stone breakwater. The proportions of that material that are: retained by the breakwater; added to the harbour deposit; and bypass Port Burwell to downdrift shores, is not known. In the long-term, some of the updrift littoral sediments bypass the armour stone breakwater and add to the harbour deposit but in the short term it is waves acting on the existing deposit that is the direct cause of sedimentation at the harbour entrance. We did not carry out any modeling to quantify the littoral transport rates and infilling rates for dredged channels outside the harbour structures. It is our expectation that any channels dredged outside the harbour will experience significant infilling in a relatively short period of time. Modeling sediment transport at the entrance is not expected to change that conclusion and is not recommended at this time. The area offshore of the pier ends and the west extension wall has filled in significantly since dredging to the seaway depth was stopped. If dredging were to completely cease at Port Burwell the infilling would continue until the sand deposit was at equilibrium with the long-term average sediment supply rates and zone of influence of the breakwater. Anecdotal evidence suggests that equilibrium has not yet been reached. There is no practical structural solution to the sedimentation at the harbour entrance that is caused by coastal processes. Extending the armour stone breakwater will not affect the processes acting on the existing harbour deposit. Extending the entrance piers would require a total length of new structures in excess of 850 metres. The cost of that work and the likelihood of obtaining approvals for that volume of infill make that solution impractical. Big Otter Creek has been identified as the largest single source of fluvial sediment on the north shore of Lake Erie. For our assessment we assumed that approximately 15,000 to 30,000 cubic metres per year of that sediment could be contributing to the sedimentation problem. That is a rough estimate only and must be considered to have significant uncertainty. Actual sediment loads should be estimated more accurately before any critical decisions are made. Water depths in Big Otter Creek and within the harbour, but north of the entrance, appear to be the result of equilibrium conditions for the channel cross-sections, the long- SbnF? ,`' Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 term flow rates and the sediment supply rate. Sand moved by wave action will affect the water depth between the piers for a short distance up from the end of the piers but that distance cannot be estimated without a wave analysis. A potential structural solution for sedimentation within the creek and the portion of the harbour not affected by wave action is to narrow the channel width by filling. Decreasing the channel cross section will increase the flow velocities and alter the equilibrium conditions for sediment transport, causing a greater amount of the sand to be transported through the harbour. In order for this solution to be effective the channel would have to be narrowed over the entire length of the creek and harbour where an increased depth is required. Sand that passes through the narrowed channel will still have to be managed as it exits the harbour. An appropriate channel width cannot be estimated without more detailed analysis. For comparative purposes we estimated that a 20 metre wide channel extending from the harbour entrance to the bridge would require filling an area of approximately 2.8 hectares, which represents 56% of the existing area. The volume of fill required to accomplish that cannot be estimated without cross-sectional data. Obtaining approvals for this amount of infilling could be a significant obstacle to overcome. There are potential major impacts associated with this type of work including the environmental aspects of filling a creek, the potential for upstream flooding and the potential for increased ice jamming. Each of these potential impacts would need to be studied in greater detail before this type of solution could be seriously considered. An alternative structural solution for the inner harbour is to construct a sediment trap to restrict the area where dredging would be required. A sediment trap alters the flow and sediment transport equilibrium conditions by increasing the channel depth over the area of the trap. The trap must be regularly emptied of sediment to be effective. The exact location and dimensions of the sediment trap are related to the characteristics of the sediment to be trapped and would require further analysis. A sediment trap could potentially be located in the vicinity of the turning basin. Due to the limitations of the structural solutions, the best solution to the sedimentation problem at Port Burwell is going to require some sort of an on-going dredging operation. To assess the dredging alternatives we assumed that the average annual dredging requirements will be in the order of 15,000 to 30,000 cubic metres. The uncertainty of that estimate has not been quantified. Sand within Big Otter Creek and the harbour must be removed as part of the dredging operation. Propeller wash dredging could be used to push a channel through the bar outside the entrance piers without actually removing that sand. Hydraulic dredging is generally the most cost effective method when sand must be removed from a problem area. From an operational perspective, open water disposal is generally preferred. If open water disposal near the harbour is an option, then hydraulic dredging of the bar outside the entrance might be cost effective compared to propeller washing. SwnRE L 23 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 If open water disposal is not permitted then de -watering the dredgate in a land based settling basin will probably be required. That is not expected to be cost effective compared to propeller washing the bar outside the entrance, but it may still be effective for dredging within the harbour as that material must be removed, not just pushed aside. The size of the settling basin required to accomplish hydraulic dredging of the harbour area is related to the physical characteristics of the dredged material as well as the flow rate of the dredged slurry. That information is not available at this time. While it is generally preferred that dredged material be returned to the littoral cell due to the importance of its role in coastal processes that may not be the case at Port Burwell. If the sand causing the sedimentation problem is the size of sub -littoral drift it can probably be removed from the littoral system with impacting downdrift coastal processes. If it is dictated that material dredged from Port Burwell must be returned to the "natural system" then a suitable location must be found to do that. It is our expectation that sand placed on the beach immediately downdrift (east) of the harbour will contribute to the sedimentation of the channel outside the entrance piers, however that may be not be a significant issue as the entrance channel is likely to fill in quickly anyways. The risk and potential consequences of that happening would have to be considered as part of the detailed design required to actually implement a long-term dredging program. From an operational point of view, the beach updrift of the armour stone breakwater could be a good location for disposing of hydraulically dredged sand. The technical feasibility of placing the dredgate there would need to be confirmed with a detailed sediment transport pathways analysis. The potential environmental and sociological impacts of this type of operation would need to be studied in detail and negotiated with affected stakeholders and approving agencies. Two types of small hydraulic dredges might be suitable for use at Port Burwell; a small manned cutter section dredge and a remotely controlled agitation dredge. The remotely controlled agitation dredge requires a cable stayed system to operate and that could be a significant disadvantage here. The timing that dredging can actually take place will play a major role in determining whether or not a long-term dredging program is feasible for Port Burwell. In -water work is typically restricted from mid March until early to mid July but approximately 45% of the Big Otter Creek sediment load occurs, on average, during March and April. The use of a sediment trap and over -dredging during the allowable working window could be one possible solution to a timing conflict. This report does not include an assessment of potential impacts or necessary approvals. Consideration must be given to the potential impacts associated with any solution contemplated for the sedimentation problem. The measures discussed in this report will cost more than has been spent on dredging in recent years and likely cost more than has been budgeted for future dredging. Notwithstanding budgetary considerations, this report presents an assessment of long- term maintenance dredging needs at Port Burwell that is as realistic as possible given the limited data available. Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 This report presents a qualitative assessment of the sedimentation problem and possible mitigation measures. Much of the quantified information is based on rough assumptions and incomplete information and must be viewed as containing significant uncertainty. It has been included to provide order of magnitude information and should be confirmed before any critical decision making. SHnREPILAN 25 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 7. CONCLUSIONS There are two primary causes of the sedimentation problem at Port Burwell; the sediment load coming down Big Otter Creek and the coastal processes acting on the nearshore deposit of sand immediately in front of the east and west piers. 2. There is no practical structural solution to the sedimentation at the harbour entrance that is caused by coastal processes. A potential structural solution to the creek and harbour sedimentation is to narrow the channel width, but that will involve significant capital cost and obtaining approvals is expected to be difficult. 3. Due to the limitations of the structural solutions, the best solution to the sedimentation problem at Port Burwell is going to require some sort of an on-going dredging operation 4. Hydraulic dredging of the creek and harbour is expected to be the most cost effective means of managing the Big Otter Creek sediment load. 5. Hydraulically dredging a channel is also expected to be the most cost effective means of managing the sand bar at the harbour entrance, if open water disposal of the dredgate is permitted. If open water disposal is not permitted then propeller wash dredging an entrance channel is recommended. 6. The long-term average annual sediment load for Big Otter Creek and the proportion of that load that contributes to the sedimentation problem needs to be better quantified in order to get a true estimate of the likely dredging requirements. wnF? E F1 r 1 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 References Aquafor Beech, 1996. Port Burwell Harbour Dredge Monitoring Study. Unpublished report prepared for the Village of Port Burwell by Aguafor Beech Limited. Interim report, July 1996. Philpott, K.L. 1983a. Lake Erie: Analysis of Harbour Deposits at Port Burwell, Port Bruce and Port Stanley. Unpublished report by Keith Philpott Consulting Limited for the Deputy General of Canada for Litigation (Alton et at verses Her Majesty the Queen). Philpott, K.L. 1983b. Lake Erie: Analysis of Sediment Flows Through the Nearshore Zone With and Without the Harbour Structures. Unpublished report by Keith Philpott Consulting Limited for the Deputy General of Canada for Litigation (Alton et at verses Her Majesty the Queen). van Raalte, G.H. and R.N. Bray. 1999. Hydrodynamic Dredging: Principles, Effects and Methods. Proc. CEDA Dredging Days 1999. Shoreplan, 2003. Wheatley Harbour Sedimentation Study. Unpublished report prepared for Public Works and Government Services Canada by Shoreplan Engineering Limited. Final Report. March 2003 SwnRErM .:� ', 27 Port Burwell Coastal Processes, Sedimentation and Dredging Review Municipality of Bayham Figures Final Report file 09-1250 Figure1 Site Plan............................................................................................................29 Figure 2 Contours from June 1999 Sounding Survey....................................................30 Figure 3 Contours from August 2003 Sounding Survey ................................................. 31 Figure 4 Location of WSC Calton Gauge.......................................................................32 Figure 5 Big Otter Creek Total Daily Sediment Load at WSC Calton Gauge ................ 32 Figure 6 Daily Distribution of Total Sediment Load........................................................33 Figure 7 Turning Basin Area Filled in 1992.................................................................... 33 Figure 8 Outline of 2000 Proposed Dredge Area........................................................... 34 Figure 9 1999 and 2003 Profiles at Harbour Entrance ................................................... 35 Figure 10 Possible Sediment Trap Locations................................................................ 36 Figure 11 Concept Design for Wheatley Harbour..........................................................37 Figure 12 Rotomoite 6000 Hydraulic Dredge................................................................. 38 Figure 13 Piranha Pumps Mini-Dredge..........................................................................38 rS w n R E M- , M',, i 28 Port Burwell Coastal Processes, Sedimentation and Dredging Review Municipality of Bayham Figure 1 Site Plan �•` � � •. � IS IRT I .26 nurrmu. 1 '+v1 `e` C ' e ... � ' turning basin -- ",.' 'IL turning Pier LAKE ERIE'— west Pier w West Extension Wall a e r , armour stone breakwater Final Report file 09-1250 !� 1983 ONTARIO BASE MAP tIN 0 100 2W SHnREPLAN 29 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 Figure 2 Contours from June 1999 Sounding Survey Depth in metres below chart datum SMnREPLAN 30 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 Figure 3 Contours from August 2003 Sounding Survey SmnREPLAN 31 Port Burwell Coastal Processes, Sedimentation and Dredging Review Municipality of Bayham Figure 4 Location of WSC Calton Gauge 4 i0 olVS'� L— I� Rlchmunn' Fao! ` Vw� HernaAa Una 02GCa26:BIG OTTER CREEK NEAR C_ LT0 1 3a Q Callan Lne �i f L 4a k,e Erle Final Report file 09-1250 4n AJ _ Raz ,9 n se._ry 42 9 L 4a k,e Erle Final Report file 09-1250 4n Raz 42 � qr:o er Figure 5 Big Otter Creek Total Daily Sediment Load at WSC Calton Gauge 35,000 �a 0 30,000 w m c 25,000 20,000 0 J 15,000 d E m 10,000 N 5,000 D 0 Jan -76 Jan -78 Jan -80 Jan -82 Jan -84 Jan -86 Jan -88 Jan -90 Jan -92 Jan -94 Jan -96 SmnREPLAN 32 Port Burwell Coastal Processes, Sedimentation and Dredging Review Municipality of Bayham Figure 6 Daily Distribution of Total Sediment Load 70,000 - Sum of Daily Loads, 1976-1996 60,000 ----Cumulative Distribution of Summed L N d c 50,000 0 40,000 J C £ 30,000 a d 20,000 i O � 10,000 LAJ 0 + + + + + + + + Jan Feb Mar Apr May Jun Jul Aug Sep Oct Figure 7 Turning Basin Area Filled in 1992 Final Report file 09-1250 T aRON � i �i 3 ■ ��- 391.0 L ■ i' �� `� Illi �: • r' .: f -.� turning a basin fill; Pot I 1174.0 ,r I 1I , 1983 Ontario Base Map 1`� ! Orthophoto SMnREPLAN 33 100°% 90% 800% C 70% c a 60% M_ :gauge: Big Otter 50% C eek near Calton 40% M 30% E U 20% 10% + 0% Nov Dec T aRON � i �i 3 ■ ��- 391.0 L ■ i' �� `� Illi �: • r' .: f -.� turning a basin fill; Pot I 1174.0 ,r I 1I , 1983 Ontario Base Map 1`� ! Orthophoto SMnREPLAN 33 Port Burwell Coastal Processes, Sedimentation and Dredging Review Municipality of Bayham Figure 8 Outline of 2000 Proposed Dredge Area - _ w • � s4 _1 I° t Dredging volume estimated at 27,000 m3 in 2000 A 11 w Final Report file 09-1250 SMnREPLAN 34 Port Burwell Coastal Processes, Sedimentation and Dredging Review Municipality of Bayham Figure 9 1999 and 2003 Profiles at Harbour Entrance 1.0 range of long-term mean monthly water levels Final Report file 09-1250 £ 0.0 position of Mend of piers t0 -1.0 E aai dredge line for 7 foot depth o -2.0—[:::Surveyed Surveyed 2003 _ 1999 dredge line for 10 foot depth -3.0 0 100 200 300 400 500 600 Offset (M) SmnREPLAN 35 Port Burwell Coastal Processes, Sedimentation and Dredging Review Municipality of Bayham Figure 10 Possible Sediment Trap Locations 1 I Final Report file 09-1250 SMnREPLAN 36 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 Figure 11 Concept Design for Wheatley Harbour X C t— VIA 0 20m 60m 100m p -A (V' tT1 _ 5 �EXiSTfIVG EXISTING LAUNCH EAST .PIER • tip RAMP + PROPOSED ARMOUR STONE —BREAKWATER EXISTING BREAKWATER 180 u 179 25-500mrn0 CORE STONE _I 176 3600± 4-6t ARMOUR STONE i 177 - 176.5± a 176 EXISTING PR©RLE 175 15001 1 t �1 15001 174 QATJA� (173.5} 17J VARIES VARIES 172 20001 171 I 770 TYPICAL SECTION from Shoreplan (2003) SmnREPLAN 37 Port Burwell Coastal Processes, Sedimentation and Dredging Review Final Report Municipality of Bayham file 09-1250 Figure 12 Rotomoite 6000 Hydraulic Dredge Figure 13 Piranha Pumps Mini -Dredge SMnREPLAN 38