Brewarrina fishway on the Barwon River 2015 this report This report summarises the findings for one key component of the Northern Basin Review. The report describes how different modelled water recovery scenarios may affect the flow regime of northern basin rivers, and in turn, how this may affect environmental outcomes. The report also describes what additional measures (referred to as toolkit measures) may be useful in securing and strengthening these environmental outcomes. The report should be read in conjunction with other reports from the review that address the social, cultural and economic impacts associated with the water recovery scenarios. The decision on whether or not to amend the current legislated sustainable diversion limit for the northern basin is based on finding a balance between social, cultural and economic impacts using a triple bottom line assessment. The findings presented here are the culmination of the environmental science element of the Northern Basin Review undertaken by the Murray-Darling Basin Authority. This report describes the assessment of how well different water recovery scenarios in the northern Murray–Darling Basin may potentially maintain or restore elements of the rivers' flow regime (i.e. base flows, freshes and overbank flows). How effectively elements of the flow regime are maintained or restored link to positive environmental outcomes, such as improved native fish numbers and distributions, more frequent opportunities for waterbird breeding and increased numbers, and healthier streamside and floodplain vegetation. The environmental science element of the Northern Review commenced with a range of scientific reviews and field studies that were undertaken on northern basin fish, birds and plants, in order to build upon the existing . This work was focused on the Barwon–Darling and Condamine–Balonne catchments and was used primarily to describe updated for the Lower Balonne and Narran Lakes catchments through description of a set of ecologically important flow indicators. The environmental science information was also used to support the environmental water requirements of the other northern basin catchments, although the 2012 channel
Condamine–Balonne, Border Rivers and Namoi catchments. catchments that have not met many of the outcomes. 390 GL A — fully implemented Basin Plan Represents the implemented Basin Plan as currently legislated. This scenario is the primary comparison scenario for the Northern Basin Review. 415 GL — water recovery more than Basin Plan Represents a similar water recovery approach to the fully implemented Basin Plan, but with a 25 GL increase to the volume of water recovered. To understand what additional environmental outcomes be possible with more water recovery. Table 3: Step 2 in the development of recovery scenarios and a brief description of each Scenario name Scenario description Why? 320 GL B — default water recovery less than Basin Plan (pro rata) Represents a 320 GL recovery volume that is based primarily on achieving an equitable recovery strategy. To test the performance of different recovery strategies (i.e. looking at how outcomes are influenced by where and how much water is recovered for each catchment) 350 GL — targeted recovery Represents Plan recovery strategy, but includes a highly targeted recovery strategy in the Condamine–Balonne. In particular targeting in-channel water recovery in the Narran River over overland flow licenses. To understand if outcomes can be improved if water recovery is targeted for particular areas, volumes and entitlement types. 390 GL B — current operations Represents the Basin Plan 390 GL scenario described above, but with an altered strategy for managing/delivering environmental flows to the Barwon–Darling. Under this option, there is no coordination of catchment flows — instead, the catchments worked individually to deliver low flows downstream to maintain connectivity with the Barwon–Darling, as per the Barwon–Darling Water Sharing Plan rules. To determine the level to which environmental outcomes in the are dependent on the assumed management strategy for environmental water. The management strategy in this scenario is largely consistent with current knowledge and operating practices, and therefore assumes there will be minimal future advances in operating capacity. Table 4: Step 3 in development of recovery scenarios and a brief description of each Scenario name Scenario description Why? 320 GL C — refined Another variation of a 320 GL scenario. This option was To test if the Basin Plan (390 GL) scenario Darling
Gwydir River (baseflow – fish movement and breeding) (frequency results shown as percent of years with at least one event) G2 1,000 ML/d for 2 days between Oct and Jan at Yarraman Bridge on the Gwydir River (fresh – cue for fish movement and breeding) (frequency results shown as percent of years with at least one event) 85 85 89 85 84 84 84 82 84 84 84 85 84 G3 45 GL inflow over 60 days between Oct and Mar at Yarraman Bridge on the Gwydir River (wetlands) (frequency results shown as percent of years with at least one event) 85 85 64 83 82 82 82 75 82 82 82 81 82 G4 60 GL inflow over 60 days between Oct and Mar at Yarraman Bridge on the Gwydir (wetlands) (frequency results shown as percent of years with at least one event) 90 80 67 70 75 75 75 61 75 75 75 74 75 G5 80 GL inflow over 60 days between Oct and Mar at Yarraman Bridge on the Gwydir River (wetlands) (frequency results shown as percent of years with at least one event) 70 60 57 63 62 62 62 47 61 61 61 62 60 G6 150 GL inflow over 60 days between Oct and Mar at Yarraman Bridge on the Gwydir River (wetlands) (frequency results shown as percent of years with at least one event) 50 40 50 46 46 46 47 25 47 47 47 46 46 G7 250 GL inflow over 60 days between Oct and Mar at Yarraman Bridge on the Gwydir (wetlands) (frequency results shown as percent of years with at least one event) 30 20 29 20 25 25 25 14 25 25 25 25 25 G8 5.4 GL inflow over 120 days between Feb and Mar and between Aug and Sep at the Mallowa Creek regulator – targeting 50 ML/d during these periods (riparian veg) (frequency results shown as percent of years with at least one event) 12 12 14 11 14 14 14 79 14 15 15 14 15 G9 4.5 GL inflow over 92 days between Nov and Jan at the Mallowa Creek regulator – targeting 50 ML/d during this 91 91 17 83 84 84 84 87 87 86 86 84 85