Survey Grade GPS Storm Surge High Water Mapping

Transcription

1 Atlantic Climate Adaptation Solutions Association Solutions d'adaptation aux changements climatiques pour l'atlantique Survey Grade GPS Storm Surge High Water Mapping November 2011 Applied Geomatics Research Group, Nova Scotia Community College

2 Report Prepared by: Dr. Tim Webster, Kevin McGuigan and Chris Webster, Applied Geomatics Research Group Centre Geographic Sciences, Nova Scotia Community College, Nova Scotia Community College, 50 Elliott Road, Lawrencetown, NS B0S 1M0. The Applied Geomatics Research Group is a team of Research Scientists, Research Associates, and graduate students, applying a suite of geomatics technologies to explore environmental, health and social issues. Edited by: Erin Taylor, Prince Edward Island Department of Environment, Labour and Justice Project Management: Prince Edward Island Department of Environment, Energy and Forestry, 11 Kent Street, Charlottetown, PE, C1A 7N8, Tel: , eotaylor@gov.pe.ca Disclaimer: This publication is not be used without permission, and any unauthorized use is strictly prohibited. ACASA, the authors, the provinces of Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador, and the Regional Adaptation Collaborative are not responsible for any unauthorized use that may be made of the information contained therein. The opinions expressed in this publication do not necessarily reflect those of ACASA, its associated provinces, or other partners of the Regional Adaptation Collaborative. This report is also available for download from the ACASA website at: Photo Credit: D. Jardine

3 Table of Contents Table of Figures...ii List of Tables... iii Introduction... 1 Methods... 2 Results... 3 Conclusions Acknowledgements Appendix Appendix i

4 Table of Figures Figure 1: Location of the survey grade GPS high water marks (red triangles) obtained in the summer of Figure 2: Souris high water marks from Jan 21, 2000 storm surge, ~ 1.75 m CGVD Figure 3: Mount Stewart bridge GPS elevations above CGVD Figure 4: Savage Harbour GPS high water marks Dec 21, 2010 storm Figure 5: Photo of the day after the Dec. 21, 2010 storm (upper left DE Jardine) and during normal conditions at Savage Harbour Figure 6: Photos of normal conditions at Savage Harbour wharf (top) and during the Dec 21, 2010 storm (bottom) (photo supplied by Mr. Randy Gallant) Figure 7: Campbellton Road high water wrack line debris that was pushed off the road after the Dec. 21, 2010 storm Figure 8: North Rustico survey sites for high water marks from the Dec 21, 2010 (1.99 m) and Dec 26, 2004 (1.85 m) storms Figure 9: Photos of North Rustico after the Dec 21, 1010 storm (top left DE Jardine) and under normal conditions. The water mark is still visible in the gift shop (lower right) Figure 10: Photos of North Rustico after the Dec 21, 1010 storm (top left DE Jardine) and under normal conditions (lower photos) Figure 11: Map of high water GPS marks for the Summerside area Figure 12: GPS elevations (CGVD28) of monitoring wells west of Summerside, blue line denotes the shoreline Figure 13: Fernwood high water marks from Jan 3, 2010 storm surge Figure 14: Fernwood photos immediately following the Jan 3, 2010 storm (top left) and after adding fill to the lot (top right). The lower photos show the rock and other debris placed on the lawn by the surge Figure 15: Borden-Carleton high water mark from the Jan 2-3, 1010 storm surge Figure 16: High water GPS survey locations for Charlottetown waterfront. Note the date marking the high water line on the crane (lower left photo inset) is incorrect Jan 21, 1999 and should read Jan 21, Figure 17: Photo by DE Jardine of the Charlottetown Yacht club damage after the Dec. 6, 2010 storm surge Figure 18: Victoria high water GPS marks for Jan 21, 2000 and Jan 3, Figure 19: Example of "wave run-up" (R) and still water level (SWL), top figure. Elevated water levels as a result of a low pressure storm system with extreme winds, lower figure. This causes a storm surge raising the water level above the predicted tide with associated wave set-up and wave run-up at the coast ii

5 Figure 20: Location of PEI HPN survey monuments List of Tables Table 1: PEI High Precision Network (HPN) of survey monuments and coordinates Table 2: Survey grade GPS elevation of high water marks...5 Table 3: GPS measurements of features that are not high water marks...7 iii

6 Introduction Tide gauge records are used to determine the water levels from storm surge and tides combined. Charlottetown is the only tide gauge the Canadian Hydrographic Service is still operating in Prince Edward Island. While it may characterize storms impacting the south coast of the island, it does not accurately reflect the water levels on the North Shore. A strong Nor easter, for example, will affect the north shore of the island more severely than the south. An accurate record of storm surge elevations and the storm characteristics are important to supplement other existing time series records of water levels (e.g. tide gauges) and predict the probability of future high water events. This is done through the development of an extreme value model, derived from the time series. The model is typically derived from a time series on annual maxima. These are rare or extreme events and the sparseness of them effects the model parameters, therefore supplementing the time series with additional information on extreme events should improve our model predictions. Using GPS to measure the high-water line after a storm event is one way to capture these extreme events that are not represented in the tide gauge records. It should be noted that the tide gauge will measure the still water level which represents the storm surge on top of the predicted tide (Appendix 1). Wind causes waves to be developed on top of the storm surge and wave run-up occurs as they approach the coast. The wave run-up elevation is usually higher than the storm surge still water elevation (Appendix 1). The method of using GPS to measure the high water mark or debris left from the water will typically measure the extent of wave run-up. The purpose of this research project was to establish a set of survey grade GPS measurements for communities around Prince Edward Island (PEI), documenting the high water level associated with recent storm surge events. Once gathered, these measurements can be used to (1) identifying areas at risk, (2) aid in generating return periods and probabilities of occurrence of flood levels, (3) document and inventory coastal vulnerability, and (4) use these data to construct inundation maps of the storm events and future sea-levels incorporating climate change. 1

7 Figure 1: Location of the survey grade GPS high water marks (red triangles) obtained in the summer of The benefits of such a research project include: 1) identifying areas at risk, 2) aid in generating return periods and probabilities of occurrence of flood levels, 3) document and inventory coastal vulnerability, and 4) use these data to construct inundation maps of the storm events and future sea-levels incorporating climate change. Methods A list of communities and high water mark descriptions was provided by Don Jardine (DEJardine Consulting). Mr. Jardine had kept excellent records on past storm surge events and had visited most sites for the recent storm events of He provided a list of the communities and dates of the storm event for the survey. In many cases the wrack line, which is formed by the debris washed up from the storm (typically consisting of seaweed and grass) was photographed or measured relative to a static feature (e.g. 10 ft from the building entrance). The field campaign was conducted July 19-21, 2011 and utilized the PEI High Precision Network (HPN) of survey control monuments for their GPS base station setup. Researchers from the 2

8 Applied Geomatics Research Group (AGRG) used a Leica system 530 and 1200 dual frequency survey grade GPS receivers to obtain Real Time Kinematic (RTK) and post processed positions (x,y,z) of water marks to a precision of 5 cm. AGRG staff was accompanied by Don Jardine and Glen Robertson from the PEI Department of Environment, Energy and Forestry during all the field visits except Souris. The closest HPN monument to the community was used to establish a GPS base position using the PEI published coordinates (Table 1, Appendix 2). The RTK system typically could maintain a radio link between the base and rover receiver up to 11 km with a clear line of site. In many locations, as a result of obstructions (e.g. building on wharves, topography) this was sometimes problematic. In those cases where RTK could not be used, we recorded raw satellite observations with the rover and later in the office used post processing with the base station observations to determine the position. The precision of 1-5 cm in elevation was maintained throughout the survey with the exception of the Jan 21, 2000 water level at Mount Stewart. We could not get a solution to centimetre level precision with post processing so we used the 1.5 m LiDAR DEM to obtain the ground elevation and assign the water level. For these LiDAR derived water marks the vertical precision changes from 5 cm to 30 cm in elevation when interpreting the data. In many locations the actual water line was not GPS accessible (e.g. water mark inside a building or along an edge of a bridge). In these situations, a GPS elevation was taken on a flat surface, typically the road or driveway, and a tape measure was used to determine the offset to the high water line. GPS positions were processed to an Arc shape point file where each point contains the high water elevation relative to the Canadian Geodetic Vertical Datum of 1928 (CGVD28) and the date of the storm event. Results The GPS high water surveys have been compiled and provided in the form of a GIS point shape file. In addition a shape file of the monitoring wells near Summerside has also been provided. High water sites have been summarized in a table and GPS elevations added (Table 2). Additional GPS measurements were taken of other features that were not high water marks such as the Mount Stewart bridge deck and some monitoring wells near Summerside (Table 3). 3

9 Table 1: PEI High Precision Network (HPN) of survey monuments and coordinates. ID HPN Location NAD83CSRS_E NAD83CSRS_N NAD83CSRS_Lat NAD83CSRS_Long Ortho_ht Ellip_ht Murray River Kinross Brudenell Peakes West Cape Rice Point Kildare Freeland Birch Hill Abrams Village Irishtown Middleton DeSable St. Peters Clearspring Dalvay Albany Summerside Hunter River Carl Val Archie Jones Bldg Tea Hill Winsloe

10 Table 2: Survey grade GPS elevation of high water marks Location Structure Event Elevation (m) CGVD28 Borden-Carleton Wharf shed near the wharf base of shed 02 Jan Campbellton / Stanley Bridge Hebrides Lane MacEwen s Island road 21 Dec Charlottetown Lower Prince St Lobster on the Wharf Lower Pownal St Charlottetown Yacht Club Lower Pownal St Charlottetown Yacht Club Fernwood inside restaurant, marked on wall, building raised 36 inches 21 Jan :30 AM 2.55 hydraulic lift on wharf 21 Jan between 1st and 2nd step at 06 Dec south entrance 59 Sunset Beach Rd top of well casing 02 Jan Sunset Beach Rd moss on trees 02 Jan Sunset Beach Rd moss on trees 02 Jan Mount Stewart 19 Egan St bottom of step 21 Jan North Rustico Riverview Dr - Wharf 21 Dec Feb 2004 Harbourside Dr Seagull s Nest Gift 12 inches above baseboard 21 Dec 2010 Shop heater on ground 26 Dec Notes Extracted from LiDAR, GPS could not get a fixed solution thus the variance in the measurements 5

11 Location Structure Event Elevation (m) CGVD28 Savage Harbour Savage Harbour Rd wharf area Savage Harbour Rd north of long yellow shed Cottage Rd and Surfside Lane , Souris MECL pole (145799) by old 21 Dec sheds 1.90 driveway into wharf 06 Dec Cottage 21 Dec #2 Highway west of Souris West bridge 1 foot below deck of bridge 21 Jan Wharf bollard where fisherman attach ropes to tie their boats up 21 Jan Summerside Harbour Dr, Holman s Wharf Arsenault s Fish Mart Notes 11 inches above floor 02 Jan We do not have this record in our notes thus an estimated water level edge of entrance of store 06 Dec Dec Harbour Dr, Holman s Wharf Arsenault s Fish Mart Harbour Dr Harbour Quay Bldg 18 inches above floor 21 Jan Harbour Dr, 102 Queen s Wharf JMK Fish Mart Victoria 4 inches above floor 02 Jan Dec Dec Main St window sill on main floor 21 Jan Jan Main St edge of pavement on south side 21 Jan Jan Nelson St storage shed 18 inches above floor 02 Jan Water St water and sand entered building 2 or 3 inches 02 Jan Wharf deck elevation Causeway Rd - west end of causeway where erosion above gabions storm waves caused erosion within 10 feet of pavement 06 Dec Maximum elevation of extent of erosion

12 Table 3: GPS measurements of features that are not high water marks Location Structure Elevation (m) CGVD28 Notes Mount Stewart Main St at River bridge over Hillsborough River on Rt 22 Savage Harbour Savage Harbour Rd - Wharf deck of the bridge for tidal monitoring outer base below bridge seaward light post on wharf landward light post on wharf Summerside MacKenzie Drive Spa site 6 well casings Tie to tidal monitoring in Hillsborough River saltwater intrusion project Harbour Dr Silver Fox Yacht Club top of new concrete sea wall 2.20 reference point 7

13 Souris: The AGRG crew arrived on July 19 and established a GPS base station near Souris over HPN 5803 Carl Val Archie (#20 Appendix 2). Two high water marks from the January 21, 2000 storm were surveyed in Souris; one at the wharf (1.72 m) and another at the bridge crossing the estuary (1.75 m) (Figure 2). Figure 2: Souris high water marks from Jan 21, 2000 storm surge, ~ 1.75 m CGVD28. 8

14 Mount Stewart: On July 20 the crew, along with Don Jardine, travelled to Peakes to setup a base station over the 609 HPN monument (#4 Appendix 2). High water marks from the January 21, 2000 storm were then surveyed in Mount Stewart. As well, other points on the bridge at Mount Stewart were surveyed for a flood risk project (Inland Flood Risk Mapping and Modelling in the Hillsborough River Basin). The high water mark at Mount Stewart could not be obtained with GPS, however we obtained an elevation from the LiDAR DEM of between m. In addition to surveying the high water mark we also obtained elevations on the Mount Stewart Bridge (Figure 3). Mount Stewart Bridge Figure 3: Mount Stewart bridge GPS elevations above CGVD28. Savage Harbour: Still using the GPS base station over HPN 809 Peakes (#4 Appendix 2), high water marks from the December 21, 2010 storm were surveyed in Savage Harbour (Figure 4). Three locations were surveyed, one based on a photograph and recollection of Don Jardine of the wrack line near an out building (Figure 5), and the others based on eye witness accounts from their memory. Following our visit, we were also sent photos by Mr. Randy Gallant of the wharf during the storm (Figure 6). 9

15 Figure 4: Savage Harbour GPS high water marks Dec 21, 2010 storm. 10

16 Photo Don Jardine Figure 5: Photo of the day after the Dec. 21, 2010 storm (upper left DE Jardine) and during normal conditions at Savage Harbour. Figure 6: Photos of normal conditions at Savage Harbour wharf (top) and during the Dec 21, 2010 storm (bottom) (photo supplied by Mr. Randy Gallant). 11

17 Campbellton Road: A base station was set up over 1575 HPN at Irishtown (#11 Appendix 2), west of New London Bay. From this base station, locations in Campbellton Road and North Rustico were surveyed. Along Campbellton Road, the location where the wrack line came over the road during the December 21, 2010 storm surge was surveyed. The high water mark (based on a wrack line) from the December 21, 2010 storm was surveyed along Campbellton Road where the storm surge caused the water to cross the road (Figure 7). Campbellton Road Dec 21, 2010 Figure 7: Campbellton Road high water wrack line debris that was pushed off the road after the Dec. 21, 2010 storm. North Rustico: High water marks from the December 26, 2004 and December 21, 2010 storms were surveyed at the Seagull s Nest Gift Shop (Figure 8). At a shed on the wharf (near the fire hall), high water marks from the White Juan (February 17, 2004) and the December 21, 2010 storm were surveyed as well (Figure 8). Photos were taken by Don Jardine following the December 21, 2010 storm (Figures 9 and 10). 12

18 Figure 8: North Rustico survey sites for high water marks from the Dec 21, 2010 (1.99 m) and Dec 26, 2004 (1.85 m) storms. Photo Don Jardine Figure 9: Photos of North Rustico after the Dec 21, 1010 storm (top left DE Jardine) and under normal conditions. The water mark is still visible in the gift shop (lower right). 13

19 Photo Don Jardine Figure 10: Photos of North Rustico after the Dec 21, 1010 storm (top left DE Jardine) and under normal conditions (lower photos). Summerside: A GPS base station was set-up over HPN 3993 Summerside (#18 Appendix 2). Several high water marks for several storm events were acquired (Figure 11). The JMK Fishmart and Arsenault Fish Mart were visited and points surveyed for storm events from January 2, 2010 ( m), December 6, 2010 ( m) and December 21, 2010 ( m). At Harbour Quay, a high water mark as a result of the water backing up through the storm sewer manhole during the January 21, 2000 storm (2.21 m) was surveyed. For future reference, the top of a new concrete wall at the Summerside Yacht Club was surveyed. Six monitoring wells along the coast west of Summerside were also surveyed for a separate saltwater intrusion project (Figure 12). 14

20 Figure 11: Map of high water GPS marks for the Summerside area. Well field at an abandoned spa near Summerside Figure 12: GPS elevations (CGVD28) of monitoring wells west of Summerside, blue line denotes the shoreline. 15

21 Fernwood: Using the GPS base station at HPN 3993 Summerside (#18 Appendix 2), high water marks from the January 2 and 3, 2010 storm in the community of Fernwood, east of where the power cable from New Brunswick makes landfall (Figure 13). Survey sites were based on evidence of the water level in the shrubs, as well as wrack line locations and eye witness reports. Wrack line elevations ranged from 2.27 to 2.45 m CGVD28. We obtained photos of the damage immediately following the January 2010 storm (Figure 14). Figure 13: Fernwood high water marks from Jan 3, 2010 storm surge. 16

22 Figure 14: Fernwood photos immediately following the Jan 3, 2010 storm (top left) and after adding fill to the lot (top right). The lower photos show the rock and other debris placed on the lawn by the surge. Borden-Carleton: The high water mark from the January 2 and 3, 2010 storm was surveyed in Borden-Carleton in the summer of 2010 based on information provided by Mr. Steve Dickie of the PEI Office of Public Safety (Figure 15). The high water elevation for Borden was between 2.31 and 2.63 m CGVD28. 17

23 Figure 15: Borden-Carleton high water mark from the Jan 2-3, 1010 storm surge. Charlottetown: On July 21, a GPS base station over HPN 5807 Jones Building (#21 on Appendix 2) was established in Charlottetown. High water marks were then surveyed at the Charlottetown Yacht Club and restaurants on the waterfront. The high water mark from January 21, 2000 ( m) was marked on one of their crane masts, although the date is incorrect (Figure 16). This may have included waves. The December 6, 2010 storm was also surveyed. At the Lobster on the Wharf restaurant, the high water mark from January 21, 2000 was surveyed. A 2.55 m elevation was obtained from a mark in the inside wall and presumably records a still water elevation. The December 6, 2010 storm surge had an elevation of 1.99 m. Photos were obtained during the December 6, 2010 storm surge (Figure 17). 18

24 Figure 16: High water GPS survey locations for Charlottetown waterfront. Note the date marking the high water line on the crane (lower left photo inset) is incorrect Jan 21, 1999 and should read Jan 21, Figure 17: Photo by DE Jardine of the Charlottetown Yacht club damage after the Dec. 6, 2010 storm surge. 19

25 Victoria: A GPS base station was set-up over HPN 2159 DeSable (#13 Appendix 2). High water marks from January 21, 2000, January 2 and 3, 2010 and December 6, 2010 were surveyed in Victoria (Figure 18). The January 3, 2010 storm event produced a high water mark between 2.27 and 2.31 m and the Jan 21, 2000 storm produced a high water mark of 2.26 m. High water marks associated with erosion along the road-causeway from the December 6, 2010 storm surge ( m) were also surveyed. Figure 18: Victoria high water GPS marks for Jan 21, 2000 and Jan 3,

26 Conclusions This project has demonstrated that using RTK survey grade GPS to obtain precise elevations for past high water storm surge events is a useful method to accurately capture the water level that flooded the shoreline. We feel the most confidence should be placed with the data associated with storms that are the most recent or where physical evidence still existed (i.e. wrack line). For example, Don Jardine visited many sites after the December 21, 2010 storm and spoke to people to document the high water mark and often supplemented this with photography. In other cases such as the benchmark January 21, 2000 storm, he obtained detailed descriptions as were provided for the Souris area. Another source of strong evidence is where people have placed permanent markers denoting the water level of the January 21, 2000 event such as the Charlottetown Yacht Club, although the date is incorrect on the crane January 21, 1999, or the Lobster on the Wharf restaurant, although they have raised their building approximately 30 cm. These local adjustments have been taken into account for the final measurements in this report. In other cases such as the Gift Shop in North Rustico where the water line mark is still evident on the wall, we have a high degree of confidence in the elevations of the December 21, 2010 storm. In many locations while surveying in high water marks, discussions with the local people about other storms would be mentioned and high water levels indicated. We have done our best to capture these events; however the dates and elevations are based on people s recollection where no physical evidence remains as is the case for the December 26, 2004 and February 17, 2004 storm surges. Also there is a slight discrepancy in the date of the January 2 or 3, 2010 storm surge. The barometric pressure dropped to its lowest point approaching midnight on January 2 as well as the strongest winds, thus the damage occurred late on the night of January 2 and the morning of January 3. In the GIS layer we denote the date of that storm and high water elevation as January 3, This type of work should be conducted annually after the storm season to capture and document the storm events. Having someone such as Don Jardine track and document the storms as they occur and capture the evidence to be used to survey the elevations is critical. High water marks on the south shore and close to Charlottetown could be compared to the tide gauge records for extreme events to determine the differences in height of the two methods, wrack line versus gauge. Adjustments could then be applied to one of the datasets to normalize it to the other so that they could be combined to increase our accuracy of modeling risk of flooding events. 21

27 Acknowledgements We would like to thank Don Jardine for showing us the water mark sites. We would like to thank Steve Dickie for describing the Borden-Carleton site and Nathan Crowell and Peter McDermott of AGRG for surveying the high water mark. 22

28 Appendix 1 Figure 19: Example of "wave run-up" (R) and still water level (SWL), top figure. Elevated water levels as a result of a low pressure storm system with extreme winds, lower figure. This causes a storm surge raising the water level above the predicted tide with associated wave set-up and wave run-up at the coast. 23

29 Appendix 2 Figure 20: Location of PEI HPN survey monuments. 24