El Niño and its Regional Effects on the Central Coast of NSW

The Central Coast region of NSW is not immune from the impact of the El Niño phenomenon. When the rest of eastern Australia experiences changing atmospheric conditions associated with a ‘sustained, positive, Sea Surface Temperature anomaly’ and with the connected shifts in the Walker Circulation, so does the Central Coast. When the wheat and wool growers of western NSW experience drought conditions arising from an El Niño episode, so, to a greater or lesser extent, does the Central Coast.  Drought is relative; relative to the normal rainfall that the local populace comes to expect and plan for.

Figure 1 below, records the estimation of total annual streamflow in the Central Coast catchment for each year since rainfall records began in 1885. Also shown for comparative purposes are the average annual stream flow estimations over selected periods - i.e. the long term average for the whole period from 1885 to 2006; the average 1900-1949; the average 1950-1990; and the average 1991-2006.

Figure 1:  Central Coast Streamflows

(Source: “WaterPlan 2050 – A long-term water supply strategy for the Central Coast” Plan Adopted August 2007,Gosford-Wyong Councils’ Water Authority. p 2).

The impact of the 1941-42 and 1982-83 El Niño episodes on the estimated amount of water flowing in the streams and rivers of the Central Coast is clearly in evidence here, as is also the devastating effects of the more recent prolonged drought beginning in the early 1990s.
What kind of impacts do such events have on the environment of the region and on the prospects of regional economic development?

Firstly, the levels of water stored away in dams are dramatically reduced during a prolonged drought. By March 2007, the total amount of water held in storage on the Central Coast had dropped to as low as 14% of total capacity despite the level 4 restrictions on water consumption put in place by Gosford/Wyong Councils’ Water Authority.

Figure 2:  Stored water resources on the Central Coast reduced to very low levels in the 2004-2006 drought

(Source: Wyong Shire Council).

Secondly, drought has an impact on those industries that are dependent on rainfall or on extraction of water from the environment. In the case of the Central Coast this includes businesses like turf grass production along the Wyong River floodplain as well as orchards, nurseries, domestic swimming pool supply, and production of bottled drinking water on the Somersby plateau. Sports fields dependent on surface water or restricted in their access to underground water can decline. Businesses reliant on tourists can suffer during prolonged drought as higher food prices reduce consumers disposable income.

During the recent prolonged El Niño-related drought in NSW, Gosford City and Wyong Shire Councils implemented a ‘Water Banking Scheme’ to help protect jobs in Central Coast businesses affected by the drought. This ‘Water Banking’ initiative arose out of suggestions from representatives of the general public during community consultation proceedings promoted by the Councils. Under the ‘Water Banking Scheme’ specified allocations of water could be purchased by Central Coast residents who:

  • bought plants from a local nursery, garden centre or landscaping company
  • filled a new pool / spa
  • topped up an existing pool after maintenance
  • layed new turf purchased from a local turf company.

Without such initiatives the effect of severe drought on local business could have been much worse.

A more subtle effect, not always apparent to the casual observer, is the impact that drought can have on the environment generally and on industries dependent on the natural habitat. During drought, vulnerable terrestrial habitats shrink. Rain forest, for example, is subject to invasion around the edges by more drought-tolerant weedy species (for example Bitou Bush and Lantana).  Sclerophyll forest is damaged by the extra hot bush fires that occur frequently during El Nino episodes; in January 2006 for example, searing temperatures and gusting winds provided the conditions to set ablaze the tinder dry bushlands between Mount White and Woy Woy on the Central Coast. The subsequent inferno destroyed homes and vehicles and burned through large areas of native forest.

Figure 3:  Water bombing a bushfire at Woy Woy, Central Coast in January 2006

(Source: Central Coast January 2006 Bushfires Photo Gallery)

Figure 4:  Aftermath of Bushfire at Woy Woy, Central Coast in January 2006

(Source: Central Coast January 2006 Bushfires Photo Gallery)

In aquatic environments, streamflows are reduced during drought. During the relatively favourable period 1950-1990 the estimated streamflow for the Central Coast averaged 220,000 megalitres per year but during the dry years of 1991-2006 the average annual streamflow for the Central Coast dropped to only 80,000 megalitres with individual years such as 2006 dropping to less than 10,000 megalitres (Figure 1).  In such severe drought conditions, localised populations of native fish adapted to life in ephemeral ponds and streams can be wiped out especially when extra demands are placed upon these water sources by enhanced extraction for human purposes. Great problems are faced by Local Government authorities in their attempts to maintain environmental flows in natural watercourses at a level sufficient to ensure the viability of vulnerable aquatic plant and animal communities.

The Wyong River is one of the major sources of drinking water for residents on the Central Coast of NSW and also important for wildlife and to refresh Tuggerah Lakes. In order to ensure enough water is left in the river for the environment, the Wyong River Weir is one of the first sites in Australia to include an integrated fishway and flow guage. The flow gauge monitors the flow over the weir to determine how much water can be extracted, thus ensuring that enough water is left in Wyong River for local wildlife and the environment.

Industries dependent on these natural resources suffer. Honey production from bee hives, dependent on forest blossom, declines. Commercial fishermen dependent on the productivity of sea grasses and estuary habitat in Tuggerah Lakes find that their catches decline when stream flows are reduced. On the Central Coast, responses to drought are managed at the whole catchment level. The catchment is managed by the two local Councils, Gosford City and Wyong Shire in coordination with the Catchment Management Authority, administered according to NSW and National legislation.

The Catchment Management Authority (CMA) manages natural resources at the whole catchment level.  To achieve this, the CMA develops Catchment Action Plans; regulates incentive programs to landholders to implement the plans; manages environmental water licences and water conservation trusts; and helps communities make decisions on local water management.  Councils are licensed to take water from the environment by the NSW Department of Water and Energy under the Water Management Act 2000.  This licence requires strict regulations regarding the manner in which the water is taken and the effect it may have on the environment.  For this reason both Councils are required to complete regular State of the Environment Reports (see Laws, Acts and Regulationsorhpan: NSW Environmental Acts- LAR ) which give an update on the overall management of the catchments within the Local Government Areas of both Councils.

Gosford and Wyong Councils are well prepared to provide water to the Central Coast community through periods of drought and to ensure that we have a water supply that can cater for an ever increasing population.  The development of Water Plan 2050 was in part a response to the severe drought conditions of 2000-2006 but also a recognition that with the potential impact of Climate Change, drier conditions may become a long term feature of the climate in south eastern Australia including the Central Coast.  Projects completed by the Councils are a combination of actions that work to achieve the objectives of the region's long term water strategy, see WaterPlan2050. Projects include a focus on system upgrades, reducing demand and accessing more water. Major projects completed in recent years include the Mardi-Mangrove Link and the Hunter Connection.

Gosford City and Wyong Shire Councils also continue to develop stormwater harvesting and recycled water projects as new sources of water for the region. Desalination may also one day be used as a back-up source of water.