Impacts on surface water, groundwater, flooding and water quality related to fire in the North East.
It is estimated that climate change impacts will lead to a decline in annual average and winter rainfall, reducing average stream-flow in the North East catchment between 25% and 45% by 2050 and inflows to the Murray basin by up to 40% by 2070. Reduced in-stream flows or more frequent drying of streams are due to declining rainfall, higher temperatures (evaporation), and increased water use of forests regenerating after fire. This directly impacts water availability for environmental and consumptive uses, including rural and urban supply. A drying climate will place increased pressure on waterways, floodplains, and wetlands already under stress. Waterways and wetlands support aquatic species and ecological communities, and provide a critical resource for other wildlife in times of drought. Waterways are also an important connective feature in the landscape where riparian vegetation is intact. Unregulated waterways in the North East are naturally variable in flow and therefore the ecological communities they support would be expected to have a reasonably high level of resilience to climate driven changes in flow. Impacts on waterways are predicted to vary with waterway type and condition.
Climate change may result in increased frequency of stream ‘cease to flow’ events. Targeted works to improve the condition of priority waterways (such as restoration of riparian vegetation, pest and weed control, in-stream works to improve habitat) are expected to reduce the severity of climate change impacts on aquatic communities, but may be inadequate to maintain condition under worst-case climate scenarios.
While the majority of predicted impacts on agricultural production in the North East are negative, climate change is likely to reduce the threat of salinity and soil acidification due to declining aquifer recharge, and subsequent lowering of the water table and associated dryland salinity. There has been considerable research undertaken on groundwater and surface water connectivity in the region, however there is still some uncertainty about groundwater connectivity and recharge, and the degree to which groundwater resources will be impacted by climate change. There is also a risk that decline in surface water runoff and resultant decline in stream flows will lead to greater extraction of ground water for stock and domestic use.
While the long-term climate trend in the region is for reduced average rainfall, there may be more intense rainfall events leading to an increase in the frequency and severity of floods. An increase in the frequency and duration of river and stream flows may increase the risk of channel deepening as well as abandonment and formation of new river channels (avulsions). This can have significant impact on infrastructure, water quality, and in-stream habitat. Existing flood-prone areas, including Myrtleford and Wangaratta, will be most vulnerable to increased flood severity and frequency, although all infrastructure in or near waterways is at risk from major floods.
The North East CMA has a long history of working with landholders and local government to reduce and manage flood risk and post-flood impacts. Measures such as riparian restoration, grade controls to slow flows, and regulation of development in flood-prone areas are used. Levees, while locally effective at managing flood waters and present in several North East towns, can increase flood risk in other areas and restrict natural flows to floodplain wetlands. The need for a Flood Response Action Plan to mitigate the impacts of flooding on people and property is identified in the North East RCS. In addition, the need for a regional Flood Strategy is identified in the North East Waterway Strategy.
An increase in the number of high fire danger days and likely increase in bushfire frequency and severity can affect both water quantity and quality. Immediate post-fire impacts on water quality include high sediment and nutrient loads due to erosion in fire-affected catchments. This is exacerbated by the increased likelihood of high rainfall events. Water quality impacts can last from days to months after a fire and affect both the condition of the in-stream environment for aquatic species and town water supplies. Indirect fire risks include damage to fencing protecting riparian areas from stock, and stock deaths causing pollution of waterways. A longer-term impact of fire is the reduced water yield from regenerating fire-affected catchments, which compounds the effects of declining rainfall. The effects of increased water uptake by regrowth forest can last from one to many decades. Some studies of the Upper Murray and Murrumbidgee River show that that regeneration of forests after a fire event have significantly reduced rainfall adjusted water yield in the Murray Darling Basin. Regeneration after planned burning may also impact upon water yield.
Continue works to improve the condition of priority waterways
Address changing ﬂood risk and post-ﬂood impacts with measures such as riparian restoration, grade controls to slow ﬂows, and regulation of development in ﬂood-prone areas
Water resource allocation and contingency planning that considers worst-case future climate scenarios