Find further information on the Conservation of Freshwater Ecosystem Values (CFEV) Program and its data at www.dpipwe.tas.gov.au/cfev.
TitleFlow change sub-index
CustodianWater and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment
CreatorSteve Carter, Environmental Dynamics
DescriptionAn index which rates the flow change of rivers according to flow variability, abstraction and regulation.
Input data
Lineage
Flow change was established as a sub-index that was derived with an expert rule system (see ‘Assigning values to ecosystem spatial units’ below). Information on expert rules systems can be found in Appendix 3 of the CFEV Project Technical Report. The input variables were flow variability, the abstraction index and the regulation index. The order of weighting for each of the input variables was abstraction index < regulation index < flow variability.
The method for assigning a flow change sub-index score to the river spatial units is provided below.
Date createdNovember 2004
Scale and coverage1:25 000; Statewide
Column headingRS_FLOW
Type of dataContinuous but has been converted to categorical format (see Table 2).
Number of classes5
Assigning values to ecosystem spatial units
A flow change sub-index score (0 = poor condition – 1 = good condition) was assigned to river spatial units as RS_FLOW using the expert rule system shown as a definition table in Table 1 (e.g. if the river section has a HIGH score for regulation index, LOW score for abstraction index and a HIGH score for flow variability, 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 flow change sub-index for rivers.
Regulation index (RS_REGI) | Abstraction index (RS_ABSTI) | Flow variability (RS_FLOVI) | Flow change score (RS_FLOW) |
H | H | H | 1 |
H | H | L | 0.2 |
H | L | H | 0.4 |
L | H | H | 0.3 |
H | L | L | 0.1 |
L | H | L | 0.5 |
L | L | H | 0.2 |
L | L | L | 0 |
The rivers spatial data layer has the continuous flow change sub-index data categorised according to Table 2. The categorical data was used for reporting and mapping purposes.
Table 2. Flow change sub-index categories for rivers.
Category | Min to max values |
1 | 0 to <0.2 |
2 | 0.2 to <0.4 |
3 | 0.4 to <0.8 |
4 | 0.8 to <1 |
5 | 1 |
CFEV assessment framework hierarchy