The results of the water management report were to be used as part of community consultation for the future setting of a minimum flow for the Benger Burn, which is found 10km south of Roxburgh.
It is listed as one of the region's significant rivers because of its habitat for ''declining species'', the Clutha flathead galaxiid and longfin eel, and for trout and salmon spawning. It is also free of weeds and very natural above 900m.
Environmental information and science director John Threlfall said options for integrated water resource management in the future included minimum flows and surface water and groundwater allocation limits.
Where the Benger Burn flowed out of the hill country and on to the flats it lost significant surface flow into the Ettrick aquifer, he said. It then resurfaced into the Benger Burn.
''Despite a base flow entering the lower reaches of the Benger Burn, it is likely the river would naturally dewater in an average or dry year.''
All 17 of the consented takes in the Ettrick area were for irrigation, horticultural, stock and domestic supply.
Available data suggested the aquifer had reached its maximum allocation but water meter data showed only 27% was being used, he said.
''If actual water takes are continuously and substantially under the consented water take amount, consents may need to be altered so future groundwater allocations can be made.''
There were three consents to take surface water in the Benger Burn catchment and there was no further primary allocation left. The peak take was only used for frost fighting, from September to December.
The distribution of native fish in the Benger Burn was the result of the natural drying of its middle reaches and presence or absence of trout, so would be largely unaffected by a minimum flow, he said.
Providing enough habitat for spawning trout or salmon between April and September and flow continuity between December and January was necessary to ensure recruitment into the lower Clutha fishery.
A minimum flow of 400 litres per second was suggested at Booth Rd for all takes from April to August, to provide for spawning, then a minimum flow of 75 litres per second from September to March for takes upstream to protect the galaxiid populations and no minimum flow from September to March for all takes downstream, he said.
The council's natural resources committee last week referred the report to the policy committee for future use in consultation during the setting of a minimum flow for the Benger Burn.
