http://hdl.handle.net/10453/200 2013-05-24T15:37:20Z http://hdl.handle.net/10453/6713 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 http://hdl.handle.net/10453/6712 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 http://hdl.handle.net/10453/6710 Groundwater flow section modelling of salinisation processes in the Champhone Catchment, Savannakhet Province, Lao PDR Lertsirivorakul Rungruang; Merrick Noel; Wiszniewski Iwona; Milne-Home William; Last Rohan Kachitvichyanukul, V; Purintrapiban, U; Utayopas, P A steady state, two-dimensional vertical section groundwater flow model has been developed for a salinised area of the Xe Champhone catchment in Savannakhet province, Southern Lao PDR. The area is underlain by evaporite beds and clastic sedimentary rocks of the Khorat Group that are the source of salt found in groundwater and surface soils. The Xe Champhone catchment is of interest because of plans for construction of several new reservoirs and extensive expansion of irrigated areas. This study provides an example of how a relatively sparse and limited data set has been used to construct and successfully calibrate a numerical flow model to investigate groundwater flow patterns and potential impacts of increased groundwater recharge on land salinisation. Results show the predominance of local flow systems and that deeper flow systems in contact with the rock salt layer operate over much longer time scales in the order of millions of years. 2005-01-01T00:00:00Z