The first few days of February 2012 saw major flooding in Narrabri and Wee Waa, and record or near-record flooding in places like Moree, St George, Charleville and Mitchell.
On the 1st and 2nd of February 2012 a stationary trough extending from the monsoon trough in the Gulf of Carpentaria to New Zealand, fed by moist coastal air, caused very heavy rainfall (see Figure 1). 24-hour falls up to about 200mm were recorded in the eastern part of Narrabri Shire, along the foothills of the Nandewars, see Table 1. This particular event came on top of more then a week of intermittent rain, including slow moving storms on the 30th of January which dumped an incredible 300mm in an evening near Cuttabri, according to the SES [1].
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 Figure 1: Synoptic chart for 5pm 1st Feb. Copyright Bureau of Meteorology. |
There was heavy rain in some locations in the upper Namoi catchment, for instance 121mm at Tamworth to 9am on the 2nd, but the highest river flood peak was caused by this local storm water. The peak from the water upstream came four days later and was 50cm below the initial peak (Figure 2). In Narrabri the main peak was at 7.11m on the Narrabri Creek gauge at 5:30pm on Thursday the 2nd. In Wee Waa the Glencoe gauge peaked at 7.28m at 6:45am on Friday the 3rd.
Wee Waa was isolated for about a week, and there was above floor flooding in several houses in the residential area near Doctors Creek in the north of Narrabri. The Francis St industrial estate in the same area was also flooded by the water from Doctors Ck, which notably inundated a car yard causing $1.3M in damage [2].
 Figure 3: Rough map of the catchment of Doctors Creek. Background image Copyright Google Maps. |
Doctors Creek refers only to a very short length of creek in the immediate vicinity of the Doctors Creek bridge on the northern edge of Narrabri. Doctors Creek drains into Narrabri Creek (the main channel of the Namoi River) just there near the bridge.
This creek is fed by Mulgate Creek, which runs south-west from near 12-Mile Hill, staying pretty close to the Killarney Gap (Bingara) Rd. Mulgate then crosses the railway line near the Narrabri saleyards and then enters Doctors Ck near the bridge.
The other main tributary of Doctors Ck is Horsearm Creek which runs roughly parallel but to the south of Mulgate Ck. Horsearm Ck is the system which runs around the Narrabri racecourse, along near the train station and then to the Doctors Ck bridge area, where Mulgate and Horsearm creeks have their confluence (although in times of high flow their floodwaters possibly also join further upstream). Horsearm Ck picks up the water from Stoney Creek as well as overland flow from the area out near the Narrabri Airport and probably as far as the Kaputar Rd.
The flash flooding in the northern area of Narrabri during this event seems to have been greatly exacerbated by historical engineering works. In the past, heavy flow down Mulgate Creek would spread out across the flood plain to the north-east of Narrabri and a substantial fraction of the flood water would cross the wheat research and the railway line to the west of there. In 1967 Professor C. H. Munro delivered a report proposing a solution to protect the wheat research and other landholders in that area, by forcing the Mulgate water, in its entirety, into Doctors Creek. The now-elevated structure of the Bingara Road is a key device in delivering this outcome.
Something like twenty years after Munro wrote his report, the DMR/RTA completed the realigned Newell Highway. In their wisdom, rather than construct a much longer bridge, or use a series of culverts to allow the water from Doctors Creek into Narrabri Creek, the RTA elected to use a solid earth embankment (ie, a dam) to keep the highway high and dry.
During this event, the Doctors Creek water was backing up behind the highway to the extent that it was perhaps as much as 2.3m higher in the creek than in the river! It seems to us that the combination of the Munro scheme and the realignment of the Newell Highway has been a double whammy which greatly exacerbates, rather than mitigates, flooding in this area of Narrabri in this kind of event.
 | Flooding near Doctors Creek in Narrabri. |
[1] "Motorists rescued as NSW floodwaters rise again", ABC News, accessed Feb 13 2012.
[2] "$1.3m damage to vehicles", The Courier, Feb 7 2012, page 1.