Increase In Recharge Rates Research Articles

Modeling the river-aquifer via a new exact model under a more general function of river water level variation

The interaction between surface water and groundwater is a significant topic in groundwater-related problems. This study suggests an exact model based on Laplace transformation to calculate the groundwater flow in river-aquifer systems. Exact models play an important role in simulating the future behavior of river-aquifer systems. Therefore, investigation of the exact models for river-aquifer systems is a hot topic in the hydraulics of groundwater flow modeling. The objective of this research is to present new exact models for simulating the hydraulics of groundwater flow in river-aquifer systems with a more general function of river level variation under recharge by means of Laplace transform method. A general function is adopted to describe the river level variation, in which some situations such as linear, exponential and power of time variations in the river level can be treated as special cases. The effects of variations in aquifer parameters on groundwater hydraulic head are evaluated. It is shown that the groundwater hydraulic head grows slower in aquifers with a greater thickness or hydraulic conductivity. In addition, the effect of changes in specific storage is too little on the groundwater hydraulic head. The variations in hydraulic heads due to changes in recharge rate with different values of thickness, hydraulic conductivity, specific storage, and length are analyzed. It is observed that the groundwater hydraulic head in an aquifer with a lesser length, higher hydraulic conductivity or higher thickness is less sensitive to a change in the recharge rate than in an aquifer with a higher length, lesser hydraulic conductivity or lesser thickness. Furthermore, it is shown that the differences in hydraulic heads due to the increase in recharge rate are not significant for different values of specific storage. The results of the present new exact models are successfully verified by the results obtained from the analytical solution of Bansal and Das. Also, for more reliability, the results are compared with those results of MODFLOW. The results show that the presented new exact models are accurate, robust and efficient. One of the advantages of the solutions is to investigate the sensitivity analysis of aquifer parameters, which has been carried out in this paper. Furthermore, in the present research a more general function describing river level variation is considered, in which the linear, exponential and power of time variations are special cases.

Impact of urbanization on groundwater recharge rates in Dübendorf, Switzerland

Groundwater, as the world’s most important reserve of available fresh water, is known to be affected by urbanization. Managing this resource in a sustainable way is critical for water resource management. Groundwater recharge rates in urban areas remain however still poorly understood and under-researched and knowledge about these rates and their expected changes under increasing urbanization is therefore of primary importance. This study aims to give insight into urban groundwater recharge by performing water budget calculations for four different time periods for an urban study site in northern Switzerland. In order to take into account uncertainty in parameter values a Monte Carlo (MC) approach was carried out.Our study highlights a strong positive correlation between groundwater recharge rates and the extent of the urban area. In detail, at the study site urban areas expanded from 6% in 1880 to 44% in 2009, leading to an increase in the mean groundwater recharge rate. However, the increase amount in recharge remains uncertain and varies between 29% and 67% depending on the parameter combination originating from the MC approach. Based on our water budget calculations, the transformation of natural landscapes into impervious areas leads to an increase in groundwater recharge rates due to the reduction of evapotranspiration that more than compensates for the increase in runoff. Furthermore, water main leakages contribute to an increase in recharge rates. Overall, we demonstrate that a better understanding of groundwater recharge changes in urban areas is required to move towards a sustainable water management. We hope that this example will encourage the hydrogeological community to pay more attention to urban groundwater recharge.

Parametric Studies on Saltwater Intrusion into Coastal Aquifers for Anticipate Sea Level Rise

Saltwater intrusion into coastal aquifers is a global issue, exacerbated by increasing demands for freshwater in coastal regions. This study investigates into the parametric analysis on saltwater intrusion in a conceptual, coastal, unconfined aquifer considering wide range of freshwater draft and anticipated sea level rise. The saltwater intrusion under various circumstances is simulated through parametric studies using MODFLOW, MT3DMS and SEAWAT. The MODFLOW is used to simulate the groundwater flow system under changing hydro-dynamics in coastal aquifer. To simulate solute transport MT3DMS and SEAWAT is used. The saltwater intrusion process has direct bearing on hydraulic conductivity and inversely related to porosity. It may also be noted that increase in recharge rate considered in the study does not have much influence on saltwater intrusion. Effect of freshwater draft at locations beyond half of the width of the aquifer considered has marginal effect and hence can be considered as safe zone for freshwater withdrawals. Due to the climate change effect, the anticipated rise in sea level of 0.88 m over a century is considered in the investigation. This causes increase in salinity intrusion by about 25%. The combined effect of sea level rise and freshwater draft considered indicated significant increase in saltwater intrusion into coastal aquifers up to 57%.

Using <sup>14</sup>C and <sup>3</sup>H to understand groundwater flow and recharge in an aquifer window

Abstract. Knowledge of groundwater residence times and recharge locations is vital to the sustainable management of groundwater resources. Here we investigate groundwater residence times and patterns of recharge in the Gellibrand Valley, southeast Australia, where outcropping aquifer sediments of the Eastern View Formation form an "aquifer window" that may receive diffuse recharge from rainfall and recharge from the Gellibrand River. To determine recharge patterns and groundwater flow paths, environmental isotopes (3H, 14C, δ13C, δ18O, δ2H) are used in conjunction with groundwater geochemistry and continuous monitoring of groundwater elevation and electrical conductivity. The water table fluctuates by 0.9 to 3.7 m annually, implying recharge rates of 90 and 372 mm yr−1. However, residence times of shallow (11 to 29 m) groundwater determined by 14C are between 100 and 10 000 years, 3H activities are negligible in most of the groundwater, and groundwater electrical conductivity remains constant over the period of study. Deeper groundwater with older 14C ages has lower δ18O values than younger, shallower groundwater, which is consistent with it being derived from greater altitudes. The combined geochemistry data indicate that local recharge from precipitation within the valley occurs through the aquifer window, however much of the groundwater in the Gellibrand Valley predominantly originates from the regional recharge zone, the Barongarook High. The Gellibrand Valley is a regional discharge zone with upward head gradients that limits local recharge to the upper 10 m of the aquifer. Additionally, the groundwater head gradients adjacent to the Gellibrand River are generally upwards, implying that it does not recharge the surrounding groundwater and has limited bank storage. 14C ages and Cl concentrations are well correlated and Cl concentrations may be used to provide a first-order estimate of groundwater residence times. Progressively lower chloride concentrations from 10 000 years BP to the present day are interpreted to indicate an increase in recharge rates on the Barongarook High.

The effectiveness of using a recharge well to mitigate flood measured in a physical model

A structural method that involves the use of a recharge well to mitigate flood in a flat area is adopted as a mitigation method for this research. The determination of the effectiveness of this method was carried out by simulating storm-water accumulation in a reduced scaled physical model. The physical model had a rainfall simulator fitted to a sand tank which contained soil materials of different grain size and different coefficient of permeability. Size of the sand tank is 100 cm 60 cm × 40 cm and a perforated pipe of 3.5 cm are fixed in the model to simulate recharge well. By varying the rainfall intensity and rainfall duration a relationship was established between the rainfall characteristics and movement of storm-water into the ground. An average of 43.3% increase in recharge rate was observed when the model was tested with the recharged well as compared to a condition in which recharge well is not present. The reduction in rainwater when the recharge well exists is 6.07% of the total rainwater .

Groundwater resources assessment using numerical model: A case study in low-lying coastal area

The impacts of climate change and human pressure in groundwater have been greatest threats facing small islands. This paper represents a case study of groundwater responses towards the climate change and human pressures in Manukan Island Malaysia. SEAWAT-2000 was used for the simulations of groundwater response in study area. Simulations of six scenarios representing climate change and human pressures showed changes in hydraulic heads and chloride concentrations. Reduction in pumping rate and an increase in recharge rate can alter the bad effects of overdrafts in Manukan Island. In general, reduction in pumping rate and an increase in recharge rate are capable to restore and protect the groundwater resources in Manukan Island. Thus, for groundwater management options in Manukan Island, scenario 2 is capable to lessen the seawater intrusion into the aquifer and sustain water resources on a long-term basis. The selection of scenario 6 is the preeminent option during wet season. The output of this study provides a foundation which can be used in other small islands of similar hydrogeological condition for the purpose of groundwater resources protection.

Optimal design of measures to correct seawater intrusion

Numerous studies have been devoted to the optimization of groundwater management strategies in coastal aquifers. However, little has been done to address the problem of initially contaminated aquifers, the subject of this paper. Corrective measures need to be optimally designed to improve water quality while minimizing changes in the existing pumping regime. To this end, we compare two optimization methods. The first one is linear and consists of maximizing pumping rates while constraining heads to prevent seawater inflow. The second one consists of minimizing the changes from current pumping rates, so as to preserve existing rights, while constraining concentrations, which leads to a nonlinear programming problem. In both cases, corrective measures include a reduction in pumping rates, inland artificial recharge, and a coastal hydraulic barrier. Not surprisingly, the nonlinear problem leads to a more efficient solution, both in terms of pumping rates and actual cleanup of the aquifer. Nevertheless, the linear formulation yields insights into the optimal allocation of pumping. More importantly, the linear formulation enables us to readily calculate the hydraulic efficiency (gain in pumping rate per unit increase in recharge rate) of corrective measures. The fact that efficiency is consistently greater than 1 proves that the hydraulic barrier not only increases resources but also protects the existing ones. Therefore we conclude that both optimization approaches are useful and should be used.

Hydrological and reactive processes during rapid recharge to fracture zones: The Äspö large scale redox experiment

The hydrochemical response of fracture zones to enhanced recharge into the upper bedrock environment has been studied during a 3 a project at the Äspö Hard Rock Laboratory (HRL) in Southeastern Sweden. Hydrochemical data obtained during the experiment provides a basis for development of a model for the impact of accelerated recharge on groundwater composition and reactive processes during repository construction and operation. Tunnel construction at the HRL resulted in a 50-fold increase in recharge rates, and a 30-fold decrease in groundwater residence times in the fracture zone studied. Up to 80% dilution of the native groundwater created the greatest impact on groundwater composition. In addition, comparison of mass balances for solutes with known conservative behaviour, and reactive solutes, indicates a significant source of HCO − 3, SO 2− 4 and Na + ions and a significant sink for Ca 2+ ions within the fracture zone. These trends are explained by ion-exchange processes and microbial degradation of organic C transported from the soil with recharge. The increased microbial activity helps maintain anoxic conditions within the fracture zone. The enhanced recharge favours the performance of the geological barrier since anoxic conditions help to protect against corrosion of engineered barriers, and because long-lived isotopes of Np, Tc and U are less soluble under reducing conditions. A secondary impact is the strong dilution which affects trace element speciation, and also the stability and possible transport of colloids, through ion strength effects. Results from this experiment are primarily significant for national radioactive waste disposal programs that consider potential repository sites in granite geology, and for other programs considering disposal in fractured rock.

Hazards induced by groundwater recharge under rapid urbanization

Abstract Urban population growth across most of Latin America and Asia is relentless. Rapid urbanization has profound impacts on the hydrological cycle, including major changes in groundwater recharge. Existing infiltration mechanisms are radically modified, and new ones introduced, with evidence of an overall increase in recharge rates. There is also widespread diffuse pollution of groundwater by nitrogen compounds (normally nitrate, but sometimes ammonium), salinity (especially sodium chloride) and dissolved organic carbon. Groundwater contamination by petroleum and chlorinated hydrocarbons, related synthetic organic compounds, and, on a more localized basis, pathogenic bacteria and viruses, is also encountered. An analysis of the processes involved is made through citing detailed case histories.