Moorabool River Environmental Water Management Plan Draft Version 2.3
The Environmental Water Management Goal
To improve the Moorabool Rivers flow-dependant ecological values and services through the provision of environmental water. The delivery of environmental water will also provide for social and cultural values for future generations. (The intent of this goal, developed and endorsed by the Moorabool Stakeholder Advisory Committee, is to ensure the effective use of the current entitlement and highlight the need for additional water to maintain and improve environmental values.)
Increase the Moorabool River Environmental Entitlement 2011 to meet the Minimum Water Recovery Target 1 within 1-4 years. This target allows for the delivery of 5,140ML per year under dry conditions. Any increase in the Environmental Entitlement may impact on urban water supply and would need to be appropriately assessed.
Pursue opportunities to secure the Minimum Water Recovery Target 2 within 5-7 years. This target allows for the delivery of 9,000ML per year under wet/average conditions.
Pursue opportunities to secure the Aspirational Water Recovery Target 3 within 8-10 years. This target allows for the delivery of 19,630ML per year.
Improved protection of environmental flows and baseflows in river reaches 1 to 4
Improvement in ecological health of the 6 ecological objective categories, including fish, platypus, vegetation, macroinvertebrates, geomorphology and water quality (outlined in Table 6.1. Ecological objectives for the Moorabool River system)
Increased native fish diversity, abundance and habitat ranges within 10 years Improved resilience Increased coverage of native vegetation through 76 hectares of revegetation and the fenced protection of 86 hectares of the rivers riparian corridor within reaches 3 and 4, consistent with the Regional Waterway Strategy 2014-2022 targets.
Farm dams, which capture water before it reaches the river, are having a significant impact on river inflows. The catchment contains more than 4000 dams, with an estimated total storage capacity of 14,400 ML. Modelling of farm dams indicates that the collection of water in farm dams results in a reduction in stream flow of 12,300 ML (Corangamite CMA 2005).
3.2 Groundwater and Surface Water Interactions
This section on groundwater and surface water interactions has been written with reference to a review of groundwater and surface water interactions documented in the 2004 FLOWS assessment (SKM, 2004b) and information from more recent investigations in the catchment. It is recognized that there are strong surface and groundwater relationships in the Moorabool River although very little is known regarding this relationship across the catchment. Despite this, groundwater gains and losses appear to represent a significant component of the water balance at many locations, including Bungal and Batesford (S Vermeeren pers comm, 2015), which is consistent with the findings of Horgan (2006) detailed below.
Harbour (2012) conceptualised baseflow to the Moorabool River East Branch to come from the newer volcanic basalt and the upper and lower tertiary aquifers. During dryer periods the baseflow from the basement aquifer may also contribute to streamflow. Baseflow could potentially sustain flow in the river all year around in this part of the catchment. Harbour (2012) and SKM (2004b) estimate baseflow contribution of between 30% and 50%, although note there is not enough gauge information at the weir to quantify the estimates. Nevertheless, this more recent work provides further supporting evidence that groundwater discharge is an important component of baseflow in FLOWS Reach 1 of the Moorabool River.
Evans (2006) undertook a study of the geology and groundwater flow systems in the West Moorabool River Catchment and their relation to river salinity. This report noted that compared to the level of knowledge available for surface water flow components, the groundwater contribution to river flow is poorly understood. Evans (2006) did note that water table elevation contours and electrical conductivity patterns suggest that groundwater does flow to and discharge into parts of the Moorabool RiverWest Branch. SKM (2004b) estimated baseflow contribution in the upper catchment (upstream of Moorabool River), to range from 50% to 60% and in the middle catchment (upstream of Lal Lal Reservoir) between 30% to 40%. No more recent information is available regarding baseflow contributions in the Moorabool River West Branch.
Horgan (2006) completed an honours thesis on the hydrogeology of the Morrisons-She Oaks Area, which corresponds with sections of the Moorabool River downstream of Lal Lal Reservoir (FLOWS Reaches 3a, 3b and 4). This report identified that stream flow data and groundwater level monitoring was largely non-existent or of insufficient quality to produce a meaningful interpretations of the groundwater – surface water interactions.
3.3 The Sustainable Diversion Limit
There is debate surrounding the quantity of water that may be harvested in a sustainable manner during the wetter months. Sinclair Knight Merz have carried out a statewide estimation (SKM, 2002) of the amount that can be harvested catchment wide in the winter months (July to October inclusive) that achieves the balance of economic, social and environmental outcomes. This is known at the Sustainable Diversion Limit and provides a conservative estimate of limits to extraction. The Sustainable Diversion Limit for the Moorabool River has been determined to be 3,482 ML/yr (SKM, 2002). Modelling for the 2004 Environmental Flows Study indicates that the average diversion at the time (including the effect of harvesting at storages) over these months was 38,000 ML/yr indicating the system is substantially over developed (SKM, 2004b).
Sustainable diversion from the Moorabool River is 3,482 ML/yr
Current diversion from the Moorabool River is 38,000 ML/yr.
5.2 Condition Trajectory
Based on a time-scale of 10 years, a decline in the overall condition of the Moorabool River system is likely to occur in the absence of increases to the environmental entitlement or additional waterway management works (Jacobs, 2015). The EWMP combined with other management documents such as the Corangamite Waterway Strategy, aim to improve environmental condition of the Moorabool. Passing flows from the larger storages do not meet minimum environmental water requirements required to maintain existing environmental values.
The ability to meet the EWMP goal and improve the Moorabool Rivers flow-dependant ecological values relies on adequate environmental flow volumes. Without additional environmental water, the ecological values will continue to decline (Jacobs, 2015). Minimum and aspirational water recovery targets have been scientifically validated through the Moorabool River Flows Study Update (Jacobs, 2015) and are detailed in Section 6.3 Water Recovery Targets & Flow Prioritisation.
The current Moorabool River Environmental Entitlement 2010 (the entitlement) was established to protect the Moorabool Rivers water dependant ecological values. The entitlement can be used to deliver environmental flows to reaches 3a, 3b and 4. The 7086 ML volume entitlement is subject to delivery rules (a maximum of 7500 ML over three years) with an average of 2500 ML per year available to be used (subject to water availability). While the establishment of the entitlement in 2010 was a big step forward in protecting the life of the river, the volume held within the entitlement falls far short of what is required to achieve the minimum flow requirements that are required to protect ecological values. The Moorabool River is one of the most flow stressed rivers in Victoria and the current entitlement provides approximately 10% of the water required to maintain its ecological values. Without additional environmental water, the ecological values of the Moorabool River will continue to decline (Jacobs, 2015).
Minimum Water Recovery Target 1
The Minimum Water Recovery Target 1 would enable the delivery of 5,140 ML/year under dry conditions. Importantly, this would require an additional allocation of 2640 ML/year to the existing entitlement, and would require carefully considered changes to the bulk entitlement rules, including alterations to share of storage capacity and inflows. This is a realistic target that has been developed in consideration of the rivers other water resource users and does not provide all of the environmental water needs for the Moorabool. Rather, it would provide the critical minimum environmental water volume to protect the highest priority ecological values.
enable the delivery of 5,140ML/year under dry conditions
Minimum Water Recovery Target 2
The Minimum Water Recovery Target 2 would enable the delivery of 9,000 ML/year under wet/average conditions. This would require carefully considered changes to the bulk entitlement rules, including alterations to share of storage capacity and inflows. This target provides the minimum environmental water volume to protect priority ecological values under wet/average conditions.
enable the delivery of 9,000ML/year under wet/average conditions
Aspirational Water Recovery Target 3
The Aspirational Water Recovery Target 3 would enable the delivery of 19,630 ML/year. This target is based on the achievement of all of the recommended flow components (low flows, freshes and high flows) and protection 43 of all of the systems identified ecological values. While it would protect the rivers values, the target is not equivalent to river flows prior to European settlement.