http://hdl.handle.net/10453/199 2013-06-19T05:08:56Z 2013-06-19T05:08:56Z 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 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 Allen David Merrick Noel http://hdl.handle.net/10453/6711 2012-11-29T03:54:41Z 2005-01-01T00:00:00Z

Imaging of Aquifers beneath watercourses Allen David; Merrick Noel Acworth, RI; Macky, G; Merrick, NP Imaging of groundwater that interacts with surface watercourses is essential for providing detail needed to accurately manage both resources. It is particularly important where one resource is saline or otherwise polluted, where spatial quantification of the interacting resources is critical to water use planning and where losses from surface waterways need to be minimized in order to transport water long distances. Geo-electric arrays or transient electromagnetic devices can be towed along watercourses to image electrical conductivity (BC) at multiple depths within and beneath those watercourses. It has been found that in such environments, EC is typically related primarily to groundwater salinity and secondarily to clay content. Submerged geo-electric arrays can detect detailed canal-bottom variations if correctly designed. Floating arrays pass obstacles easily and are good for surveying constricted rivers and canals. Transient electromagnetic devices detect saline features clearly but have inferior ability to detect fine changes just below beds of watercourses. All require that water depth be measured by sonar or pressure sensors for successful elimination of effects of the water layer on the data. Presentation of the data using a 3D presentation technique where EC is imaged along vertical ribbons drawn along the watercourse; is almost essential for handling the data produced because the meandering paths of rivers and canals combined with the shear volume of data typically acquired results in a gee-referencing dilemma that cannot be accommodated using traditional presentation techniques. An extensive set of EC Imaging case studies, distributed across canals and rivers of the Australian Murray-Darling Basin, has been collected. They reveal the interaction of various rivers and canals with the underlying groundwater resources. At some sites, watercourses cross prior iver channel sands that are being recharged and are suitable for use as water storages with low evaporation losses. Canals and reservoirs that cross such prior river channel sands can be sealed but, with geophysical assistance in mapping aquifers, development of underground water storages with controlled recharge may be more lucrative. At some other sites, little connection between aquifers and surface watercourses is evident. Finally, at downstream ends of geological basins, sites where saline groundwater flows into, or is on the verge of flowing into rivers are evident.

2005-01-01T00:00:00Z