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Under certain flow conditions, fluid flow through porous media starts to deviate from the linear relationship between flow rate and hydraulic gradient. At such flow conditions, Darcy’s law for laminar flow can no longer be assumed and nonlinear relationships are required to predict flow in the Forchheimer regime. To date, most of the nonlinear flow behavior data is obtained from flow experiments on packed beds of uniformly graded granular materials (Cu = d60/d10 Cu n Cu values and low porosity values. The present study shows that for granular material with wider grain size distributions (Cu > 2), the d10 instead of the average grain size (d50) as characteristic pore length should be used. Ergun constants A and B with values of 63.1 and 1.72, respectively, resulted in a reasonable prediction of the Forchheimer coefficients for the investigated granular materials.

A wide variety of well drilling techniques and well completion methods is used in the installation of dewatering and artificial recharge wells for the purpose of construction dewatering. The selection of the optimal well type is always a trade-off between the overall costs of well completion and development, the optimal well hydraulics of the well itself, the hydraulic impact of the well on its surroundings, and the required operational life span of the well. The present study provides an analytical framework that can be used by dewatering and drilling companies to quantify the contribution to head loss of typical dewatering and artificial-recharge well configurations. The analysis shows that the placement of partially penetrating wells in high-permeability layers could promote the use of quick and cheap installation of naturally developed wells using jetting or straight-flush rotary drilling. In high-permeability layers, such wells can be favorable over wells completed with filter pack, which require extensive well development to remove the fines from the filter cake layer. The amount of total head loss during discharge/recharge at a volumetric rate of 20 m3/h per meter of filter length, into or from a gravely aquifer layer, is reduced by factors of 3–4 while using naturally developed well types instead of well types completed with a filter pack that contains a filter cake layer due to borehole smearing.

The efficiency of heat recovery in high-temperature (>60 °C) aquifer thermal energy storage (HT-ATES) systems is limited due to the buoyancy of the injected hot water. This study investigates the potential to improve the efficiency through compensation of the density difference by increased salinity of the injected hot water for a single injection-recovery well scheme. The proposed method was tested through numerical modeling with SEAWATv4, considering seasonal HT-ATES with four consecutive injection-storage-recovery cycles. Recovery efficiencies for the consecutive cycles were investigated for six cases with three simulated scenarios: (a) regular HT-ATES, (b) HT-ATES with density difference compensation using saline water, and (c) theoretical regular HT-ATES without free thermal convection. For the reference case, in which 80 °C water was injected into a high-permeability aquifer, regular HT-ATES had an efficiency of 0.40 after four consecutive recovery cycles. The density difference compensation method resulted in an efficiency of 0.69, approximating the theoretical case (0.76). Sensitivity analysis showed that the net efficiency increase by using the density difference compensation method instead of regular HT-ATES is greater for higher aquifer hydraulic conductivity, larger temperature difference between injection water and ambient groundwater, smaller injection volume, and larger aquifer thickness. This means that density difference compensation allows the application of HT-ATES in thicker, more permeable aquifers and with larger temperatures than would be considered for regular HT-ATES systems.

The subsurface may provide opportunities for robust, effective, sustainable, and cost-efficient freshwater management solutions. For instance, via aquifer storage and recovery (ASR; Pyne, 2005): “the storage of water in a suitable aquifer through a well during times when water is available, and the recovery of water from the same well during times when it is needed”. This can be successful in storing and recovering both potable and irrigation water. ASR is attractive due to the limited space requirements above ground and the generally successful conservation of water quality (Maliva and Missimer, 2010). The recovery efficiency (RE) of ASR is defined as the part of the injected water that can be recovered with a satisfying quality. Several factors can limit the RE during ASR in brackish-saline aquifers, such as the simultaneous abstraction of injected freshwater and ambient, more saline groundwater. This can be a result of ‘bubble drift’, which happens when the infiltrated bubble is transported away from the ASR well by the local or regional hydraulic gradient. However, the RE can be particularly limited in brackish–saline aquifers by the density difference between the injected freshwater and ambient brackish or saline groundwater. This is because this density difference causes the freshwater to float upwards in the aquifer (‘buoyancy effect’), while denser saline water is recovered by lower parts of the well (Esmail and Kimbler, 1967; Merritt, 1986; Ward et al., 2007). Both water types are thus blended in the ASR well to produce a brackish, generally unsuitable water quality.Freshwater availability is more and more stressed in coastal areas, where brackish and saline groundwater is commonly present. Therefore, the ability to increase the RE of ASR systems provides a true benefit because it would significantly amplify the potential of freshwater management. The general objective of this study is therefore to quantify and increase the performance (indicated by RE) of relatively small-scale ASR systems in areas with brackish-saline groundwater, taking into account recently developed well configurations for performance optimization.