Class boundaries

CNR-IRSA activities related to INHABIT

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Class boundaries

Through a common action program known as Common Implementation Strategy (CIS) various Authorities and Member States involved in WFD implementation have established a framework to put WFD objectives into practice. Within this strategy, the results of the first intercalibration exercise for the WFD has led to a common definition of ecological status and class boundaries for different Member States have been issued.

In Italy the STAR_ICMi (STAR Intercalibration Common Metric index) has been adopted as official method for the purposes of the intercalibration exercise. Thorough the STAR_ICMi official values for the assessment of ecological state are derived. The approach considered to derive class boundaries is inspired by the REFCON guidance. The figure reports a graphic example on how ecological class boundaries have been derived, starting from definition of reference conditions as prompted by the REFCOND guidance. The procedure considered the following steps:

  • collection of samples from references sites;
  • calculation of the median value of STAR_ICMi used for the calculation of the Ecological Quality ratio (EQR);
  • calculation of the 25th percentile of STAR_ICMi set as High-Good state boundary.

In other words the procedure considers the calculation of the STAR_ICMi for reference sites samples and sets the value of the 25th percentiles of the obtained values as boundary limit between the High status and the Good status. Boundaries for the remaining classes are calculated by dividing the interval of STAR_ICMi values between the 25th percentile and 0 into 4 equal parts. Therefore, the boundary between Good and Moderate status will result from the H/G boundary multiplied by 0.75.

The presented procedure has been adopted in Italy for the definition of class boundaries for river macrotypes considered within the intercalibration exercise for Alpine, Central and Mediterranean GIG. A brief description of WFD intercalibration macrotypes for rivers is here reported.


IC river type

Synthetic description


Small-medium size, high altitude, calcareous


Small-medium size, high altitude, siliceous


Small size, lowland, sandy substrate, siliceous


Medium size, lowland, mixed geology


Large size, lowland, mixed geology


Small size, lowland, calcareous


Small Mediterranean mid-altitude streams (200-800m asl)


Small and medium Mediterranean lowland streams (<400m asl)


Large lowland rivers


Small and medium Mediterranean mountain streams (400-1500m asl)


Small lowland temporary streams (<300m asl)


Class boundaries for large Mediterranean rivers (R-M3) have been borrowed from R-M2 and R-M4 macrotypes; such types are not considered at the moment for inclusion into intercalibration process and some adjustments could be required.

Reported class boundaries have been adopted for all river types considered in MacrOper system. Detailed correspondence between national type and intercalibration macrotype is reported in DM 260/2010.

River types comprised within the Italian borders are reported to European intercalibration macrotypes according to the following scheme:

Alpine GIG

  • HER 1, 2, 3 and 4 (Alps), all national types: R-A1 or R-A2 according to catchment geology;

Central/Blatic GIG

  • HER 1, 2, 3, 4, 5 and 7 in hilly or lowland areas and HER 6 (Po plain northward of Po river), all national types: R-C;

Mediterranean GIG

  • HER 8-21 (Mediterranean) and HER 6 (Po plain southward of Po river), perennial rivers: R-M1-R-M4 (according to table 2 DM 260/2010 and updates);
  • HER 8-21 (Mediterranean) and HER 6 (Po plain southward of Po river), temporary rivers: R-M5.