Flooding of the 8 Mile Creek section of the Forest Creek system A.K.A the Wanganella Wetland

7 February 2020
Philip N Maher

 

 

Late last year the New South Wales Department of Planning, Industry and Environment put a flow of environmental water down the 8 Mile Creek at Wanganella. The water was being pumped out of Billabong Creek a few kilometres east of the Cobb Highway and into the 8 Mile Creek. The main wetland in the creek is situated behind the Wanganella sandhill revegetation area. It is partially on the Travelling Stock Route and partially on private land. The aim was primarily to keep some of the cumbungi and phragmites alive. Since the creek stopped receiving annual flows in the early 2000s (ironically to save water for the environment) most of the cumbungi, in particular, has died. It can only live about five years without receiving water. When the creek last received a natural flood in 2016 the ibis and other birds basically had nowhere to nest as most of the cumbungi had died out, not having flooded since 2010. In 2010 about 13,000 pairs of straw- necked ibis nested but in 2016 none nested even though it was a similar sized flood event. The issue also in 2016 was that even though there was a major flood down the Billabong/Forest Creek system, the Forest Creek did not get as high nor stay up as long as it did historically. My friend, the late Rick Webster, a local ecologist working on wetlands, and I concluded that there was now not enough cumbungi left in the creek system to hold the water up and spread it out, as it had previously done. The lack of cumbungi also rendered the creek largely useless as a waterbird breeding area.

 

This situation led to the current decision to flood the main swamp in the creek in an endeavour to get some cumbungi and phragmites back into the system so the birds would have somewhere to nest the next time it flooded. It was also an experiment to see how well the area could be flooded just by pumping from the Billabong Creek a few kilometres upstream from Wanganella, as opposed to water coming all the way down from the Forest Creek offtake (in the Billabong Creek) between Conargo and Jerilderie.  It has been too difficult to maintain water levels in the creek when birds are nesting. In 2016, a pair of nesting brolga (one of the last pairs in the district) was left high and dry when the water dropped away and they were forced to abandon their nest with eggs. 

 

The experiment this year has been partially successful in that it has succeeded in getting some cumbungi and phragmites back into the creek system. It has been highly beneficial for waterbirds, and land birds, as many species in good numbers have been present since the flooding commenced in November. 

 

Where the experiment has not been successful is that only about one-third of the wetland has been flooded and only to a shallow depth. The main area where the ibis and other species used to nest barely received any water.  The reason for this is that the small weir downstream of the wetland is not capable, in its current form, to back up enough water to flood the wetland.  I suspect the remedy to this problem would involve spending more money on the weir and maybe constructing a levee. If the wetland could be flooded to a good depth the rewards would be great as a huge variety of waterbirds would breed there. Species that have bred there in the past include the aforementioned brolga, Australasian and little bitterns, Australian painted snipe, red-kneed dotterel, black-tailed native hen , spotted, spotless and Baillon’s crakes, three species of ibis, royal spoonbill,  three species of grebe, whiskered tern, as well as a large assortment of ducks.

 

The Forest Creek system used to be a haven for Australasian bitterns in the 1970s, 80s and 90s. On one occasion in the 1980s I flushed up twelve Aust. bitterns at one small wetland and on another occasion eight birds from another small wetland.  It was not uncommon to see a couple of bitterns in roadside gutters along the highway in the 1980s. It is now a threatened species with possibly under a thousand left. 

 The Wanganella wetland satellite image 7 December 2019

 

 

Timeline and notes on the wetland and waterbird status October 2019 — February 2020

24 October 2019: Pumping started from the Billabong Creek into the Forest Creek system a few kilometres upstream from the Cobb Highway.

28 October 2019: Water reaches the highway and starts flowing over to the west side.
  

4 November 2019:  The first black ducks are observed.

 11 November 2019: The pumping stopped due to water escaping over the weir downstream of the highway which prompted the DPIE to raise height of spillway.
 

15 November 2019: The first grey teal observed, and more black ducks.
 

17 November 2019: Pumping restarted. 
 

29 November 2019:  Substantial body of shallow water northwest of the revegetation sandhill. Reedwarblers calling in cumbungi that has greened up in the creek bed upstream of the highway.  Sightings on shallow floodwater included a pair of white-bellied sea-eagle, ~30 black-winged stilt, ~10 whiskered terns, 1 swamp harrier, hardhead, Australasian grebe.

 

6 December 2019: A pair of gull-billed terns on the shallow floodwater. 
 

9 December 2019: Pumping stopped due to water going over spillway. 

 14 December 2019: First black-tailed native hens seen near the highway, a pair of brolga turned up on shallow floodwater northwest of the sandhill, ~1000 grey teal present, ~50 black-winged stilt, ~20 black-tailed native hen, ~ 50 whiskered tern, ~ 6 glossy ibis, 1 Australasian shoveler. 

 

 

 

 

16 December 2019: The pair of brolga still present, ~10 great cormorants, a pair of white-breasted sea eagles still present over shallow floodwater having dogfight with pair of wedge-tailed eagles, 3 swamp harriers, 6 Australian pelican, ~150 straw-necked ibis, ~ 20 Australian white ibis, ~ 10 white-faced herons, ~10 white-necked herons, ~ 20 glossy ibis, 2 royal spoonbills, ~10 yellow-billed spoonbills, ~3 whistling kites, ~30 black-tailed native hens, 4 red-kneed dotterels, 2 masked lapwings, ~ 30 whiskered terns, ~6 white-fronted chats, ~200 welcome swallows, ~50 tree martins.

20 December 2019: Shallow floodwater northwest of the sandhill, ~12 sharp-tailed sandpipers, 2 red-capped plovers, ~70 red-kneed dotterel. 

 

29 December 2019: 1 silver gull, 1 hoary-headed grebe, a pair black-fronted dotterel, white-fronted, crimson and orange chats feeding around perimeter of the wetland, black duck with 4 small ducklings observed, the first breeding here this season, 

1 January 2020: 1 red-necked stint, 1 greenshank

9 January 2020: Pumping started again.

13 January 2020: Most of the birds have cleared out due to the food chain being disrupted by the water dropping and then rising again.

21 January 2020: Clutch of grey teal seen. 

24 January 2020: Great egret; still very few waterbirds present. Water level now at about the maximum possible without doing more work on the weir. 

27 January 2020: Pumping finished for this flooding event. 

29 January 2020: A few waterbirds are starting to come back as the water levels are dropping slightly, darter, ~50 black-winged stilt, ~20 red-kneed dotterel, 5 sharp-tailed sandpipers. Big flocks of welcome swallows, tree martins and white-fronted chats. A black falcon seen hunting the small birds. 

 

2 February 2020:  More waterbirds turning up now that water levels are dropping. Eight red-necked avocet, the first seen in the district for some years. A pair of pink-eared ducks seen, ~30 red-kneed dotterel, ~20 glossy ibis, ~6 whiskered tern, ~ 200 white-fronted chats, a pair of orange chats feeding around drying out swamp, golden-headed cisticola calling in phragmites  (a scarce bird in the district at present), a brown quail flushed from around the edge of the swamp. 

5 February 2020: Still more waterbirds turning up as water levels drop, swamp harrier hunting over swamp, collared sparrowhawk probably after chats, an immature black-shouldered kite hunting around the drying out swamp, first seen in district for some months. A big mob of ducks comprising ~800 grey teal, ~150 pink-eared duck, ~20 Australasian shoveler, a couple hardhead. More waders returning ~80 red-kneed dotterel, ~20 sharp-tailed sandpipers, 8 red-necked avocets still present, ~10 rainbow bee-eaters mainly immatures feeding around the wetland and adjoining sandhill, little grassbird calling in phragmites. Hundreds of welcome swallows, tree martins and white-fronted chats feeding around wetland

8 February 2020 An immature white-bellied sea eagle circling over shallow floodwater, stirring up the birds. This was a different bird to the pair I have been seeing here on and off for the last couple months. 
Collared sparrowhawk: male tried unsuccessfully to catch a white-fronted chat within 50 metres of me.
Goshawk/sparrowhawk: another bird seen poorly at nearby sandhill; unsure as to which species it was. 
Australian spotted crake: one bird seen under a clump of drying out goosefoot bushes, the first record here this season. 
Red necked avocet: 8 birds still present. 
Sharp-tailed sandpiper: at least 30 birds present this morning; the most recorded here this season. 
Red-kneed dotterel: over 100 birds present; the highest number recorded here this season. 
White-faced heron: at least 20 birds present. 
White-necked heron: at least 10 birds present. 
Hoary headed grebe: at least 15 present, all in full breeding plumage. 
Glossy ibis : around 6 birds still present. 
White-fronted chat: well over 100 birds present; biggest flock seen for many years. 

12 February 2020 Water levels are slowly dropping, waterbird numbers are starting to decline.
Highlights today were:
Latham’s snipe: 1 bird flushed, the first record here this season. 
White bellied sea eagle: 1 adult seen. 
Red-necked avocet: 8 birds still present. 
Australasian shoveler: ~ 10 birds still present. 
Hoary-headed grebe: ~ 15 birds still present. 
Sharp-tailed sandpiper: 27 birds still present. 
Red-kneed dotterel: numbers down, only about 20 seen today.