Saltwater Zone Research Articles

Risk Assessment of Groundwater and its Application. Part I: Risk Grading Based on the Functional Zoning of Groundwater

The functional zoning of groundwater is the basis for the rational development and utilization, scientific management and effective protection of groundwater. Based on the distribution, type, hydrogeological condition and exploitation status of groundwater in Tianjin, and considering the resource supply, ecological environment maintenance and geological environment stability simultaneously, the function zoning of shallow groundwater has been divided into the non-central water supply area in built-up zones, the fragile marsh zones, the fragile nature reserve zones, the polluted groundwater zones and the salt water zones. And the deep groundwater has been divided into the non-central water supply area in built-up zones, the central supply area in built-up zones, the land subsidence zones, polluted groundwater zones and the salt water descending zones. Firstly, this paper selected dominant factors of groundwater development and utilization risk based on the different groundwater function zoning results, distinguished them into natural factors and human factors, and developed the risk assessment index systems. Secondly, the risk assessment systems for shallow and deep groundwater were built according to the characteristics of respective aquifers, and the weight of each evaluation index was calculated by AHP (Analytic Hierarchy Process) method. Then, each of the unit risk grade was determined by the method of fuzzy synthetic evaluation on basis of these index attributes and the corresponding weights, and results were distributed in space using ArcGIS to obtain the groundwater risk grade map of various aquifers in different groundwater function zones of Tianjin city. Finally, the risk grade in each district of Tianjin was determined by superimposing the district boundaries on these maps. Groundwater development and utilization risk grades based on the functional zoning of groundwater can provide a scientific basis for management of groundwater and a method for determining groundwater level.

Distribution of saline and freshwater in groundwater in Thai Binh province and solution for reasonable exploitation

Thai Binh is a coastal province of Red River Delta in Vietnam, having administrative boundaries at the river systems and coastlines that cause groundwater quality varies complicatedly. Today in Thai Binh province, the groundwater in Holocene and Pleistocene aquifers is exploited for domestic use. But, beside the quality of groundwater in this region is not uniform, it is interspersed between salt water and fresh water zones in Holocene and Pleistocene aquifers. Nowaday, under the force of groundwater exploitation activity for domestic purposes, agricultural activities, the impact of climate change and sea level rise issues, the quality of distribution of groundwater here change. According to the recent research results, groundwater quality and distribution of salt water - fresh water there have many changes compared with the research results of the Northern Division for Water resources Planning and Investigation in the year 1996. For the the Holocene aquifer (qh), distribution area of salt water zone has been narrowed. Besides, saline cleaning process occurred in some coastal areas in Tien Hai, Thai Thuy and a part of Quynh Phu district. For the Pleistocene aquifer (qp), compared with research result in 1996, the boundaries between saline and fresh water at the present time is not change so much. By assessing the status of the distribution of saline and fresh water zones in groundwater in Thai Binh and the movement of this boundary, author’s research results will be the basis that helps the managers give out reasonable exploiting and sustainable using methods for these natural resources.
 Thái Bình là một tỉnh ven biển thuộc vùng châu thổ sông Hồng của Việt Nam, được bao bọc bởi hệ thống sông biển khép kín làm cho chất lượng nước ngầm biến đổi rất phức tạp. Hiện nay, tại Thái Bình có 2 tầng chứa nước chính phục vụ ăn uống sinh hoạt là tầng chứa nước Holocen và tầng chứa nước Pleistocen. Tuy nhiên, chất lượng nước ngầm ở các tầng chứa nước này không đồng đều, có sự phân bố xen kẽ giữa các khoảnh nước mặn và nước nhạt. Hiện nay, dưới tác động của hoạt động dân sinh, sản xuất nông nghiệp, khai thác nước phục vụ sinh hoạt cùng ảnh hưởng của biến đổi khí hậu và sự dâng cao của mực nước biển đã làm thay đổi chất lượng và quy mô phân bố nước ngầm khu vực. Theo những kết quả nghiên cứu mới nhất của tác giả cho thấy diện tích phân bố của các vùng nước mặn - nước nhạt của các tầng chứa nước trên địa bàn tỉnh đã có nhiều thay đổi so với kết quả nghiên cứu trước đây của Liên đoàn Địa chất thủy văn – Địa chất công trình miền Bắc năm 1996. Với tầng chứa nước Holocen, diện tích phân bố các khoảnh nước mặn bị co hẹp và đang có sự nhạt hóa tại một số khu vực ven biển thuộc Huyện Tiền Hải, Thái Thụy và một phần thuộc huyện Quỳnh Phụ. Trong tầng chứa nước Pleistocen (qp), so với kết quả nghiên cứu năm 1996, ranh giới mặn – nhạt tại thời điểm hiện tại đã có sự thay đổi nhưng không lớn. Kết quả nghiên cứu này là cơ sở giúp các nhà quản lý đề xuất giải pháp, phân vùng khai thác và sử dụng hợp lý nguồn tài nguyên thiên nhiên này đặc biệt trước tình trạng khan hiếm nước như hiện nay trên địa bàn tỉnh Thái Bình.

Mapping groundwater conditions in different geological environments in the northern area of UAE using 2D earth resistivity imaging survey

A water resources database was developed and used to characterize the geological and hydrogeological settings of groundwater aquifers in the northern part of the United Arab Emirates. An intensive 2D Earth Resistivity Imaging (ERI) survey was conducted in selected areas to assess the available groundwater resources and delineate the salt-water intrusion. Drilling information of the existing monitoring wells as well as their records of water table elevations and groundwater salinity were used to measure the horizontal and vertical variations in lithology, degree of saturation, and groundwater salinity and thus to improve the interpretation of ERI data. The results of the chemical analyses of water samples collected from the wells along with the 2D ERI survey profiles were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections resulting from the inversion of 2D ERI data to identify and map three zones of water-bearing formation (fresh, brackish, and salt-water zones) in the coastal areas. The results indicated that the depth to the fresh-brackish interface exceeded 50 m at the upstream of the wadies and was in the order of 10 m or less in the vicinity of shoreline. Because of the high resistivity contrast between dry and water saturated fractured rocks; this method was very successful in detecting water-filled fractures and cavities in the carbonate aquifer. The application of this method was unsuccessful in clayey aquifers as it was not possible to isolate lenses of gravel and/or saturated with saline or brackish water from the surrounding clayey materials.

Stakeholder Analysis for Sustainable Land Management of Pak Phanang River Basin, Thailand

Pak Phanang river basin, one of the most important river basins, is situated in the middle of the southern peninsula of Thailand. The construction of a water gate in 1999 to prevent salt water intrusion and separate freshwater from salt water zones has resulted in changes of the natural ecosystem and the locals’ livelihood. The study aimed to identify important stakeholder groups and assess their relationships, relative power and importance for the sustainable resources use of the area. The data of this study were collected through literature reviews, focus group discussions with local stakeholders and individual interviews, using the techniques of Participatory Rapid Appraisal and conceptual content analysis. The study revealed that the most advantageous stakeholders in the coastal saltwater zone were shrimp farmers and stakeholders of related industries characterized by their relatively high input, technology and knowledge. For the coastal plain area with irrigation facilities, the majority of rice farmers benefited from increasing paddy production by intensive farming of up to 2-3 crops per year. These stakeholders’ interest was conformed to the national and regional development strategies and the implementations driven by the government ministers/officials, and the royal project committees. The disadvantageous stakeholders were small-scale shrimp and rice farmers, local fishers and nypa palm harvesters, with limited investment in farming facilities to meet the changing ecosystem and the degrading of natural resources and mangrove forest. This problem was also interested by external stakeholders such as academics in the local and regional educational institutions and NGOs in identifying the needs of these disadvantageous stakeholders for sustainable land use and prevention of the critical ecosystem.

Using chlorofluorocarbons (CFCs) and tritium to improve conceptual model of groundwater flow in the South Coast Aquifers of Laizhou Bay, China

AbstractThe southern coastal plain of Laizhou Bay, which is the area most seriously affected by salt water intrusion in north China, is a large alluvial depression, which represents one of the most important hydrogeological units in the coastal region of northern China. Chlorofluorocarbons (CFCs, including CFC‐11, CFC‐12 and CFC‐113) and tritium were used together for dating groundwater up to 50 years old in the study area. There are two cones of depression, caused by intensive over‐exploitation of fresh groundwater in the south and brine water in the north. The assigned CFC apparent ages for shallow groundwater range from 8 a to >50 a. A binary mixing model based on CFC‐113 and CFC‐12 concentrations in groundwater was used to estimate fractions of young and pre‐modern water in shallow aquifers and to identify groundwater mixing processes during saltwater intrusion. Discordance between concentrations of different CFC compounds indicate that shallow groundwater around the Changyi cone of depression is vulnerable to contamination. Pumping activities, CFC contamination, mixing and/or a large unsaturated zone thickness (e.g. >20 m) may be reasons for some groundwater containing CFCs without tritium. Saline intrusion mainly occurs because of large head gradients between fresh groundwater in the south and saline water bodies in the north, forming a wedge of saline water below/within fresh aquifer layers. Both CFC and tritium dates indicate that the majority of the saline water is from >50 a, with little or no modern seawater component. Based on the distribution of CFC apparent ages, tritium contents plus chemical and physical data, a conceptual model of groundwater flow along the investigated Changyi‐Xiaying transect has been developed to describe the hydrogeological processes. Three regimes are identified from south to north: (i) fresh groundwater zone, with a mixing fraction of 0.80–0.65 ‘young’ water calculated with the CFC binary mixing model (groundwater ages <34 a) and 1.9–7.8TU of tritium; (ii) mixing zone characterized by a mixing fraction of 0.05–0.65 young groundwater (ages of 23–44 a), accompanied by local vertical recharge and upward leakage of older groundwater; and (iii) salt water zone, mostly comprising waters with ages beyond the dating range of both CFCs and tritium. Some shallow groundwater in the north of the Changyi groundwater depression belongs to the >50a water group (iii), indicating slow velocity of groundwater circulation and possible drawing in of saline or deep groundwater that is tracer‐free. Copyright © 2012 John Wiley & Sons, Ltd.

A method for estimating the fresh water–salt water interface with hydraulic heads in a coastal aquifer and its application

Examining the descriptions of piezometric heads at two points in both the salt water and fresh water zones reveals that when the groundwater flow system is in steady state and satisfies the Dupuit assumption, the location of the fresh water–salt water interface in a homogeneous, isotropic, and unconfined coastal aquifer can be estimated based on a piezometric head of fresh water at a point in the fresh water zone (from the water table to the interface) vertically lined up with a piezometric head of salt water at a point in the salt water zone (from the interface down). Research shows that the new method is a general relation and that both the Hubbert relation describing the location of the interface and the Ghyben–Herzberg relation are special cases of this method. The method requires two piezometric wells to be close to each other and each tapping into a different zone. Measurements of piezometric heads at a well cluster consisting of piezometric wells tapping separately into fresh water and salt water zones near Beihai, China at 5-day intervals for 15 months are used to illustrate the estimation of interface location. The depth of the interface for well H5 ranges from 32 to 72 m below the sea level.

ADAPTIVE DIVERGENCE BETWEEN FRESHWATER AND MARINE STICKLEBACKS: INSIGHTS INTO THE ROLE OF PHENOTYPIC PLASTICITY FROM AN INTEGRATED ANALYSIS OF CANDIDATE GENE EXPRESSION

Debate surrounding the integration of phenotypic plasticity within the neo-Darwinian paradigm has recently intensified, but is largely dominated by conceptual abstractions. Advances in our capacities to identify candidate genes, and quantify their levels of expression, now facilitate the study of natural variation in inherently plastic traits, and may lead to a more concrete understanding of plasticity's role in adaptive evolution. We present data from parapatric threespine stickleback (Gasterosteus aculeatus) demes inhabiting geologically recent, freshwater and saltwater zones of a large estuary. Reaction norms for survival confirm adaptation to local salinity conditions. Analysis of osmoregulatory candidate gene expression within an ecological quantitative genetics framework suggests putative mechanisms underlying adaptive variation, and provides insights into the role of ancestral trait plasticity in this divergence. A sodium-potassium ATPase (ATP1A1) is identified as a candidate gene for freshwater adaptation. In addition to heritable variation for gene expression, we infer significant correlation between measures of expression and individual fitness. Overall results indicate a loss of plasticity in the freshwater deme. We discuss how this is consistent with adaptation facilitated by ancestral plasticity as a heuristic example that may prove useful for future, explicit tests of the genetic assimilation hypothesis.

Brief Review on Methods of Estimation of the Location of a Fresh Water–Salt Water Interface with Hydraulic Heads or Pressures in Coastal Zones

AbstractMethods of estimation of the location of a sharp fresh water–salt water interface with hydraulic heads or pressures are relatively simple and are widely used. Progress has been made in the recent decade toward the mathematical relations describing the position of the sharp interface using hydraulic heads or pressures in coastal zones. This paper reviews several methods for estimation of the location of fresh water–salt water interface in coastal aquifers, including the classical Ghyben–Herzberg relation. The location of the fresh water–salt water interface in a coastal homogeneous, isotropic unconfined aquifer can be estimated based on piezometric heads at two points in the same vertical line tapping, respectively, the salt water zone (including the interface) and the fresh water zone (from the water table to the interface) when the groundwater flow system is in a steady state and satisfies the Dupuit assumption. If pressures are measured at two points in the fresh water and salt water zones in the same vertical line in the coastal aquifer under the same assumption, then the position of the interface can still be estimated with the pressure data. If the Dupuit assumption is not met in coastal aquifers and the vertical fresh water head gradients can be approximated with a straight line, the position of the interface can roughly be estimated by using the water level data in a partially penetrating well during drilling of the well.

Characteristics of Piezometric heads and determination of fresh water–salt water interface in the coastal zone near Beihai, China

Changes in hydraulic heads with space and time and evolution of the location of fresh water–salt water interface are important for groundwater development in coastal aquifers. Measurements of piezometric heads at 11 well clusters consisting of three piezometric wells of different depths with a 5-day interval for 15 months show that the piezometric heads at nearly all the wells near the northwestern coast in Beihai decrease with increasing depth and increase with increasing distance from the coast. Changes in piezometric heads at the wells during the measurement period were caused by seasonal precipitation and induced by the tide. The depth of the sharp interface between fresh water–salt water can be estimated based on measurements of piezometric heads at a piezometric well tapping at a point in the salt water zone below the interface and measurements of the water table at the same well. The calculations of the interface for well H5 range from 40 to 80 m below sea level in the measurement period, which are believed to be more reasonable than those estimated with the Ghyben–Herzberg relation.

Geoelectrical and hydrogeochemical studies for delineating seawater intrusion in the outlet of Wadi Ham, UAE

The Quaternary aquifer of Wadi Ham, UAE has been overexploited during the last two decades to meet the increasing water demands. As a result, the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated. In this paper, a 2D earth resistivity survey was conducted in Wadi Ham in the area between Fujairah and Kalba to delineate the seawater intrusion. Existing monitoring wells were used to measure the horizontal and vertical variations in water salinity and thus to improve the interpretation of earth resistivity imaging data. Results of vertical electrical soundings and chemical analyses of collected water samples were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections resulting from the inversion of 2D resistivity data to identify three zones of water-bearing formation (fresh, brackish, and salt-water zones). Along the four 2D resistivity profiles, the depth to the fresh-brackish interface exceeded 50 m at the western part of the area and was in the order of 10 m or less in the eastern side near the shoreline. Depth to the brackish-saline water interface reached about 70 m in the western side and was in the order of 20 m in the eastern side. The thickness of the fresh water zone decreases considerably in the farming areas toward Kalba and thus the degree of seawater intrusion increases.

Integrating Hydrogeochemical and Geophysical Data for Testing a Finite Volume Based Numerical Model for Saltwater Intrusion

In this paper, hydrogeological and geophysical data are used to validate a numerical model developed to predict seawater intrusion into coastal aquifers. The cell-centered finite volume method is adopted here to solve the set of coupled partial differential equations describing the motion of saltwater and freshwater separated by a sharp interface. These equations are based on the Dupuit approximation and are obtained from integration of 3D flow equations for fresh and salt water zones over the vertical dimension. In order to have flexibility upon complex configurations domain, non structured grid meshing is utilized. To approximate the diffusion fluxes, Green-Gauss type reconstruction, based on diamond-cell and least squares interpolation, is performed. The model is first validated using academic test case studies with known closed form solutions. The mathematical model has been calibrated using hydrogeochemical and geophysical data. The geophysical method applied in this study has been a frequency domain electromagnetic method. In this method the apparent electrical conductivity is measured by induction using two separate hand-held transmitter and receiver coils. During the operation the transmitter coil is energized by a low frequency alternating current that radiates an electromagnetic field and the receiver coil detects the resulting field. Taking into account the relationship between the bulk conductivity of the subsoil and the conductivity of groundwater, EM soundings have been interpreted to provide complementary information to hydrogeochemical data to outline the fresh–saltwater interface. This methodology has been applied to the case of saltwater intrusion into the Llobregat delta aquifer, near Barcelona, Spain.

Saltwater intrusion into the freshwater aquifer in the eastern shore of Virginia: a reconnaissance electrical resistivity survey

Contrasts between apparent high resistivity of the saturated freshwater zones and apparent low resistivity of the saturated saltwater zone are recorded on 111 Schlumberger sounding field curves. The field measurements are inverted to subsurface layers. Generally, resistivity decreases with depth from the high value of the unsaturated zone near the surface to the low values of the saltwater saturated zone at depth of 30 to 130 m. Contour maps are constructed for variations of resistivity at depths of 3, 5, 10, 20, 30, 40, 50, 60, 70, 100 and 130 m. Resistivity contours of less than 30 Ω m, are indicated at depths of 5–20 m near the narrow bands of Chesapeake Bay and the Atlantic Ocean in the coastal regions of Accomack County. Within the area covered by the cities of Onancock, Accomac, and Wachapreaque, low-resistivity contours of less than 30 Ω m are observed from 30 to 60 m depth. In 70 to 130 m depth range, a major part of Accomack County is covered by low-resistivity contours of 10 to 30 Ω m which connect the Chesapeake Bay to the Atlantic Ocean. Vertical profiles of the contour maps indicate the shape of the saltwater plumes. The interface appears to be as shallow as 30 m where intrusion has occurred, and extends downward to a depth of 130 m where the saltwater of the Atlantic ocean and Chesapeake Bay are connected.

Electromagnetic methods for mapping freshwater lenses on Micronesian atoll islands

The overall shape of freshwater lenses can be determined by applying electromagnetic methods and inverse layered-earth modeling to the mapping of atoll island freshwater lenses. Conductivity profiles were run across the width of the inhabited islands at Mwoakilloa, Pingelap, and Sapwuahfik atolls of the Pohnpei State, Federated States of Micronesia using a dual-loop, frequency-domain, electromagnetic profiling system. Six values of apparent conductivity were recorded at each sounding station and were used to interpret layer conductivities and/or thicknesses. A three-layer model that includes the unsaturated, freshwater, and saltwater zones was used to simulate apparent-conductivity data measured in the field. Interpreted results were compared with chloride-concentration data from monitoring wells and indicate that the interface between freshwater and saltwater layers, defined from electromagnetic data, is located in the upper part of the transition zone, where the chloride-concentration profile shows a rapid increase with depth. The electromagnetic method can be used to interpret the thickness of the freshwater between monitoring wells, but can not be used to interpret the thickness of freshwater from monitoring wells to the margin of an island.

Allozyme Variation and Systematics of the Nerodia fasciata-Nerodia clarkii Complex of Water Snakes (Serpentes: Colubridae)

extensive area of the coastal plain of eastern North America. They are parapatric with the closely related N. sipedon along the fall line and hybridization between these two species sometimes occurs in areas of habitat disturbance. Nerodia f. clarkii, N. f. compressicauda, and N. f. taeniata are inhabitants of a narrow coastal saltwater zone and are distributed almost continuously from the middle Atlantic coast of Florida to southern Texas and including the Florida Keys. These snakes are physiologically well adapted to exploit their saline environment. The geographic ranges of the two ecologically distinct groups sometimes overlap in the saltwater-freshwater ecotone, yet, because of their divergent adaptations, they are for the most part microallopatric in these areas. Analyses of allozyme data from 33 protein coding loci by several methods show that, except for areas of considerable habitat disturbance, gene flow between the two groups is very slight or absent and is on the same order as that seen between the freshwater group and N. sipedon. Elevation to species level is recommended for the two groups. Within-group divergence is minimal at the allozyme level, and the question of whether N. f. taeniata arose from ancestral N. f. clarkii or ancestral N. f. compressicauda could not be resolved by analyses of these data.

Theory and application of an approximate model of saltwater upconing in aquifers

Motion and mixing of salt water and fresh water are vitally important for water-resource development throughout the world. An approximate model of saltwater upconing in aquifers is developed, which results in three non-linear coupled equations for the freshwater zone, the saltwater zone, and the transition zone. The description of the transition zone uses the concept of a boundary layer. This model invokes some assumptions to give a reasonably tractable model, considerably better than the sharp interface approximation but considerably simpler than a fully three-dimensional model with variable density. We assume the validity of the Dupuit-Forchheimer approximation of horizontal flow in each layer. Vertical hydrodynamic dispersion into the base of the transition zone is assumed and concentration of the saltwater zone is assumed constant. Solute in the transition zone is assumed to be moved by advection only. Velocity and concentration are allowed to vary vertically in the transition zone by using shape functions. Several numerical techniques can be used to solve the model equations, and simple analytical solutions can be useful in validating the numerical solution procedures. We find that the model equations can be solved with adequate accuracy using the procedures presented. The approximate model is applied to the Smoky Hill River valley in central Kansas. This model can reproduce earlier sharp interface results as well as evaluate the importance of hydrodynamic dispersion for feeding salt water to the river. We use a wide range of dispersivity values and find that unstable upconing always occurs. Therefore, in this case, hydrodynamic dispersion is not the only mechanism feeding salt water to the river. Calculations imply that unstable upconing and hydrodynamic dispersion could be equally important in transporting salt water. For example, if groundwater flux to the Smoky Hill River were only about 40% of its expected value, stable upconing could exist where hydrodynamic dispersion into a transition zone is the primary mechanism for moving salt water to the river. The current model could be useful in situations involving dense saltwater layers.

Residual flow procedure for sea water intrusion in unconfined aquifers

AbstractA simplified procedure is presented for the analysis of sea water intrusion in unconfined aquifers. It involves the finite element method with a residual flow procedure which combines transformation of the salt water zone into the fresh water zone that has the same pressure distribution as that of the salt water. This procedure avoids simultaneous solutions of governing differential equations for both flow and mass transport. Numerical results are compared with laboratory observations.

A numerical solution for the movement of an interface in a layered coastal aquifer

This paper deals with seawater intrusion in a coastal aquifer, where close to the coast the aquifer is divided into a number of subaquifers by impervious, relatively thin layers. As a result of changing the total fresh-water discharge to the sea, seawater intrusion occurs as a separate advancing wedge in each of the subaquifers. Assuming everywhere flow normal to the coast line, and essentially horizontal in both the fresh-water and the salt-water zones, the complete mathematical model is first stated in terms of depth to the interface in each subaquifer. A numerical finite-difference scheme is then presented for solving the model for the case of a two-layered aquifer. Principles of a method for extending the model to a larger number of subaquifers is described.

Compte rendu ornithologique camarguais pour les années 1978 et 1979

This bird report covers the years 1978 and 1979 and completes a period of 30 years of observations by a contingent of resident and visiting ornithologists in the Rhône delta and neighbouring Crau and Alpilles. It presents not only observations of rare species or unusual numbers of birds, but also indicates the results of several long term monitoring programmes concerning in particular, waterfowl and allied species. A climatological report summarizes the most important meteorological phenomena of the two years, the most striking of which were the very wet spring of 1978 and the dry summer of 1979. The winter of 1978-1979 must surely be remembered in northern and central Europe as one of the most severe this century. In the Mediterranean, however, it was much less severe and, fortunately, had none of the disastrous effects of the previous hard winters of 1956 and 1962-1963. “ La Crau ”, a unique stony desert area and former delta of the River Durance, is suffering seriously from the spread of industry and from agricultural reclamation. Some of the first census work to be carried out here shows just how important the area is for breeding Stone Curlews, Little Bustards and Pin-tailed Sandgrouse in particular. The sandgrouse population is an isolated one, the species occurring elsewhere in Europe only in parts of Spain. Observations of sea birds are not carried out systematically and more thorough sea-watching would probably show that many of the species mentioned here are regularly wintering in the “ Golfe du Lion ”. Unusually high numbers of Black-necked Grebes appear each autumn in the saline “ Etang de Lavalduc ” (up to 4,500), which makes it an internationally important site for this species. Whilst the herons as a group maintain their numbers, several notable changes have taken place in recent years. The reed-nesting Grey Heron continues to increase whilst the Purple clearly shows the opposite trend. The Cattle Egret, occuring only as an accidental visitor less than 15 years ago, appears now to have reached the peak of colonisation with the numbers of breeding pairs levelling off. Autumn roost counts show the total of individuals at close to 2,000. The first indications of roughly how many Bitterns breed in the Camargue are given whilst the second only record of White Storks breeding in the delta involved one semi-captive male and a wild female carrying a ring. This was a chick transplanted from Morocco to a nest in Alsace as part of a reintroduction programme in 1975. The flamingos again had two successful breeding seasons and the summer population for the south coast of France peaked at over 35,000 birds both years. Particularly interesting data are being gathered from the sightings of “ Darvic-ringed ” birds, 1858 of which have thus been marked over the past three years. 24 % of these have already been read outside France. Amongst the Anseriiformes, the wintering Bewick’s Swan population was the highest yet recorded with a maximum of 85 in January 1979. During this same period four species of geese were present with Greylags and Bean’s both reaching one hundred or more individuals. Counts of Shelducks have shown how important the salines are both as a breeding area and winter quarters, and a ringing programme has thrown some light on their movements. For other ducks the overall wintering population has been quite high with a peak of 122,000 in January 1979. In general the number of diving ducks was below average but this was compensated for by several of the surface feeders being present in large numbers, in particular Teal, Gadwall and Shoveler. The list of raptor observations is as impressive as ever and includes a second estimate of the breeding Marsh Harrier population with results slightly superior to those obtained ten years earlier. The eighth complete census of breeding Laro-limicoles was carried out in the brackish and salt water zone of the greater Camargue area. All species are maintaining their numbers and attention is drawn to the increasing populations of Mediterranean and Slender-billed Gulls. Nearctic waders already observed in the delta included sightings of Buff-breasted Sandpiper and Wilson’s Phalarope whilst the Pectoral was only the second reported. Eagle Owls in “ Les Alpilles ” appear to be increasing with 30 pairs recorded. Passerines have not been ignored entirely ; the continued increase of breeding Stonechats is encouraging whilst the successful nesting of a pair of Bed-billed Quelea in the Camargue adds an exotic flavour to this report.

Geology of Wagon Wheel Nuclear Stimulation Project, Pinedale Field, Wyoming

Wagon Wheel is a project planned to stimulate a well in gas reservoirs of the Pinedale anticline by means of nuclear explosives. The Pinedale field, in the northern part of the Green River basin of southwest Wyoming, is potentially productive from almost 10,000 ft of lower Fort Union, Lance-Lewis, and Mesaverde sandstones. Attempts to produce the field conventionally have proved uneconomic because of low permeability. The first nuclear stimulation experiment, Gasbuggy, in northwest New Mexico, was detonated in 1967 using a 29-kiloton explosive. Technical questions answered by Gasbuggy resulted in the program at Wagon Wheel, which will be an attempt to define the economics of use of nuclear stimulation. Project Rulison was the second test to stimulate natural gas reservoirs and utilized a device of approximately 40 kilotons. The most recent test, Project Rio Blanco, used three 30-kiloton explosives fired simultaneously. Project Rulison and Project Rio Blanco are in the Piceance basin of western Colorado. Wagon Wheel 1 was drilled to 19,000 ft to evaluate the entire Mesaverde section. Gas was detected on mud-logging equipment throughout the basal Fort Union, Lance-Lewis, and Mesaverde, below the top of the gas reservoir at 7,972 ft. The well has been plugged back to 11,700 ft as a possible emplacement hole in which five 100-kiloton explosives will produce a chimney from 9,000 to 11,650 ft. Reserves in this interval are calculated at 207 Bcf of gas in place per square mile. Extensive logging, coring, and testing were carried out in the program, including special logs for rock-mechanics study. Two special wells in addition to the Wagon Wheel 1 were drilled to evaluate the aquifers above the gas reservoir. Potable water extends to a depth of 3,730 ft. Salt water is present from 3,730 to 5,630 ft. Low-quality subpotable water extends from 5,630 to 7,140 ft. The saltwater zone is interpreted to be a tongue of Wasatch extending from the west into Eocene arkose derived from the Wind River Range on the east. Plans call for sequential detonation of five explosives spaced at intervals from 9,220 to 11,570 ft, to produce a continuous chimney from 9,000 to 11,650 ft. There will be a safety margin of 1,600 ft between the top of fractures and the bottom of the known aquifers.

Geology of Wagon Wheel Nuclear Stimulation Project: ABSTRACT

Project Wagon Wheel, if executed will be an attempt to stimulate gas reservoirs of the Pinedale anticline by means of nuclear explosives. The Pinedale field, located in the northern Green River basin of southwest Wyoming, is potentially productive from a section totaling nearly 10,000 ft of lower Fort Union, Lance-Lewis, and Mesaverde sandstone equivalents. Attempts to produce the field conventionally have proved uneconomical due to low permeability. Because its requirements exceeded the state of nuclear technological development, Wagon Wheel was not selected for the first gas stimulation experiment. Project Gasbuggy, in northwest New Mexico, was detonated in 1967 using a 26 kiloton device. Data produced in Gasbuggy were utilized in planning Wagon Wheel, which is an actual attempt at economic use of nuclear energy. Wagon Wheel No. 1 was drilled to 19,000 ft to evaluate the entire Mesaverde section. Gas was detected by mud-logging equipment below 7,972 ft depth throughout the basal Fort Union, Lance-Lewis, and Mesaverde. The well has been plugged back to 11,700 ft leaving approximately 3,700 ft of proved gas-bearing section available for stimulation. This interval will accommodate the 5 100-kiloton explosives planned. In-place End_Page 652------------------------------ gas reserves for this section are calculated at 252 billion cu ft/sq mi. Extensive logging, coring, and testing have been carried out in the program, including special logs for rock mechanics study. Cores were compared with those from Gasbuggy as to compressive strength, shear behavior, and potential for fracturing. Petrographic analyses indicate better fracture potential at Wagon Wheel due to a higher degree of grain to grain contacts and lower clay content. Environmental protection studies include examination of surface waters, springs and wells, man-made structures, mines, flora, fauna, and general land use. The most important aspect from a geologic standpoint is protection of the extensive groundwater aquifers above the gas reservoir. Two wells, in addition to the Wagon Wheel No. 1, were drilled for the purpose of evaluating those aquifers. Potable water extends to a depth of approximately 3,600 ft. Salt water occurs from 3,600 to approximately 5,200 ft. Low quality subpotable water extends from 5,200 to about 7,200 ft. The saltwater zone is interpreted to be in a tongue of Wasatch Formation extending from the west into Eocene arkoses derived from the Wind River Range on the east. Plans call for sequential detonation of 5 explosives spaced at intervals from 9,220 to 11,560 ft to produce a more or less continuous chimney from about 8,700 to about 11,600 ft. There will be a safety margin of 1,500 ft between the top of fractures and the bottom of known aquifers. End_of_Article - Last_Page 653------------