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Tidal characteristics in the Gulf of Khambhat, northern Arabian Sea – based on observation and global tidal model data

Mitra Aditi, Kumar V. Sanil, Jena Basanta K.

Oceanologia

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2020

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No. 62 (4PA)

443--459

EN

Tidal characteristics of the Gulf of Khambhat are described based on measured and modelled sea-level data. Data were recorded at three locations inside and two locations outside the Gulf with record lengths of 6-12 months to study the tidal propagation. A northward increase in tidal amplitude is noticed from Daman (eastern side) and Diu (western side) and attains maxima at Bhavnagar. A similar trend is followed by the amplitude of the major tidal constituents, although there are discrepancies for that of the minor constituents. The non-tidal factor which influences the sea-level is the local wind, especially the alongshore component of wind. A positive correlation is obtained between the sea-level and the meridional component of wind at each location. Harmonic analysis of sea-level data shows that M2 is the major tidal constituent which propagates in a non-linear fashion inside the Gulf. Tides from two global tide models (MIKE21 and FES2014) have been compared with the measured data, which could be used for further prediction of the tides and sediment transport in the Gulf. The tide elevation derived from the MIKE21 model has further been used for the harmonic analysis of tide. The tides predicted using one-month data are up to 10% smaller than those predicted using the one-year data. The global tide model FES2014 data performs well with measured data for offshore locations, whereas it fails to predict the same for the inner Gulf locations. The study manifests the fact that to understand the dynamics of complex tidal areas, regional models should better be used than global tidal models.

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Evaluation of morphodynamics of Miani Hor, a coastal lagoon of Lasbela, Balochistan, Pakistan

Syed Naeem Ahmed, Siddiqa Tahira, Sohoo Niamatullah

Oceanologia

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2020

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No. 62 (1)

45--55

EN

In compliance to the estuarine areas having access to the sea and riverine water, Miani Hor, a coastal water body in Lasbela, Pakistan could be categorized as a lagoon due to its shallowness, elongation to the coast, connectivity with the adjacent Sonmiani Bay and occasional receiving of rainwater. In the present paper, Miani Hor was studied to understand its dynamics, and to compare it with the categories of lagoons as proposed by Kjerfve (1986). The result of the field data of water quality and water movement as well as satellite imagery of different years show that this is a tide-dominated lagoon with a single inlet, and it was formed in the last glaciation period. Its only inlet is stable and remains open even during the period of high energy waves offshore Sonmiani Bay that generate strong littoral drift. The data suggest that unlike choked lagoons, as proposed by Kjerfve (1986) for classification of the single-inlet lagoons with limited tidal influence, Miani Hor has a small (0.08) ratio of the channel cross-sectional area to the lagoon surface area. The lagoon channel filters out high energy waves but allows strong tidal signals to penetrate the lagoon. The paper suggests that Kjerfve (1986) classification requires modification by incorporating another class “relaxed lagoons” for the single inlet tide-dominated lagoons.

3

Tide and mean sea level trend in the west coast of the Arabian Gulf from tide gauges and multi-missions satellite altimeter

Siddig Nada Abdulraheem, Al-Subhi Abdullah Mohammed, Alsaafani Mohammed Ali

Oceanologia

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2019

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No. 61 (4)

401--411

EN

Hourly data of the relative sea level from seven stations on the west coast of the Arabian Gulf, for the period 1979-2008 have been analyzed. The harmonic constituents of tide show pure diurnal tide at Murjan Island, semidiurnal type at Mina Salman and mixed type with semidiurnal dominance at the remaining five stations. Based on Multi-Missions Satellite Altimetry data, the mean sea level trend estimate was about 2.8 ± 0.4 mm/year for global ocean and about 3.6 ± 0.4 mm/year for the Arabian Gulf. Among the seven tide gauge stations, the highest sea level trend is found at Mina Salman (3.4 ± 0.98 mm/year) that agrees with the local estimate from the Multi-Missions Satellite Altimetry data. The minimum trend is found at Jubail (1.6 ± 0.71 mm/ year) and Ras Tanura (0.7 ± 0.31 mm/year). At Arrabiyah Island station, the sea level trend is about 2.4 ± 0.66 mm/year, which is obtained after removing the interruptions from a relatively longer duration (15 years) data. This is in agreement with other stations and the estimates from the altimetry. The tidal analysis and trend estimation for Jubail station (29 years) have been conducted for the first time. At Murjan Island, the decadal cycle is evident from the long sea level data, giving the current estimate of trend more reliability as compared with previous studies.