River naturalness

Find further information on the Conservation of Freshwater Ecosystem Values (CFEV) Program and its data at www.dpipwe.tas.gov.au/cfev.

Attribute data

TitleRiver naturalness score

CustodianWater and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment

CreatorSteve Carter, Environmental Dynamics

DescriptionAn index which rates the relative ‘naturalness’ or condition of rivers based on a selection of input variables.

Input data

1. CFEV River geomorphic condition attribute data
2. CFEV River biological condition attribute data

Lineage

Two facets were considered fundamental to assessing river condition:

1. changes in river geomorphology caused by human land use, flow regulation, and water infrastructure (e.g. dams), which affect both the water and sediment regime,
2. changes in river biology caused by the establishment of exotic species and changes to river habitats (flow regime, substrate, water quality, etc.).

As such, a condition assessment for rivers was carried out in two parts: a geomorphic and a biological condition assessment. Figure 1 illustrates all the inputs that were either directly or indirectly used to generate an overall biophysical Naturalness score (N-score) for rivers. Some of the variables (including the final N-score) were calculated using expert rules systems as indicated. Information on expert rules systems can be found in Appendix 3 of the CFEV Project Technical Report.

Figure 1. Flow-chart outlining data used in the rivers condition assessment to derive a Naturalness score (N-score). Note: variables were combined using expert rule systems where indicated.

The last step in the rivers condition assessment is described in more detail here. The N-score for rivers was generated from a combination of the equally-weighted geomorphic condition and biological condition sub-indices and assigned to spatial units using the rules described below (see ‘Assigning values to ecosystem spatial units’).

Date createdNovember 2004

Scale and coverage1:25 000; Statewide

Column headingRS_NSCORE

Type of dataContinuous but has been converted to categorical format (see Table 2).

Number of classes3

Assigning values to ecosystem spatial units

An N-score (0 = poor condition – 1 = good condition) was assigned to river spatial units as RS_NSCORE using the expert rule system shown as a definition table in Table 1 (e.g. if the river section has a HIGH score for geomorphic condition and a LOW score for biological condition, then assign a score of 0.3). Using fuzzy logic enables input data and output results to be continuous rather than categorical as implied here (i.e. inputs and output data can range on a continuous scale between 0 and 1, and the process of executing the expert rule system will determine its membership as being HIGH or LOW) (refer to Appendix 3 of the CFEV Project Technical Report for more information on expert rules systems).

Table 1. Expert rules system definition table for the naturalness score for rivers.

The rivers spatial data layer has the continuous naturalness data categorised according to Table 2. The categorical data was used for reporting and mapping purposes.

Table 2. Naturalness categories for rivers.

CFEV assessment framework hierarchy

1. Rivers>Statewide audit>Condition assessment