Environmental Engineering Reference
In-Depth Information
Table 6.2. Physical, chemical and geographical characteristics that can be used
in the Water Framework Directive Systems A and B to define typologies for
matching test sites to reference sites
SYSTEM A
Altitude typology
Size typology based on
catchment area
Geology typology
Small 10-100 km
2
High > 800m
Calcareous
Medium 100-1000 km
2
Mid altitude 200-800m
Siliceous
Large 1000-10 000 km
2
Lowland < 200m
Organic
10 000 km
2
Very large
>
SYSTEM B
Obligatory factors
Optional factors
Altitude
Distance from river source
Latitude
Energy of flow (function of
flow & slope)
Longitude
Mean water width
Geology
Mean water depth
Size
Mean water slope
Form and shape of the main
riverbed
River discharge (flow) category
Valley shape
Transport of solids
Acid neutralising capacity
Mean substratum composition
Chloride
Air temperature range
Mean air temperature
Precipitation
condition produced by pre-existing RIVPACS-type System B models (RIVPACS,
UK; SWEPAC(SRI), Sweden; PERLA, Czech Republic) were more effective (i.e.,
produced lower standard deviations of O/E ratios where O is an individual
reference site and E is the expected end group mean) than models based solely
on the WFD System A variables or null models based solely on a single expect-
ation of the average across all reference sites (Davy-Bowker et al.
2006
). This is
primarily because System A uses very broad categories of map-derived variables
that have limited ecological relevance, whereas RIVPACS-type System B models
are typically based on continuous variables selected for their ecological
significance.
