Determining trade-off between sustainable yield and baseflow in the Kulnura - Mangrove Mountain aquifer system using simulation optimisation modelling
- Publication Type:
- Thesis
- Issue Date:
- 2007
Open Access
Copyright Clearance Process
- Recently Added
- In Progress
- Open Access
This item is open access.
The public water supply in the Gosford-Wyong area of New South Wales is reliant on
streams that originate in elevated sandstone country. About half of the stream flow is
believed to be baseflow from the sandstone aquifer system in the Kulnura - Mangrove
Mountain area. At the same time as the population is growing steadily on the coast,
there is increased demand for groundwater for horticultural, agricultural and industrial
purposes along the sandstone ridges. Hence, good groundwater management is critical,
to ensure that stream baseflow is not jeopardised.
A management model that couples a simulation model with an optimisation model has
been developed for the Kulnura-Mangrove Mountain aquifer system to evaluate the
trade-offs between increased aquifer yields and baseflow reduction. The project has
been successful in developing trade-off curves for sustainable yield versus reduction in
baseflow. It is believed that this is the first time that rigorous trade-off curves for
sustainable yield have been developed for a stream-aquifer system in Australia.
The objectives of this research were to determine the sustainable yield(s) of the aquifer
system in relation to extraction limits from both groundwater and surface water; to
determine the magnitude, distribution and dynamics of baseflow to the streams which
drain the Kulnura - Mangrove Mountain aquifer; to determine groundwater entitlement
limits that would preserve baseflow to streams in order to facilitate groundwater
allocation policy; and to explore how groundwater extraction limits would change for
tolerable reductions in baseflow.
The simulation model is necessarily coarse, with 500 m spatial resolution, as replication
of a very large regional aquifer was required. Given the wide variation in vertical relief
in the area, approximately 400 metres, it was necessary to divide the vertical profile into
30 layers. Otherwise, it would not have been possible to track the many baseflow-receiving
creeks that descend from high elevations to the sea.
The calibration results of the simulation model show that the model performs very well
in representing the values and the patterns of groundwater level for both steady state and
transient conditions, is able to reproduce large vertical hydraulic gradients between
aquifer layers, and also replicates baseflow reasonably well.
The optimisation model was developed with the objective of preserving stream
baseflow within tolerable limits while maximising the pumping rates from the aquifer
system. Constraints were designed in terms of hydraulic gradient, with reduction
tolerance ranges from 0.1 % to 10 %. Conversion from hydraulic gradient reduction to
baseflow reduction was achieved by running reported optimal production patterns
through the model in simulation mode. This work differs from that of previous
researchers in not making a pre-emptive assumption of linearity between groundwater
pumping and stream baseflow.
A very large optimisation problem has been solved in this study, consisting of up to
5700 decision variables and 8000 constraints. The study has been successful in
generating trade-off curves that will provide a scientific basis for government /
community decisions on responsible water allocation between computing users.
Please use this identifier to cite or link to this item: