A Stochastic Texture-based Approach for Evaluating Solute Travel Times to Groundwater at Regional Scale by Coupling GIS and Transfer Function

AbstractInterpreting and predicting the evolution of non-point source (NPS) pollution of soil and surface and subsurface water from agricultural chemicals and pathogens, as well as overexploitation of groundwater resources at regional scale are continuing challenges for natural scientists. The presence and build up of NPS pollutants may be harmful for both soil and groundwater resources. Accordingly, this study mainly aims to developing a regional-scale simulation methodology for groundwater vulnerability that use real soil profiles data. A stochastic approach will be applied to account for the effect of vertical heterogeneity on variability of solute transport in the vadose zone. The approach relies on available datasets and offers quantitative answers to soil and groundwater vulnerability to non-point source of chemicals at regional scale within a defined confidence interval. The study area is located in the Metaponto agricultural site, Basilicata Region-South Italy, covering approximately 12000 hectares. Chloride will be considered as a generic pollutant for simulation purposes. The methodology is based on three sequential steps: 1) designing and building of a spatial database containing environmental and physical information regarding the study area, 2) developing travel time distributions for specific textural sequences in the soil profile, coming from texture-based transfer functions, 3) final representation of results through digital mapping. Distributed output of soil pollutant leaching behavior, with corresponding statistical uncertainties, will be visualized in GIS maps. Of course, this regional-scale methodology may be extended to any specific pollutants for any soil, climatic and land use conditions

Climate change and the performance of pressurized irrigation water distribution networks under mediterranean conditions: Impacts and adaptations

Numerous previous studies have modelled the impact of climate change on crop water requirements and hence future water resource needs for irrigated agriculture. Fewer have considered the impacts on the performance of irrigation systems and the required engineering and managerial adaptations. This study considers the impacts and adaptations for a typical pressurized pipe irrigation system. The dry years of the baseline period (1970-90) in the southern part of Italy are expected to become the average or even wet year by the 2050s, according to HadCM3 projections. Under these conditions, the large water distribution systems designed to satisfy the baseline dry years will fail unless appropriate engineering or managerial adaptations are made. The resilience of District 8 of the Sinistra Ofanto to the possible future increase in irrigation demand has been assessed. A stochastic weather generator was used to generate future weather under the IPCC A1 and B1 emissions scenarios, taking into consideration the outputs of the HadCM3 model. A daily water balance model was used to quantify the actual and future peak water demand of the district. The reliability of each hydrant under baseline and future demand was calculated using a stochastic hydraulic model and the failure zones identified. Under the current design, the system can tolerate a peak demand discharge up to 1,500 l.s (-1), which is below the 2050s' average (1,720 l.s(-1)). Above that value, the performance of the system will fall drastically as the number of unreliable hydrants will increase. In the future, assuming the same cropping pattern, the threshold discharge (1,500 l.s(-1)) will be exceeded 80% of the time and, as an average, 20% of the system's hydrants will be failing during the peak demand periods. The adaptation options available to farmers and system managers in response to the increasing demand are discussed

Darcian preferential water flow and solute transport through bimodal porous systems: Experiments and modelling

Soils often exhibit a variety of small-scale heterogeneities such as inter-aggregate pores and voids which partition flow into separate regions. In this paper a methodological approach is discussed for characterizing the hydrological behaviour of a heterogeneous clayey–sandy soil in the presence of structural inter-aggregate pores. For the clay soil examined, it was demonstrated that, coupling the transfer function approach for analyzing BTCs and water retention data obtained with different methods from laboratory studies captures the bimodal geometry of the porous system along with the related existence of fast and slow flow paths. To be effectively and reliably applied this approach requires that the predominant effects of the soil hydrological behaviour near saturation be supported by accurate experimental data of both breakthrough curves (BTCs) and hydraulic functions for high water content values. This would allow the separation of flow phases and hence accurate identification of the processes and related parameters

Darcian preferential water flow and solute transport through bimodal porous systems: Experiments and modelling

Soils often exhibit a variety of small-scale heterogeneities such as inter-aggregate pores and voids which partition flow into separate regions. In this paper a methodological approach is discussed for characterizing the hydrological behaviour of a heterogeneous clayey-sandy soil in the presence of structural inter-aggregate pores. For the clay soil examined, it was demonstrated that, coupling the transfer function approach for analyzing BTCs and water retention data obtained with different methods from laboratory studies captures the bimodal geometry of the porous system along with the related existence of fast and slow flow paths. To be effectively and reliably applied this approach requires that the predominant effects of the soil hydrological behaviour near saturation be supported by accurate experimental data of both breakthrough curves (BTCs) and hydraulic functions for high water content values. This would allow the separation of flow phases and hence accurate identi fication of the processes and related parameters