Providence Portal - NSW

Outlet of the 16.6 km long Murrumbidgee - Eucumbene tunnel running from Tantangara Dam to Lake Eucumbene. Up to 19 cumecs flows out of the 3m diameter tunnel and along the flume. Large concrete blocks act as energy dissipators which agitate the water mixing in air to slow the water flow. They become visible during drought conditions,during tunnel outages or when water needs to be held in Tantangara Dam. At such times the water in the flume has only a small flow due to seepage in the tunnel. Algae are able to grow a metre or so in length as there is no turbulence to break their strands.

By 2018 nearly 60 years of erosion at low water levels has gouged out the rock and soil along the lower half kilometre of the 700 m channel leading into the Eucumbene River. At Lake Eucumbene levels above 60 % or 1150 m, the portal outflow harmlessly mixes with the lake. Since 2000 the water has been below this level in all but 2004, and erosion has caused the 10 metre high banks of tunnel spoil to collapse and the watercourse is in need of remediation with rip rap to stabilise the channel.
In March 2021 expensive 7 figure earthworks works have stabilised the channel using using large boulders and the unstable banks have been flattened back by bulldozers.