In the San Luis Valley (SLV), Colorado legislation passed in 2004 requires that hydraulic head levels in the confined aquifer system stay within the range experienced in the years 1978–2000. While ...some measurements of hydraulic head exist, greater spatial and temporal sampling would be very valuable in understanding the behavior of the system. Interferometric synthetic aperture radar (InSAR) data provide fine spatial resolution measurements of Earth surface deformation, which can be related to hydraulic head change in the confined aquifer system. However, change in cm‐scale crop structure with time leads to signal decorrelation, resulting in low quality data. Here we apply small baseline subset (SBAS) analysis to InSAR data collected from 1992 to 2001. We are able to show high levels of correlation, denoting high quality data, in areas between the center pivot irrigation circles, where the lack of water results in little surface vegetation. At three well locations we see a seasonal variation in the InSAR data that mimics the hydraulic head data. We use measured values of the elastic skeletal storage coefficient to estimate hydraulic head from the InSAR data. In general the magnitude of estimated and measured head agree to within the calculated error. However, the errors are unacceptably large due to both errors in the InSAR data and uncertainty in the measured value of the elastic skeletal storage coefficient. We conclude that InSAR is capturing the seasonal head variation, but that further research is required to obtain accurate hydraulic head estimates from the InSAR deformation measurements.
Key Points
High quality InSAR deformation data were measured in an agricultural area
Deformation data display similar seasonal trend as hydraulic head data
Uncertainties in InSAR‐derived head measurements are not well constrained
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Rock physics attempts to relate the geophysical response of a rock to geologic properties of interest, such as porosity, lithology, and fluid content. The geophysical properties estimated by ...field‐scale surveys, however, are impacted by additional factors, such as complex averaging of heterogeneity at the scale of the survey and artifacts introduced through data inversion, that are not addressed by traditional approaches to rock physics. We account for these field‐scale factors by creating numerical analogs to geophysical surveys via Monte Carlo simulation. The analogs are used to develop field‐scale rock physics relationships that are appropriate for transforming the geophysical properties estimated from a survey into geologic properties. We demonstrate the technique using a synthetic example where radar tomography is used to estimate water content.
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IntroductionYoung people aged 16 to 24 have the highest prevalence of genital chlamydia and gonorrhoea compared with other age groups and re-infection rates following treatment are high. Long-term ...adverse health effects include subfertility and ectopic pregnancy, particularly among those with repeated infections. We developed the safetxt intervention delivered by text message to reduce sexually transmitted infection (STI) by increasing partner notification, condom use and (STI) testing among young people in the UK.Methods and analysisA single-blind randomised trial to reliably establish the effect of the safetxt intervention on chlamydia and gonorrhoea infection at 1 year. We will recruit 6250 people aged 16 to 24 years who have recently been diagnosed with chlamydia, gonorrhoea or non-specific urethritis from health services in the UK. Participants will be allocated to receive the safetxt intervention (text messages designed to promote safer sexual health behaviours) or to receive the control text messages (monthly messages asking participants about changes in contact details) by an automated remote online randomisation system. The primary outcome will be the cumulative incidence of chlamydia and gonorrhoea infection at 1 year assessed by nucleic acid amplification tests. Secondary outcomes include partner notification, correct treatment of infection, condom use and STI testing prior to sex with new partners.Ethics and disseminationEthics approval was obtained from NHS Health Research Authority - London – Riverside Research Ethics Committee (REC reference: 15/LO/1665) and the London School of Hygiene & Tropical Medicine. We will submit the results of the trial for publication in peer-reviewed journals.Trial registration numberInternational Standard Randomised Controlled Trials Number: ISRCTN64390461. Registered on 17th March 2016. WHO trial registration data set available at: http://apps.who.int/trialsearch/Trial2.aspx?TrialID=ISRCTN64390461.Trial protocol version12, 19th July 2018.
High rates of land subsidence, caused by groundwater overdraft, are resulting in millions of dollars of infrastructure damage in California's San Joaquin Valley (SJV). In recent years, the use of ...interferometric synthetic aperture radar (InSAR) has enabled us to substantially improve our understanding of this subsidence. However, only very occasionally have the InSAR data been integrated with a physical model of subsurface compaction. Here, we have used InSAR and other data to parameterize and calibrate a 1D compaction model. We applied our model to a study area in the SJV where we had access to the necessary information on hydraulic head to develop model inputs. Our model simulated subsidence in the three aquifer system layers over the period 1952–2017, and is the first 1D compaction model in the SJV to simulate multiple aquifer system layers from the 1950s to 2017. The results from our model suggest that previous studies have significantly underestimated the time constants governing the slow, residual compaction of subsurface clays. We suggest that residual compaction of clays is a process that continues for decades‐to‐centuries, indicating that to significantly reduce subsidence requires some recovery of head, not just a stabilization. We also show how compaction in the lower, confined aquifer has accounted for over 90% of subsidence in the past 20 years. Although our study area is small, our findings are likely representative of the subsiding regions of the SJV, and our methodology can be applied to unconsolidated aquifer systems exhibiting subsidence worldwide.
Key Points
We integrated head and other measurements to create a 1D compaction model, simulating subsidence from 1952 to 2017 in the San Joaquin Valley
The majority of compaction occurred in the lower aquifer, and the time scales for the residual compaction of clay ranged from 64 to 1,008 years
In order to significantly reduce subsidence, there must be some recovery of head, not just a stabilization
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Working with airborne electromagnetic (AEM) data acquired in the Kaweah Subbasin in the Central Valley of California, USA, we developed a new approach for imaging the bedrock surface and the ...confining Corcoran Clay layer. Our approach, which incorporated the prior knowledge of the targets for the improved imaging, included multiple L2‐norm and Lp‐norm inversions as well as an interpolation process. The major improvement in imaging the targets was made in the Lp‐norm inversion step by incorporating prior knowledge. For the Corcoran Clay, pairs of resistivity and driller's logs at two wells guided the selection of the primary resistivity model and were used to increase the accuracy of the estimated Corcoran Clay thickness. The bedrock surface was poorly constrained by well data in the existing groundwater model, appearing as a flat surface. Acquired AEM data covered most of the area, so we had higher confidence in the obtained map of the bedrock surface at depths ranging from 15 to 160 m. There was relatively good agreement between the location of the Corcoran Clay in the AEM data (depth ranging from 50 to 130 m and thickness ranging from 3 to 25 m) and the existing groundwater model, with both depth and thickness showing ∼15% relative difference. The AEM data provided information about the continuity of the Corcoran Clay that is challenging to capture in the well data. The locations of the bedrock and Corcoran Clay were used in a structurally constrained inversion to improve the imaging of the smaller‐scale resistivity structure.
Plain Language Summary
A groundwater model is a representation of a groundwater system used to both understand the properties and processes of the subsurface, and to manage the groundwater resource. An important step in developing a groundwater model is describing the large‐scale structure, the “plumbing system” that controls the groundwater flow. Given the size of many groundwater models, obtaining an accurate description of the large‐scale structure can be a challenging task. The traditional approach has involved the drilling of wells. While wells can provide accurate information at the location of the wells, the spatial sampling of the subsurface that can be accomplished through the drilling of wells is limited. An airborne electromagnetic (AEM) method provides an alternative by using a geophysical measurement to map out the electrical resistivity to depths of hundreds of meters. Working with AEM data acquired in the Kaweah Subbasin in the Central Valley of California, we were able to image the large‐scale structure—the bedrock surface and a thick confining clay layer. The key improvement was made by incorporating prior knowledge into the inversion of the data. Once we had obtained the large‐scale structure, we found that this could be used to improve the imaging of the smaller‐scale structure.
Key Points
Airborne electromagnetic (AEM) data were used to map out the large‐scale structure in the Kaweah subbasin in California's Central Valley
A new approach to the inversion of AEM data improved the accuracy in estimates of the bedrock surface and the confining Corcoran Clay layer
The defined large‐scale structure was used in a structurally‐constrained inversion to improve the imaging of smaller‐scale structure
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Understanding how rainfall and snowmelt influence baseflow, the groundwater‐fed component of streamflow, is essential for sound water resources management. Current approaches to understand the ...spatial couplings between these processes and baseflow are limited. The most commonly used methods include geochemical tracers and hydrologic models. A key limitation of the first is cost, while the second is limited by the need for simplifying assumptions. This study developed a data‐driven approach which leverages satellite Earth observation data and ground‐based data to assess the degree to which baseflow is influenced by upstream rainfall and snowmelt in California's Sierra Nevada. The procedure involved: (1) separation of baseflow from streamflow time series using a low‐pass filtering technique, (2) quantification of aquifer drainage timescales through baseflow recession analysis, (3) application of time series and information theory methods to identify the areas which have the greatest impacts on baseflow through both rainfall and snowmelt, and (4) characterization of the elevation zones which have a prevailing influence on baseflow. Results suggest that areas which have the strongest impact on baseflow through rainfall and snowmelt are not necessarily the areas which experience the highest annual rates of snowmelt or rainfall; snowmelt occurring in the 3000–3700 m elevation range was found to be the most important driver of baseflow.
Signal processing and information theory methods are applied to remotely sensed data describing rainfall and snowmelt and ground‐based data describing streamflow in order to determine the areas which have a high degree of influence on downstream baseflow. We isolate the baseflow component of streamflow via baseflow recession, carefully distinguish between the impacts of liquid and solid precipitation, and leverage a physics – guided statistical analysis of drainage timescales to set the temporal constraints in our signal processing and information theoretic methods.
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Laboratory NMR relaxation time (T2) measurements at 2 MHz were used to quantify the amount of toluene and bis(2‐ethylhexyl)phthalate (BEHP) in the presence of water in sand‐clay mixtures. NMR ...measurements were made on water, toluene, or BEHP in each sand‐clay mixture to understand the role of clay and iron content on the T2 of each fluid; we then made NMR measurements on mixtures of water and the contaminants in each sand‐clay mixture. Our ability to resolve the NMR response of the contaminant from that of water and to quantify the amount of the contaminant varied significantly with the clay and iron content of the sand‐clay mixtures. Detection limits as low as 3% contaminant (i.e., percent of the pore fluid, by weight) were observed in some sand‐clay mixtures. Our results suggest that NMR measurements could quantify toluene if some clay is present but are unlikely to be useful for quantifying BEHP.
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Randomised controlled trials (RCTs) are generally regarded as the gold standard for evaluating health care interventions. The level of uncertainty around a trial's estimate of effect is, however, ...frequently linked to how successful the trial has been in recruiting and retaining participants. As recruitment is often slower or more difficult than expected, with many trials failing to reach their target sample size within the timescale and funding originally envisaged, the results are often less reliable than they could have been. The high number of trials that require an extension to the recruitment period in order to reach the required sample size potentially delays the introduction of more effective therapies into routine clinical practice. Moreover, it may result in less research being undertaken as resources are redirected to extending existing trials rather than funding additional studies.Poor recruitment to publicly-funded RCTs has been much debated but there remains remarkably little clear evidence as to why many trials fail to recruit well, which recruitment methods work, in which populations and settings and for what type of intervention. One proposed solution to improving recruitment and retention is to adopt methodology from the business world to inform and structure trial management techniques.We review what is known about interventions to improve recruitment to trials. We describe a proposed business approach to trials and discuss the implementation of using a business model, using insights gained from three case studies.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
In this laboratory study, we assessed the measurement of nuclear magnetic resonance (NMR) relaxation times as a means of monitoring iron mineralization processes. We conducted experiments in which ...columns containing ferrihydrite‐coated quartz sand reacted with aqueous Fe(II) solutions to form goethite, lepidocrocite and magnetite. An observed increase in the volume of water relaxing with long relaxation times in the NMR relaxation time distribution corresponds to the formation of goethite and lepidocrocite; a decrease in the average (mean log) relaxation time, and a broadening of the relaxation time distribution, corresponds to the formation of magnetite. These results indicate that NMR relaxation times are sensitive to changes in iron mineralogy and illustrate the potential use of NMR for monitoring iron mineralization processes.
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