Recharge Mound Research Articles

Developing managed aquifer recharge (MAR) to augment irrigation water resources in the sand and gravel (Crag) aquifer of coastal Suffolk, UK

Managed aquifer recharge (MAR) offers a potential innovative solution for addressing groundwater resource issues, enabling excess surface water to be stored underground for later abstraction. Given its favourable hydrogeological properties, the Pliocene sand and gravel (Crag) aquifer in Suffolk, UK, was selected for a demonstration MAR scheme, with the goal of supplying additional summer irrigation water. The recharge source was a 4.6 km drainage channel that discharges to the River Deben estuary. Trialling the scheme in June 2022, 12,262 m3 of source water were recharged to the aquifer over 12 days via a lagoon and an array of 565 m of buried slotted pipes. Groundwater levels were raised by 0.3 m at the centre of the recharge mound with an approximate radius of 250 m, with no detrimental impact on local water features observed. The source water quality remained stable during the trial with a mean chloride concentration (133 mg L−1) below the regulatory requirement (165 mg L−1). The fraction of recharge water mixing with the groundwater ranged from 69% close to the centre and 5% at the boundary of the recharge mound, leading to a reduction in nitrate-N concentration of 23.6 mg L−1 at the centre of the mound. During July–September 2022, 12,301 m3 of recharge water were abstracted from two, 18 m boreholes to supplement surface irrigation reservoirs during drought conditions. However, the hydraulic conductivity of the Crag aquifer (∼10 m day−1) restricted the yield and thereby reduced the economic viability of the scheme. Construction costs for the MAR system were comparatively low but the high costs of data collection and securing regulatory permits brought the overall capital costs to within 18% of an equivalent surface storage reservoir, demonstrating that market-based mechanisms and more streamlined regulatory processes are required to incentivise similar MAR schemes.

Issues of Stream-Aquifer Interactions in Grout Lined Channels in Urban Watersheds

Grout lined storm drains are used worldwide to convey storm runoff away from urban areas. They also convey dry weather flows such as car wash runoff, lawn runoff, and other “nuisance flows” in urban centers. Areas in Southern California and elsewhere have shallow water tables where dry weather flows in grout lined storm drains consist primarily of perennial groundwater baseflows. In these areas, groundwater leaks through cracks, joints, weepholes, and intentional dewatering structures into storm drains and eventually flows into natural channels, coastal wetlands, and estuaries. The “lined” sections of these channels are not always impervious; in fact, the lining of the channels often affords excellent opportunities to collect groundwater samples at discrete points that are usually not present along unlined channels where well control is sparse or where technical or legal issues prevent installation of piezometers. Frequently, as much as 95% of the nutrient and trace element loading to urban catchments during dry weather is from seepage of groundwater that is laden with pollutants. This project presents several examples of our experiences in conducting stream/aquifer studies in lined and semi-lined channels in Southern California. Sub-projects include evolution of groundwater quality along flowpaths, detection of unwanted recharge mounds in shallow groundwater systems due to leaky water main pipes, and comparisons of water quality in lined and unlined sections of a creek. Tools that are utilized and described in the paper include isotopic tracers; trace element and standard inorganic constituents; and innovative sampling methods.

Comparison of Simulation Methods for Recharge Mounds Under Rectangular Basins

Various methods for predicting recharge mounds that form beneath basins during recharge and the subsequent decay after recharge stops have been developed over the past half a century. In this paper several analytical methods were compared for very rapid, rapid and moderately rapid hydraulic conductivity values. Subsequently, the results were matched with numerical methods. Results obtained indicate minimal deviations among analytical solutions for predicting infiltration mounds at low recharge time (≤50 days). In addition, the deviations can be easily amended. Numerical solutions predict higher infiltration mounds (up to 32 % for the results chosen) compared to analytical methods, a variation attributed to the fewer assumptions made when solving governing groundwater equations. Yet at the lowest hydraulic conductivity rate (1.6 m/day) used in this investigation, numerical solutions are comparable to analytical solutions. Despite general unanimity on the superiority of numerical over analytical solutions for predicting infiltration mounds; the two methods have not been tested with observed field data. As a result, and to assist in discerning the best approach, analytical and numerical solutions were validated against results from three distinct field observations. The best match was noted between analytical and observed recharge mounds. In conclusion the practical applicability of each solution under various hydro-geologic conditions is summarized in the form of a table.

Geotechnical Parameters Impact on Artificial Ground Water Recharging Technique for Urban Centers

Water scarcity is a serious problem throughout the world for both urban & rural community. Urban centers in India are facing an ironical situation of water scarcity today. This paper includes an Analytical solution, Numerical modeling, Empirical approaches, In-situ test results to predict recharge (rate) mound of the ground-water and capacity of recharge well which is essential for the proper management of suitable artificial ground-water recharge systems to maintain water balance and stop salt water intrusion. Authors have derived analytical equation for predicting growth as well as decline of the ground-water mound depending on the intensity of recharge rate qr with different value of permeability k, depth of pervious strata H and diameter of well d, also studying the effects of variation in the geotechnical parameters on water-table fluctuations. In this paper to study the impact of numerical modeling using quadratic equation for unconfined aquifer base on rainfall intensity P and a change in saturated thickness H with variation in piezometric level. Empirical approaches are for evaluation of correct value of k of an undercharged unconfined aquifer with drawdown s0, influence zone L, recharge rate qr. In-situ test results give actual correlation between value of recharging rate of well and permeability on field. Authors have verified recharging rate of installed well from all approaches. A result obtained from the various field case studies gives the validation of the derived equation. Scientific quality measures of aquifer water are also recorded.

Wastewater disposal at safari lodges in the Okavango Delta, Botswana

Many safari lodges in the Okavango Delta obtain their water supply from boreholes in near-surface aquifers while disposing of their wastewater via soak-aways, creating a potential risk of contamination of their water supply. Most islands in the Delta contain sites where the groundwater has become salinised as a result of transpiration by island vegetation. This study of wastewater disposal at such a site on Chitabe Island, which involved surveying of the water table, measurement of groundwater salinity, field bacteriological screening and groundwater flow modelling has revealed that although water disposal has created a recharge mound, the depression in the water table induced by transpiration by island vegetation is such that pollutants will remain confined to the region of maximum groundwater depression. Although the soils are sandy, they exhibit significant filtration effects on bacteria. The field assay used in this study was unable to detect coliform and E. coli bacteria in groundwater within a distance of 20 m from the disposal point. Modelling of groundwater flows indicates that boreholes located on the outer fringes of the island are secure from contamination. The study suggests that disposal of wastewater into areas where the groundwater is salinised provides a sustainable solution to the problem of wastewater disposal in the Okavango Delta.

FROZEN SOIL IMPACT ON GROUND WATER‐SURFACE WATER INTERACTION1

ABSTRACT: Ground water and surface water interaction in the prairie pothole region of the United States and Canada is seasonally dominated by the presence of thick, frozen soil layers that affect infiltration. During a spring thaw, the subsoil may remain frozen, preventing infiltration. The impact of the frozen soil layer on the timing of infiltration of depressional‐focused recharge to the ground water is not clearly understood. The objective of this paper is to relate changes in the water table during spring to changes in frost depth and soil water content. A depression and adjacent upland study site were instrumented with CRREL‐type frost tubes, neutron probe access tubes, and ground water monitoring wells. Increases in water table levels in a depression occurred before the frost layer decomposed and infiltrating water quickly formed a recharge mound. Water table responses at the upland site took place as two events. The first event was a gradual rise, probably caused by the lateral dissemination of the recharge mound. The second rise was a rapid rise coinciding with the decomposition of the soil frost layer. Because of the accumulation of surface water in depressions, agricultural practices that remove water from a field can affect water resources management by limiting the addition of water recharge to unconfmed ground water.

Groundwater pollution due to sugar-mill effluent, at Sonai, Maharashtra, India

Analyses of 126 samples collected from 18 dug wells in the shallow basaltic aquifer over a period of 7 months have revealed spatial as well as temporal changes in the chemical properties of groundwater. While the temporal changes have been attributed to dilution and concentration phenomena governed by climatic factors, the spatial variations in the geochemical characteristics of groundwater appeared to be related to pollution due to effluents from the Mula Sugar Factory. The cause of groundwater pollution is the effluent carried by a stream flowing through the area. Fluctuations in the groundwater table, influent water quality character of the stream, less capacity to accommodate large volume of effluent and occurrence of zero base flow (under natural conditions) in the stream are the factors favoring infiltration of constituents of waste water into the underlying weathered basaltic aquifer. Pollutants have entered into the shallow aquifer by downward percolation through the zone of aeration to form a recharge mound at the water table and, further, lateral movement below the water table. The plume of polluted groundwater has a lateral extent of a few meters in the upstream area and more than 400 m on either side of the stream in the downstream part. The zone of polluted groundwater has an areal extent of more than 3.5 km2. Groundwater is the only source available for drinking and agricultural purposes. It is recommended that the base of the lagoons and the stream used for release of plant effluent should be waterproofed for the protection of groundwater in the Sonai area.

Delineation of Preferred‐Flow Paths by Response to Transient Lagoon Exfiltration

AbstractObservations of hydraulic head response to lagoon leakage into an extremely heterogeneous aquifer allow qualitative identification of spatial patterns in heterogeneity. In a 150–hour leakage experiment over such an aquifer, the fluid mass balance was estimated using a stage‐fluctuation model while transient response was observed in downgradient wells and springs. Based on timing with respect to pond leakage, water‐level response at different locations within the aquifer may be identified as either within or outside the influence of preferred‐flow paths (PFPs). Flows at springs 150–200 m from the pond increased by 20–60% above baseline flows, showing initial increase within ca. 40 hours. Synoptic water‐level rise patterns observed during the test describe enlargement of a recharge mound from beneath the pond and suggest the spatial pattern of PFPs to > 150 m distant. An analytical model assuming homogeneity (Hantush, 1967), applied to water‐level response for wells > 30 m from the pond, overestimated K by > 1 order of magnitude in comparison to slug‐test estimates. This discrepancy is attributed to the inferred presence of linearly continuous heterogeneities causing preferential flow. Large‐scale hydraulic tests such as this sample the spatial structure for conductive pathways and may be of utility in parameterization of numerical flow models. In contrast, slug‐test results give local parameter estimates, but more limited information on PFP distribution.

Combined use of watershed, aquifer and crop simulation models to evaluate groundwater recharge through percolation ponds

Percolation ponds are constructed in many parts of the tropics to augment fast-depleting groundwater resources. Increased agricultural productivity due to additional well irrigation water is the direct benefit from the pond schemes. Usually, location-specific empirical relationships are adopted for hydrologic and economic design of ponds. In this paper, an approach is presented to evaluate hydrologic pond design, by combining watershed, aquifer and crop simulation models of the pond system. A watershed model (CAPSIM) was developed based on the ‘state variable approach’ describing the dynamic catchment-pond hydrologic processes such as runoff, runoff due to interflow, evapotranspiration, direct percolation, pumping and irrigation. CAPSIM operates on a daily basis, using rainfall and pan evaporation data. Based on the Alternating Direction Implicit Algorithm (ADIA), a finite difference Aquifer Simulation model (ASIM) was developed to simulate two-dimensional recharge mounds beneath the pond. Predictability of CAPSIM and ASIM was verified with observed field data from one pond site, from which the models were improved. The models were further validated separately for three pond locations and for different years of weather data, by comparing observed pond and well water levels. The crop model, SAHEL, was adapted to the rice-growing environments of pond command areas, by representing water stress, runoff and well irrigation. Total Additional well Irrigation made possible Due to recharge (AID-recharge) in two space dimensions during a crop season was predicted by linking CAPSIM and ASIM. AID-recharge thus computed was input to the crop model for predicting the spatial distribution of crop response to different well irrigation scenarios. A series of ‘distance-capacity-yield’ curves were developed, which quantify the benefits associated with a modification in the pond structure. The batch of models thus linked could serve as a decision support tool for pond designers for evaluating desired hydrologic economic strategy.

Dupuit-Forchheimer theories for the shape of groundwater recharge mounds

The nonlinear Dupuit-Forchheimer theory and two linearized versions are considered as to their applicability for giving accurate results on recharge mound shapes beneath strip and square basins. Results on mound rises from the approximate theories are compared with those from the nonlinear theory to determine criteria for the use of the approximate theories.

Fate of silicate minerals in a peat bog

An investigation of silicate weathering in a Minnesota mire indicates that quartz and aluminosilicates rapidly dissolve in anoxic, organic-rich, neutral- pH environments. Vertical profiles of pH, dissolved silicon, and major cations were obtained at a raised bog and a spring fen and compared. Profiles of readily extractable silicon, diatom abundance, ash mineralogy, and silicate surface texture were determined from peat cores collected at each site. In the bog, normally a recharge mound, dissolved silicon increases with depth as pH increases, exceeding the background silicon concentration by a factor of two. Silicate grain surfaces, including quartz, are chemically etched at this location, despite being in contact with pore water at neutral pH with dissolved silicon well above the equilibrium solubility of quartz. The increasing silica concentrations at circum-neutral pH are consistent with a system where silicate solubility is influenced by silica-organic-acid complexes. Silica-organic-acid complexes therefore may be the cause of the almost complete absence of diatoms in decomposed peat and contribute to the formation of silica-depleted underclays commonly found beneath coal.

URBAN STORM RUNOFF EFFECTS ON EXCHANGEABLE CATIONS AND PERCOLATING WATER CONSTITUENTS BELOW RECHARGE BASINS

Inorganic contaminants are present in storm-water runoff from urban residential areas. The disposition of the major cations and anions in the alluvium deposits of a recharge basin, percolating water, and the mound of soil water below the basin were investigated relative to a nearby control site. This investigation was a component of the USEPA's Nationwide Urban Runoff Program in Fresno, California. The study basin has received urban storm-water runoff from a residential area for 16 yr. The recharge effects to a depth of 21 m have been an increase in exchangeable Ca2+ and K+, a decrease in exchangeable Mg2+, and a minor increase in the exchangeable Na+ with depth. The specific electrical conductance of the percolating water increased from an input value of 0.056 dS m−1 to 0.097 dS m−1 at a depth of 20.7 m where the recharge mound had formed. The concentrations of the major dissolved cations and anions in the urban residential storm-water runoff are low. The results indicate that these ions are not detrimental to the physicochemical properties of the surface soils or deep alluvium strata or to the groundwater quality resulting from recharging urban residential storm-water runoff. These results are important to the continued conservation of urban storm water and the preservation of the chemical and physical properties of the retention/recharge basin surface soils and deep alluvium stratum essential for continuing efficient basin recharge.

Strip Basin Recharge to Inclined Water Table

The hydrodynamics of recharge mounds that develop on an inclined water table beneath a strip recharge basin are considered. The nonlinear potential (NLP) theory is used to predict the motion of the water table resulting from the recharge operation. The theoretical derivation of the NLP theory uses the saturated flow equations for a homogeneous isotropic medium. Solutions to the NLP theory for recharge to an inclined water table are obtained by using a finite difference method. A few examples of flow patterns showing the motion of the recharged and native water are given. The mathematical model can be utilized to predict the response and movement of recharged water in the design and operation of recharge facilities.

Microcomputer Model of Artificial Recharge Using Glover's Solution

ABSTRACTAn interactive program written for an APPLE II+ 48K computer is presented which solves Glover's (1960) analytical solution for recharge from a rectangular basin. The program is capable of graphically displaying the rise and decline of the recharge mound for either an infinite homogeneous medium or for a stream aquifer system.

Growth of Ground‐Water Mound in Response to Recharge

ABSTRACTIt was proposed that the horizontal extent of the ground‐water mound is limited for finite times of recharge from strip basins even in infinite aquifers. A method of identifying the extent of the ground‐water mound using solutions of the equation of flow for finite aquifers was suggested. These solutions were obtained using two different procedures of linearization, those of Baumann and Hantush, and Laplace transforms. The resulting expressions were of a general nature and the equations of Hantush for infinite aquifers were shown to follow as a special case. The range of validity of the two procedures of linearization was tested using experimental results from sand tank models of finite aquifers, available in literature. The Baumann linearization was valid (correct to within ±5 percent of experimental values) up to a water table rise less than 0.4 times the initial height of the water table. The Hantush linearization was valid (correct to within ±2 percent of experimental values) for the entire range of water table rise studied, i.e. up to three times the initial height of the water table. The Hantush procedure was thus shown to have wider applicability. However, both procedures were found to yield results which have satisfactory agreement with experimental results over larger ranges than earlier reported for infinite aquifers.The effect of variation of the horizontal extent of the recharge mound on the water table profile was studied by treating the limit of the horizontal mound itself as a parameter. The water table rise was computed using the Hantush linearization procedure for different values of the ratio B/L (B/L = 15, 20, 25, 30, 35, 40 and ∞) where 2B is the horizontal extent of the mound and 2L the width of the recharge strip. The finite extent of the ground‐water mound in an infinite aquifer was given by that value of B/L for which the predicted profile was identical to that produced when B/L =∞.

Fossil Ground‐Water Gradients in Arid Regional Sedimentary Basins

ABSTRACTThe hypothesis that present‐day ground‐water gradients in arid regional sedimentary basins are a decay feature of very old recharge mounds is examined using a resistance network analogue. A longitudinal section model of a conceptual basin with some specific control of aquifer permeability and ground‐water age is used.With reasonable combination of aquifer permeability and specific yield it is shown that an acceptable head decay could have occurred over the past 10,000 years to produce the present‐day gradient. In the model adopted, decreasing permeability with depth was found to be required to accord with 14C ground‐water age data.Although the model is not considered to be definitive for any particular aquifer the results show that fossil gradient conditions could exist in the regional basins for long periods and should be taken account of in ground‐water resources assessments.

Hydrodynamics of Perched Mounds

Perched recharge mounds are developed beneath artificial ground-water recharge basins where there are one or more horizontal semipervious layers located beneath the basin. In this paper the shape of these perched mounds is investigated using the saturated flow equations and the Dupuit-Forchheimer approximation. Finite difference techniques were used to solve for the mound shape for rising and steady-state mounds for both a strip and circular basin. Analytical solutions were obtained for certain limiting conditions. The results for the maximum mound thickness are presented in the form of dimensionless curves involving permeability of semipervious layer and the soil above the layer, thickness of layer, effective porosity and recharge rate from the basin. The equations and assumptions used for a single layer can also be used for a multiple layer situation. A computer program was developed for a three layer case and its use is illustrated with a numerical example.

Unconfined Aquifer Characteristics and Well Flow

Numerical solutions are developed for determination of aquifer characteristics and unsteady radial flow through injection wells in unconfined aquifers under constant drawdown and injection pressure conditions. These solutions are based on a numerical solution of the basic differential equation of flow. Appropriate dimensionless parameters are introduced to transform the basic differential equation of flow into an explicit form. Dimensionless graphical solutions are presented for the rate and accumulative volume of discharge and recharge and the radius of expansion of recharge mounds versus time for a range of drawdown and injection pressure values. Numerical examples are presented by applying these solutions to hypothetical field conditions.