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TitleWaterbodies hydrology sub-index
CustodianWater and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment
CreatorSteve Carter, Environmental Dynamics
DescriptionAn index which assesses the hydrology for waterbodies according to impacts associated with catchment disturbance, regulation, abstraction and lake level manipulation.
Input data
Lineage
The hydrology sub-index was developed to integrate changes in water regime from catchment vegetation clearing, flow abstraction, flow regulation (by upstream storages) and manipulation of waterbody levels.
Waterbody hydrology sub-index values were derived using 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 catchment disturbance, abstraction index and regulation index. Lake level manipulation was used as a modifier for the overall hydrology expert rule system, with the hydrology score being lowered (poorer condition) according to the lake level manipulation score.
The experts weighted abstraction index as having the greatest influence on waterbody hydrology, followed by catchment disturbance and then regulation index.
The method for assigning a hydrology sub-index score to the waterbodies spatial units is provided below.
Date createdFebruary 2005
Scale and coverage1:25 000; Statewide
Column headingWB_HYDRO
Type of dataContinuous but has been converted to categorical format (see Table 3).
Number of classes5
Assigning values to ecosystem spatial units
A hydrology sub-index score (0 = poor condition – 1 = good condition) was assigned to waterbody spatial units as WB_HYDRO using the expert rule system shown as a definition table in Table 1 (e.g. if the waterbody has a HIGH score for catchment disturbance, LOW score for regulation and a HIGH score for abstraction, then assign a score of 0.9). 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). The hydrology score was there adjusted further depending on the lake level manipulation score for the waterbody as specified in Table 2.
Table 1. Expert rule system definition table for the hydrology sub-index for waterbodies.
Catchment disturbance (WB_CATDI) | Regulation index (WB_REGI) | Abstraction index (WB_ABSTI) | Hydrology score (WB_HYDRO_ |
H | H | H | 1 |
H | H | L | 0.4 |
H | L | H | 0.9 |
L | H | H | 0.6 |
L | L | H | 0.5 |
H | L | L | 0.3 |
L | H | L | 0.1 |
L | L | L | 0 |
Table 2. Expert rule system definition table for modifying the hydrology sub-index for waterbodies, according to lake level manipulation scores.
Lake level manipulation (WB_LLEVELM) | multiply by Index (Factor) |
1 | 1 |
0.8 | 0.9 |
0.6 | 0.6 |
0.4 | 0.5 |
0.2 | 0.4 |
0 | 0.2 |
The waterbodies spatial data layer has the continuous hydrology sub-index data categorised according to Table 3. The categorical data was used for reporting and mapping purposes.
Table 3. Hydrology sub-index categories for waterbodies.
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