Artificial Recharge Basins Research Articles

Hybridization of GALDIT method to assess actual and future coastal vulnerability to seawater intrusion.

In the recent years, the coastal aquifer of Jijel plain (North Algeria) located on the south of the Mediterranean Sea was utilized for cities growth and agricultural development of the region. Consequently, overexploitation and seawater intrusion were identified as major risks to the groundwater resource. In this work, a new approach integrating groundwater vulnerability method and numerical model for predicting the actual and future seawater is proposed. The groundwater vulnerability assessment has been performed by applying the GALDIT method using GIS and the MODFLOW model was used to simulate the actual and future groundwater level of the aquifer over the period 2020-2050. Three scenarios were simulated under water demand and climate conditions (drought, recharge) to obtain the changes in the groundwater level variation. The results of the GALDIT model application to the actual conditions (year 2020) showed that the high class of groundwater vulnerability is located in the coastal fringe and the terminal stretches of wadis where the seawater intrusion limit is located at a distance range between 840 and 1420m from the shoreline. However, the results for predicting future groundwater vulnerability showed that the scenario which proposed the artificial recharge basins, although predicting a worrying situation compared to the actual condition, has the best figure of the groundwater vulnerability assessment and seawater intrusion despite the other two scenarios. In this case the limit in the year 2050 is located between distances of 850-1640m from the shoreline with a forward speed of seawater intrusion of 1-8m/year, compared to the reference year 2020. This showed that groundwater level variation and recharge were the key factors in controlling groundwater vulnerability to seawater intrusion. The presented new approach can be used to mapping the actual and future groundwater vulnerability assessment to seawater intrusion and groundwater resources management in any coastal areas worldwide.

Combining COSMO-SkyMed satellites data and numerical modeling for the dynamic management of artificial recharge basins

Many urbanized areas in the world are using artificial recharge basins (ARB) as an efficient solution to maintain adequate groundwater recharge while coping with flooding problems. The effective management of these basins to adequately maintain their functionality over mid-to-long term requires a suitable monitoring network. Here, we explored the use of a temporal satellite analysis to closely evaluate the efficiency of the ARB in terms of infiltration capacity, depending on hydraulic conditions of the topsoil transitioning from unclogged to clogged conditions in the ARB.COSMO-SkyMed synthetic aperture radar (SAR) images were integrated with ground data and numerical modeling to advance the capability for monitoring low water levels and flooded areas within the ARB. The understanding of biofilm development and effects was achieved by identifying anomalous drawdown phases, by constraining ponding boundary conditions in the numerical model, and by estimating subsequent infiltration rate changes under progressive clogging.With appropriate meteorological conditions (consecutive rainfall events separated by few dry days), the biofilm could develop rapidly and cover large surfaces (e.g., 22 ha) in about two months. During this process, the hydraulic conductivity of the basin surface could decrease by more than three orders of magnitude, completely altering the relationship with the local groundwater regime. Quantitative estimation of the evolution of the infiltration rate provides crucial insights about the overall recharge behavior of ARBs to make reliable economical plans in both the design and monitoring phase.

Tracer test modeling for characterizing heterogeneity and local-scale residence time distribution in an artificial recharge site

Abstract. Artificial recharge of aquifers is a technique for improving water quality and increasing groundwater resources. Understanding the fate of a potential contaminant requires knowledge of the residence time distribution (RTD) of the recharged water in the aquifer beneath. A simple way to obtain the RTDs is to perform a tracer test. We performed a pulse injection tracer test in an artificial recharge system through an infiltration basin to obtain the breakthrough curves, which directly yield the RTDs. The RTDs turned out to be very broad and we used a numerical model to interpret them, to characterize heterogeneity, and to extend the model to other flow conditions. The model comprised nine layers at the site scaled to emulate the layering of aquifer deposits. Two types of hypotheses were considered: homogeneous (all flow and transport parameters identical for every layer) and heterogeneous (diverse parameters for each layer). The parameters were calibrated against the head and concentration data in both model types, which were validated quite satisfactorily against 1,1,2-Trichloroethane and electrical conductivity data collected over a long period of time with highly varying flow conditions. We found that the broad RTDs can be attributed to the complex flow structure generated under the basin due to three-dimensionality and time fluctuations (the homogeneous model produced broad RTDs) and the heterogeneity of the media (the heterogeneous model yielded much better fits). We conclude that heterogeneity must be acknowledged to properly assess mixing and broad RTDs, which are required to explain the water quality improvement of artificial recharge basins.

Clogging of an Effluent Dominated Semiarid River: A Conceptual Model of Stream‐Aquifer Interactions1

Abstract: Water managers in arid and semiarid regions increasingly view treated wastewater (effluent) as an important water resource. Artificial recharge basins allow effluent to seep into the ground relieving stressed aquifers, however these basins frequently clog due to physical, chemical, and biological processes. Likewise effluent is increasingly used to maintain perennial base flow for dry streambeds, however, little is known about the impact of effluent on streambed hydraulic conductivity and stream‐aquifer interactions. We address this issue by investigating: if a clogging layer forms, how the formation of a clogging layer alters stream‐aquifer connections, and what hydrologic factors control the formation and removal of clogging layers. We focused on the Upper Santa Cruz River, Arizona where effluent from the Nogales International Waste Water Treatment Plant sustains perennial flow. Monthly sampling, along a 30 km river reach, was done with two foci: physical streambed transformations and water source identification using chemical composition. Historical dataset were included to provide a larger context for the work. Results show that localized clogging occurs in the Upper Santa Cruz River. The clogging layers perch the stream and shallow streambed causing desaturation below the streambed. With these results, a conceptual model of clogging is established in the context of a semiarid hydrologic cycle: formation during the hot premonsoon months when flow is nearly constant and removal by large flood flows (>10 m3/s) during the monsoon season. However, if the intensity of flooding during the semiarid hydrologic cycle is lessened, the dependent riparian area can experience a die off. This conceptual model leads us to the conclusion that effluent dominated riparian systems are inherently unstable due to the clogging process. Further understanding of this process could lead to improved ecosystem restoration and management.

六郷扇状地における地下水人工涵養の実施と成果

The Rokugo alluvial fan lies around 39° 25' N and 140° 34' E in northern Japan. The distance between the proximal fan at 90 meters above sea level and the distal fan at 45 meters is about four kilometers. The unconfined aquifer of the fan consists mainly of gravel and sand. Four artificial recharge basins were constructed on the central part of the fan. Observation in struments are wells and piezometers installed in depths of 20 m and 50 m. In this paper, the author discusses the effects of artificial recharge using the basin No.2 at the center of the fan. The recharge experience was done during the period when ground water level was affected by melting snow, from April 8 to May 2, 1998. Results obtained are as follows : first, artificial recharging caused a rise in the hydraulic head, which was related to the Rokugo town area situated on the distal fan, and second, because the author supplied the basin No.2 with water with a low water temperature after snow melted, the characteristic phenomenon of ground water temperature was recorded by piezometers in a depth of 20 m at both sites of central and distal fan. Consideration of this point is a theme for future studies. As a synthetic judgment, the artificial recharge of ground water contributes to sustainable aquifer management in the alluvial fan.

Gas-partitioning tracer test to quantify trapped gas during recharge.

Dissolved helium and bromide tracers were used to evaluate trapped gas during an infiltration pond experiment. Dissolved helium preferentially partitioned into trapped gas bubbles, or other pore air, because of its low solubility in water. This produced observed helium retardation factors of as much as 12 relative to bromide. Numerical simulations of helium breakthrough with both equilibrium and kinetically limited advection/dispersion/retardation did not match observed helium concentrations. However, better fits were obtained by including a decay term representing the diffusive loss of helium through interconnected, gas-filled pores. Calculations indicate that 7% to more than 26% of the porosity beneath the pond was filled with gas. Measurements of laboratory hydraulic properties indicate that a 10% decrease in saturation would reduce the hydraulic conductivity by at least one order of magnitude in the well-sorted sandstone, but less in the overlying soils. This is consistent with in situ measurements during the experiment, which show steeper hydraulic gradients in sandstone than in soil. Intrinsic permeability of the soil doubled during the first six months of the experiment, likely caused by a combination of dissolution and thermal contraction of trapped gas. Managers of artificial recharge basins may consider minimizing the amount of trapped gas by using wet, rather than dry, tilling to optimize infiltration rates, particularly in well-sorted porous media in which reintroduced trapped gas may cause substantial reductions in permeability. Trapped gas may also inhibit the amount of focused infiltration that occurs naturally during ephemeral flood events along washes and playas.

Modeling of Artificial Recharge Basins of Different Shapes and Effect on Underlying Aquifer System

The influence of artificial recharge by a rectangular basin was computed using an algorithm based on the finite-element method. Ground-water head and flux in the underlying aquifer system were calculated for the rectangular basin. In addition, head distributions also were computed for circular, square, hexagonal, and triangular recharge basins with equal area and for the same recharge rate as the rectangular basin. A lower ground-water mound buildup was found for higher-perimeter basin shapes and vice versa. Influence of variation in hydraulic conductivity beneath the recharge basin due to gradual clogging of the aquifer pore spaces was investigated and the mass balance for the rectangular basin was checked. Time variant analysis computed a time of 82.3 days to stabilize the mound. The buildup was higher initially followed by a much slower growth as steady state was approached.

Water quality changes related to the development of anaerobic conditions during artificial recharge

Artificial recharge basins or spreading sites commonly exhibit reductions in infiltration rates after prolonged periods of submergence. This loss in infiltration rate has often been shown to be associated with a large population of anaerobic or facultative anaerobic bacteria in the material underlying the basin floor. An artificial recharge experiment in a spreading basin at Lubbock, Texas, showed a significant change in the chemical quality of recharged water that was associated with the growth of anaerobic bacteria. Sulfate‐reducing bacteria reduced the sulfate concentration of the recharge water at this location by 80 mg/l. The bicarbonate concentration was increased by more than 150 mg/l, and the pH decreased 1 unit during the same time period. The change in chemical quality occurred suddenly and corresponded to a dramatic decrease in the infiltration rate in the basin. These observations on the chemical changes in recharged water make it possible to differentiate between anaerobic bacteria and other causes of reduced hydraulic conductivity in this recharge basin. The anaerobic conditions appear to start at depth and work toward the surface, thereby suggesting a process that involves adsorption of organic material and consumption of dissolved oxygen with depth.