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TitleWaterbody sediment input sub-index
CustodianWater and Marine Resources Division, Department of Primary Industries, Parks, Water and Environment
CreatorSteve Carter, Environmental Dynamics
DescriptionAn index which rates the impact of sediment input on waterbodies according to catchment disturbance, sediment quality and the presence of exotic riparian vegetation.
Input data
Lineage
The sediment input scores were calculated 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, exotic riparian vegetation and sediment quality. In developing the rule system, experts rated catchment disturbance as being the main factor influencing sediment and nutrient input into waterbodies, followed by the type of land use (sediment quality) and exotic riparian vegetation. Data on potential nutrient inputs associated with land use impacts (the CFEV Waterbodies Land use (nutrients) data) was used as a surrogate for sediment quality in the expert rules system.
The Tyler corridor was used as a context for the overall sediment input value. This reflects the reduced risk of nutrient enrichment effects on lake ecology in waters with naturally lower euphotic depths – especially blackwater lakes west of the Tyler corridor.
The method for assigning a sediment input sub-index score to the waterbody spatial units is provided below.
Date createdFebruary 2005
Scale and coverage1:25 000; Statewide
Column headingWB_SEDIN
Type of dataContinuous but has been converted to categorical format (see Table 2).
Number of classes5
Assigning values to ecosystem spatial units
A sediment input sub-index score (0 = poor condition – 1 = good condition) was assigned to waterbody spatial units as WB_SEDIN using the expert rule system shown as a definition table in Table 1.
Table 1. Expert rules system definition table for the sediment input sub-index for waterbodies east of the Tyler corridor.
Catchment disturbance (WB_CATDI) | Exotic riparian vegetation (WB_CRIVE) | Sediment quality (Land use (nutrients) (WB_NUTRI) | Sediment input score (WB_SEDIN) |
H | H | H | 1 |
H | H | L | 0.7 |
H | L | H | 0.8 |
L | H | H | 0.5 |
L | L | H | 0.3 |
H | L | L | 0.4 |
L | H | L | 0.2 |
L | L | L | 0 |
An additional rule was applied to take into account the position of the waterbody with respect to the Tyler corridor (i.e. east, west or within corridor), which states that if a waterbody is located either within or west of the Tyler corridor, and:
An example of applying the rules is that if the waterbody is east of the Tyler corridor, and has a HIGH score for catchment disturbance, a HIGH score for exotic riparian vegetation and a LOW score for sediment quality, then assign a score of 0.7). 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 waterbodies spatial data layer has the continuous sediment input sub-index data categorised according to Table 2. The categorical data was used for reporting and mapping purposes.
Table 2. Sediment input 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