Index of Wetland Condition (IWC)
Description and method logic
The IWC is used principally to assess wetland condition. The technique also advises management decisions and targets while assessing threats to a wetland. It has six weighted sub-indices based on the characteristics that define wetlands: wetland catchment; physical form; hydrology; soils; water properties; and biota.
The Index of Wetland Condition (IWC) is a standard method developed in Victoria for rapid assessment of wetland condition. It is based on the state of the biological, physical and chemical components of the wetland ecosystem and their interactions. The method aims to differentiate natural from human induced changes in wetland condition and assist in management decisions. It has six weighted sub-indices based on the characteristics that define wetlands: wetland catchment; physical form; hydrology; soils; water properties; and biota. It is primarily a site/habitat based assessment (individual wetland scale), some measures require wetland catchment scale assessment.
The technique is suitable for use at all naturally occurring, non-flowing wetlands without a marine hydrological influence in Victoria, at any time of the year. It is designed to assess wetland condition in a single visit.
IWC can be used as a tool for surveillance of wetland extent and condition over a 10-20 year timeframe.
The IWC takes the form of a hierarchical index. It has six weighted sub-indices based on the characteristics that define wetlands: wetland catchment; physical form; hydrology; soils; water properties; and biota. Possible measures for each sub-index have been selected by identifying commonly accepted and well recognised threats and impacts in Victoria that affect wetland condition and relating them to key ecological components of wetlands. The measures were then assessed against suitability for rapid assessment. A methods manual provides details of how to collect the recommended measures.
The methodology makes use of the IWC wetland mapping tool; a publicly available mapping tool on the DSE website. This is necessary for assessing changes in actual salinity concentration, while also providing evidence for changes in vegetation and wetland fauna from pre-European times.
Each sub-index is scored out of 20. The total index score is then calculated by summing each sub-index score multiplied by its respective weight. The wetland is then assigned a linguistic condition category based on its total numerical score. Refer to the IWC Assessment Procedure for more information.
Criteria groupings of the method
Criteria or sub-indices are based on the characteristics that define wetlands: wetland catchment, physical form, hydrology, soils, water properties and biota.
Data on pre European salinity, land use adjacent to the wetland, width of wetland buffer, percentage of wetland perimeter with a buffer, reduction in wetland area, wetland area with changed bathymetry, action that have changed the water regime and their severity, nutrient enrichment, degree of wetland soil disturbance and wetland vegetation quality assessment.
An understanding / ability to identify and assess wetland Ecological Vegetation Classes in Victoria is required to assess the vegetation component of the IWC. Refer to the IWC Assessment Procedure for more information on necessary skills.
Field assessment, field sheets / mobile app for field data entry, desktop mapping, data management system for data curation and reporting
IWC result for a wetland in five categories:
The methodology also produces disaggregated, unweighted sub-index scores.
Criteria by category
Physical and chemical
Management and planning
The technique requires a general expertise in NRM and expertise in wetland Ecological Vegetation Class identification and assessment – i.e. botanical expertise. Various NRM authorities, consultants, botanists and government departments and agencies are likely to use this methodology.
Last updated: 16 December 2020
This page should be cited as:
Department of Environment and Science, Queensland (2020) Index of Wetland Condition (IWC), WetlandInfo website, accessed 1 February 2023. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/resources/tools/assessment-search-tool/index-of-wetland-condition-iwc/