Andrew G. Sherin

Integrating Geoscience Data for Environmental Planning in Severn Sound

Abstract

An effective tool for use by geoscientists and environmental planners has been developed by integrating several geoscientific data sets from several sources for Severn Sound. Severn Sound is an enclosed embayment of Lake Huron, one of the Great Lakes and has been designated an Area of Concern by the International Joint Commission. Three examples of geoscience data integration are presented: the production of interpreted seismic profiles to show the depth of sediments and their vertical distribution; the construction of an integrated terrestrial / lacustrine digital elevation model; and the draping of lacustrine surficial geology of the DEM to investigate relationships between topography, morphology and sediment type.

Introduction

The Geological Survey of Canada (Atlantic) (GSC Atlantic) has been working since the summer of 1995 with the Severn Sound Remeadial Action Plan (RAP) to develop a geological framework to support environmental planning and remeadial action in Severn Sound and its watershed.

Data from a variety of sources has been integrated into one environment using ArcInfo Version 7.0.4 and Arcview Version 2.1. The Arcview product will be delivered to the Severn Sound Remeadial Action Plan Implementation Office for their use in environmental planning. The products will also be used by geologists at the GSC Atlantic to provide advice to the Severn Sound RAP and to contribute to GSC Atlantic’s Great Lakes quaternary geology research program.

Background

Severn Sound is an enclosed embayment on the southeastern shore of Georgian Bay in Lake Huron, one of the Great Lakes (see location in Figure 1). The Sound is shallow with the principle water input from the Severn River, part of the Trent / Severn waterway which links Lake Ontario to Lake Huron. The Sound has several ecologically important wetlands on its shores. Some of the islands on its northern shore are part of the Georgian Bay Islands National Park.

The human population around Severn Sound increases greatly in the summer. There are significant year round population centres in Midland and Penetanguishene. In the summer it is a popular tourist destination and refuge for city dwellers from southern Ontario. Recreational boating is ubiguotous.

Agriculture is the principle activity in the southern areas of the Severn Sound watershed. The total watershed covers an area of 1,000 square kilometres.

Severn Sound has been designated as an Area of Concern by the International Joint Commission, one of 43 such sites on the Great Lakes. The primary problems are eutrophication and excessive algal production caused by phosphorus from sewage treatment plants, agricultural activities, shoreline development and other sources.

Severn Sound marks the contact between the PreCambrian rocks of the Canadian Shield and the Phanerozoic rocks of the St. Lawrence Platform. Figure 1 shows in green the contact of the Grenville Province of Canadian Sheild. The Grenville Province is composed of mostly metamporphic rocks which have been massively deformed. The irregular and folded morphology of these rocks is largely responsible for the numerous islands which is a stricking feature of the north shore of the Sound. South and west of this contact are relatively flat lying sedimentary rocks of Ordivician age. The south shore is chacterized by low relief plains of bedrock and glacial drift with numerous wetlands.

Severn Sound Remeadial Action Plan

The Severn Sound Remeadial Action Plan was developed by a team of scientists from the Province of Ontario and the Canadian Federal government, working closely with local stakeholders through a Public Advisory Committee.

The Implementation Office for the RAP is located at the Wye Marsh Wildlife Centre in Midland, Ontario, Canada.

The Remeadial Action Plan (RAP) addresses environmental problems through actions in six main categories:

phosphorous control
habitat restoration and enhancement
prevention of contamination
planning to sustain ecosystem health
monitoring progress and effectiveness
enhancement of public awareness of environmental issues

The principle objectives of the GSC Atlantic's collaboration with the RAP were to:

to describe the distribution of bottom sediments and features to establish the geological and structural framework of the bottom of Severn Sound.
to complete the mapping of the lakebed to determine the thickness and distribution of bottom sediments which may be associated with contaminants, both the surficial geology and the quaternary geology.
to investigate and document anthropogenic debris to determine if remeadial action is required.
to obtain sediment core samples of bottom features which may form traps for contaminated sediments, to verify the sonar interpretation of bottom sediments and to establish sedimentation rates.
to obtain sediment samples from selected wrecks in Severn Sound with known date of sinking to establish sediment deposition and transport.

Data Sources

Geological Survey of Canada (Atlantic)'s geophysical surveys

In the summer of 1995, GSC Atlantic conducted a high resolution seismic and sidescan sonar survey of Severn Sound in collaboration with McQuest Geophysical of Burlington, Ontario and the Ontario Ministry of Environment and Energy. The track lines for this survey are shown in red in Figure 2. This survey was followed up by submersible and ROV investigations in collaboration with the Canadian Department of National Defence and bottom sampling surveys in the summer of 1996. This paper describes work only on the data sets acquired in 1995.

The high resolution seismic data was interpreted by GSC Atlantic and McQuest Geophysical scientists. The acoustic horizons were digitized and converted to a set of ASCII files of x,y,z coordinates using Hydro navigation software which merges positional data with depth to acoustic horizon. The sidescan sonar data was similarly interpreted and digitized in AutoCad by McQuest Geophysical. The ASCII files and AutoCad dxf files were sent to the GSC Atlantic for integration with other data sets and final product development.

Canadian Hydrographic Service bathymetric data

Three digital data sets were obtained from the Department of Fisheries and Oceans' Canadian Hydrographic Service.

The Electonic Navigation Chart (ENC) for Severn Sound was provided as a CARIS(1) file. The ENC contained shoreline, bathymetric contours, selected bathymetric soundings, artificial shorelines such as wharves and breakwaters and other navigation related information.

Two digital field sheets, also in CARIS format, were also provided containing additional contour information and detailed bathymetric soundings for the central part of Severn Sound.

Province of Ontario Topographic Maps

Twenty three digital data files of topographic data from the Province of Ontario were obtained through the Severn Sound RAP Implementation Office. The files, which surrounded Severn Sound, contained drainage, contour, spot elevation, stream and lake information and were provided as ArcInfo export files.

Ontario Geological Survey Quaternary Geology Map

A digital file of terrestrial Quaternary Geology from the Ontario Geological Survey was provided through the Severn Sound RAP Implementation Office as Shapefiles.

Tools for Data Integration

Interpreted Seismic Profiles

Interpreted seismic profiles were constructed from the ASCII files provide by McQuest Geophysical using customized AML programs and the dynamic segmentation feature of ArcInfo V. 7.0.4.

The profiles show sediment thicknesses and the vertical distribution of sediment types. They were produced using the procedure outlined below.

A coverage of the geophysical track lines was contructed from GPS data and a route system built on the survey lines.
The makecov AML was run to generate a coverage containing points and arcs for each horizon and each survey line. The z value for the horizon was added to the PAT. The AML makes extensive use of the UNIX utilities awk and sed to reformat the ASCII files. The makecov AML also measured the distance of the interpreted points along the survey line and added it to the PAT.
The makeprof AML took the distance along track and the depth to acoustic horizon information from the PAT and created a profile coverage, where x was the distanace along track and y was the depth to acoustic horizon.
These individual coverages for each horizon were appended to create one coverage for each survey line. The coverages were edited to create profiles like those shown in Figure 3.

The depth to horizon information was also used to construct surfaces of acoustic horizons so their horizontal extent could be visualized.

Digital Elevation Models

An integrated terrestrial / lacustrine DEM was constructed for Severn Sound and surrounding area using the bathymetric data from the Canadian Hydrographic Service and the topographic data from the Province of Ontario. Files containing contours, spot elevations and elevation attributed lake shorelines, and streams were created using Arctools for input to Topogrid. The shoreline from the topographic data was used to define the transition from terrestrial to lacustrine because its higher resolution. The bathymetric data was adjusted to match the horizontal datum and the vertical datum of the topographic data.

The resulting DEM is shown as a colour shaded relief map in Figure 4.

Draping

The surficial geology map, shown in Figure 5, has been transparently draped over the DEM to investigate relationships between topogaphy, morphology and sediment type. This was accomplished by converting the colours of the geology map's polygons to hue and saturation grids and combining them with hillshade information from the DEM. Figure 6 is an example of this draping procedure.

Conclusion

The shaded relief map in particular is valuable not only for use by scientists and environmental planners but as a public education tool since is provides an accessible visualization of the regional morphology. Figure 4 shows the differences in morphological character between the north and south shores of Severn Sound. It also unveils submerged morphology like the channels seen in the central part of the Sound.

The draping of the surficial geology transparently over the DEM assists the scientist in correlating morphology, topography and sediment types. The area covered by Figure 6 shows a possible correlation between ridges in the DEM and glacial drift deposits.

The integration of the above mentioned data sets has provided an effective tool for the use of GSC (Atlantic) scientists and the Severn Sound RAP Implementation Office to meet the objectives of the collaborative project and contribute to the actions of the Remeadial Action Plan.

Acknowledgements

The author would like to acknowledge Keith Sherman, the Severn Sound RAP Coordinator, Darren Keys and Mike Benner of McQuest Geophysical and the Hydrographic Data Centre, Central and Arctic Region of the Canadian Hydrographic Service for providing the data sets. Steve Blasco, GSC Atlantic's senior scientist on the project supported and provided helpful review of this work. Clayton Levert performed most of the data processing for building the profiles and the DEMs.

End Notes

CARIS or Computer Aided Resource Information System is a product of Universal Systems Ltd. of Fredericton, New Brunswick, Canada.

Andrew G. Sherin
Information Systems Specialist
Geological Survey of Canada (Atlantic)
Bedford Institute of Oceanography
1 Challenger Drive
P.O. Box 1006
Dartmouth, Nova Scotia, Canada
B2Y 4A2
Telephone: (902) 426-7582
Fax: (902) 426-4104
E-mail: sherin@agc.bio.ns.ca