Main Storage Reservoir Research Articles

Pre-eruptive dynamics at the Campi Flegrei Caldera: from evidence of magma mixing to timescales estimates

We review pre-eruptive dynamics and evidence of open-system behavior in the volcanic plumbing system beneath Campi Flegrei Caldera, together with estimates of magma residence time, magma ascent, and mixing-to-eruption timescales. In detail, we compile pre- and syn-eruptive dynamics reported in the literature for (a) the Campanian Ignimbrite ~ 40 ka, (b) the Neapolitan Yellow Tuff (~ 15 ka), and (c) the recent activity within the Phlegrean area. We first summarize geochemical and textural evidence (e.g., magma mixing, crystal disequilibria, vertical zonings, and isotopic records) of open-system behavior for the pyroclasts erupted in the last 40 ky at Campi Flegrei Caldera. We show that the fingerprint of open-system dynamics is ubiquitous in the deposits associated with the volcanic activity at the Campi Flegrei Caldera in the last 40 ky. Then, we describe the results of geophysical and petrological investigations that allow us to hypothesize the structure of the magma feeding system. We point to a trans-crustal magmatic feeding system characterized by a main storage reservoir hosted at ~ 9 km that feeds and interacts with shallow reservoirs, mainly placed at 2–4 km. Finally, we define a scenario depicting pre-eruptive dynamics of a possible future eruption and provide new constraints on timescales of magma ascent with a physical model based on magma-driven ascending dyke theory. Results show that considerably fast ascent velocities (i.e., of the order of m/s) can be easily achieved for eruptions fed by both shallow (i.e., 3–4 km) and deep (i.e., ~ 9 km) reservoirs. Comparing the results from experimental and numerical methods, it emerges that mixing-to-eruption timescales occurring at shallow reservoirs could be on the order of minutes to hours. Finally, we highlight the volcanological implications of our timescale estimates for magma ascent and mixing to eruption. In particular, explosive eruptions could begin with little physical ‘warning’, of the order of days to months. In this case, the onset of volatile saturation might provide pre-eruptive indicators.Graphical

Succession of phytoplankton functional groups in Macau’s two shallow urban border reservoirs under multiple changing factors

The community diversity of phytoplankton is quite high, and hundreds of phytoplankton species can coexist. Aggregating phytoplankton species into different phytoplankton functional groups (PFGs) can better assess and predict the potential structural and functional effects of aquatic ecosystems. The continuous interaction of key PFGs is the key cause of cyanobacterial blooms in drinking water supply systems, especially in shallow border reservoirs, but the reasons have not been understood. This study was carried out in Macau’s two shallow border reservoirs, the Main Storage Reservoir (MSR) and Sai Pa Van Reservoir (SPVR). Then, phytoplankton samples from these reservoirs were collected monthly over a four-year period (from January 2011 to December 2014) to reveal key factors driving PFGs succession and their synthetic effects on the dominant species. The trophic state index (TSI) of TN and TP of the two reservoirs ranged from 36.25 to 83.95 and 8.32–56.13, respectively, indicating that the SPVR and MSR were between a eutrophic and hypereutrophic state. The phytoplankton analysis results showed that there were 14 dominant PFGs and 8 dominant PFGs in the MSR and SPVR, respectively. The group S1 was always predominant in the SPVR during the succession of PFGs, while the succession of PFGs in the MSR were quite different, the PFGs could mainly be summarized as S1/SN/X1 (2011) → X1/J/B/TB/P (2012, 2013) →S1/X1/J (2014). In addition, redundancy analysis (RDA) through stepwise discriminant analysis was used to analyze the dominant PFGs and abiotic factors in both reservoirs. The results indicated that the turbidity value of the reservoir was the key factor influencing groups S1, Lo and SN in the SPVR. However, the different PFGs were influenced by the turbidity, NH3–N, NO3–N and EC values of the reservoir in the MSR. The relationship between PFGs and environmental factors was described by stepwise regression analysis. The investigation of the different ecological responses between the interconnected reservoirs was useful for targeted water source protection.

Integrating Support Vector Regression with Particle Swarm Optimization for numerical modeling for algal blooms of freshwater

Algae-releasing cyanotoxins are cancer-causing and very harmful to the human being. Therefore, it is of great significance to model how the algae population dynamically changes in freshwater reservoirs. But the practical modeling is very difficult because water variables and their internal mechanism are very complicated and non-linear. So, in order to alleviate the algal bloom problems in Macau Main Storage Reservoir (MSR), this work proposes and develops a hybrid intelligent model combining Support Vector Regression (SVR) and Particle Swarm Optimization (PSO) to yield optimal control of parameters that predict and forecast the phytoplankton dynamics. In this process, collected data for current month’s variables and previous months’ variables are used for model predict and forecast, respectively. In the correlation analysis of 23 water variables that monitored monthly, 15 variables such as alkalinity, Bicarbonate (HCO3-), dissolved oxygen (DO), total nitrogen (TN), turbidity, conductivity, nitrate, suspended solid (SS) and total organic carbon (TOC) are selected, and data from 2001 to 2008 for each of these selected variables are used for training, while data from 2009 to 2011 which are the most recent three years are used for testing. It can be seen from the numerical results that the prediction and forecast powers are respectively estimated at approximately 0.767 and 0.876, and naturally it can be concluded that the newly proposed PSO–SVR is working well and can be adopted for further studies.

Using Principle Component Regression, Artificial Neural Network, and Hybrid Models for Predicting Phytoplankton Abundance in Macau Storage Reservoir

Principle component regression (PCR), artificial neural network (ANN), and their combination used as data-driven models were selected to apply in this study to predict (based on the current-month variables) and forecast (based on the last 3-month-ahead variables) the phytoplankton dynamics in Macau Main Storage Reservoir (MSR) that is experiencing algal bloom in recent years. The models used the comprehensive 8 years’ monthly water quality data for training and the most recent 3 years’ monthly data for testing. Twenty-four water quality variables including physical, chemical, and biological parameters were involved, and comparisons were made to select the best models that can be applied to MSR. Simulation results revealed that ANN has better accuracy and generalization performance in comparison with PCR both for the prediction and the forecasted model. Using principal component analysis (PCA) for the data, inputs did not show better performance for the ANN, implying that eliminating the uncorrelated variables do not increase the prediction capability for the adopted model. Globally, in contrast with previous studies showing that the hybrid model can handle both linear and nonlinear components of the problems well, the PCR-ANN in this study obtain no better improvement.

Detecting small gravity change in field measurement: simulations and experiments of the superconducting gravimeter—iGrav

In order to detect small gravity changes in field measurements, such as with CO2 storage, we designed simulations and experiments to validate the capabilities of the iGrav superconducting gravimeter. Qualified data processing was important to obtain the residual gravity from the iGrav's raw gravity signals, without the tidal components, atmosphere, polar motion and hydrological effects. Two simulations and four designed experiments are presented in this study. The first simulation detected the gravity change during CO2 injection. The residual gravity of CO2 leakage was targeted with the second simulation from the main storage reservoir to secondary space underground. The designed experiments monitored the situation of gravity anomalies in the iGrav's records. These tests focused on short-term gravity anomalies, such as gravity changes, step functions, repeat observations and gradient measurements from the iGrav, rather than on long-term tidal effects. The four laboratory experiments detected a decrease in gravity of −0.56 ± 0.15 µGal (10−8 m s−2) with a 92.8 kg weight on the top of the iGrav. A step function occurred in the gravity signals, when the tilt control was out of balance. We also used a professional camera dolly with a track to observe repeated horizontal movements and an electric lift table for controlled vertical movements to measure the average gradient of −2.67 ± 0.01 µGal cm−1.

Spatio-temporal variations of phytoplankton structure and water quality in the eutrophic freshwater reservoir of Macau

In small-scale pumped-storage reservoirs, physical disturbances have been suggested to be one of the main factors influencing phytoplankton structure and water quality. This study presented data on dynamic changes of the phytoplankton structure and the quality of raw water sampled monthly from January 2011 to June 2012, in three locations (with two different water levels each) of a small pumped-storage reservoir of Macau main storage reservoir. The trophic state index, phytoplankton structure indices, and multivariate statistical techniques were applied for assessing trophic state, phytoplankton community, and spatio-temporal variations of the reservoir, respectively. The results showed that the reservoir was categorized as a eutrophic–hypereutrophic reservoir, with the dominance of Cyanophyta in 2011, and of Chlorophyta and Bacillariophyta in 2012. Lowest diversity/evenness and highest dominance happened in June 2011, while highest diversity/evenness and lowest dominance occurred in May 2012. Principle component analysis identified four factors that can explain 80.8% of the total variance of the water quality data, and cluster analysis generated two clusters of spatial similarity among the six sampling points and two clusters of temporal similarity among the 18 months. Discriminant analysis results revealed only three parameters (TP, NO3-N, and Chl-a) that could afford 100% correct assignation in temporal analysis, while no spatial variation was found in spatial analysis. This study highlighted the usefulness of combination of these methods for the evaluation and interpretation of complex water quality data-sets and assessment of pollution level of small-scale eutrophic reservoirs. The results from the study can be used in developing monitoring program of freshwater bodies.

Eutrophication analyses and principle component regression for two subtropical storage reservoirs in Macau

Eutrophication analyses of two subtropical storage reservoirs in Macau, the Special Administrative Region of China, namely Main Storage Reservoir (MSR) and Sai Pa Van Reservoir (SPVR), were performed in this study. Totally, 17 monthly water parameters including, five hydrological parameters (precipitation, imported volume, exported volume, water level, and hydraulic retention time), four physical parameters (temperature, pH, turbidity, and conductivity), seven chemical parameters (dissolved oxygen, Ammonium, nitrite, nitrate, total nitrogen (TN), orthophosphate (PO43-), and total phosphorus (TP)), and one biological parameter (phytoplankton abundance) were sampled and monitored in 2010. The correlation analysis and principle component regression (PCR), that is, principle component analysis (PCA) followed by multiple linear regression (MLR), were used to simplify the complexity of the relationships and to predict the phytoplankton abundance levels as well. The eutrophication analyses results showed that both reservoirs were in eutrophic status with the trophic state indices of 58–72 for MSR and 51–71 for SPVR, respectively. Phytoplankton abundance in both reservoirs were found to be linearly correlated with turbidity, temperature, and TP, while anti-correlated with conductivity, TN, nitrate, TN/TP, and water level. The PCA showed that three PCs with Eigen value over one, can explain 84.6% of total variation of the water parameters in MSR, while only two PCs can explain 70.8% for SPVR. The MLR models can be used for predicting phytoplankton abundance in the reservoirs with the predictive power of 0.90 in MSR, while only of 0.67 in SPVR.

Integrating Principle Component Analysis and Canonical Correlation Analysis for Monitoring Water Quality in Storage Reservoir

Water quality monitoring is of great importance in managing drinking water lakes or reservoirs. However, developing such an effective monitoring system used in evaluating water quality is difficult, due to spatial and temporal variation in water quality that are usually hard to interpret. Principle component analysis (PCA) and canonical correlation analysis (CCA) techniques were used in this study to determine the principle water parameters, and explore the relationship between the physical and chemical water parameters, respectively in Macau Main Storage Reservoir (MSR) that is experiencing algal bloom in recent years. Twenty-eight water parameters including physical and chemical parameters were monitored each month from Jan 2001 to Dec 2010. The results showed that using PCA, six of the water quality parameters were found less important in explaining the monthly variation of the water quality and thus excluded from the further CCA, while applying CCA, the first six canonical correlations were 0.998, 0.988, 0.937, 0.778, 0.606 and 0.453, indicating that electro-conductivity and chloride compounds were the dominant (highly scored) variables of the physical parameters and chemical parameters, respectively. These results are helpful in understanding the main physical and chemical parameters involved in MSR, thus improving the water quality monitoring system in drinking water reservoirs.

Assessment of carbon dioxide plume behaviour within the storage reservoir and the lower caprock around the KB-502 injection well at In Salah

Surface uplift has been detected over all three of the In Salah CO2 injection wells with corresponding subsidence also observed over the gas production area. The distinctive two-lobed uplift pattern over KB-502 has attracted much research interest, as it suggests the tensile opening of a structural discontinuity at depth. The latest reservoir simulation effort at Imperial College involved the implementation of a non-sealing fault (zone) with dynamic transmissibility in the revised reservoir/overburden model and adopted a holistic approach to matching of the estimated flowing bottomhole pressure (FBHP) at KB-502. Based upon the current knowledge of the Krechba stress field and time-elapse InSAR surface uplift images, tensile opening of a pre-existing fault (zone) aligned with the maximum horizontal stress direction and its subsequent growth was analysed with reference to CO2 injection FBHP at KB-502. The history matching results, in terms of the dynamic behaviour of the fault (zone) transmissibility, are found to be consistent with the stress analysis and the field observations.A new interpretation is proposed for the two-lobed surface uplift pattern observed over KB-502. It is postulated that, prior to March 2006 when the injection pressure peaked, the two-lobed surface response was caused primarily by CO2 injection-induced tensile opening of a non-sealing fault zone and its subsequent confined growth (lateral propagation and widening) within the C10 formation. The increasingly pronounced surface uplift pattern observed after March 2006 (against the backdrop of a steady decline in the FBHP), is predominantly a result of localised CO2 migration into and pressurisation of a fracture (or fault damage) zone in the lower caprock by elevated injection pressure, at the top of the tight sandstone formation (C10.3), which is overlying the main storage reservoir (C10.2).

The Use of Geodetic Leveling For Crustal Motion and Deformation Studies: A 30-Year Case Study in Ahmadu Bello University, Zaria

This paper examines the stability of some benchmarks on the main campus of Ahmadu Bello University, Zaria, and reports the deformation studies of the area around the University dam. This dam serves as the main storage reservoir for the water supply to the University and surrounding communities. In order to study the deformation around the University dam and the stability of benchmarks, several surveys were carried out between 1976 and 2006. Within the period under review, it was revealed that the maximum downward displacement (settlement) of 96.44mm was recorded between 1976 and 2006 for a monitoring station (CP4) situated centrally along the embankment of the dam. The maximum upward displacement (uplift) of 8.03mm was recorded between 1976 and 2002 at a ground point (CP12) located in a roundabout in front of Faculty of Medicine of the University. The monitoring Station CP4 had the greatest average absolute displacement of 3.22mm per annum over the period of thirty years. Detailed results and analysis will be discussed in this paper.. The Information Manager Vol. 7 (2) 2007: pp. 28-39

Automatic Recording and Control Devices in Tacoma's Water System

ELIMINATE, wherever possible, the unreliable features in the operation of the water supply and distribution systems of Tacoma, Wash., which are due to the manual operation of certain control units, numerous automatic recording and pressure control devices have been installed during the last few years. The use of these devices has improved pressure conditions over large areas, particularly during times of peak demand, has lessened the demands on operators, and has provided the department with necessary basic information for making additional future improvements. The principal source of Tacoma's water supply is the Green River, from which water is piped to the city through a gravity system. The intake for this system is located approximately 28 mi. east of the city in the foothills of the Cascade Mountains, the crest of the diversion dam being at an elevation of 908 ft. A single pipe line, 26.6 mi. long and of varying diameter, conveys 52 m.g.d. to McMillin Reservoir, the main storage reservoir on the system.* Capacity of the two compartments of McMillin Reservoir is 110 mil.gal., and its water level is held at 588 ft. From the reservoir, two large pipe lines, with a combined capacity of 92 m.g.d., supply the water to the distribution system in the city. The older of these lines is 15.3 mi. long and was designed for gravity flow opera-

Electric and magnetic fields

Surface uplift has been detected over all three of the In Salah CO2 injection wells with corresponding subsidence also observed over the gas production area. The distinctive two-lobed uplift pattern over KB-502 has attracted much research interest, as it suggests the tensile opening of a structural discontinuity at depth. The latest reservoir simulation effort at Imperial College involved the implementation of a non-sealing fault (zone) with dynamic transmissibility in the revised reservoir/overburden model and adopted a holistic approach to matching of the estimated flowing bottomhole pressure (FBHP) at KB-502. Based upon the current knowledge of the Krechba stress field and time-elapse InSAR surface uplift images, tensile opening of a pre-existing fault (zone) aligned with the maximum horizontal stress direction and its subsequent growth was analysed with reference to CO2 injection FBHP at KB-502. The history matching results, in terms of the dynamic behaviour of the fault (zone) transmissibility, are found to be consistent with the stress analysis and the field observations.A new interpretation is proposed for the two-lobed surface uplift pattern observed over KB-502. It is postulated that, prior to March 2006 when the injection pressure peaked, the two-lobed surface response was caused primarily by CO2 injection-induced tensile opening of a non-sealing fault zone and its subsequent confined growth (lateral propagation and widening) within the C10 formation. The increasingly pronounced surface uplift pattern observed after March 2006 (against the backdrop of a steady decline in the FBHP), is predominantly a result of localised CO2 migration into and pressurisation of a fracture (or fault damage) zone in the lower caprock by elevated injection pressure, at the top of the tight sandstone formation (C10.3), which is overlying the main storage reservoir (C10.2).