Extent Of Saltwater Intrusion Research Articles

Extent of saltwater intrusion and freshwater exploitability in the coastal Vietnamese Mekong Delta assessed by gauging records and numerical simulations

Climate change-driven sea level rise has intensified salinity intrusion (SI) in deltas worldwide, posing significant threats to the exploitation of freshwater resources. In the Vietnamese Mekong Delta (VMD), the third largest delta globally, SI is a recurring challenge along the coastline, degrading freshwater resources for agricultural and domestic use and affecting socio-economic development. In this paper, we investigate the spatiotemporal extent of salinity intrusion in the Ben Tre Province, the hotspot of salinity disaster within the VMD. Long-term salinity monitoring data (25 years from 1996 to 2020) has been analyzed, and a 1D (Mike 11) coupled with 3D hydrodynamic model (Mike 3) was developed. Three scenarios were used to investigate the freshwater resources exploitation: (i) the year of investigation (2021), (ii) 2021 to 2030 climate change impacts, considering different annual exceedance probability of the upstream Mekong discharge (i.e., average flow, relatively low, low and very low), and (iii) extreme salinity intrusion (i.e., the 2016 condition). Our results indicated that salinity patterns are well-stratified at the beginning and end of the dry season but well-mixed during the middle period. Furthermore, over the last 25 years, SI has progressively increased and started earlier in the dry season. The modeling scenarios for SI have also revealed a growing complexity in the exploitation of freshwater resources, highlighting challenges related to timing, depth, and geographical location. The exceedance probability scenarios disclosed higher and deeper salinity intrusion along the channel in VMD, ranging from 50 % to 95 %. This poses significant limitations on the feasibility of freshwater exploitation throughout the Ben Tre Province. Under the current trajectory of climate change, the 2030 scenario anticipates salinity intrusion reaching further inland from the 2021 scenario. This is likely to exacerbate the existing challenges in freshwater resource exploitation, even with comprehensive water infrastructure. We, therefore, propose several management strategies to adapt to salinity intrusion: storing freshwater in main rivers, maintaining consistent operation of water infrastructure systems, and encouraging water-saving distribution and exploitation methods. Moreover, we also recommend supporting the development of new drought-tolerant crop patterns.

Modelling the Spatial Distribution and Future Trends of Seawater Intrusion due to Aquaculture Activities in Coastal Aquifers of Nizampatnam, Andhra Pradesh

Coastal aquifers suffer from saltwater intrusion due to several natural and anthropogenic activities and they pose a severe problem in many coastal regions of India. Anthropogenic activities like saltwater aquaculture activities and salt pans are one of the major causes for saltwater intrusion into freshwater aquifers in coastal regions. Along with these activities, over-exploitation of fresh groundwater for domestic and agriculture purpose also leads to infiltration of saltwater into shallow freshwater aquifers. To address this effect, it is necessary to understand the spatial distribution and extent of the saltwater intrusion in coastal areas. In the present study, SEAWAT model is used to delineate the saltwater intrusion effect and predict the extent of saltwater intrusion resulting from anthropogenic activities in the Nizampatnam coastal area, Andhra Pradesh. The simulation was carried out for the period 2016 to 2018 revealing a change in the extent of the saltwater intrusion up to 2 km into the inland areas from the coast as well as in the vicinity of fishponds. Based on the hydrological conditions observed during the study period and leveraging the calibrated model, saltwater intrusion prediction was carried out for the next two decades. The results show that anthropogenic activities will lead to saltwater intrusion into freshwater aquifers up to 6 km into inland areas from coast at a rate of 200 m/year. Therefore, the sustainable management plans are essential for protecting the freshwater aquifers from the saltwater intrusion in the Nizampatnam coastal area.

Integrated geophysical characterization of saltwater intrusion in Lagos State, Eastern Dahomey Basin, Southwestern Nigeria

Integrated geophysical methods of Electrical resistivity tomography (ERT), Induced Polarization (IP), and Well Logging were employed in this study to delineate the lateral and depth extent of saline water intrusion in Oniru area of Lagos State, South-western Nigeria due to reported saltwater contamination of some wells at relatively shallow depths. Ergo, improving the scientific understanding of fresh and saline waters occurrence in the coastal areas of Lagos State.Five traverses, each of variant lengths (100 to 200 m) were established for both ERT and IP as space permitted. For each profile level, Wenner electrode configuration was adopted with a minimum electrode spacing of 3 m and maximum electrode spacing of 50 m. Ten levels were achieved for profiles 1, 2, 4, and 5 while eight levels were accomplished for profile 3. The ERT and IP data were processed using RES2DINV 2-D resistivity data processing software. The well log data utilized were acquired from two existing lithological logs within the study area to validate the results of the ERT and IP.The unconsolidated sandy formation was characterized by high resistivity with corresponding low to medium chargeability while the clay units were characterized by low resistivity with equivalent high chargeability. The sandy formation saturated by saltwater was characterized by very low resistivity with corresponding low chargeability while that of freshwater was characterized by medium to high resistivity with corresponding low chargeability. The integrated geophysical methods of ERT, IP and borehole logging in the study area identified three lithological sequences. The first layer corresponded to high resistivity values of unconsolidated sandy topsoil, mostly less than 5 m. However, in profiles 3 and 4, it occurred as saturated marshy topsoil. The top layer was underlain by sand/clayey sand formation, which was observed to have pockets of saline water intrusion as evinced from the results of the ERT and IP data. The saline water-bearing zones were observed to intermingle with the freshwater-bearing sand units. The freshwater-saline water transition tends to be conspicuous especially in profiles 3 and 5. The base of profiles 1 and 2 was occupied by clay units which were evident from the results of the borehole log, the ERT, and the IP sections.The integrated geophysical method was able to successfully delineate the fresh and saline water interface and extent of saltwater intrusion within the study area and thus would provide a reliable database for future groundwater development and management within the study area.

Simulation of coastal aquifer using mSim toolbox and COMSOL multiphysics

Fluctuations in groundwater levels along the coast have a significant impact on the extent of saltwater intrusion into freshwater aquifers. This study aims to simulate the groundwater flow and solute transport in the region by using the mSim toolbox in the MATLAB and COMSOL Multiphysics. The investigation is focussed on a micro-basin of Pavanje river located along the west coast of India. The model results are calibrated and validated against the field observations. The results show that the variation of the water table over the year is significant and range from about 3–14 m. There exists a reasonable correlation between the simulated and observed values of groundwater level and salinity. The wells that are most vulnerable to seawater intrusion in the region are identified. The COMSOL model estimated a salinity range of 0–20 mol/m3. Additionally, the model is used to understand the response of coastal aquifer to various stress scenarios. The study reveals that reduced recharge rate with increased pumping has a serious impact on aquifer system.

Exploration of the effects of storm surge on the extent of saltwater intrusion into the surficial aquifer in coastal east-central Florida (USA)

Climate change such as altered frequency and intensity of storm surge from tropical cyclones can cause saltwater intrusion into coastal aquifers. In this study, a reference SEAWAT model and a diagnostic SEAWAT model are developed to simulate the temporal variation of surficial aquifer total dissolved solids (TDS) concentrations after the occurrence of a storm surge for exploration of the effects of storm surge on the extent of saltwater intrusion into the surficial aquifer in coastal east-central Florida (USA). It is indicated from the simulation results that: (1) rapid infiltration and diffusion of overtopping saltwater resulting from storm surge could cause a significant and rapid increase of TDS concentrations in the surficial aquifer right after the occurrence of storm surge; (2) rapid infiltration of freshwater from rainfall could reduce surficial aquifer TDS concentrations beginning from the second year after the occurrence of storm surge in that the infiltrated rainwater could generate an effective hydraulic barrier to impede further inland migration of saltwater and provide a downgradient freshwater discharge for saltwater dilution and flushing counteracting the effects of storm surge on the extent of saltwater intrusion; and (3) infiltrated rainwater might take approximately eight years to dilute and flush the overwhelming majority of infiltrated saltwater back out to the surrounding waterbodies, i.e., the coastal lagoons and the Atlantic Ocean.

Monitoring saltwater intrusion in Rupert Bay, Qu\xe9bec, Canada, after the partial diversion of a major tributary

As part of a large hydroelectric project in northern Québec (Canada), a portion of the flow of the Rupert River was diverted toward the existing La Grande hydroelectric complex. As a result of the partial diversion, the discharge of the Rupert River at its mouth is reduced by an average of 50% annually. This corresponds to an 18% decrease in the total freshwater inflow into the bay and, thus, to a shift of the upstream limit of the saltwater intrusion in Rupert Bay. Changes in saltwater intrusion had been predicted numerically as part of the project’s environmental impact assessment (EIA). In the project’s conditions of authorization, monitoring the hydraulic conditions and the extent of saltwater intrusion in the Rupert Bay was required by government authorities. The objective of this paper is to present the results of this environmental monitoring and, more specifically, to validate the modifications predicted in the EIA in terms of both saltwater intrusion limit and hydraulic conditions in the Rupert Bay. Results obtained during 2 years of monitoring are within the predicted trends and order of magnitude of changes anticipated in the EIA. The results, thus, confirm that the shift of the upstream limit of the saltwater front along the channels of the bay was conservatively predicted by numerical modeling.

A study on the status of saltwater intrusion in the coastal hard rock aquifer of South India

Groundwater of the coastal regions represents a fragile environment. A study has been attempted in the hard rock aquifer of the south-eastern part of India. A total of 135 groundwater samples were collected and analysed for major cations and anions. The domination of cations and anions was in the order of Na+ > Ca2+ > Mg2+ > K+ for cations and Cl− > HCO3 − > SO4 2− > H4SiO4 > NO3 − > PO4 − > F− in anions. The water is neutral to alkaline in nature with pH ranging from 6.30 to 9.20 with an average of 7.57. The ions analysed were used for standard plots, ratio of different ions and correlation between them helped to evaluate the active hydrogeochemical process and extent of saltwater intrusion in the coastal aquifer. The electrical conductivity (EC) contour shows that the groundwater quality is poor along the coast due to saltwater intrusion. The Piper and chadda’s plot shows that most of the groundwater samples fall on Na–Cl water type may be due to saltwater intrusion in the eastern part study area. The ratios of Cl−/HCO3 − ranged between 0.24 and 152.50 and have strong positive relationship with Cl− concentrations; it was found that about 30 % of the groundwater samples were strongly affected by the saline water in the study area. The Na+/Cl− ratios ranged from 0.20 to 3.73, and most of the groundwater samples fall close to the contamination region. Agricultural and salt pan land use pattern decrease the water quality due to impact of anthropogenic processes and seawater intrusion. Statistical analysis was also used to obtain the objectives, and it was found that the seawater intrusion is the major factor controlling the groundwater chemistry followed by other factors such as weathering and fertiliser impact.

Influence of saltwater wedges on irrigation water near a river estuary

Paddy fields irrigated using water from the Shinkawa River in Niigata, Japan, are subject to adverse effects associated with the occurrence of saltwater wedges in the river. The extent of saltwater intrusion in the river varies, depending on river discharge and tidal amplitude. In this study, field observations and numerical simulation of the Shinkawa River estuary were applied to ascertain the influence of saltwater wedges on paddy cultivation during the irrigation period. The saltwater wedge was surveyed using an echo-sounding profiling system (SC-3); results indicated that the longitudinal profiles of the saltwater wedge were 4.7 and 2.2 km from the river mouth sluice gate at the high water mark of spring tide and at the low water mark of neap tide, respectively. According to the vertical profiling using electrical conductivity (EC) meters at bridges crossing the river, there was a rigid interface between freshwater and saltwater with a thin halocline zone of approximately 0.25 m. These profiles were well reproduced by the one-dimensional, two-layer, unsteady flow model. The results of the model simulation and EC observation indicate that when the vertical position of the halocline rises to 1.2 m below the inlet of the water intake pumping station, the EC value rises sharply to 1,500 μs/cm, which is an unsuitable level for irrigation water. It is estimated that for about 23 % of the total irrigation period, pump operation is halted as a result of this mechanism.

Effect of Sea‐Level Rise on Salt Water Intrusion near a Coastal Well Field in Southeastern Florida

A variable-density groundwater flow and dispersive solute transport model was developed for the shallow coastal aquifer system near a municipal supply well field in southeastern Florida. The model was calibrated for a 105-year period (1900 to 2005). An analysis with the model suggests that well-field withdrawals were the dominant cause of salt water intrusion near the well field, and that historical sea-level rise, which is similar to lower-bound projections of future sea-level rise, exacerbated the extent of salt water intrusion. Average 2005 hydrologic conditions were used for 100-year sensitivity simulations aimed at quantifying the effect of projected rises in sea level on fresh coastal groundwater resources near the well field. Use of average 2005 hydrologic conditions and a constant sea level result in total dissolved solids (TDS) concentration of the well field exceeding drinking water standards after 70 years. When sea-level rise is included in the simulations, drinking water standards are exceeded 10 to 21 years earlier, depending on the specified rate of sea-level rise.

Saltwater Intrusion Modeling in the Aquifer Bounded by Manila Bay and Parañaque River, Philippines

The continual extraction and indiscriminante use of groundwater for residential sectors could cause a decrease in the groundwater level in Paranaque and Las Pinas City; and allows saltwater to penetrate into the aquifer due to the proximity of Manila Bay. This study models the present condition and extent of saltwater intrusion in the aquifer bounded by Paranaque River and Manila Bay. The model is simulated using a 3D finite element modeling software (FEMWATER) that is capable of modeling the groundwater flow condition in the aquifer. Moreover, the model can also be used to predict the future condition of the aquifer for better groundwater management. This study aims to raise public awareness of the extent of the problem and the possible side effects incurred. The model will serve as a basis for further studies on remediation techniques and saltwater intrusion control in the coastal aquifer of Paranaque City.

Intrinsic random function of order k kriging of electrical resistivity data for estimating the extent of saltwater intrusion in a coastal aquifer system

A saltwater intrusion study using electrical resistivity distribution was conducted in a coastal aquifer system in the southeastern part of Busan, Korea. This aquifer system is divided into four layers according to the hydrogeologic characteristics, and the horizontal extent of intruded saltwater is determined at each layer through the geostatistical interpretation of electrical resistivity data. Intrinsic random function of order k (IRF-k) kriging is performed with covariance models to produce the plane of spatial mean resistivities. The kriged estimates are evaluated by cross validation, and they showed a good agreement with the true values. The statistics of cross validation represented low errors for the estimates. In the resistivity contour maps more than 5 m below the surface, a dominant direction of saltwater intrusion was observed beginning from the east side. These results led the authors to conclude that the application of geostatistical technique to electrical resistivity data is useful for assessing saltwater intrusion in a coastal aquifer system.

Assessing the Extent of Saltwater Intrusion in A Tropical Coastal Environment Using Radar and Optical Remote Sensing

The Alligator River Region (ARR) of the Northern Territory, Australia, has been identified as being particularly susceptible to saltwater intrusion. The Parks and Wildlife Commission of the Northern Territory (PWCNT) have attempted to restrict the intrusion and preserve the natural environment by creating physical earth barrages. A consequence of the intrusion is the conversion of freshwater paperbark (Melaleuca spp.) swamps into extensions of the mangrove margin. During this process stands of dead Melaleuca result and juvenile mangroves (primarily Avicennia marina) invade and establish in the affected areas. The use of Airborne Polarimetric Synthetic Aperture Radar (AirSAR) fused with Thematic Mapper (TM) is investigated as a means for mapping Melaleuca dieback as a measure of the extent of the saltwater intrusion. Individually the sensors cannot map areas of salt affected Melalecua as there is confusion with other cover types in the study area. The combined data set were evaluated for the most useful components of the optical and AirSAR data in resolving the overlap of land cover types and a map of Melalecua dieback was produced. A total of 0.4% of the Study Area or 2.25 square km was identified as being affected by recent saltwater intrusion with an aerial assessment yielding 100% accuracy. The individual areas range from 100 to 3100 square metres and are typically located along tidal creek lines or at the edge between floodplain and woodland. The high identification accuracy using this methodology may allow the use of Melalecua dieback as a bio-indicator of environmental change in tropical floodplain systems.

Salt Water Intrusion in the Summerside Area, P.E.I.

ABSTRACTSalt water intrusion is an acute problem in the coastal areas of Prince Edward Island. In the town of Summerside, ground‐water supplies are developed from an aquifer hydraulically connected with the sea. Over the past ten years, there has been progressive contamination of the aquifer, particularly in wells close to the seashore.Investigations including test drilling, aquifer testing and chemical studies were undertaken in Summerside to study the nature and extent of the salt water intrusion.Landward encroachment of the saline water is aided by the relatively high transmissivity of the fractured Permo‐Carboniferous sandstone which comprises a semiconfined aquifer. Two separate zones of salt water contamination exist—namely an upper zone from a depth of 0 to 80 feet caused by a landward hydraulic gradient of the fresh water due to heavy pumping and a second zone at a depth of 350 to 400 feet due to intermittent pumping resulting in a raising and thickening of the zone of diffusion. The extent of salt water intrusion is depicted, using hypothetical sections.

Saltwater Intrusion in the United States

The occurrence of saline water is described in terms of geologic and hydrologic conditions. The three general mechanisms of intrusion are considered. The extent of salt water intrusion is given usi...