The characteristics of the Waiwhetu artesian aquifer beneath Wellington Harbour including the spatial distribution and causes of submarine spring discharge

<p>This thesis is a study of the sub-harbour Waiwhetu Artesian Aquifer, and in particular the nature and characteristics of artesian leakage from submarine springs. This aquifer is a sheet of gravel and other coarse sediments which continues from the Lower Hutt Valley and extends beneath Wellington Harbour where it varies in thickness from approximately 70m against the Wellington Fault scarp to just over 20m thick against the eastern harbour margin. The water it contains is a valuable resource supplying approximately one third of Wellington's municipal water consumption. At present, there are plans to utilise this artesian water source to a greater extent in the future, to support a greater burden of the region's water requirements. However concerns over possible salt-water intrusion and contamination of the aquifer led to an interest in developing a better understanding of the characteristics of this artesian system, particularly beneath the harbour floor. Harbour floor depressions were selected as likely sources of artesian water leakage based on the presumption that they had been formed by the action of leaking artesian water from beneath. Eleven depression 'zones' were investigated by recording the salinity of the water within the depressions using a portable conductivity/temperature meter. SCUBA diver's observations and bathymetric mapping revealed that depressions ranged in width from 53m to 369m (at the harbour floor) and 12m to 69m (at the depression base), with depths ranging from 13.3m to 31.3m below sea level. Only a few depressions were found to be actively discharging significant amounts of artesian water. SCUBA diver investigations found this leakage to be typically concentrated at a number of small and discrete spring 'vents' located on the base of the active depression. Typical salinities recorded ranged from 28 - 33 ppt within a few centimetres of the discharge vents. Deployment of an S4 current meter in two depressions showed that spring vent discharges vary with the pattern of abstraction from the pumping stations in the Lower Hutt Valley and as a consequence of the tidal cycle. High tides generate a greater load on the underlying aquifer, which in turn compresses the aquifer structure to a greater extent than at low tides, thus 'squeezing' out more water. Almost all of the recorded leakage was found to occur from a cluster of submarine springs within one of the depression zones, roughly 1100 metres from the Hutt River mouth. One other notable area of leakage was found close to Seaview Wharf. No significant leakage was observed or recorded from the two deep depressions south of Somes Island, which had previously been considered to be the major outlet of artesian leakage in the harbour. Lower than normal salinity values were also recorded in the harbour entrance. In this region the aquiclude is hypothesised to peter out, allowing artesian water to escape from the aquifer through a large area of the seabed in the form of widespread leakage as opposed to the concentrated, or discrete, form associated with spring vent discharge. Seismic profiles were used to map the extent of the sub-harbour Waiwhetu Artesian Aquifer and its upper confining aquiclude, the Petone Marine Beds. This work showed that the aquifer gravels extend across the entire harbour area. However, the water-bearing capacity of these deposits was found to be inconsistent. Preferential pathways, present as paleochannels (relic river channels), can be mapped within the aquifer. They concentrate the flow of groundwater through the aquifer and as such supply the submarine spring regions with much higher rates of water flow than the inter-paleochannel areas. The harbour floor depressions are thought to have formed as a consequence of the deformation of aquifer and aquiclude deposits during intense shaking associated with earthquakes leading to the removal of portions of the confining aquiclude. This typically occurs from a combination of raised piezometric pressures as a result of consolidation of the aquifer material during shaking, and from failure of the aquiclude by liquefaction. This rupture of the aquiclude results in the release of large volumes of artesian water through the aquiclude and to the sea. As this flow of water moves upward through the aquiclude, it erodes and transports away the fine sediment that forms this member. The features left behind are the characteristic harbour floor depressions we associate with submarine spring discharge. The abstraction of water from the Waiwhetu Artesian Aquifer (for the Wellington municipal water supply) lowers the piezometric pressure within the aquifer close to the abstraction zone. As such, the relocation of the abstraction focus (during 1980) to three kilometres inland from Petone Foreshore has greatly improved the 'health' of the subharbour aquifer and has similarly reduced the threat of salt-water intrusion. Data gathered during this study implies that while the two deep depressions south of Somes Island are unlikely to be a threat with regard to salt-water intrusion, the cluster of depressions off the Hutt River mouth could be a site of salt-water entry if piezometric pressures in the aquifer beneath them dropped low enough. Spring discharge velocities collected over one spring vent indicate that the presently set minimum piezometric Petone Foreshore level (below which abstraction must cease) needs to be revised.</p>

The characteristics of the Waiwhetu artesian aquifer beneath Wellington Harbour including the spatial distribution and causes of submarine spring discharge

<p>This thesis is a study of the sub-harbour Waiwhetu Artesian Aquifer, and in particular the nature and characteristics of artesian leakage from submarine springs. This aquifer is a sheet of gravel and other coarse sediments which continues from the Lower Hutt Valley and extends beneath Wellington Harbour where it varies in thickness from approximately 70m against the Wellington Fault scarp to just over 20m thick against the eastern harbour margin. The water it contains is a valuable resource supplying approximately one third of Wellington's municipal water consumption. At present, there are plans to utilise this artesian water source to a greater extent in the future, to support a greater burden of the region's water requirements. However concerns over possible salt-water intrusion and contamination of the aquifer led to an interest in developing a better understanding of the characteristics of this artesian system, particularly beneath the harbour floor. Harbour floor depressions were selected as likely sources of artesian water leakage based on the presumption that they had been formed by the action of leaking artesian water from beneath. Eleven depression 'zones' were investigated by recording the salinity of the water within the depressions using a portable conductivity/temperature meter. SCUBA diver's observations and bathymetric mapping revealed that depressions ranged in width from 53m to 369m (at the harbour floor) and 12m to 69m (at the depression base), with depths ranging from 13.3m to 31.3m below sea level. Only a few depressions were found to be actively discharging significant amounts of artesian water. SCUBA diver investigations found this leakage to be typically concentrated at a number of small and discrete spring 'vents' located on the base of the active depression. Typical salinities recorded ranged from 28 - 33 ppt within a few centimetres of the discharge vents. Deployment of an S4 current meter in two depressions showed that spring vent discharges vary with the pattern of abstraction from the pumping stations in the Lower Hutt Valley and as a consequence of the tidal cycle. High tides generate a greater load on the underlying aquifer, which in turn compresses the aquifer structure to a greater extent than at low tides, thus 'squeezing' out more water. Almost all of the recorded leakage was found to occur from a cluster of submarine springs within one of the depression zones, roughly 1100 metres from the Hutt River mouth. One other notable area of leakage was found close to Seaview Wharf. No significant leakage was observed or recorded from the two deep depressions south of Somes Island, which had previously been considered to be the major outlet of artesian leakage in the harbour. Lower than normal salinity values were also recorded in the harbour entrance. In this region the aquiclude is hypothesised to peter out, allowing artesian water to escape from the aquifer through a large area of the seabed in the form of widespread leakage as opposed to the concentrated, or discrete, form associated with spring vent discharge. Seismic profiles were used to map the extent of the sub-harbour Waiwhetu Artesian Aquifer and its upper confining aquiclude, the Petone Marine Beds. This work showed that the aquifer gravels extend across the entire harbour area. However, the water-bearing capacity of these deposits was found to be inconsistent. Preferential pathways, present as paleochannels (relic river channels), can be mapped within the aquifer. They concentrate the flow of groundwater through the aquifer and as such supply the submarine spring regions with much higher rates of water flow than the inter-paleochannel areas. The harbour floor depressions are thought to have formed as a consequence of the deformation of aquifer and aquiclude deposits during intense shaking associated with earthquakes leading to the removal of portions of the confining aquiclude. This typically occurs from a combination of raised piezometric pressures as a result of consolidation of the aquifer material during shaking, and from failure of the aquiclude by liquefaction. This rupture of the aquiclude results in the release of large volumes of artesian water through the aquiclude and to the sea. As this flow of water moves upward through the aquiclude, it erodes and transports away the fine sediment that forms this member. The features left behind are the characteristic harbour floor depressions we associate with submarine spring discharge. The abstraction of water from the Waiwhetu Artesian Aquifer (for the Wellington municipal water supply) lowers the piezometric pressure within the aquifer close to the abstraction zone. As such, the relocation of the abstraction focus (during 1980) to three kilometres inland from Petone Foreshore has greatly improved the 'health' of the subharbour aquifer and has similarly reduced the threat of salt-water intrusion. Data gathered during this study implies that while the two deep depressions south of Somes Island are unlikely to be a threat with regard to salt-water intrusion, the cluster of depressions off the Hutt River mouth could be a site of salt-water entry if piezometric pressures in the aquifer beneath them dropped low enough. Spring discharge velocities collected over one spring vent indicate that the presently set minimum piezometric Petone Foreshore level (below which abstraction must cease) needs to be revised.</p>

A study of salt water intrusion in the Kallada river, south west coast of Kerala, India

Munroe Island in Kollam District of Kerala is a typical backwater village situated at the confluence of the Ashtamudi backwater and the Kallada river system. It is an amalgamation of eight small islands with a total area of 13.4 sq. km. Salinity intrusion has been a serious threat in the downstream areas of Kallada river for more than one and half decades, affecting the groundwater quality of Munroe Island. The present study focuses on the seasonal variation in physico-chemical characteristics of the underground water system of Munroe island and Kallada river with special reference to saline water intrusion. Physico-chemical analysis of ground water revealed that samples were unsuitable for drinking due to higher content of Na, Ca, and K. Microbiological analysis of island groundwater showed the presence of coliform and E-coli bacteria above the permissible limit. Results indicated a significant correlation between salinity and major anions viz., Cl− and SO42 and cations viz., Mg, Na, Ca, and K of both river surface and island groundwater. In the present study it is clearly evident the occurrence of salt water intrusion in Kallada river from Ashtamudy lake and the its severity become higher during premonsoon season. The results also indicated that the salinity increase in kallada river has a negative impact on island ground water quality. The paper also suggest suitable management strategies for overcoming the salt water intrusion thereby upgrading island sustainability.

Study of Groundwater quality, its impact on human health and Agriculture and Salt Water intrusion in and around Gandhidham, Kachchh, Gujarat

Hydrogeochemical studies were carried out in Gandhidham Taluka, Kachchh, Gujarat in post Monsoon season to assess the quality of groundwater and its suitability for drinking, irrigation, and industrial purpose. In this study, the groundwater contamination of Gandhidham which is mostly used as a potable source, for irrigation and industrial use along with Narmada water is carried out and compared with the recommended standards set by the Bureau of Intense Standards (BIS) and the WHO. The sample analyzed for the post-monsoon seasons reveals that some of the groundwater sources exceed the permissible limit of WHO and BIS. In this study the physiochemical parameters like electrical conductivity, pH, TDS, chlorides, fluorides Sulfate, Nitrate, and heavy metals like sodium, potassium, cobalt, iron, chromium, copper, Zinc are analyzed. Groundwater samples were collected and analyzed in post-monsoon seasons 2015, 2016, and 2020 which proves that most of the samples are not fit for drinking. Most of the samples are good for irrigation but not for the long run as a high evaporation rate leads to salinity and finally to degradation of soil quality. Analytical data studies in the study area reveal that there is a saltwater intrusion in the coastal areas of Gandhidham. The results of statistical analysis prove the elevated concentrations of some chemical elements leading to pollution with heavy metals are related to anthropogenic and industrial activities leading to contamination. Keywords: Groundwater quality, Saltwater intrusion, Heavy metals, Kachchh, Gujarat

Establishment of soil strength in a nourished wetland using thin layer placement of dredged sediment

Coastal wetlands are experiencing accelerated rates of fragmentation and degradation due to sea-level rise, sediment deficits, subsidence, and salt-water intrusion. This reduces their ability to provide ecosystem benefits, such as wave attenuation, habitat for migratory birds, and a sink for carbon and nitrogen cycles. A deteriorated back barrier wetland in New Jersey, USA was nourished through thin layer placement (TLP) of dredged sediment in 2016. A field investigation was conducted in 2019 using a cone penetrometer (CPT) to quantify the establishment of soil strength post sediment nourishment compared to adjacent reference sites in conjunction with traditional wetland performance measures. Results show that the nourished area exhibited weaker strengths than the reference sites, suggesting the root system of the vegetation is still establishing. The belowground biomass measurements correlated to the CPT strength measurements, demonstrating that shear strength measured from the cone penetrometer could serve as a surrogate to monitor wetland vegetation trajectories. In addition, heavily trafficked areas underwent compaction from heavy equipment loads, inhibiting the development of vegetation and highlighting how sensitive wetlands are to anthropogenic disturbances. As the need for more expansive wetland restoration projects grow, the CPT can provide rapid high-resolution measurements across large areas supplying government and management agencies with vital establishment trajectories.

Hydrostratigraphic setting and groundwater dynamics in high salinized low-lying farmlands at the southern margin of the Venice Lagoon

&lt;p&gt;&lt;strong&gt;Hydrostratigraphic setting and groundwater dynamics in high salinized low-lying farmlands at the southern margin of the Venice Lagoon&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&lt;sup&gt;1&lt;/sup&gt;&lt;/strong&gt; Institute of Geosciences and Earth Resources, National Research Council, Padova, Italy&lt;/p&gt;&lt;p&gt;&lt;sup&gt;2&lt;/sup&gt; Institute of Marine Sciences, National Research Council, Venice, Italy&lt;/p&gt;&lt;p&gt;&lt;sup&gt;3&lt;/sup&gt; Department of Geosciences, University of Padova, Padova, Italy&lt;/p&gt;&lt;p&gt;&lt;sup&gt;4 &lt;/sup&gt;Regione Veneto - Soil Defence Regional Directorate, Venice, Italy&lt;/p&gt;&lt;p&gt;&lt;sup&gt;5 &lt;/sup&gt;Land Reclamation Authority Adige Euganeo, Este-Padova, Italy&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;* Corresponding author: [email protected]&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Key words: salt-water intrusion, groundwater dynamics, coastal plain, Venice&lt;/p&gt;&lt;p&gt;The coastal plain at the southern margin of the Venice lagoon is a low-lying territory, which is the result of river diversions, channeling, and hydraulic reclamation that took place over the last centuries. The mechanisms controlling the exchanges between surface water and groundwater progressively shifted from natural to artificial ones. Presently, most of this territory lays at ground elevation up to 3 m below the mean sea level and a complex network of drainage channels and pumping stations regulates the depth of the water table both to prevent flooding-waterlogging and to allow irrigation. Being at the lagoon margin and next to the sea, the aquifers of this area are heavily affected by salt-water intrusion that jeopardizes the farmlands productivity and specifically damages the crop yield. Focusing on the geology and stratigraphic architecture of the first 25-meters of the subsoil, in which the shallow aquifers are included, the sedimentary record consists in Pleistocene alluvial deposits and Holocene deposits. The latter show the typical transgressive wedge including prodelta, littoral and back barrier depositional environments. Specifically, the Holocene littoral sands contain the unconfined aquifer, which is almost continuous along the whole coastal strip. &amp;#160;Sedimentary bodies as paleo-channels and remnants of littoral ridges, commonly hosting unconfined aquifers, are present all over coastal plain. Pleistocene alluvial deposits contain the first locally confined aquifer.&lt;/p&gt;&lt;p&gt;Several past studies have revealed the complexity of freshwater-saltwater exchanges imposed by the concomitance of various forcing factors. However, a specific study on the dynamic of saline contamination of the groundwater is still missing. We present here the preliminary results of an ongoing research aimed to characterize the groundwater dynamics and disentangle mechanisms that control groundwater salinity in the shallow aquifer system of the low-lying farmlands adjacent to the southern Venice lagoon margin and the Brenta-Bacchiglione river mouth. The results of detailed analyses from various perspectives (based on sedimentary cores, continuous hydrological and hydrogeological data, geophysical surveys) are properly integrated to describe the dynamics in the shallow aquifer system. Particular attention is payed to the hydro-morpho-stratigraphic system in relation to the mechanisms driving the freshwater-saltwater exchanges. This research is developed in the frame of the Interreg Italy-Croatia project MoST (Monitoring Sea-water intrusion in coastal aquifers and Testing pilot projects for its mitigation), which addresses to improve the quality and sustainability of the human management of water resources in coastal areas.&lt;/p&gt;

Comparing methods to estimate chloride natural background levels to assess sea water intrusion

&lt;p&gt;In order to assess the anthropogenic impacts on groundwater quality we generally need to identify the natural conditions or Natural background levels (NBLs) within groundwater systems, which are used as references to assess the evolution of the contamination status. This information, in addition to the threshold values (TVs), which are derived from NBLs and based on specific criteria values for legitimate water uses and the environment (terrestrial and aquatic ecosystems), is required to appropriately assess of the chemical status of groundwater in accordance with the European Water Framework Directive and to analyse and propose potential measures where they are required.&lt;/p&gt;&lt;p&gt;In literature, different methodologies are available to assess NBLs and reference TVs for different geochemical substances based on the available measurements of groundwater salinity (e.g. based on probability plots). In this work we analyze and compare three previously proposed methods for derivation of chloride NBLs, which is a conservation solute and is closely related to salt water intrusion in inland and coastal aquifers. We discuss and compare their applicability in pilots located in different settings (southern /northern European / Mediteranean/ North Sea /Baltic Sea) covering different typologies (detrital, karstic, fissured aquifers) and management issues (overexploitation, land use and land cover changes, etc). We perform sensitivity analysis to different constraints applied to remove samples affected by human activity (Nitrate and the brackish saline constraints) in the assessment of NBLs. Finally, based on this analysis, we propose a general approach for derivation of NBLs that could be applied to any of the tested pilots as well as other similar settings in Europe.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;This research has been partially supported by the SIGLO-AN project (RTI2018-101397-B-I00) from the Spanish Ministry of Science, Innovation and Universities (Programa Estatal de I+D+I orientada a los Retos de la Sociedad).&lt;/p&gt;&lt;p&gt;This work has been partially supported by the GeoE.171.008-TACTIC and GeoE.171.008-HOVER projects from GeoERA organization funded by European Union&amp;#8217;s Horizon 2020 research and innovation program.&lt;/p&gt;

eDNA reveals widespread presence of marine fish in the Panama Canal

Shipping corridors can be hotspots for biological invasions as they connect the world’s oceans and dissolve dispersal barriers between these aquatic systems. As a consequence, multiple opportunities for biotic exchange arise and the resulting establishment of non-native species often causes adverse ecological and economic impacts. In this study, a combined effort of traditional gillnetting and eDNA-based surveys was implemented to characterize the fish community of the Panama Canal, which is a key region for biotic exchange as it connects the Pacific and Atlantic Oceans in Central America. The Canal was recently expanded and new lock systems installed potentially providing novel opportunities for fish to enter the Canal. Using COI metabarcoding, we detected a total of 142 taxa, including thirteen potentially new records for the freshwater part of the Canal. Furthermore, we found evidence for the presence of 16 Atlantic and 10 Pacific non-native marine fish inside different sections of the Canal. Identifications based on molecular data did not cover all species caught with gillnets, but generally provided a more complete image of the fish fauna. Diversity indices based on eDNA surveys revealed significant differences across different sections of the Canal reflecting in part the prevailing environmental conditions. The observed changes in the fish community may be attributed to the recent expansion of the lock systems, which facilitates species migration directly by enlarging the canal entrances on either side of the Isthmus and indirectly by allowing more salt water to enter the Canal and thus increasing the overall salinity. Given the potential ecological and socio-economic consequences of non-native species crossing the Canal and establishing in the ocean basins on either end, it seems advisable to evaluate limiting salt water intrusion as well as implementing additional barriers to species dispersal (acoustic/electric/chemical deterrents) as a precautionary measure.

Advanced monitoring of soil salinization risk in the Neretva Delta agroecosystem

&lt;p&gt;This paper presents the concept of the project &amp;#8220;Advanced monitoring of soil salinization risk in the Neretva Delta agroecosystem&amp;#8221; (Delta Sal). Aim of the project is to develop and implement an advanced system for monitoring, forecasting and reporting the water and soil conditions in the Neretva Delta agroecosystem that is primarily used for agriculture. Selected pilot location is specific due to its biodiversity &amp;#8211; water network within the delta consists of surface irrigation and drainage canal network, carst aquifer dominated by the tidal regime while also replenished by the freshwater from the upstream river flow, all of which are used for citrus fruits production while at the same time influencing the water regime of adjacent protected salt marshes ecosystem. Neretva Delta is dominated by the traditional farming methods practiced in the polder systems. Salt water intrusion is present in the entire delta, which is reflecting on the irrigation water quality and subsequently on the agricultural production of citruses that are salt-sensitive horticultural crops. Extensive spatial and temporal monitoring of water quality data through multisensory monitoring stations will be used for development of guidelines for salt stress alleviation in citrus fruits. This paper presents the outline of the project, methodology of analysis and selection of representative agricultural parcels for the research, rationale of farmer&amp;#8217;s current decision-making that affects the agricultural landscape pattern and proposed monitoring network. Monitoring is focused on continuous real-time measurements of surface water levels and index water velocity using radars, shallow and deep piezometers for monitoring of ground water levels, rain gauges, multiparameter water quality measurements (dissolved oxygen, water depth, electrical conductivity, total dissolved solids, salinity, pH, oxidation reduction potential, temperature, nitrate and chloride). Data is transmitted in real-time to the cloud-based interface for remote access. Integrated data management will be used in the upcoming project stages for analysis of salt water intrusion on Neretva Delta agricultural production. Final outcome of the project are guidelines for Neretva Delta management with the future outlook in the climate change context, compliant with UNFCCC convention under which this area falls into one of the most vulnerable areas in Croatia.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Acknowledgment:&lt;/p&gt;&lt;p&gt;&amp;#8222;This work has been supported in part by the European Regional Development Fund under the project Advanced monitoring of soil salinization risk in the Neretva Delta agroecosystem (KK.05.1.1.02.0011)&amp;#8220;&lt;/p&gt;

The Breede River estuary (Cape Province, South Africa): A historical perspective on hydrology, geomorphology, and sedimentology

A hitherto unpublished historical dataset of the Breede River estuary, Western Cape, South Africa, that was collected in the summer season of 1983 is presented. Bathymetric, physiographic, and sedimentological data were collected at 1–1.5-km intervals between the mouth and the Malgas ferry crossing at km 35. The remaining estuary up to km 52 was not surveyed. Sedimentologically, the estuary could be divided into a lower marine sand reach (mouth to km 5), a mixed sand/mud reach (km 5–18.5), and a fluvial sand reach upstream of km 18.5. Hydrological data were collected at three midstream anchor stations (mouth, km 14.5, and km 24) which were occupied for complete tidal cycles. Five parameters were recorded: tidal elevation, current velocity, salinity, temperature, and light transmittance. Pronounced velocity asymmetries of the tides were revealed by phase delays between the times of low (high) water and corresponding slack water (turn of the tide), as well as considerable up-estuary delays in the occurrence of high and low tides. The mode of tidal wave propagation was synchronic (constant height) up to a distance of ~23 km at spring high tide and ~13 km at neap high tide, from where it proceeded in hyposynchronic mode (progressive decrease in height). Peak surface velocities reached 1.5 m/s at Station 1 (mouth), 0.6 m/s at Station 2 (km 14), and 0.45 m/s at Station 3 (km 24). The marine sand reach and parts of the mixed sand/mud and fluvial sand reaches were distinctly flood dominated as revealed by the orientation of bedforms. Salt water intrusion reached up to km 25, where river background levels were reached. Suspended sediment concentrations (turbidity) varied from 55–85 mg/l at the mouth, 65–200 mg/l in the mixed sand/mud reach, and 55–85 mg/l in the fluvial sand reach. At the time of observation, the Breede River estuary was in a well-mixed hydrological state. The fluvial sand reach displayed numerous, up to 18-m-deep scour pools. Grain-size distributions revealed distinct differences between the individual estuary sections, the sand/mud, and marine sand reaches, in particular, being characterized by up to four, mostly mixed hydraulic populations. Offshore seismic profiles suggest that the Duiwenhoks River, located 14 km to the east of the Breede mouth, was a tributary of the latter during Pleistocene sea-level lowstands. From a global perspective, the Breede River estuary conforms physically to typical small estuaries that are only marginally impacted by human interferences.