http://hdl.handle.net/10453/106 2013-05-21T23:20:27Z 2013-05-21T23:20:27Z Middlemis Hugh Merrick Noel Williams Robert http://hdl.handle.net/10453/6712 2010-07-21T22:42:30Z 2005-01-01T00:00:00Z

Dynamic River-Aquifer interaction modelling and optimal interception of saline groundwater discharge Middlemis Hugh; Merrick Noel; Williams Robert Acworth, RI; Macky, G; Merrick, NP The Murray River reach at Mildura, Australia, has been identified since the early 1970s as a place where saline groundwater discharge to the river has been exacerbated by the presence of a weir and a lock. It is believed that salt-laden groundwater has been entering the river in response to a normal operating head difference of 3.6 metres between upstream and downstream water levels. Deep groundwater, which has salinities several times those of seawater moves upwards to the river under a strong vertical gradient. In an effort to intercept this flow, the New South Wales Government install ed a dewatering network in 1979 known as the Buronga Salt Interception Scheme. Effluent is piped to a large gypsum swamp a few kilometres to the north. The area has been the subject of several modelling studies since the mid 1980s, initially with an analytical model, then a finite element model and more recently a finite difference now model and solute transport model. A coupled optimisation model has been used to derive optimal pumping rates for an expanded network of interceprion bores by insisting that groundwater heads remain at or below river levels. The river and the aquifer system are highly interactive. As a result, there is a highly dynamic variation in fluxes 10 and from the riv cr. The latest numerical model replicates the dynamics of the system faithfully. At times of high river flow, relatively fresh river water recharges the aquifers. During low river flow, saline groundwater enters the river below the weir. The river salt load estimates from the solute transport modelling are in good agreement with estimates based on multiplying water fluxes with local salinities. Given the good agreement, the latter approach is regarded as a sufficient indicator of sail loads. achieved with much less effort. The solute model predicts a "warm spot" immediately downstream of the weir, where elevated groundwater salinities can be expected. The solute modelling was useful in showing the importance of including the dynamics of hydraulic stresses, rather than the common assumption of steadystate flow. It was also instructive in showing the dilution that occurs upstream of tile weir and that flood recharge had to be added to the flow model to account for some observed fresh water zones. Salt load estimates with transient modelling are about five limes higher than steady-stare estimates. due to river dynamics and the slower response time of groundwater. After a high river flow event, groundwater levels near the river will remain elevated for some tirrc and salt-laden groundwater will discharge to the river until a new equilibrium is achieved. It is ironic that a fresh high flow event in the river causes a subsequent salt pulse in the river due to discharge of salty groundwater from a temporary mound. It is clear from the simulation modelling, and measured vertical head differences that the interception scheme's operation could be improved. The optimisation analysis recommends an increase of about 45% in pumping rates.

2005-01-01T00:00:00Z Allen David Merrick Noel http://hdl.handle.net/10453/6713 2010-07-21T22:39:13Z 2005-01-01T00:00:00Z

Towed geo-electrode arrays for analysis of surface water groundwater interaction Allen David; Merrick Noel Simms, J High productivity analysis of surface water groundwater interaction is possible using GPS positioned vertical electrical conductivity imaging along with depth recording. Short submerged geoelectric arrays provide a great deal of detail right at the base of surface water bodies: however they cannot be used in treacherous waterways with debris scattered through them. Long floating arrays can be towed through such waterways and have the additional benefit of greater depth of exploration. Floating arrays also can have reasonable resolution at the base of surface water bodies provided that they are designed optimally and that data from them is inverted effectively. Array design must optimize a balance of signal strength maximization, exploration depth resolution weight and drag minimization crosstalk and current leakage minimization and simple minimal response to three dimensional heterogeneity. Pragmatic interpretation of the huge volumes of data that are typically acquired is best achieved using three dimensional "ribbon' images. Prominent features of interest are in most cases related to groundwater salinity. Low conductivity anomalies often indicate fresh surface water seepage into more saline groundwater. High conductivity anomalies that intersect the bases of surface water bodies usually indicate saline inflow to the surface water bodies.

2005-01-01T00:00:00Z Newton Philip J Yunusa Isa http://hdl.handle.net/10453/6714 2013-04-18T23:44:52Z 2003-01-01T00:00:00Z

Future roles for native woody species in Australian agricultural landscapes Newton Philip J; Yunusa Isa Wilson, BP; Curtis A Australian broadacre agricultural lands are dominated by annual crop and pasture species with relatively shallow root depths compared to perennial species and low accumulation of above ground biomass. Deterioration of the environment in these landscapes by dryland salinity, nutrient losses, soil degradation, emission of greenhouse gases and loss of biodiversity may be averted by phases of native woody species and shrubs. Recently, lucerne and other herbaceous perennials have begun to be incorporated into broadacre cropping systems for hydrological control. There are indications, however, that lucerne may not be as efficient as woody species in dewatering the soil profile. Some recent studies in America have shown that mitigation of net global warming potential by lucerne was significantly less than woody species, due to nitrous oxide emissions and lime requirements in the lucerne and resistance of woody species to decomposition in the soil. Pastures such as lucerne have different biodiversity values compared with native woody species. Phases of different ages of native woody species are likely to provide multiple niches for enhanced biodiversity, provided biological assets are maintained when cropping and/or pasture phases are resumed. Problems perceived with use of woody species often centre on loss of income during the early years of their growth. However, forecast markets for emerging bio-energy industries, and ecosystem services incentives could provide worthwhile returns. This hypothetical approach using native woody species is untested scientifically and research is needed to ascertain their utility in a range of Australian environments. The selected examples we have shown focus on environmental outcomes and would depend on favourable socio-economic structures for implementation. We envisage that optimisation of overall environmental gains could be achieved in a six year time frame.

2003-01-01T00:00:00Z Alkhatib Mohammed Abdelmohdi Merrick Noel http://hdl.handle.net/10453/6715 2012-11-25T23:49:34Z 2005-01-01T00:00:00Z

Stream baseflow preservation with optimal aquifer management Alkhatib Mohammed Abdelmohdi; Merrick Noel Acworth, RI; Macky, G; Merrick, NP The public water supply in the Gosford-Wyong area of New South Wales, Australia, 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 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. The study area consists of nine catchments and is located north of Sydney and inland from Gosford with an area of about 1,400 km2. Baseflow has been estimated for seven flow gauges located at the creeks by applying a digital filtering algorithm to separate the baseflow from the total stream flow. The groundwater hydrographs for 20 monitoring bores show strong correlation with residual rainfall mass, which suggests that rainfall recharge provides the major control on aquifer behaviour. Hydrographs at the same location show that, under natural conditions, there is a huge vertical head difference between layers of alternating sandstone (as much as 30 metres). A management model that couples a simulation model (MODFLOW -SLRFACT) with an optimisation model (OPTl MAQ) has been developed to preserve stream baseflow, MODFLOI,V -SURFACT was selected 10 simulate the complex multi-layer Kulnura-Mangrove aquifer system. The model has an area of 40 km x 59 km with approximately 400 m difference in elevation. The model was divided into 30 flat layers that reflect the alternation between sheet and massive facies in the Hawkesbury Sandstone Formation. A uniform cell size 500 m x 500 m results in a grid mesh of 118 rows and 80 columns. The model was calibrated for both steady state and transient conditions. The results of steady-state calibration revealed that the model perfonms very well in representing the values and the patterns of the composite groundwater level contours map. Also. the results showed a good agreement between the observed and computed target values across all the model layers with a coefficient of determination of 0.994. The transient model started in January 1985 and ended in October 2003 with a monthly stress period, The results of the transient calibration illustrated that the model matched very well with all observed hydrographs, even in the areas that have high vertical head difference, Also, the results showed a good agreement between the estimated baseflow and that simulated by MODFLOW -SURFACT for all the flow gauges. OPTIMAQ software, based on generic optimisation software (GAMS). solves the management problem with linear or nonlinear objectives by using the response matrix approach. OPTIMAQ was linked successfully with MODFLOW -SURFACT to compose the management model for the multi-layer aquifer system in the Kulnura- Mangrove area. The main target for the management model is to preserve baseflow in the creeks by determining the optimal limits on groundwater extraction from the existing or planned bores. The objective function of the management model is to maximise the pumping rates of the bores, subject to groundwater level constraints imposed along the creeks. In effect, this approach determines a sustainable yield for the aqui fer system that is compliant with surface water constraints.

2005-01-01T00:00:00Z