Sensitivity, Hazard, and Vulnerability of Farmlands to Saltwater Intrusion in Low-Lying Coastal Areas of Venice, Italy

Saltwater intrusion is a growing threat for coastal aquifers and agricultural practices in low-lying plains. Most of the farmlands located between the margin of the Southern Venice lagoon and the Northern Po delta, Italy, lie a few meters below mean sea level and are drained by a large network of artificial channels and hydraulic infrastructures to avoid frequent flooding and allow agricultural practices. This work proposes an assessment of the vulnerability to saltwater intrusion, following a new concept of the hazard status, resulting in combining the depth of the freshwater/saltwater interface and the electrical resistivity of the shallow subsoil. The sensitivity of the farmland system was assessed by using ground elevation, distance from freshwater and saltwater sources, permeability, potential runoff, land subsidence, and sea-level rise indicators. Relative weights were assigned by a pairwise comparison following the Analytic Hierarchy Process approach. The computed vulnerability map highlights that about 30% of the farmlands is under strong and extreme conditions, 28% between marginal and moderate, and 40% under negligible conditions. Results from previous vulnerability assessments are discussed in order to explain their differences in terms of hazard status conceptualization and sensitivity characterization of farmland system.

Spatial and temporal variations of hydrodynamics and sediment dynamics in Indus River Estuary,Pakistan

<p>Field investigations were conducted to study the seasonal variation of hydrodynamics and sediment transport in Indus River Estuary (IRE), Pakistan. The data of water levels, currents, salinity, and suspended sediment concentration (SSC) were collected hourly covering both wet and dry seasons. Tidal amplitudes were higher near the mouth than those at the middle and upper estuary. The ebb phase lasted longer than that of the flood during the wet season. The asymmetric tidal pattern with higher ebb velocity was observed during the wet season. A slight difference in current velocity was found during the dry season. The flood currents were higher at middle estuary than those in wet season. During the wet season, salinity variation within a tidal cycle slightly increased from the upper estuary to the mouth. Salinity was substantially higher during the dry season than the wet season at all three stations, with the absence of the flood-ebb variation, showing a strong saltwater intrusion. The SSC data revealed that the sediments were mainly brought into the estuary by freshwater discharge during the wet season. Sediment re-suspension process persists during the dry season, due to the tidal currents. A stronger saltwater intrusion occurred in the dry season due to weak river discharge. An estuarine turbidity maximum zone was formed near station-2 due to the combined effects of tides, river discharge and saltwater intrusion. Overall, field observations have shown a significant spatial and temporal variation in flood/ebb and wet/dry seasons for hydrodynamics and sediment transport in IRE.</p>

Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

<p>Saltwater intrusion studies in coastal Papua New Guinea (PNG) are a rarity despite recognized vulnerabilities to salination of coastal groundwater resources. For many seaside communities such as Maopa the threat of salination is exacerbated by high extraction rates by a growing population and the likelihood of the effects of climate change. Saltwater intrusion can be addressed using various methods, including direct water sampling from wells and electrical resistivity measurements. This study advances knowledge of a previous assessment of saltwater intrusion and groundwater in this region that used DC Schlumberger resistivity soundings, through an extensive and cost-effective Transient ElectroMagnetic (TEM) survey. The study aims to map the lateral and vertical extent of salination and the characterization of groundwater in the landward direction over seven lines of TEM soundings along Keakalo Bay. The TEM method proved successful in identifying four main geoelectric layers. The top layer has a highly variable resistivity (range of 5 to 355 Ωm) inferred as the vadose zone. Beneath this layer is a layer of intermediate resistivity (100 Ωm > p ≥ 20 Ωm) characterizing a perched freshwater aquifer with a thickness range of 3.2 to 15 m. An intermediate layer of low resistivity (20 Ωm > p ≥ 3 Ωm) was detected at the boundary separating the freshwater aquifer from the inferred saltwater intrusion. This layer is typically thicker than the freshwater aquifer and is referred to as the mixing zone. The deepest layer constituting the salination zone has a very low resistivity (3 Ωm > p ≥ 0.4 Ωm), occurring at depths of up to 42 m. The depth to the salination zone varied from deep in the middle of the survey area to shallow in the fringes of the survey. This pattern is reflective of surface seawater infiltration marked by mangrove forest in the interior and subsurface infiltration from the coast. Similar depth trends but at shallower depths were also observed for the mixing zone, and the freshwater region. In some cases the mixing area overwhelms the freshwater regions. Layering confirmed groundwater resource and salination patterns as those of basic models reflective of small island hydrology, except that salination and the freshwater boundary were less distinctive due to the relatively high thickness of the dispersion zone. The use of different sounding parameters in line 7 provided useful information about the nature of the deep basement unit and thickness of the overlying unconsolidated quaternary sediment.</p>

Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

<p>Saltwater intrusion studies in coastal Papua New Guinea (PNG) are a rarity despite recognized vulnerabilities to salination of coastal groundwater resources. For many seaside communities such as Maopa the threat of salination is exacerbated by high extraction rates by a growing population and the likelihood of the effects of climate change. Saltwater intrusion can be addressed using various methods, including direct water sampling from wells and electrical resistivity measurements. This study advances knowledge of a previous assessment of saltwater intrusion and groundwater in this region that used DC Schlumberger resistivity soundings, through an extensive and cost-effective Transient ElectroMagnetic (TEM) survey. The study aims to map the lateral and vertical extent of salination and the characterization of groundwater in the landward direction over seven lines of TEM soundings along Keakalo Bay. The TEM method proved successful in identifying four main geoelectric layers. The top layer has a highly variable resistivity (range of 5 to 355 Ωm) inferred as the vadose zone. Beneath this layer is a layer of intermediate resistivity (100 Ωm > p ≥ 20 Ωm) characterizing a perched freshwater aquifer with a thickness range of 3.2 to 15 m. An intermediate layer of low resistivity (20 Ωm > p ≥ 3 Ωm) was detected at the boundary separating the freshwater aquifer from the inferred saltwater intrusion. This layer is typically thicker than the freshwater aquifer and is referred to as the mixing zone. The deepest layer constituting the salination zone has a very low resistivity (3 Ωm > p ≥ 0.4 Ωm), occurring at depths of up to 42 m. The depth to the salination zone varied from deep in the middle of the survey area to shallow in the fringes of the survey. This pattern is reflective of surface seawater infiltration marked by mangrove forest in the interior and subsurface infiltration from the coast. Similar depth trends but at shallower depths were also observed for the mixing zone, and the freshwater region. In some cases the mixing area overwhelms the freshwater regions. Layering confirmed groundwater resource and salination patterns as those of basic models reflective of small island hydrology, except that salination and the freshwater boundary were less distinctive due to the relatively high thickness of the dispersion zone. The use of different sounding parameters in line 7 provided useful information about the nature of the deep basement unit and thickness of the overlying unconsolidated quaternary sediment.</p>

On the Understanding of the Hydrodynamics and the Causes of Saltwater Intrusion on Lagoon Tidal Springs

Springs are common features on the Yucatán coast. They can discharge either under the sea (submarine) or inland in coastal lagoons and wetlands. Previous observations of a coastal lagoon located on the northern Yucatán Peninsula (La Carbonera) reported sea water intrusion on a spring that discharge on a coastal lagoon (lagoon tidal spring). The saltwater intrusion occurs when the tide is at its lower level, which is the opposite to what has been reported for submarine springs in the Yucatán Peninsula. In this study, the hydrodynamics of the spring is analyzed and the driving forces controlling the seawater intrusion are identified and discussed. Time series of water levels, salinity, and velocity measurements in the lagoon, the aquifer, and the spring are analyzed by means of tide component decomposition and cross-correlations analysis of the tide signals. Results show that the main driving forces causing the intrusion are the density differences and pressure head gradients, and the mechanisms influencing the driving forces driving those differences are the tides, the friction in the lagoon, and the confinement of the aquifer; other mechanisms are discussed to present a complete idea of the complexity of the interactions between the coastal aquifer, the coastal lagoons, and the sea.

Science in Service of our Communities

In the Golden Isles of Georgia, the Gullah art of braiding sweetgrass into baskets can be traced back over 400 years to its West African roots. This skill is passed on from generation to generation, preserving the oral history, sovereignty, and culture of the Gullah people. Local and indigenous coastal communities, like the Gullah-Geechee, have a deep connection with their natural environment as they depend on forests, fisheries, and wildlife resources for their livelihood and culture. These frontline communities are also facing a complex web of challenges that include rising sea levels, coastal erosion, saltwater intrusion, encroaching development and increasing property taxes, and loss of fisheries and other coastal livelihoods. As communities develop strategies to address these complex challenges, they need access to place-based research and education that is unique to their people, culture, and ecology.