Conditions 2018
Environmental watering in 2017–18 aimed to improve the health of black box woodland on the Hattah Lakes floodplain and to consolidate some of the ecological outcomes that were triggered by natural floods in spring 2016.
Looking back two years to July 2016, it was not anticipated that any water for the environment would be provided to Hattah Lakes. The seasonal outlook was dry and some of the lower-lying lakes had received water three times in the previous four years, so wetland drying was considered appropriate to draw down lake levels to allow seeds to germinate and plants to establish themselves on the edges of the wetland.
Winter and spring 2016 were wetter than expected, so a decision was made to deliver water for the environment to Hattah Lakes during September and October 2016 to align with the wet conditions. Late October and November 2016 brought the largest floods in the River Murray in the last two decades. The Hattah Lakes and floodplain were inundated for 16 consecutive weeks and reached a maximum level of 44.6 m AHD (Australian Height Datum), providing perfect conditions for the recovery of black box trees that had not been flooded since the 1990s.
The ecological productivity boost and increase in new plant growth associated with floods can be short-lived without significant watering in the subsequent year. Over 110 GL of water for the environment was delivered to the Hattah Lakes between July and October 2017 to support the further germination, growth and recovery of black box trees. The water delivery aimed to inundate as much of the Hattah Lakes as possible within the constraints of the available infrastructure. Water levels throughout the lakes reached 44.85 m AHD, which is the highest inundation by environmental or flood water since the 1970s. Recent monitoring indicates that black box health has improved, with tree canopy cover increasing in areas that received water for the environment in 2017–18.
Scope of environmental watering
Table 1 Potential environmental watering actions and objectives for the Hattah Lakes
Potential
environmental watering1 | Environmental
objectives |
|---|
Wetland watering |
Natural inundation of Chalka Creek and Hattah Lakes | - Allow natural connectivity between Hattah Lakes and the River Murray
- Allow exchange of carbon, nutrients and biota between the wetlands and the River Murray
|
Wetland drying |
|
Drying of Hattah Lakes
| - Maintain the lake bed herbland as water levels recede
- Allow drying of lakes to manage carp and improve wetland condition
|
1 The Hattah Lakes pump station will also be operated to meet annual maintenance requirements.
