scholarly journals Improving Stage–Discharge Relation in The Mekong River Estuary by Remotely Sensed Long-Period Ocean Tides

2020 ◽  
Vol 12 (21) ◽  
pp. 3648
Author(s):  
Hongrui Peng ◽  
Hok Sum Fok ◽  
Junyi Gong ◽  
Lei Wang
Keyword(s):  
Time Series ◽  
Water Level ◽  
Water Discharge ◽  
Remotely Sensed ◽  
Tidal Height ◽  
Global Ocean ◽  
Ocean Tide ◽  
Ocean Tides ◽  
Long Period ◽  
Short Period

Ocean tidal backwater reshapes the stage–discharge relation in the fluvial-to-marine transition zone at estuaries, rendering the cautious use of these data for hydrological studies. While a qualitative explanation is traditionally provided by examining a scatter plot of water discharge against water level, a quantitative assessment of long-period ocean tidal effect on the stage–discharge relation has been rarely investigated. This study analyzes the relationship among water level, water discharge, and ocean tidal height via their standardized forms in the Mekong Delta. We found that semiannual and annual components of ocean tides contribute significantly to the discrepancy between standardized water level and standardized water discharge time series. This reveals that the long-period ocean tides are the significant factors influencing the stage–discharge relation in the river delta, implying a potential of improving the relation as long as proper long-period ocean tidal components are taken into consideration. By isolating the short-period signals (i.e., less than 15 days) from land surface hydrology and ocean tides, better consistent stage–discharge relations are obtained, in terms of improving the Pearson correlation coefficient (PCC) from ~0.4 to ~0.8 and from ~0.6 to ~0.9 for the stations closest to the estuary and at the Mekong Delta entrance, respectively. By incorporating the long-period ocean tidal height time series generated from a remotely sensed global ocean tide model into the stage–discharge relation, further refined stage–discharge relations are obtained with the PCC higher than 0.9 for all employed stations, suggesting the improvement of daily averaged water level and water discharge while ignoring the short-period intratidal variability. The remotely sensed global ocean tide model, OSU12, which contains annual and semiannual ocean tide components, is capable of generating accurate tidal height time series necessary for the partial recovery of the stage–discharge relation.

scholarly journals Evaluation of global ocean tide models based on tidal gravity observations in China

2020 ◽  
Author(s):  
Hongbo Tan ◽  
Chongyong Shen ◽  
Guiju Wu
Keyword(s):  
High Precision ◽  
Earth Tide ◽  
Global Ocean ◽  
Ocean Tide ◽  
Ocean Tides ◽  
Ocean Tide Model ◽  
Tidal Forces ◽  
The Earth ◽  
Gravity Observation ◽  
Ocean Tide Models

<p>Solid Earth is affected by tidal cycles triggered by the gravity attraction of the celestial bodies. However, about 70% the Earth is covered with seawater which is also affected by the tidal forces. In the coastal areas, the ocean tide loading (OTL) can reach up to 10% of the earth tide, 90% for tilt, and 25% for strain (Farrell, 1972). Since 2007, a high-precision continuous gravity observation network in China has been established with 78 stations. The long-term high-precision tidal data of the network can be used to validate, verifying and even improve the ocean tide model (OTM).</p><p>In this paper, tidal parameters of each station were extracted using the harmonic analysis method after a careful editing of the data. 8 OTMs were used for calculating the OTL. The results show that the Root-Mean-Square of the tidal residuals (M<sub>0</sub>) vary between 0.078-1.77 μgal, and the average errors as function of the distance from the sea for near(0-60km), middle(60-1000km) and far(>1000km) stations are 0.76, 0.30 and 0.21 μgal. The total final gravity residuals (Tx) of the 8 major constituents (M<sub>2</sub>, S<sub>2</sub>, N<sub>2</sub>, K<sub>2</sub>, K<sub>1</sub>, O<sub>1</sub>, P<sub>1</sub>, Q<sub>1</sub>) for the best OTM has amplitude ranging from 0.14 to 3.45 μgal. The average efficiency for O<sub>1</sub> is 77.0%, while 73.1%, 59.6% and 62.6% for K<sub>1</sub>, M<sub>2</sub> and Tx. FES2014b provides the best corrections for O<sub>1</sub> at 12 stations, while SCHW provides the best for K<sub>1 </sub><sub>,</sub>M<sub>2</sub>and Tx at 12,8and 9 stations. For the 11 costal stations, there is not an obvious best OTM. The models of DTU10, EOT11a and TPXO8 look a litter better than FES2014b, HAMTIDE and SCHW. For the 17 middle distance stations, SCHW is the best OTM obviously. For the 7 far distance stations, FES2014b and SCHW model are the best models. But the correction efficiency is worse than the near and middle stations’.</p><p>The outcome is mixed: none of the recent OTMs performs the best for all tidal waves at all stations. Surprisingly, the Schwiderski’s model although is 40 years old with a coarse resolution of 1° x 1° is performing relative well with respect to the more recent OTM. Similar results are obtained in Southeast Asia (Francis and van Dam, 2014). It could be due to systematic errors in the surroundings seas affecting all the ocean tides models. It's difficult to detect, but invert the gravity attraction and loading effect to map the ocean tides in the vicinity of China would be one way.</p>

Slugging Fatigue Assessment for Steel Lazy Wave Risers

2021 ◽  
Author(s):  
Brad Campbell ◽  
Puneet Agarwal ◽  
Christopher Curtis ◽  
Guangqiang Yang ◽  
Angshuman Singha ◽  
...  
Keyword(s):  
Time Series ◽  
High Amplitude ◽  
Spatial And Temporal Variability ◽  
Full Time ◽  
Spatial Integration ◽  
Local Weight ◽  
Long Period ◽  
Global Weight ◽  
Bubble Density ◽  
Short Period

Abstract The objective of this paper is to introduce a new analysis methodology for assessment of riser fatigue due to slugging. Under certain flow regimes, a multiphase (oil-gas-water) flow can result in slug flow, in which a sequence of relatively high density slugs and relatively low density bubbles propagate along the flowline and the riser. The variation of slug and bubble density at a location with time is random, and slug characteristics can also change significantly along the riser length. Due to local and global weight variations, the riser undergoes cycles of bending which cause fatigue. By explicitly modeling full spatial and temporal variability and randomness of slugs, the new analysis method is significantly more accurate than other methods and it captures physics of riser's slugging response. The slugging fatigue of a steel lazy wave riser was analyzed in Orcaflex software by modeling a repeating pair of slug and bubble with constant slug and bubble densities and associated lengths over the 3-hour simulation time. A separate slug train was propagated in five sub-segments of the riser. To model a more accurate and realistic representation of slugging behavior, the time series of density was extracted at each node from the multiphase flow simulator Olga. Statistical and spectral analysis of the Olga output showed that assumptions of constant slug-bubble density, and of slug behavior being uniform over long segments of riser are too simplistic. Therefore, full time series of density at each node was input into the riser analysis using the existing capabilities of Orcaflex software. As the Orcaflex slug form approach was computationally expensive, we also developed an extrenal slug loader, which provides same level of accuracy while being computationally fast and full automated. The new method shows that the cyclic riser response at the touchdown point (TDP) is composed of two parts. One is the relatively short period (~20-60 seconds) fluctuations that occur because of local weight variations as a slug-bubble passes a riser node. The other is the relatively long period (~10-30 minutes) fluctuations that occur due to global weight variations, which are due to spatial integration of density time series over the lower catenary. These long period fluctuations drive the TDP fatigue. Preliminary field measurements with an ROV, while inducing temporary slugging in the riser, confirmed analytical predictions of long period and high amplitude motions at hog bend. This paper presents a new and significantly more accurate method for analyzing riser fatigue due to slugging. Previously unknown behavior of very long period and high amplitude riser motions is identified and explained. SLWR response to slugging can be an important contributor to the overall fatigue design budget especially at the TDP. This work reflects ExxonMobil's on-going efforts to ensure that we maintain safe designs as we adopt systems new to us in new and challenging environments.

Characterising hydrodynamic controls on groundwater in a coastal urban aquifer using time and frequency domain responses at multiple spatiotemporal scales

2020 ◽  
Author(s):  
Ashley M Patton ◽  
Gabriel C Rau ◽  
Corinna Abesser ◽  
David R James ◽  
Peter J Cleall ◽  
...  
Keyword(s):  
Time Series ◽  
Frequency Domain ◽  
Time Series Data ◽  
Monitoring Network ◽  
Signal Propagation ◽  
Tidal River ◽  
Capital City ◽  
Series Data ◽  
Ocean Tide ◽  
Ocean Tides

<p>Urban environments often have highly variable and evolving hydrogeology. Coastal cities present even greater challenges to hydraulic and thermal conceptualisation and parameter estimation due to their complex dynamics and the heterogeneity of ocean-influenced hydraulic processes. Traditional methods of investigation (e.g. pump tests, invasive sampling) are time consuming, expensive, represent a snapshot in time and are difficult to conduct in built-up areas, yet properties derived from them are crucial for constructing models and forecasting urban groundwater evolution.</p><p>Here we present a novel approach to use passive sampling of groundwater head data to understand subsurface processes and derive hydraulic and geotechnical properties in an urban-coastal setting. This is illustrated using twenty years of high frequency (hourly) time-series data from an existing groundwater monitoring network comprising 234 boreholes distributed across Cardiff, the capital city of Wales, UK. We have applied Tidal Subsurface Analysis (TSA) to Earth, Atmospheric and Oceanic signals in groundwater time-series in the frequency domain, and also generated Barometric Response Functions in the time domain. By also observing the damping and attenuation of the response to ocean tides with distance from the coast and tidal rivers, this combination of analyses has enabled us to disentangle the influence of the different tidal components and estimate spatially distributed aquifer processes and parameters.</p><p>The data cover a period pre and post construction of a barrage across the coastline, impounding the city’s rivers. We were therefore able to observe a huge decrease in the subsurface ocean tide signal propagation following this human intervention, through the coastal and tidal river boundaries. These changes reveal variations in hydraulic responses and values of hydraulic diffusivity between different lithologies, notably with made-ground deposits being much less sensitive to ocean tides than the underlying sand and gravel aquifer. By being able to map the spatial variations in hydraulic response and barometric efficiency for the first time (and therefore formation compressibility and extent of aquifer confinement) we have been able to refine interpretations (and in some cases overcome misconceptions) derived from previous inferences made solely from borehole logs. We anticipate that linking the improved hydraulic characterisation, enabled by the new methodology, will also help better characterisation of the subsurface thermal regime, and management of shallow geothermal energy resources in coastal urban aquifers.</p>

Long-period tides observed with a superconducting gravimeter at Syowa Station, Antarctica, and their implication to global ocean tide modeling

1997 ◽  
Vol 103 (1-2) ◽  
pp. 39-53 ◽  
Author(s):  
Tadahiro Sato ◽  
Masatsugu Ooe ◽  
Kazunari Nawa ◽  
Kazuo Shibuya ◽  
Yoshiaki Tamura ◽  
...  
Keyword(s):  
Superconducting Gravimeter ◽  
Global Ocean ◽  
Ocean Tide ◽  
Syowa Station ◽  
Long Period

scholarly journals Historic maps as a data source for socio-hydrology: a case study of the Lake Balaton wetland system, Hungary

2013 ◽  
Vol 10 (6) ◽  
pp. 7733-7781
Author(s):  
A. Zlinszky ◽  
G. Timár
Keyword(s):  
Time Series ◽  
Water Level ◽  
Water Cycle ◽  
Social Systems ◽  
Water Level Fluctuations ◽  
Lake Balaton ◽  
Hydrological Data ◽  
Short Period ◽  
Historic Maps

Abstract. Socio-hydrology is the science of human influence on the water cycle and the influence of the water cycle on human social systems. This newly emerging discipline inherently involves a historic perspective, often focusing on time scales of several centuries. While data on human history is typically available for this time frame, gathering information on the hydrological situation during such a period can prove difficult: measured hydrological data for such long periods are rare, while models and secondary datasets from geomorphology, pedology or archaeology are typically not accurate enough over such a short period. In the first part of this study, the use of historic maps in hydrology is reviewed. Major breakthroughs were the acceptance of historic map content as valid data, the use of preserved features for investigating situations earlier than the map, and the onset of digital georeferencing and data integration. Historic maps can be primary quantitative sources of hydro-geomorphological information, they can provide a context for point-based measurements over larger areas, and they can deliver time series for a better understanding of change scenarios. In the second part, a case study is presented: Water level fluctuations of Lake Balaton were reconstructed from maps, levelling logs and other documents. An 18th century map system of the whole 5700 km2 catchment was georeferenced, integrated with two 19th century map systems and wetlands, forests and open water digitized. Changes in wetland area were compared with lake water level changes in a 220 yr time series. Historic maps show that the water level of the lake was closer to present-day levels than expected, and that wetland loss pre-dates drainage of the lake. The present and future role of historic maps is discussed. Historic hydrological data has to be treated with caution: while it is possible to learn from the past, the assumption that future changes will be like past changes does not always hold. Nevertheless, old maps are relatively accessible datasets and the knowledge base for using them is rapidly growing, and it can be expected that long-term time series will be established by integrating georeferenced map systems over large areas. In the Appendix, a step-by-step guide to using historic maps in hydrology is given, starting from finding a map, through georeferencing and processing the map to publication of the results.

scholarly journals Regional Evaluation of Minor Tidal Constituents for Improved Estimation of Ocean Tides

2021 ◽  
Vol 13 (16) ◽  
pp. 3310
Author(s):  
Michael G. Hart-Davis ◽  
Denise Dettmering ◽  
Roman Sulzbach ◽  
Maik Thomas ◽  
Christian Schwatke ◽  
...  
Keyword(s):  
Sea Level ◽  
Satellite Altimetry ◽  
Tide Gauge ◽  
Sea Surface ◽  
Global Ocean ◽  
Ocean Tide ◽  
Ocean Tides ◽  
Tidal Constituents ◽  
Ocean Tide Models ◽  
Tidal Correction

Satellite altimetry observations have provided a significant contribution to the understanding of global sea surface processes, particularly allowing for advances in the accuracy of ocean tide estimations. Currently, almost three decades of satellite altimetry are available which can be used to improve the understanding of ocean tides by allowing for the estimation of an increased number of minor tidal constituents. As ocean tide models continue to improve, especially in the coastal region, these minor tides become increasingly important. Generally, admittance theory is used by most global ocean tide models to infer several minor tides from the major tides when creating the tidal correction for satellite altimetry. In this paper, regional studies are conducted to compare the use of admittance theory to direct estimations of minor tides from the EOT20 model to identify which minor tides should be directly estimated and which should be inferred. The results of these two approaches are compared to two global tide models (TiME and FES2014) and in situ tide gauge observations. The analysis showed that of the eight tidal constituents studied, half should be inferred (2N2, ϵ2, MSF and T2), while the remaining four tides (J1, L2, μ2 and ν2) should be directly estimated to optimise the ocean tidal correction. Furthermore, for certain minor tides, the other two tide models produced better results than the EOT model, suggesting that improvements can be made to the tidal correction made by EOT when incorporating tides from the two other tide models. Following on from this, a new approach of merging tidal constituents from different tide models to produce the ocean tidal correction for satellite altimetry that benefits from the strengths of the respective models is presented. This analysis showed that the tidal correction created based on the recommendations of the tide gauge analysis provided the highest reduction of sea-level variance. Additionally, the combination of the EOT20 model with the minor tides of the TiME and FES2014 model did not significantly increase the sea-level variance. As several additional minor tidal constituents are available from the TiME model, this opens the door for further investigations into including these minor tides and optimising the tidal correction for improved studies of the sea surface from satellite altimetry and in other applications, such as gravity field modelling.

scholarly journals Ocean-tide parameters from the simultaneous long-period analysis of the orbits of Starlette and Stella

1997 ◽  
Vol 15 (2) ◽  
pp. 263-271 ◽  
Author(s):  
N. M. Harwood ◽  
G. G. Swinerd
Keyword(s):  
Ocean Tide ◽  
Ocean Tides ◽  
Orbital Inclination ◽  
Period Analysis ◽  
Analysis Techniques ◽  
Long Period ◽  
Simultaneous Fitting ◽  
One Year ◽  
Ocean Tide Models ◽  
Right Ascension

Abstract. The orbits of two geodetic satellites, Starlette and Stella, have been analysed in order to determine ocean-tide parameters. The orbit of Starlette has been determined over a three-year period and Stella over a one-year period. Long-period analysis techniques have been used to determine the evolutions of the orbital inclination, eccentricity and right ascension of the ascending node for each satellite due to ocean tides. The ocean-tide parameters have been determined in a simultaneous fitting of the theoretical orbital variations to the observed variations. The results are compared with ocean-tide models.

Discussion following the presentation by F. Deubner

1977 ◽  
Vol 36 ◽  
pp. 69-74
Keyword(s):  
List Type ◽  
The Sun ◽  
Type Number ◽  
Harmonic Motion ◽  
Locally Excited ◽  
Long Period ◽  
Coherent Wave ◽  
Short Period ◽  
Global Modes

The discussion was separated into 3 different topics according to the separation made by the reviewer between the different periods of waves observed in the sun :1) global modes (long period oscillations) with predominantly radial harmonic motion.2) modes with large coherent - wave systems but not necessarily global excitation (300 s oscillation).3) locally excited - short period waves.

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