Wetland identification, delineation, classification and evaluation require specialised field, laboratory and desktop investigations skills. Wetland assessments should be coordinated and led by professionals with specific expertise and experience in wetland processes (e.g. wetland ecology, hydrology and sedimentology). An understanding of the dynamic nature of wetlands and their response to seasonal conditions and longer-term climate variability is particularly important.

To amend wetland mapping, adequate information needs to be supplied to DBCA to support the application. To ensure that all landowners and land managers are aware of the assessments and the potential implications a Wetland Dataset Modification Request Form must be completed and supplied with the application. Applications to amend a wetland dataset need to be forwarded directly to DBCA for review via email wetlands@dbca.wa.gov.au.

Where both wetland delineation (extent or type) and evaluation (management category) are being disputed it is recommended that you confirm the wetland delineation of a site prior to undertaking a wetland evaluation. If both applications are submitted at the same time and there is insufficient evidence to support the proposed delineation change then the wetland evaluation may need to be resubmitted to align with the final wetland boundaries and classification (type).

The identification and delineation of a wetland is reliant upon characteristics of hydrology, soils and wetland vegetation (Hill et al. 1996). DBCA guidance for identification and delineation of wetland is outlined in Wetland identification and delineation information sheet (DBCA 2017), which is available for download below.

Any investigation into the delineation of a geomorphic wetland boundary or demonstration of the presence/absence of a wetland should incorporate information addressing all three wetland determining characteristics. A single characteristic may not provide sufficient justification for the delineation of a geomorphic wetland boundary.

The following information should be submitted to support a wetland delineation review, depending on the wetland characteristics and the proposed modification*.

Hydrological information including**:

• aerial photographs overlaid with topographical and groundwater elevation contours relative to AHD and geomorphic wetland type boundary from the current dataset
• any available groundwater data (e.g. Perth Ground Water Atlas, Department of Water) · site specific profile of maximum groundwater level across the wetland (i.e. from on-site hand auger holes incorporating measurements from the wetland centre and margins focusing on the areas between the proposed boundary and the mapped boundary).
• visual observations or indicators of inundation or waterlogging (e.g. water marks).
• Hydrological monitoring data using groundwater monitoring wells (where available) from the site or in the vicinity of the site. There is no expectation that wells will be installed for this purpose.

Soil information including**:

• available information from existing maps and databases (see Soil classification in Western Australia on the Department of Primary Industries and Regional Development website for guidance)
• evidence of soil characteristics (for example particle size, texture, colour, organic carbon, peat, carbonate muds)
• evidence of an impervious layer (for example clay, granite)
• evidence of depth and extent of anthropogenic fill
• soil profile logs, referenced to AHD, analyses along transects from the centre to the margins of the wetland (i.e. description of the soil components from an auger sample for example at 10cm intervals along the core) and the date
• location of auger sample sites on a georeferenced map, illustrated with an aerial photograph
• if available, evidence of biogenesis associated with waterlogging or inundation (for example algal or invertebrate remains)
• if available, evidence of biochemical processes associated with aeration/waterlogging or inundation (for example mottling, sulfidic minerals, water/soil chemistry)
• analyses of the variation between wetland and dryland soil profiles discussing:
  • the existing mapped wetland (as per the dataset)
  • the area proposed for modification.
  • the area outside of the existing mapped wetland (i.e. dryland)

It is important to note that the use of broad scale soil mapping (e.g. 1:250 000) is not considered sufficient for site specific wetland delineation.

Vegetation information including:

• a vegetation survey in accordance with the Environmental Protecton Authority's Technical Guidance – Flora and Vegetation Surveys for Environmental Impact Assessment” at the level of a ‘detailed survey’
• the vegetation survey should include:
  • vegetation unit mapping – this information allows us to establish the potential extent of wetland vegetation
  • at least one sample plot (10m x 10m) per mapped vegetation unit with additional plots to demonstrate the variation of floristics and condition within the unit - this information allows for a comparison against wetland Floristic Community Types (FCT)
  • location of the plot sites illustrated on an aerial photograph
  • a description of the vegetation units including the variation between plots within a unit
  • a comprehensive flora list for each vegetation unit noting facultative and obligate wetland species and their distribution across the site. 
• analyses of the variation between wetland and dryland vegetation units discussing:
  • the existing mapped wetland (as per the dataset)
  • the area proposed for modification
  • the area outside of the existing mapped wetland (i.e. dryland)

It is important to note that the absence of wetland vegetation alone, does not provide sufficient justification for an existing mapped wetland area to be modified to ‘No longer a wetland’. Where wetland vegetation has been cleared, a wetland may still retain hydrological or ecological functions and cultural or scientific values.

Proposed wetland boundaries should consider the entire geomorphic wetland and not be restricted to cadastral boundaries or a particular study area.

* DBCA Identification and delineation guidelines were written for the Swan Coastal Plain. They will not be relevant to all wetland types throughout the state. If guidance on wetland delineation is required for wetlands in other regions, please contact DBCA on wetland@dbca.wa.gov.au. 

** Where possible it is useful to provide this information as conceptual hydrological and hydrogeological models showing the spatial and vertical distribution of soils and geological units, sources of surface water and groundwater entering and leaving the site and their interactions with the surface.

Wetland evaluation is the process of assessing and documenting a wetland’s values by considering information about its attributes and functions. Some wetland datasets, such as Geomorphic Wetlands of the Swan Coastal Plain dataset, have been evaluated and assigned wetland management categories.

If the wetland boundaries are not in dispute then A methodology for the evaluation of wetlands on the Swan Coastal Plain (the methodology) can be applied to evaluate the management category of a wetland. The methodology is a detailed guide on how to undertake an evaluation and also has guidance on how to apply management category boundaries where the current boundaries do not reflect the current conditions on the ground. The methodology can be downloaded below.

The evaluation methodology is written for the Swan Coastal Plain (SCP) but can be applied in other portions of the state with some alterations. DBCA’s Species and Communities program should be consulted before applying the methodology outside of the Swan Coastal Plain.

Wetland evaluation considers the inter-related values of a wetland and therefore the management category should represent the entire geomorphic wetland without being constrained to cadastral boundaries. However, in the case of extensive wetlands (generally of greater than 70 ha and excluding lakes and sumplands (Hill et al. 1996a)) which have been disturbed, a separate management category will be assigned to portions of a wetland in order to reflect the remaining values. This approach recognises the diverse condition and land uses of extensive wetlands, and the importance of remnant wetland vegetation.

It is acknowledged that access to all areas of a geomorphic wetland may not be possible due to property ownership, however, as much information as possible should be submitted.

Please note that the evaluation process to assign a management category is a scientific assessment of wetland values and should not be viewed as a means to facilitate or prevent development proposals. In assessing requests to modify the dataset, DBCA relies on technical information only, and does not consider any associated development proposals.

For ease of use the following templates and forms for the methodology are provided separately as word documents and can be downloaded below:

• Wetland evaluation desktop and site assessment template 
• Evaluation criteria template