National Water Commission

The Lower Limestone Coast water management area covers about 13,533 km2 and is located in the south east of South Australia adjoining the Victorian border. Major towns include Mt Gambier, Naracoorte and Millicent with a total population in the WMA of over 63,000. It is fairly flat landscape covered with stranded, beach ridge, ranges (20-50 metres high) that run parallel to the coast. Land use predominantly consists of dry land farming, vineyards and plantation forestry. Total value of agriculture in the Lower Limestone Coast WMA is over $3.3 billion coming from dryland farming - $500 million, wine grapes - $1.5 billion (value added) and forestry - $1.3 billion (http://www.lcrdb.com/region.htm).
 
While there are a number of small rivers in the WMA (Mosquito Creek, Morambro Creek and Reedy Creek) they are not generally diverted for consumptive use, instead discharge to a series of coastal lakes.

Almost all irrigation is from groundwater with 90 sub-units defined for groundwater management with a total entitlement of 540,716 ML and a total use for 2004-05 of 279,943 ML.

Groundwater in the majority of the region is allocated by licence in designated Prescribed Wells Areas. The management of ground/surface water, together with associated catchment ecosystems is detailed in the 2003–08 South East Catchment Water Management Plan. Overall, water is managed by the South Australian Department of Water, Land and Biodiversity Conservation with bulk water supplied by SA Water.




Figure 1 Lower Limestone Coast water management area locality map

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Rainfall in 2004-05 was 565 mm (Table 1), which is about 91% of the long term average and about 94% of the rainfall over the last 10 years (Figure 2). Rainfall decreases steadily across the water management area from south to north (~30% decline). Rainfall in the area occurs primarily during the winter (Figure 3).

Runoff in the area is via a mixture of natural streams and drains. The runoff is extremely variable with little relationship to rainfall, which indicates that streamflow is more related to irrigation drainage use (Figure 4). Increased use of groundwater for both irrigation and silviculture, have resulted in slightly reduced groundwater levels in the water management area (Figure 5).

Table 1 Summary of the Lower Limestone Coast water management area contextual information

Figure 2 Annual rainfall for the Lower Limestone Coast water management area (modified from BOM, 2006)




Figure 3 Monthly rainfall and evaporation for the Lower Limestone Coast water management area (modified from BOM, 2006 & Climate Atlas)




Figure 4 Modelled natural streamflow hydrograph for Lower Limestone Coast water management area for Drain L @ Boomaroo Park (gauge A2390505)




Figure 5 Representative bore hydrograph for the Lower Limestone Coast water management area

Summary of the total water resources in the basin

Table 2 Summary of water balance in the Lower Limestone Coast water management area, 2004-05

Figure 6 Water balance summary diagram for Lower Limestone Coast water management area

Outcomes from the water cycle report

The following information becomes apparent from Table 2.

• There are no major storages in the Lower Limestone Coast.
• The error in the water balance was about 40% of the total runoff and recharge.
• The captured rainfall, outflows and extraction and diversions estimates dominated the water balance representing more than 95% of the overall balance. The Water 2010 estimates were generally within an accuracy of ±100% (Category D) which would imply that the water balance was also within this error bound.
• Surface water flow out of the area (including baseflow) was 375,757 ML.
• Approximately 24% of groundwater recharge was discharged to surface water as baseflow.
• Irrigation is a significant water use in the area with over 270,000ML of groundwater used (~25% of inflows).
• In 2004-05 the environments’ share of the total flow in the Lower Limestone Coast WMA was unknown.
• Data could not be obtained for the following items in the water balance:
• Minor farm and catchment dams
• Soil - unsaturated zone storage volumes
• Drainage to groundwater from irrigation
• Groundwater discharge to springs
• The volume of self extracted water
• The volume of effluent recycling
• The volume of water held in river channels
• Seepage from irrigation channels
• Seepage from wetlands
• Urban diversions
• Groundwater discharge to ET

Download 2004-05 water cycle report: