Roper River Modelling Study
The Roper River catchment drains an area of 81,800 square kilometres.
Dry season flows are maintained by groundwater discharge from the Tindall Limestone and the Dook Creek Formation.
The 2006 field season included measurement of flow gaugings along each of the flowing creeks and rivers of the Roper River catchment (Flying Fox Creek, Mainoru River, Wilton River and Roper River).
The Roper River at Elsey Station down stream of Mataranka was flowing at 5000 litres per second in October 2006. The flow at Roper Bar, approximately 140 km downstream, at the same time was 1900 litres per second.
This reduction in flows indicates that approximately 3000 litres per second is being used by the environment.
This use by the environment during the dry season has been seen to be relatively constant with time varying between 2500 litres per second and 3000 litres per second.
Examples of information gathered:
Hydralab installation
During December of 2006 field equipment capable of continuous logging of water levels and water quality has been installed in Rainbow Spring at Mataranka to provide data on changes in the water level of the spring (related to the spring discharge rate) and the electrical conductivity, temperature and pH of the water (related to source of the spring water).
This information will be used in modelling.
Important Historical Accounts of Flow Variability
The estuary ecosystem of the Roper River is dependent on the freshwater input from the river. The amount of freshwater that enters the estuary during both the dry and wet seasons determines the location of the freshwater/saltwater interface in the river.
When the freshwater inflow is very low, the interface migrates up the estuary. In low flow years such as those of the 1960’s the interface migrated so far up the estuary that Ngukurr community’s river water supply was affected.
In talking with the Yugul Mangi Rangers at Ngukurr this phenomena not only occurred in the 60’s but also in the early 50’s. In fact the river water was too salty to drink for a couple of years and the community moved for that period to Mission Gorge where a permanent freshwater supply was available.
This historic account provides important information on the variability of water quality and quantity of the Roper River when records are sparse.
The low flow periods are related to rainfall and in viewing the rainfall record (see chart below) of Katherine as an indication, it is noted that rainfall in 1951/52 was the lowest on record.
Working with Indigenous Rangers
A workshop was undertaken with the Mimal Rangers at Bulman introducing them to the project and data collection techniques.
After the workshop the rangers assisted with flow gaugings and bore monitoring. Work with the rangers will be ongoing throughout the project.
