A12. River Hydromorphology Assessment Technique

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1. Introduction[edit]

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.

2. Objectives[edit]

  • Provide a visual assessment of the river using information from desktop studies, aerial photography (wiki link), historical data and field surveys
  • Hydromorphological assessment of rivers, focusing on departure from a natural state, to determine support for ecology

3. Method summary[edit]

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

In order to generate a WFD classification status, at least 1 full 500m RHAT survey and 2 spot checks need to be carried out (NIEA, 2014).

The location of a RHAT survey should be carefully considered using desktop investigation. This ensures pressures and impacts are considered in the assessment. This method of combining desktop and field analysis ensures time is spent surveying rivers accurately, and status classifications are taking into account all channel features, riparian land use and floodplain condition. RHAT survey forms are available explaining the scoring system and abbreviations used in the survey.

Guidance sheets tell the surveyor what the score should be evaluating, considering how far the features are from a semi-natural condition, and advice on what would be typical for different river types.

4. Advantages[edit]

  • Compare river’s current condition to semi-natural state to determine how ecology is supported
  • Morphological condition related to WFD status for standardised comparison
  • Comparability with RHS analysis, as has been adapted and uses similar methods

5. Limitations[edit]

  • Surveying directly following river restoration enhancements may lead to decreased RHAT scores, as some restoration modifications can initially appear severely artificial before they have developed and channel hydromorphology has adapted to the new installation. However, this reduction in RHAT score should only be temporary and subsequent surveys should record higher scores if the restorative works are taking shape (i.e. vegetation is developing) (NIEA, 2014). This can lead to misinterpretation in the score analysis

6.Recommendation for method application[edit]

  • Desktop investigation prior to field work ensures time is not wasted in the field, and status classifications are not misrepresentative of landscape condition
  • NIEA recommend reading the Training Manual before carrying out a RHAT survey
  • Surveys should be carried out over the summer months (May – September) in order to view channel features at low flows. If surveying outside of this time period, an amended score should be allocated, taking into account features which may be submerged, hence not visible (NIEA, 2014)

7. More information see[edit]