ANALISIS PASANG SURUT MENGGUNAKAN METODE LEAST SQUARE DI WILAYAH PERAIRAN ENDE, NUSA TENGGARA TIMUR

Abstrak Telah dilakukan penelitian tentang analisis pasang surut menggunakan metode Least Square di wilayah perairan Ende, Nusa Tenggara Timur. Penelitian ini bertujuan untuk menentukan komponen harmonik pasang surut menggunakan metode Least Square serta menganalisis tipe pasang surut menggunakan bilangan Formzahl. Berdasarkan hasil analisis data, diketahui bahwa komponen pasang surut yaitu M2, S2, N2, K1, O1, Q1 dan tipe pasang surut di perairan Ende termasuk tipe campuran condong keharian ganda (mixed tide prevailing semidiurnal) dengan nilai Formzhal (F) setiap bulannya adalah (0,38), (0,31), (0,25), (0,28), (0,38), (0,44), (0,41), (0,33), (0,25), (0,27) (0,35) dan 0,42. Hasil analisis pasang surut menunjukkan nilai amplitudo harmonik pasang surut ganda utama M2 dan S2 lebih dominan dibandingkan komponen pasang surut tunggal utama K1 dan O1. Kata Kunci: Least Square, Campuran Condong Harian Ganda, Perairan Ende. Abstract Research on tidal analysis has been done using the Least Square method in the sea area surrounding Ende, East Nusa Tenggara. This research aims to determine the components of tidal harmonics using the Least Square method and to analyze the type of tides using Formzhal number. Based on the results of analysis data, it is known that tidal harmonic components are M2, S2, N2, K1, O1, Q1 and the type of tides in Ende sea included mixed type of tide prevailing semidiurnal with Formzhal (F) value of (0.38), (0.31), (0.25), (0.28), (0.38), (0.44), (0.41), (0.33), (0.25), (0.27), (0.35), and 0.42. The results show the amplitude of the main tidal component M2 and S2 is the dominant component in the Ende Sea compared to the main single tidal component K1 and O1. Keywords: Least Square, Mixed Tide Prevailing Semidiurnal, Ende Sea.

Impacts of Sea Level Rise and River Discharge on the Hydrodynamics Characteristics of Jakarta Bay (Indonesia)

Jakarta city has been vulnerable to sea level rise and flooding for many years. A Giant Seawall (GSW) was proposed in Jakarta Bay to protect the city. The impacts of sea level rise and river discharge on the tidal dynamics in Jakarta Bay and flooding areas in Jakarta city were investigated using the finite-volume coastal ocean model (FVCOM). Model results showed that the bay is diurnally dominated by the K1 tidal component. The diurnal tides propagate westward, while the semidiurnal tides propagate eastward in the bay. The rise of sea level increases the diurnal tidal component and the inundation areas due to the increased tidal forcing: when considering a sea level rise of 0.6 m, the K1 amplitude increases by ~1% (0.25 cm) near the coastline and the current magnitude increases by 16.6% (0.05 m/s). The inundation area increases with the sea level rise in the low land elevation areas occurring near the coastlines: the inundation area increased by 29.68 km2 (7.1%) with a sea level rise of 0.6 m. The increase of river discharge amplified the diurnal tidal component as well as the inundation areas at the river mouth due to increased fluvial forcing: if 10 times the mean river discharge occurs, the K1 amplitude increases by ~1% (0.25 cm) and the current magnitude increases by 100% (0.4 m/s), and the inundation areas increase by 26.61 km2 (6.2%). The K1 tidal phase remains almost unchanged under both the sea level rise and river discharge conditions. The combined increase of sea level rise and the river discharge amplifies the inundation areas and the tidal currents due to increased tidal and fluvial forcing. The construction of GSW would decrease the tidal prism and dissipation effects of the bay, thus slightly increasing the K1 amplitude of the tidal level: by less than 1% (0.2 cm). There would be no significant change of phase lag for the K1 component. Although this study is site specific, the findings could be applied more widely to any open-type bays.

Surface currents in the Porsanger fjord in northern Norway

We describe surface currents in the Porsanger fjord (Porsangerfjorden) located in the European Arctic in the vicinity of the Barents Sea. Our analysis is based on surface current data collected in the summer of 2014 using High Frequency (WERA, Helzel Messtechnik GmbH) radar system. One of our objectives was to separate out the tidal from the nontidal components of the currents and to determine the most important tidal constituents. Tides in the Porsanger fjord are substantial, with tidal range on the order of about 3 m. Tidal analysis attributes to tides about 99% of variance in sea level time series recorded in Honningsvaag. The most important tidal component in sea level data is the M2 component, with amplitude of ~90 cm. The S2 and N2 constituents (amplitude of ~20 cm) also play a significant role in the semidiurnal sea level oscillations. The most important diurnal component is K1 with amplitude of about 8 cm. The most important tidal component in analyzed surface currents records is the M2 component. The second most important component is the S2. Our results indicate that in contrast to sea level, only about 10-30% of variance in surface currents can be attributed to tidal currents. This means that about 70-90% of variance is due to wind-induced and geostrophic currents.

Tidal Hydrodynamics in the Lower Columbia River Estuary through Depth Averaged Adaptive Hydraulics Modeling

The adaptive hydraulics (AdH) numerical code was applied to study tidal propagation in the Lower Columbia River (LCR) estuary. The results demonstrate the readiness of this AdH model towards the further study of hydrodynamics in the LCR. The AdH model accurately replicated behavior of the tide as it propagated upstream into the LCR system. Results show that the MSf tidal component and the M4 overtidal component are generated in the middle LCR and contain a substantial amount of tidal energy. An analysis was performed to determine the causes of MSf tide amplification, and it was found that approximately 80% of the amplification occurs due to nonlinear interaction between the M2 and the S2 tidal components.

On the flushing of Port Phillip Bay: an application of HF ocean radar

HF ocean radar can produce maps of surface current in coastal ocean and estuarine waters by providing coverage in both the space and time dimensions. The deployment of COSRAD in Port Phillip Bay for two successive five-day periods provided hourly values of surface currents over the topographically complex area at the south end of the bay. Analysis of the current data provided tidal ellipses for the validation of numerical models, with resultant residual currents of the order of 0·05 m s–1. The repeated hourly maps were the basis for producing Lagrangian tracks; most tracks resulted in trapped paths which remained for long periods of time in the matrix of channels and sand-banks. A ‘tidal run’ technique was developed to calculate the length of Lagrangian tracks over one phase (ebb or flood) of the main tidal component. All tidal runs were about equal to, or shorter than, the length of the relevant channel; this indicates that tidal forcing is not effective in flushing the bay. In contrast, the observed residual currents can be an effective flushing agent if they persist for three days or longer. It is suggested that phenomena on the scale of meteorological to seasonal forcing are the effective flushing agents for Port Phillip Bay.

N₂ and M₂ lunar tides: atmospheric resonance revisited

A numerical model has been used to calculate the atmospheric response to forcing at periods in the region of 12-13.5 h. The results show that the response is enhanced in the neighbourhood of 13 h. These results have been compared with lunar tidal analyses of mesospheric wind data and geomagnetic variations at a number of stations. It is found that the N2 lunar tidal component (period 12.66 h) is significantly enhanced relative to the main lunar tidal component M2 (period 12.42 h) in both types of data, compared with what would be expected from the gravitational tidal potential. This supports the predictions of the numerical model. An appreciable phase shift is also found in the experimental data between the N2 and M2 tides, agreeing in sense with what would be expected for a resonance at a period around 13 h.

Tidal currents in Yell Sound and the outer regions of Sullom Voe

SynopsisCurrents were measured along two routes through Yell Sound to Sullom Voe in the Shetland Islands. Current meter moorings were deployed by the consulting engineers Peter Fraenkell and Partners for one month at 20 positions with three meters which measured the flow from near surface to a depth of 20 metres. The accuracy of these measurements is considered and the difficulty of making measurements in this region is illustrated.The paper discusses the nature and variability of the currents that were measured and resolves the currents into a tidal and non-tidal component. An analysis procedure is developed for removing the tidal component and for producing tidal current vectors for each position. From this the general tidal circulation pattern is constructed and discussed. It is shown that tidal currents along the eastern route are too high at certain states of the tide for safe navigation.Current surges of significant magnitude are shown to exist throughout the area. These are driven by the tidal motion and it is suggested that they are an effect of travelling gyres which are generated in the lee of islands and shallow banks when the tidal streams are largest.