3.0 General Mapping Procedures
General mapping procedures for detailed estuary mapping are outlined below and follow similar approaches to other RIC standards. The estuary mapping methodology includes the following tasks:
This mapping system is flexible in its use of applicable and available data sources depending on estuary size, composition, and location. The materials required to implement this standard are discussed below.
The preferred inventory base for estuary mapping are high resolution colour aerial photos collected during low tide (Zoltai & Vitt, 1995). Low tide colour aerial photos are considered the best data source for mapping estuarine physical and biological units. The air photographs should be georeferenced and produced in a digital format. Scales of 1:5,000 to 1:10,000 are preferred. Alternatively, black and white high resolution, vertical low tide photos can be used. There is some loss of resolution with these photographs, although they are less expensive to obtain.
A base map is required for initial boundary delineation, providing control points for aerial photos, and providing geodetic control for ground surveys. As a general guideline, mappers should seek out the most accurate base map available for a site. Some alternatives include hydrographic charts, the Watershed Atlas, or TRIM maps. The BC Watershed Atlas provides a `true' shoreline at a 1:50,000 scale. TRIM data provides considerable topographic and planimetric control, however it should be noted that TRIM data are designed for use at 1:20,000 and were gathered from 1:63,000 aerial photos. TRIM 2 aerial photos, however are acquired at 1:40,000 scale. Digital coastline data are also available from the Canadian Hydrographic Service (CHS), although they often omit landward features required for aerial photo control. In addition, there is not a consistent systematic coverage at appropriate scales for estuary mapping.
In most instances, mappers may be forced to combine elements from these different map systems to create a base map. The accuracy of the base map is less of an issue when differential GPS is utilized for ground survey. However, ground control is still required for proper air photo pre-typing of the biophysical properties.
An overview of larger estuaries may be provided by satellite imagery. Classification of satellite data can be used as a coarse filter for vegetation types. Satellite data has been commonly used for broad scale change detection (regarding in-filling rather than vegetation change) in estuaries in the U.S.
Airborne multi-spectral scanners have only recently been applied to typing coastal vegetation. They have been found to be useful for broad vegetation typing, and can be of use in pre-typing broad vegetation classes and change detection. Spectrographic resolution of finer distinctions in vegetation is primarily limited by variance due to the presence of old vegetation (Aitken & Borstad, 1995; Zacharias et al. 1992). However, the fine spatial resolution of such sensors (e.g. 0.8 m) is one of their key attributes in fine scale estu-ary mapping. At present, these new technologies are generally prohibitively expensive.
Historical air photos, reports and other existing inventory data for the study area permit an assessment of the relative stability of the features. This procedure also facilitates investigation of the influence of anthropogenic impacts on the estuary and may assist in explaining conditions that are difficult to interpret in the field. The original B.C. Estuary Series Maps, using the classification system of Hunter et al. (1983) are comparable with the present system.
Other types of data, including ground or air 35 mm photography, aerial video imagery, and any other existing relevant sources may be useful. While georeferencing is not possible from these media, they can provide invaluable typing assistance, especially in recognizing features more apparent from a profile rather than a vertical image.
The estuary overview database is designed to provide general information on the overall character of the estuary. Examples of overview information include total area of the watershed, watershed name, and measures of discharge. This overview information allows a regional comparison between estuaries, which can then be integrated with more detailed biotic and physical information collected at much large scales.
Pre-typing can be completed using digital enlargements of air photos or on transparent overlays on aerial photos. Study area boundaries and biotic and physical units can be identified and mapped from aerial photos. Preferably, a digitizing tablet may be used to enter pre-typed boundaries directly into a GIS. Whether manual or digital, each of the required layers (tidal elevation, biological unit, and physical unit) should be pre-typed on a separate sheet/layer. Boundaries that coincide should be copied from the relevant layer rather than redigitized.
A minimum polygon size of 0.5 cm2 is recommended, following the TEM guidelines (RIC, 1998). This corresponds to an area of 0.125 ha at a scale of 1:5,000, and 0.5 ha at 1:10,000. Items smaller than the minimum polygon size may be included as point or line features (e.g. plot locations or man-made features).
Estuary field work involves a combination of marine and terrestrial sampling strategies. The objectives of the field survey are to confirm polygon boundaries and designations, to collect further biophysical data, and to refine the classification of the mapped units.
The field survey intensity of biological resources can be based on the guidelines outlined in the Standards for Terrestrial Ecosystem Mapping (TEM) (RIC, 1998) and should be based on a `minimum sampling density', where the number of ground sites depends on the overall study area. For estuaries of 20 to 500ha, and map scales of 1:5,000, a survey intensity of approximately one plot per hectare is recommended. Based on an average polygon size of 3 to 4 cm2, this level of ground inspection means that most polygons will be checked. The TEM methodology further recommends a ratio of full plots to ground inspections to visual checks at a ratio of 2:15:83.
TEM presents these survey intensity guidelines to assist in the design of the field program. The survey intensity selected for the specific estuary project will be dependent on the project objectives and the level of confidence required in the final mapping. Increased reliability is achieved through higher survey intensity and larger scale mapping (RIC, 1998).
Field work should be conducted during the lowest tides of the summer months. Ideally, sampling should take place as close as possible to the dates of the source material (air photos or airborne scanner data), but late enough in the growing season for the grasses to have flowered. Pre-typed data should be fully available to field staff.
While in the field, special attention should be paid to the location of vege-tative, surficial geology and 'form' boundaries not evident in aerial photography. New poly-gon boundaries should be generated and the sampling strategy altered accordingly. A new boundary is generated on the appropriate layer whenever there is a significant change in the appropriate factor. Generating new polygon edges may be accomplished using a series of GPS waypoints, or through taking a GPS fix at the center of the new polygon and delineating edges using stan-dard survey techniques.
The final stage of the mapping project involves the completion of photo-typing and the finalizing of polygon boundaries and labels for each of the data layers. Before beginning, all relevant information should be available including pretyped air photos and digital files, field data, and other existing data for the area.
The most important part of quality control is attention to detail and standardization at all stages of the mapping project. Reviews and reports at each stage of the project provide a method of evaluating and tracking progress.
Quantitative Assessment: A sample of the map polygons should be assessed in the field by the mapping project supervisor or designate. The objective of this assessment is to provide statistics on the accuracy of the polygon designations and to "audit" the mapping project. The process utilized may vary, but the following is recommended:
Estuarine systems represent a complex interweaving of geomorphic and vegetation influenced forms, modified by salinity, flow, anthropogenic factors and others. As such, application of this classification system requires professional interpretation and a commitment to integration of biological and physical information. It is recommended that mapping be conducted in a team approach to ensure integration of the different types of information and to reduce field costs. A minimum level of profes-sional experience is suggested for mappers in order to ensure a consistency and professional treatment of estuarine mapping as outlined in this manual. These requirements should be applied to all persons responsible for conducting, coordinating, directing or reporting on estuarine mapping projects. Requirements include:
Geomorphology and Physical:
Registered Professional Geoscientist and/or Master of Science degree in geology or physical geography, with a specialty relating to geomorphology. Alternately, a Bachelor of Science with an equivalent combination of training and experience. Demonstrated knowledge and experience related to:
Marine Biology:
Master of Science in biology, with a specialty in marine biology. Alternately, a Bachelor of Science with an equivalent combination of training and experience. Demonstrated knowledge and experience related to: