David Pulido-Velazquez

An efficient conceptual model to simulate surface water body‐aquifer interaction in conjunctive use management models

[1]xa0In conjunctive use management models, the surface and subsurface components must be simultaneously simulated because of the hydraulic interactions and to the combined operating rules inherent to such schemes. When many management alternatives have to be simulated over long time horizon or when optimizing complex large-scale systems, an efficient tool for surface water body-aquifer interaction simulation is needed. In this paper, we present a parsimonious conceptual model as an alternative approach to simulate aquifer storage and surface water body-aquifer interaction for linear aquifers (linear response of head to stresses). The formulation is deduced from a finite difference model preserving its approach of the geometry, boundary conditions, hydrodynamic parameters (heterogeneity), and spatial distribution of the stresses. It does not require any additional assumption. The solution, obtained using eigenvalue techniques, is formulated with an explicit state equation that is a function of time and does not need to be calculated in a sequential way (that is, time is not discretized). The structure of the solution finally deduced allows a simple conceptual interpretation of surface water body-aquifer interaction phenomenon as the drainage of a number of independent linear reservoirs. The parameters and initial conditions of each linear reservoir are mathematically defined in a univocal way from the original calibrated finite difference model preserving its characteristics. In most practical cases, an accurate solution can be obtained with a reduced number of linear reservoirs. Therefore this multireservoir conceptual definition enables an important reduction in the dimension of the model matrices and provides a straightforward means of incorporating the accuracy of more complex calibrated distributed-parameter numerical models for simulating surface water body-aquifer interaction within conjunctive use management models and with a minimum computational cost. Several case studies (synthetic and real world cases) are used to illustrate the applicability of the methodology.

Economic Value of Climate Change Adaptation Strategies for Water Management in Spain’s Jucar Basin

AbstractAlthough many recent studies have quantified the potential effects of climate change on water resource systems, the scientific community faces now the challenge of developing methods for as...

A two-step explicit solution of the Boussinesq equation for efficient simulation of unconfined aquifers in conjunctive-use models

[1]xa0Mathematical models that simultaneously simulate surface and groundwater components and their interaction are required to evaluate management alternatives in conjunctive-use systems. Complex systems and scenarios defined over long time periods often force the use of computationally efficient aquifer models. Thus the groundwater flow equation needs to be solved using explicit techniques such as influence functions or the eigenvalue technique. The eigenvalue technique provides a continuous-in-time solution using a state equation with important computational advantages. These methods are strictly applicable only to confined aquifers, which are modeled with a linear groundwater flow equation. However, many commonly exploited aquifers connected with the surface system are unconfined and should be simulated using the nonlinear Boussinesq equation. A two-step explicit solution of the unconfined groundwater flow problem is presented for aquifers with nearly horizontal bottom. It is based on a new approach to linearize the Boussinesq equation. Using a change of variable, it is possible to define an equation with a structure similar to the linear groundwater flow equation. The only difference is found in a term that depends on the solution. Approaching this term by means of a fictitious stress, we obtain a linear equation analogous to the confined groundwater flow equation. The boundary conditions can also be formulated as a function of this new variable with linear expressions. Therefore the unconfined groundwater flow problem can be solved by applying the superposition principle, and the solution can be obtained with a reduced computational cost using the eigenvalue technique.

A Methodology to Analyse and Assess Pumping Management Strategies in Coastal Aquifers to Avoid Degradation Due to Seawater Intrusion Problems

In this paper we will focus on an interesting and complex problem, the analysis of coastal aquifer management alternatives in aquifers affected by seawater intrusion problems. A systhematic method based on an approximation of the safe yield concept for coastal aquifers and a simple model approach to the problem is proposed to help in the decision making process. It is based on the assessment of an index, that we have called the Pumping Reduction to Achieve a Natural Good Status (PRANGS), which we have defined as the minimum reduction in pumped abstractions necessary to maintain seawater intrusion below the value estimated for the natural regime under different climate conditions: humid (PRANGSh), intermediate (PRANGSi) and dry years (PRANGSd). It requires to solve an optimization problem (for each of the climate conditions: humid, intermediate and dry years), whose objective function is to minimize the reduction in pumping whilst ensuring intrusion does not exceed the natural regime ones. A simulation model that provides a valid approximation of seawater intrusion is needed. The methodology was applied to a well-known Spanish Mediterranean aquifer, the Oropesa-Torreblanca Plain aquifer. The optimization problem was solved using an iterative process from a constant density flow simulation model of the aquifer, assuming a direct relationship between piezometric drawdown and seawater intrusion.

Spatiotemporal estimation of snow depth using point data from snow stakes, digital terrain models, and satellite data

Snow availability in Alpine catchments plays an important role in water resources management. In this paper, we propose a method for an optimal estimation of snow depth (areal extension and thickness) in Alpine systems from point data and satellite observations by using significant explanatory variables deduced from a digital terrain model. It is intended to be a parsimonious approach that may complement physical-based methodologies. Different techniques (multiple regression, multicriteria analysis, and kriging) are integrated to address the following issues: We identify the explanatory variables that could be helpful on the basis of a critical review of the scientific literature. We study the relationship between ground observations and explanatory variables using a systematic procedure for a complete multiple regression analysis. Multiple regression models are calibrated combining all suggested model structures and explanatory variables. We also propose an evaluation of the models (using indices to analyze the goodness of fit) and select the best approaches (models and variables) on the basis of multicriteria analysis. Estimation of the snow depth is performed with the selected regression models. The residual estimation is improved by applying kriging in cases with spatial correlation. The final estimate is obtained by combining regression and kriging results, and constraining the snow domain in accordance with satellite data. The method is illustrated using the case study of the Sierra Nevada mountain range (Southern Spain). A cross-validation experiment has confirmed the efficiency of the proposed procedure. Finally, although it is not the scope of this work, the snow depth is used to asses a first estimation of snow water equivalent resources.

Global Assessment of Seawater Intrusion Problems (Status and Vulnerability)

In this research paper we propose a novel method to perform an integrated analysis of the status and vulnerability of coastal aquifers to seawater intrusion (SWI). The method is based on a conceptual approach of intrusion that allows to summarised results in a visual way at different spatial scales, moving from steady pictures (corresponding to instantaneous or mean values in a period) including maps and 2D conceptual cross-sections and temporal series of lumped indices. Our aim is to help in the identification of coastal groundwater bodies at risk of not achieving good chemical status according to the Water Framework Directive. The indices are obtained from available information about aquifer geometry and historical monitoring data (chloride concentration and hydraulic head data). This method may be applied even in cases where a reduced number of data are available. It does not require complex modelling and has been implemented in a GIS tool that encourages its use in other cases. Analysis of the evolution of historical time series of these indices can be used to assess resilience and trends with respect to SWI problems. This method can be also useful to compare intrusion problems in different aquifers and temporal periods.

Experimental Evaluation of Straight Line Programs for Hydrological Modelling with Exogenous Variables

The estimation of the future streamflows is one of the main research topics in hydrology and a very important task for water resources management. The aim of this work is to use symbolic regression in order to model the hydrological balance. Specifically, we use genetic programming to solve the symbolic regression problem. Nevertheless, in this work we use Straight Line Programs instead of trees to encode algebraic expression. Results shows that this representation for algebraic expressions could improve the results in both accuracy and computational time.

Using Multiple Monthly Water Balance Models to Evaluate Gridded Precipitation Products over Peninsular Spain

The availability of precipitation data is the key driver in the application of hydrological models when simulating streamflow. Ground weather stations are regularly used to measure precipitation. However, spatial coverage is often limited in low-population areas and mountain areas. To overcome this limitation, gridded datasets from remote sensing have been widely used. This study evaluates four widely used global precipitation datasets (GPDs): The Tropical Rainfall Measuring Mission (TRMM) 3B43, the Climate Forecast System Reanalysis (CFSR), the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN), and the Multi-Source Weighted-Ensemble Precipitation (MSWEP), against point gauge and gridded dataset observations using multiple monthly water balance models (MWBMs) in four different meso-scale basins that cover the main climatic zones of Peninsular Spain. The volumes of precipitation obtained from the GPDs tend to be smaller than those from the gauged data. Results underscore the superiority of the national gridded dataset, although the TRMM provides satisfactory results in simulating streamflow, reaching similar Nash-Sutcliffe values, between 0.70 and 0.95, and an average total volume error of 12% when using the GR2M model. The performance of GPDs highly depends on the climate, so that the more humid the watershed is, the better results can be achieved. The procedures used can be applied in regions with similar case studies to more accurately assess the resources within a system in which there is scarcity of recorded data available.

An Index-Based Method to Assess Impacts of Global Change on Seawater Intrusion Problems

Global change (GC) might produce important changes in the components of the water balance in coastal aquifers modifying the dynamic of the seawater intrusion (SWI). An assessment of these impacts on freshwater-seawater interaction requires an integrated analysis of quantity and quality issues. In this paper we propose a method to assess and summarise impacts of GC on SWI at different spatial scale. It requires generating consistent plausible future scenarios taking into account climate change, Land Use and Land Cover (LULC) change and Sea Level Rise (SLR) in coastal aquifers. We propose an integrated analysis of the hydrological impacts of potential future scenarios based on a sequential coupling of mathematical models: rainfall-recharge models, agronomic water requirements and irrigation returns models, and fluid density-dependent flow models. We intend to use these models’ results (hydraulic head and chloride concentration maps) to apply an indices-based method to assess and summarize SWI problems (status and vulnerability) at different spatial scale, moving from maps to 2D conceptual cross sections and lumped indices. It can help to identify coastal groundwater bodies in risk of not achieving a good status in accordance with the Water Framework Directive and to identify possible management strategies to reduce existing impacts. The temporal evolution of the indices can be used to assess resilience and trends respect to SWI problems in the historical period and future potential scenarios. In this work we show the results obtained for the Plana de Oropesa-Torrablanca aquifer but different groundwater (GW) bodies and temporal periods can be compared.

Spectral Analysis of Time Series of Carbonate Aquifer of Sierra Gorda

Both Moon and Sun induce Earth tides. Signatures of the Earth’s crustal tides could be recorded in the groundwater in the form of rise and fall of its piezometric surface. In relationship with this phenomenon, there is a scarcity of these kinds of studies in carbonate aquifers. Spectral analysis has been applied in Sierra Gorda aquifer located in the southern of Spain in order to determine the presence and statistical significance of cycles from different time data series like air temperature, barometric pressure, electrical conductivity, pH and piezometric level located in the north border of the aquifer. Diver and Hidrolab sensors to collect data every 1 and 6 h were installed in some of these springs and piezometric borehole. The piezometric data series have more than 25,000 hourly data. The period studied start in November 2010 and end in September 2013. In this site, it has been observed some spectral peaks that could be linked with crustal tides related to cyclic movement of Moon and Sun around Earth. The most significant peaks in piezometric levels that could be related to Moon and Sun show values of 12 h, 1 day, 14 days and 28 days. On the other hand, similar signal is recorded by pH and conductivity temporal data. The influence of Earth tides on pH and conductivity is less studied and would be necessary new investigations on this aquifer to confirm this possibility. The spectral signature of temperature and barometric data is quite different to others variables studied.