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ECOFACT ECOFACT | River Hydromorphology Assessment Technique (RHAT)

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RHAT Surveys

The Environmental Protection Agency (EPA) in the Republic of Ireland and the Northern Ireland Environment Agency (NIEA), through the North South Shared Aquatic REsources (NS SHARE) project, have collectively developed a Rapid Assessment Technique (RAT) to allow for in-field assessment and classification of rivers in terms of their hydromorphology. This was utilised in the characterisation and evaluation of watercourses under the requirements of the EC Water Framework Directive (EC/60/2000), colloquially known as the WFD Directive.

The RAT methodology has been modified by the NIEA to meet more practical application requirements and has been re-named as the River Hydromorphology Assessment Technique (RHAT); taking account of the River Habitat Survey (RHS) methodology developed by the UK Environment Agency. The RHAT methodology is a useful tool to assess the departure of hydromorphological features from ‘naturalness’ and allows for the assignment of a morphological classification directly related to WFD status i.e. High, Good, Moderate, Poor or Bad; based on semi-qualitative and quantitative criteria. Hydromorphological criteria assessed in the RHAT include:

  • Channel morphology and flow types
  • Channel vegetation
  • Substrate diversity and condition
  • Barriers to continuity
  • Bank structure and stability
  • Bank and bank top vegetation
  • Riparian land cover
  • Floodplain interaction

The River Hydromorphology Assessment Technique (RHAT) utilises a checklist form employed on the river bank and completed based on visual observations made by the assessor. ECOFACT employ the RHAT scheme during river corridor studies as a visual assessment tool to provide a standardised approach in determining the hydromorphological factors affecting a watercourse with regard to meeting WFD ‘Good Status’ requirements.

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