Applying 3D Geostatistical Simulation to Improve the Groundwater Management Modelling of Sedimentary Aquifers: The Case of Doñana (Southwest Spain)

Mathematical groundwater modelling with homogeneous permeability zones has been used for decades to manage water resources in the Almonte-Marismas aquifer (southwest Spain). This is a highly heterogeneous detrital aquifer which supports valuable ecological systems in the Doñana National Park. The present study demonstrates that it is possible to better characterize this heterogeneity by numerical discretization of the geophysical and lithological data available. We identified six hydrofacies whose spatial characteristics were quantified with indicator variogram modelling. Sequential Indicator Simulation then made it possible to construct a 3D geological model. Finally, this detailed model was included in MODFLOW through the Model Muse interface. This final process is still a challenge due to the difficulty of downscaling to a handy numerical modelling scale. New piezometric surfaces and water budgets were obtained. The classical model with zones and the model with 3D simulation were compared to confirm that, for management purposes, the effort of improving the geological heterogeneities is worthwhile. This paper also highlights the relevance of including subsurface heterogeneities within a real groundwater management model in the present global change scenario.

The dynamic programming management model of groundwater with covariates: a case study for the Songyuan area, Jilin Province, China

This research analysed the action and characteristics of the relationship between mutual-feed joint-variations of groundwater. On this basis, a theory and method for constructing a dynamic programming management model for groundwater with covariates was proposed which used the state transition equation method. The model was solved using the differential dynamic programming (DDP) method. Thereafter, the groundwater system of the Songyuan area in western Jilin Province was treated as an area of interest to study the major problem of the relationships governing mutual-feed joint-variation. Based on the numerical simulation model, the research paid more attention to Qianguo County and Fuyu County and established a dynamic programming management model of the groundwater with covariates for these areas. Then the optimised amount of pumping, the groundwater level, and the covariates were solved simultaneously. To sum up, this research enriched the theory and method for dealing with mutual-feed joint-variations in the groundwater management model. Thereby, it established a theoretical foundation and provided technical support for the solution of various practical problems.

Payments for Watershed Services as Adaptation to Climate Change: Upstream Conservation and Downstream Aquifer Management

Economically optimal groundwater extraction allocates water over space and time to its highest and best social use. But optimal management of water resources also requires optimal investment in watershed capital, even as the climate is changing. We augment a standard coastal groundwater management model with stock-dependent extraction costs to include recharge-enhancing natural and produced capital whose depreciation can be offset by investment in each period. In some parts of the world, including Hawaii, results from climate models suggest that mean annual rainfall will decrease but that the frequency of storms may increase. In the case of coastal aquifers, the implication is that runoff to the ocean will increase and groundwater recharge will decrease. Accordingly, the groundwater-extraction/watershed-investment problem is further extended to allow natural recharge to decline in response to climate change. The tendency of falling recharge is partially offset by increasing investment in watershed capital. If precipitation decreases sufficiently, however, it may be that optimal conservation eventually declines as the cost of increasing groundwater recharge correspondingly increases. Thus adaptation to climate change may involve an initial stage of increased conservation investment followed by controlled depreciation of natural capital. That is, instruments of adaptation may become increasingly ineffective as climate change progresses.

Estimation of Suitable Groundwater Safe Yield under the Unusually Constraints of Environmental Conditions in Taipei Basin, Taiwan

The Taipei Basin in Taiwan is an extremely special case under the constraints of environmental conditions. Pumping of groundwater in the basin was banned in 1968 due to the land subsidence. Since then, groundwater level in the Taipei basin has risen over the years and the land subsidence has also stopped. However, due to the continuous rise of groundwater level, the soil liquefaction potential of saturated sand soil strata has increased. Thus, the groundwater in Taipei basin should be controlled based on the suitable groundwater level to reduce the possibility of land subsidence or soil liquefaction. This study proposes a novel performance of groundwater management model, which considers the three aspects of safe yield, soil liquefaction, and land subsidence. In this process, a three-dimensional groundwater numerical model is primarily established with MODFLOW, and the safe yield and groundwater level are deduced through the Hill method. The second part requires an estimation of the soil liquefaction potential by applying the Seed97 method. The third part of the process includes an estimation of the subsidence of sand by adopting the Ishihara method and the subsidence of clay blanket through the Terazaghi method. Finally, combine the limited groundwater level through the application of the said methods, the proper scope for the level of groundwater in the Taipei Basin is then estimated. Hence, the maximum amount of groundwater that can be pumped could be estimated based on the suitable lower limit of groundwater level, and the minimum amount of groundwater that can be pumped could be estimated based on the suitable upper limit of groundwater level. The study result indicates the central region in the basin has a high potential of soil liquefaction, while the periphery of the basin has a high potential for land subsidence. In consideration of three environmental limited constraints, namely, safe yield of groundwater, soil liquefaction, and land subsidence, could estimate the maximum groundwater amount that can be generated per annum is about 0.77x109m3 to 1.03x109m3, while the minimum groundwater amount per annum is about 0.53x 109m3 to 0.71x109m3.