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TitleRiver geomorphic condition sub-index
CustodianWater and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment
CreatorSteve Carter, Environmental Dynamics
DescriptionAn index which rates the geomorphic condition of rivers according to sediment input, flow change, sediment capture and geomorphic responsiveness.
Input data
Lineage
The geomorphic condition sub-index was derived using an expert rule system which used inputs describing the degree of change in sediment and flow regimes from a pre-European settlement state (inputs: sediment input, flow change and sediment capture (note, values of the regulation index were used as a surrogate for a sediment capture index) (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 CFEV assessment of the physical condition of rivers is largely rule-based. Most of the rules and relationships between drivers and responses were dependent on the geomorphic context. An attribute was required which would describe the responsiveness of a river sections’ geomorphic type to provide an input into the analysis.
Geomorphic responsiveness was used to set a context for the geomorphic condition expert rule system. It gives an indication of the likely degree of responsiveness of channel form to anthropogenic changes in flow and/or sediment regime. The sensitivities were derived from the attributes of the geomorphic mosaics, with highly alluvial and fine sediment geomorphic types rated highly responsive, bedrock controlled systems rated low, and all others rated medium. The geomorphic condition score was generally lower if the river section was of a geomorphic type that was highly responsive.
Experts rated flow change as having the most influence on geomorphic condition, followed by sediment input and then sediment capture.
The method for assigning a geomorphic condition sub-index score to the river spatial units is provided below.
Date createdNovember 2004
Scale and coverage1:25 000; Statewide
Column headingRS_GEOM
Type of dataContinuous but has been converted to categorical format (see Table 2).
Number of classes3
Assigning values to ecosystem spatial units
A geomorphic condition sub-index score (0 = poor condition – 1 = good condition) was assigned to river spatial units as RS_GEOM using the expert rule system shown as a definition table in Table 1. A context was set to take into account the geomorphic responsiveness rating for the river section. An example of applying the rules is that if the river section has a HIGH score for sediment input, LOW score for flow change and a HIGH score for sediment capture, and it has a geomorphic responsiveness rating of M, then assign a score of 0.35). 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 geomorphic condition sub-index for rivers.
Sediment input (RS_SEDIN) | Flow change (RS_FLOW) | Sediment capture (Regulation index) (RS_SEDCA) | Geomorphic condition score (RS_GEOM) Geomorphic responsiveness (RS_GEORESP) | ||
L | M | H | |||
H | H | H | 1 | 1 | 1 |
H | H | L | 0.8 | 0.8 | 0.8 |
H | L | H | 0.4 | 0.35 | 0.3 |
L | H | H | 0.6 | 0.6 | 0.6 |
H | L | L | 0.2 | 0.15 | 0.1 |
L | H | L | 0.3 | 0.3 | 0.3 |
L | L | H | 0.1 | 0.08 | 0.05 |
L | L | L | 0 | 0 | 0 |
The rivers spatial data layer has the continuous geomorphic condition sub-index data categorised according to Table 2. The categorical data was used for reporting and mapping purposes.
Table 2. Geomorphic condition sub-index categories for rivers.
Category | Min to max values |
1 | 0 to <0.2 |
2 | 0.2 to <0.8 |
3 | 0.8 to 1 |
CFEV assessment framework hierarchy