The Northern Territory Disease Control Bulletin
Territory Health Services, Centre for Disease Control
Northern Territory disease control bulletin; E-Journals; PublicationNT; Northern Territory disease control bulletin
Date:2002-03; This publication contains may contain links to external sites. These external sites may no longer be active.; Made available via the Publications (Legal Deposit) Act 2004 (NT).
Communicable diseases; Reporting; Northern Territory; Statistics; Periodicals
Northern Territory Government
Northern Territory disease control bulletin
v. 9 no. 1
Attribution International 4.0 (CC BY 4.0)
Northern Territory Government
The Northern Territory Disease Control Bulletin Vol 9, No.1, March 2002 23 the Minister. The water was drained to St Marys Creek near the Racecourse area, where it rapidly infiltrated a pervious sand aquifer. However pumping only resulted in minor reductions in the water level in the swamp because of further rain in December 2001 and periodic excess capacity effluent releases. In early February 2001 there were cases of MVE in Alice Springs following heavy summer rain and effluent discharges which flooded Ilparpa swamp. Extreme numbers of mosquitoes occurred around the swamp. Fogging operations were carried out regularly but it became clear that better solutions were required. Plans were drawn up in July 2001 for a drain from the swamp after recommendations from the DHCS EHO advising that a gravity drain and high volume drainage was required to reduce continuing mosquito numbers within a short time frame in preparation for significant summer rain events. PAWA and ASTC jointly constructed the necessary culverts and the drain. One potential delay for the drain was native title approval, but after discussions initiated by a local Lands Department officer, the Lands, DHCS officers and traditional owners agreed on the requirements and process, and speedy approval was given for the works. The gravity drain was started in December 2001 but was delayed by rain and flooded conditions. Partial drainage completed in early February saw water levels retreat from marginal flooded grass areas that were major sources of mosquitoes. Minor drain extensions into the swamp were largely completed in March and saw major reductions in extent and depth of the swamp. When completed the drain was capable of flows up to 700L per second. Insect growth regulation Through 2001 the swamp remained relatively full despite the temporary pumping operation and it was clear to DHCS officers that the coming summer posed high risks of further outbreaks of MVE. The DHCS EHO advised PAWA that a contingency plan needed to be developed to conduct larval control should Culex annulirostris numbers exceed 600 in an adult carbon dioxide light trap. PAWA agreed and commenced preparations in consultation with DHCS MEB and EHO and ASTC officers in October 2001. It was decided to trial the newly approved mosquito control agent, methoprene pellets, an insect growth regulator, in early summer when Culex annulirostris numbers started to increase. Compared to other chemicals, methoprene pellets have a label residual of 30 days. If applied at a critical time, this would require only one or two control operations compared with weekly applications with other control agents. If found to work effectively under NT climatic conditions, this agent would lead to more effective and less costly control. Following a swamp assessment for mosquito breeding in late December 2001 by MEB, local DHCS and Alice Springs Town Council EHOs, methoprene pellets were applied by helicopter over the entire swamp area using a special granule applicator hung below the helicopter. PAWA paid for the application costs and assisted with the operational aspects of the program. At the same time PAWA agreed to discontinue any further discharge from the sewage ponds into the swamp to allow for water levels to drop. Additional sprinkler dispersal was used to reduce effluent release levels. Outcome of efforts As a combined result of the drainage works, reduced effluent release, and reduced summer rain, water levels dropped significantly and swamp margins had receded drastically by early February 2002. This water level reduction and the methoprene pellets application decreased mosquito numbers near the swamp below pest level (less than 600 per trap) in February 2002 compared to the same time the previous year, when mosquito numbers exceeding 17,000 per trap were recorded. By early March less than 50 common banded mosquitoes per trap were recorded around Ilparpa. The combination of mosquito control through the use of methoprene pellets, the reduction of sewage overflow into the swamp, and drainage works, has successfully reduced the mosquito numbers and thus the potential risk for mosquito borne disease in the Ilparpa Valley area and to Alice Springs residents. Conclusion There are still issues to be overcome with the rehabilitation of the swamp and a long-term solution, but the light is at the end of the tunnel and groups are interacting. This outcome was a great example of cooperation between very diverse groups including community groups and both local and NT government working to a common end. Well done everybody! *************
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