Existing Environment - Interactive Investor

Water levels in Bibra Lake have maintained a repeatable pattern of highs and lows
over the seasons, as well as within a 20-year cycle; however, there are not enough
years of data to conclude whether this is a consistent pattern.
Historical aerial photography (Figure 5.6-8 through to Figure 5.6-14) shows various
water levels in the lakes over time. The figures include the MRS road reserve
boundary to provide context. Although taken at differing times of the year, the aerial
images show that the water level in North and Bibra lakes has remained relatively
similar over most years. During winter 2010, water levels were dry or low in the
lakes. Low water levels indicated on aerial photography from 1978 (Figure 5.6-11)
are consistent with the readings down to RL (Reduced Level) 12.5m Australian Height
Datum (AHD) in 1978 (Figure 5.6-7). Variations in water level appear in the
surrounding wetlands:
Horse Paddock Swamp and Murdoch Drain had evident surface water in the
1947/1948, 1970 and 1989 photos;
Lower Swamp and Roe Swamp had evident surface water in the 1978 photo, with
only a small area of surface water in Horse Paddock Swamp and Murdoch Drain;
None of the peripheral swamp systems showed obvious surface water in the
1958/1959 photo or the 1999 photo; and
The only surface water showing in the 2008 historical aerial photograph was in the
lower end of Murdoch Drain; there is no obvious surface water in the other
peripheral swamp systems.
While the water levels in the lakes appear to have been relatively consistent, these
variations in surface water within the peripheral systems indicate a shallow surface
water system sensitive to groundwater expression and surface water contributions.
Alternatively, it may be due to natural vegetative succession, as a result of changing
land use practices.
Water levels in North and Bibra lakes appear less sensitive to change, possibly
reflecting their larger storage volumes and deeper vertical profiles. Conversely, the
peripheral swamps have smaller storage volumes, varying base levels and varying
interfaces with the surrounding topography. Therefore, whether surface water shows
or not depends on the rising groundwater intrusion through variably pervious wetland
sediments and runoff generated in adjacent catchment areas.
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