Assessment of a groundwater quality monitoring network using vulnerability mapping and geostatistics: A case study from Heretaunga Plains, New Zealand

A groundwater monitoring network can provide quantity and quality data necessary to make informed decisions regarding the state of the environment. A properly designed monitoring system provides a representative understanding of the state of the monitored area. The selection of the optimum number of monitoring sites and their spatial distribution is a major challenge for the hydrogeologist.On the one hand, improper distribution of monitoring sites or insufficient number of sites will not provide a representative view of the state of the environment. On the other hand, if the sampled sites are too many, the information obtained is redundant and the monitoring network is costly and inefficient.A new methodology combining vulnerability mapping and geostatistics is proposed to help define the most efficient groundwater quality monitoring network on a regional scale.Vulnerability mapping identifies areas with high pollution potential, and in turn, prioritises for monitoring. A geostatistics methodology is then used to interpret the obtained data and to examine the spatial distribution of monitored parameters at different sites. The accuracy of spatial mapping reflects the effectiveness of the distribution of the monitoring sites.The methodology was applied to assess the nitrate monitoring network in the Heretaunga basin, Hawke's Bay, New Zealand. The DRASTIC approach was used to prepare a vulnerability map for the area of study, and kriging variance was used to check the spatial distribution of the sites. Based on this study, it was found that some areas with high vulnerability are not covered within the existing network indicating the number of monitoring sites and their distribution is not efficient. Some sites should be dropped and some others need to be added to the existing network.     

Conjunctive use of canal and groundwater in Punjab,Pakistan: management and policy options

Data from 41 watercourses commands in Pakistan show that, as expected, farmers in head end reaches of canals receive more canal water than those in tail end reaches. Contrary to conventional wisdom, however, these head end farmers also use more groundwater than those at the tail end. Overall, groundwater plays a more important role in irrigation than surface water, ranging from 65% dependence on pumped water in head end areas to over 90% in tail end areas. This means that groundwater is no longer supplemental to canal water, but is an integral part of the irrigated agricultural environment. However, the cropping choices of farmers appear to reflect the amount of good quality canal water they receive: head end farmers are able to grow more high value basmati rice in the summer and more vegetables in the winter, leaving tail enders to rely on less valuable crops such as fodder and wheat.Tail end areas are not only deprived of their fair share of surface water: they have to pump proportionately more groundwater which shows decreasing quality towards the tail. Typically, head end areas have groundwater with EC values of less than 1.0 dS/m, rising to over 2.0 dS/m in tail end areas. When the quality of both surface and groundwater used by farmers is examined, only the top 40% of the distributary gets water of adequate quality, the next 40% get below average quality, while the tail 20% of farmers irrigate with water that is classified as saline.Because of higher dependence on more expensive groundwater tail enders use less water per unit area, thereby reducing the leaching requirement. The result is a clear increase in soil salinity from head to tail along distributary canals, and there is some evidence of land abandonment in tail end watercourses due to excess salinity.The implications of these results are far reaching. Government policy includes plans to divert significant quantities of fresh canal water to areas underlain by saline groundwater on the basis that farmers already have adapted to pumping fresh groundwater. The results reported suggest that if this policy were implemented, there is a risk that over-dependence on fresh groundwater could lead to an intensification of the rate of soil salinization and deterioration of quality in areas currently classified as fresh groundwater zones.At present, the location and utilization of privately owned shallow tubewells is not monitored, and thus it is not possible for government agencies to determine just how much water of different qualities is being used. Further, canal water deliveries, public deep well monitoring, watercourse monitoring programs, soil salinity measurements, and agricultural performance monitoring are all scattered among different agencies and organizations, making the task of effective conjunctive management of surface and groundwater even more difficult.Conventional wisdom: Groundwater in Pakistan ... where it exists within the canal system ... is used to supplement surface water supplies to meet peaks in demand. (WAPDA, 1990)     

Life Cycle Assessment of biomass production in a Mediterranean greenhouse using different water sources: Groundwater, treated wastewater and desalinated seawater

An experimental biomass crop of Nicotiana tabacum was grown over a nine-month period inside a greenhouse situated in Almería, south-eastern Spain. Two irrigation methods corresponding to treated urban wastewater and groundwater, were arranged. No significant differences were observed in the total biomass produced on the treated wastewater and groundwater plots, which ranged from 17 to 28 kg m⁻², depending on plant density. Environmental Life Cycle Assessment (LCA) was applied in order to gain knowledge of the potential impacts of using either treated wastewater, groundwater, or desalinated water for irrigation. The LCA study included all the processes involved in agricultural production up to the final plant cutting. Since desalinated water was not actually used in the experiment, the experimental data from tobacco irrigated with groundwater was used in the LCA. Impact categories included were: global warming; acidification; water eutrophication; primary energy use; as well as aquatic and terrestrial ecotoxicity. Special attention was put on the ecotoxicity of emerging and priority pollutants in treated wastewater, as well as on soil quality impacts, namely soil organic carbon deficit and soil salinisation. The results show that using desalinated water leads to higher environmental impacts in several impact categories, including global warming, energy use, soil quality, and aquatic ecotoxicity. As an example, primary energy use increases by 80% and 50% as compared to using treated wastewater and groundwater, respectively. On the other hand, wastewater pollutants in irrigation water may involve a relevant contribution to terrestrial ecotoxicity. For this reason, the impact score of the wastewater-irrigated crop is 23% and 35% higher as compared to the crop using desalinated water and groundwater, respectively.     

Analysis of Manual and Centralised Supervisory Control Operations to Improve Level of Service: A Case Study of Pyramid Hill No 1 Channel, Victoria, Australia

The current challenge facing irrigation inAustralia is tofind ways to improve the operationalperformance of existing systems rather thanconstructing new ones. Unsteady flowsimulation models are often used as keytools to study and test improvedoperational scenarios for existing systems.While these models are generally notrecommended for real-time control, researchhas shown that they are able to simulatecanal response for different test scenariosfor operations planning. This paperpresents the results of two alternativemodes of operation for the Pyramid Hill No.1 Channel in northern Victoria, Australia.The channel is currently under manualoperation. Centralised control is the mostimmediate option considered by theirrigation authority to enable remotesupervision and control of the canal toimprove the channel operation and level ofservice standards. This type of control istermed Supervisory Control and DataAcquisition (SCADA). The two alternativeoperational scenarios were simulated andanalysed using the unsteady flow-simulationmodel DUFLOW. Specific performanceindicators were defined to compare the twomodes of operations based on the simulationresults. The results show that SCADAoperation has considerable potential toclosely match the discharges at thedownstream regulator with those ordered byfarmers while maintaining the water surfaceelevations within allowable fluctuationtolerance throughout the length of thecanal.