River and stream water quality and ecology - Greater Wellington ...

River and stream water quality and ecology in the Wellington region: State and trends
Appendix 2: River Environmental Classification (REC)
As outlined in Section 2.1, rivers and streams in the Wellington region are diverse and
some may have differing water quality simply due to their size, climate and underlying
geology rather than due to human-induced impacts. To reduce this bias, comparisons
between RSoE sites are undertaken using the River Environment Classification (REC).
REC characterises river environments at six hierarchical levels, corresponding to a
controlling environmental factor (Snelder et al. 2003). The factors, in order from the
largest spatial scale to the smallest, are climate, source-of-flow, geology, landcover,
network position and valley landform. The first four REC factors are explained in
Table A2.1. See Appendix 1 for the REC description for each RSoE site.
Table A2.1: REC classification levels, classes, mapping characteristics and criteria used to
assign river segments to REC classes (after Snelder et al. 2003)
Classification level
and scale
Climate
(10 3 – 10 4 km 2 )
Source of flow
(10 2 – 10 3 km 2 )
Geology
(10 – 10 2 km 2 )
Landcover*
(10 km 2 )
Classes and notation
Warm extremely wet
(WX)
Warm wet (WW)
Warm dry (WD)
Cool extremely wet (CX)
Cool wet (CW)
Cool dry (DC)
Mountain (M)
Hill (H)
Low elevation (L)
Lake (Lk)
Alluvium (Al)
Hard sedimentary (HS)
Soft sedimentary (SS)
Volcanic basic (VB)
Volcanic acidic (VA)
Plutonic (Pl)
Miscellaneous (M)
Bare (B)
Indigenous forest (IF)
Pastoral (P)
Tussock (T)
Scrub (S)
Exotic forest (EF)
Wetland (W)
Urban (U)
Mapping
characteristics
Mean annual
precipitation, mean
annual potential
evapotranspiration,
mean annual
temperature.
Catchment rainfall
volume in elevation
categories, lake
influence index.
Proportions of each
geological category in
section catchment.
Proportions of each
landcover category in
section catchment.
Class assignment criteria
Warm: mean annual temperature ≥
12˚C
Cool: mean annual temperature 500 mm and 50% annual precipitation volume
>1,000 m ASL
H: 50% precipitation volume 400 to
1,000 m ASL
L: >50% rainfall 0.033
Class = spatially dominant geology
category unless combined soft
sedimentary geological categories
exceed 25% of catchment area, in
which case class = SS.
Class = spatially dominant landcover
category unless pastoral exceeds 25%
of catchment area, in which case class
= P, or unless urban exceeds 15% of
catchment area, in which case class =
U.
* It is important to note that landcover types that are not classified as dominant using the REC criteria may still significant affect river and stream
water quality and ecology. Further, in many cases, the current ‘condition’, as measured at each RSoE site, is the result of the cumulative impacts
of all landcover types and associated activities in the upstream catchment.
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