Changes In Tidal Range Research Articles

Impacts of 150 Years of Shoreline and Bathymetric Change in the Coos Estuary, Oregon, USA

Estuaries worldwide have evolved over the past few centuries under development activities like dredging and shoreline reclamation, which commonly lead to increased channel depths and reduced intertidal areas. The Coos Estuary offers a useful example of how these changes, common to diverse global estuaries, have altered tidal and salt dynamics, with implications for estuarine habitats. In the past 150 years, the primary navigation channel has been deepened from ~ 6.7 to 11 m, generating a 12% decrease in estuary area and 21% increase in volume. To evaluate the present and future impacts on the Coos and similar estuaries, a hydrodynamic model was implemented using a detailed bathymetric dataset compiled from multiple data sources including agency charts, water-penetrating lidar, and single-beam-sonar small-vessel surveys. The model was then re-run using grids constructed from 1865 survey data and a future proposed dredging plan. Changes in the hypsometry from 1865 to present have driven a 33% increase in tidal amplitude, an 18% increase in salinity intrusion length, a doubling of the subtidal salt flux, and an increase in ebb dominance of currents. A proposed channel-depth increase from 11 to 14 m is predicted to generate a negligible change in tidal range and a small increase in the salinity intrusion length. These results highlight the utility of curating high-resolution bathymetric datasets for coastal management applications through modeling. The historical and modern models quantify how local bathymetric modifications can significantly alter tidal and salinity regimes and provide context for estuarine response to global climate-change drivers.

Cyclical patterns and (im)mobilization mechanisms of phosphorus in sediments from a small creek estuary: Evidence from in situ monthly sampling and indoor experiments

Internal phosphorus (P) mobility is crucially important to overlying water ecosystems, while its spatiotemporal variations and mechanisms remain to be studied, especially in dynamic estuarine sediments. In this study, in situ monthly field sampling and indoor experiments were combined to measure the soluble reactive P (SRP), soluble Fe and diffusive gradients in thin films (DGT)-labile P/S in the overlying water, sediment and porewater in the Jiuxi River Estuary by employing high-resolution dialysis (HR-Peeper), the DGT technique and a MicroRhizon sampler. The consistent tendency between DGT-labile S and P in most seasons indicates that P mobilization was dominated by intense dissimilatory sulfate reduction (DSR), causing high SRP concentrations and active exchange with the overlying water. The circannual cyclical pattern of P is summarized, where in addition to temperature, monthly changes in runoff and tidal range are crucial external factors to control long-term P cycling via changed redox environments and terrigenous materials inputs. The mobile P, Fe and S present higher values during flood tides and lower values during ebb tides in tidal simulation experiments, demonstrating that the short-term cycling of P, Fe and S in intertidal surface sediments is highly redox-sensitive and controlled by tidal processes. The results also reveal that DSR greatly facilitates P mobility and release, while sediment oxidation and the induced enhancement in DIR and Fe cycling can effectively control P immobilization.

Study of Physical Vulnerability Mapping of the Coastal Areas of North - East Aceh

The coastal physical vulnerability study conducted in the North-East coast region of Aceh, which was focused on the calculation of the physical vulnerability index based on the Coastal Vulnerability Index (CVI) method which was integrated with the Geographic Information System (GIS) to determine the most dominant contribution to coastal vulnerability. The index is calculated based on six variables: geomorphology, coastal erosion, slope, changes in sea level, wave height and tidal range. Basically, the emphasis on methodological aspects is related to: (i) the use of GIS techniques to construct, interpolate, filter, and sample data for shoreline networks, (ii) physical vulnerability calculations using the CVI method approach, and (iii) values CVI is applied in vulnerability maps using the GIS program by providing CVI ratings to three levels, namely low, medium, and high. The results of this study indicate that the coastal physical vulnerability of the North East Aceh region is dominated by a moderate level of vulnerability of 83.61% with 51 sub-districts, and then a low vulnerability of 9.84% with 6 sub-districts, and a high vulnerability of 6.56% with 4 sub-districts out of a total of 61 Districts in 10 Regencies / Cities on the North-East coast of Aceh. According to physical conditions, each variable has the same weight, so that each variable has the same contribution to the vulnerability index of the North-East coastal region of Aceh.

Hydrodynamic time parameters response to meteorological and physical forcings: toward a stagnation risk assessment device in coastal areas

Identifying zones of stagnation and deposition of terrigenous matter or contaminants induced by human activity is a key issue in coastal areas. In this paper, circulation processes and potential contaminant stagnation and deposition zones were assessed using hydrodynamic time parameters forced with meteorology. The study focused on an Eulerian time parameter, the local e-flushing time (eFT). The hydrodynamic modeling of coastal zones was applied to two bays of New Caledonia, located downstream of open mining sites. Numerous simulations were performed to classify the influence of forcing conditions on the eFT variability. The need to consider meteorological forcings rather than average weather conditions for the calculation of eFTs was demonstrated. In coastal zones, high wind velocity was the major forcing influencing eFTs, but below a threshold wind velocity, tidal range and river inputs became significant parameters. Spatial variations of eFT values, depending on meteorological conditions, induced varying risks of stagnation zones. General responses of the bays’ hydrodynamics and the exposure of zones to potential contaminants were defined under various forcings. Our findings demonstrate that strong turbulence zones are not always characterized by short eFTs because of antagonistic forcing effects. Diurnal tidal alternations were also proven to have less influence on eFT variations than tidal range changes over a lunar cycle.

PHYSICAL IMPACT OF SEA LEVEL RISE TO THE COASTAL ZONE ALONG THE EAST COAST OF PENINSULAR MALAYSIA

Sea level rise around the world caused by global warming since decade and effects on coastal especially country below mean sea level and country island. The prediction of sea level rise by 2100 is over 3m. Sea level rise increases caused by melting ice and thermal expansion. The impact of sea level rise concentrated along the coastal area. This paper studied the impact of sea level rise to physical parameters along the East Coast of Peninsular Malaysia. Seven physical variables such as geomorphology, shoreline change rate, coastal slope, lithology, maximum wave height, mean tidal range and sea level change were chosen to find an physical vulnerability index. The index also was mapped using ArcGIS software to picture the vulnerability. The worst area for physical vulnerability index is along the Pahang coastline especially Kuantan district. The prevention and adaptation from government and nongovernment agencies should be taken to reduce the effects of sea level rise.

Assessing changes of mangrove forest in a coastal region of southeast China using multi-temporal satellite images

Mangroves provide many ecological, economic, and social benefits to humans. In the Jiulong River Estuary of Fujian Province, China, many mangroves have been lost largely due to human activities and so artificial planting has been implemented. However, the spatial and temporal dynamics of mangrove forests are still largely unknown at this location. This study aimed to identify changes to mangrove distribution and aboveground biomass (AGB) in three periods (1995–2004, 2004–2014 and 1995–2014) in order to influence mangrove management. Landsat satellite imagery and the threshold value method were used to classify mangroves. Landsat satellite imagery, field-based biomass investigations, elevation data and an allometric biomass equation were employed to develop an AGB model using a multiple linear regression method. Both mangrove area and AGB increased from 1995 to 2014 with an increase rate of 5.5% and 7.2% for mangrove area and AGB, respectively. Mangrove expansion was the main cause for AGB and area increase. In addition, AGB increase due to the growth of mangroves without extending the area also has great potential in AGB increase. Similar to AGB, above-ground carbon increased from 57 t C/ha in 1995 to 79 t C/ha in 2014, which demonstrated that mangroves in this region can help to mitigate climate warming. However, a large-scale continuous decrease of mangrove forest in the JRE was observed, likely caused by growing human activities. Moreover, tidal range change during 2004–2014 resulted in a more adverse impact on mangroves.

Deformations of Land, Sea and Gravity Levels by the 2009 Samoa Earthquake

The Samoa Islands were struck by the September 2009 earthquake of Mw 8.1. We study the effect on the land level by means of GPS monitoring and on ocean level by tide-gauge records. This allows us to present a new picture of the interaction of crustal movements, gravitational adjustment and sea level changes. The land level exhibits a co-seismic uplift followed by a post-seismic crustal subsidence. The ocean level records a fall, significantly larger than the uplift and delayed by several months, followed by a significant rise, by far exceeding the crustal subsidence and delayed by several months. This indicates a significant contribution from changes in gravity (geoidal eustasy), besides relative sea level changes due to crustal movements. High amplitude, and high frequency changes in tidal range provide evidence of changes in gravity and geoidal eustasy.

Coupling of sea level and tidal range changes, with implications for future water levels

Are perturbations to ocean tides correlated with changing sea-level and climate, and how will this affect high water levels? Here, we survey 152 tide gauges in the Pacific Ocean and South China Sea and statistically evaluate how the sum of the four largest tidal constituents, a proxy for the highest astronomical tide (HAT), changes over seasonal and interannual time scales. We find that the variability in HAT is significantly correlated with sea-level variability; approximately 35% of stations exhibit a greater than ±50 mm tidal change per meter sea-level fluctuation. Focusing on a subset of three stations with long records, probability density function (PDF) analyses of the 95% percentile exceedance of total sea level (TSL) show long-term changes of this high-water metric. At Hong Kong, the increase in tides significantly amplifies the risk caused by sea-level rise. Regions of tidal decrease and/or amplification highlight the non-linear response to sea-level variations, with the potential to amplify or mitigate against the increased flood risk caused by sea-level rise. Overall, our analysis suggests that in many regions, local flood level determinations should consider the joint effects of non-stationary tides and mean sea level (MSL) at multiple time scales.

Tides in the Last Interglacial: insights from notch geometry and palaeo tidal models in Bonaire, Netherland Antilles

The study of past sea levels relies largely on the interpretation of sea-level indicators. Palaeo tidal notches are considered as one of the most precise sea-level indicators as their formation is closely tied to the local tidal range. We present geometric measurements of modern and palaeo (Marine Isotope Stage (MIS) 5e) tidal notches on Bonaire (southern Caribbean Sea) and results from two tidal simulations, using the present-day bathymetry and a palaeo-bathymetry. We use these two tools to investigate changes in the tidal range since MIS 5e. Our models show that the tidal range changes most significantly in shallow areas, whereas both, notch geometry and models results, suggest that steeper continental shelves, such as the ones bordering the island of Bonaire, are less affected to changes in tidal range in conditions of MIS 5e sea levels. We use our data and results to discuss the importance of considering changes in tidal range while reconstructing MIS 5e sea level histories, and we remark that it is possible to use hydrodynamic modelling and notch geometry as first-order proxies to assess whether, in a particular area, tidal range might have been different in MIS 5e with respect to today.

Local adaptation along an environmental cline in a species with an inversion polymorphism

Polymorphic inversions are ubiquitous across the animal kingdom and are frequently associated with clines in inversion frequencies across environmental gradients. Such clines are thought to result from selection favouring local adaptation; however, empirical tests are scarce. The seaweed fly Coelopa frigida has an α/β inversion polymorphism, and previous work demonstrated that the α inversion frequency declines from the North Sea to the Baltic Sea and is correlated with changes in tidal range, salinity, algal composition and wrackbed stability. Here, we explicitly test the hypothesis that populations of C.frigida along this cline are locally adapted by conducting a reciprocal transplant experiment of four populations along this cline to quantify survival. We found that survival varied significantly across treatments and detected a significant Location x Substrate interaction, indicating local adaptation. Survival models showed that flies from locations at both extremes had highest survival on their native substrates, demonstrating that local adaptation is present at the extremes of the cline. Survival at the two intermediate locations was, however, not elevated at the native substrates, suggesting that gene flow in intermediate habitats may override selection. Together, our results support the notion that population extremes of species with polymorphic inversions are often locally adapted, even when spatially close, consistent with the growing view that inversions can have direct and strong effects on the fitness of species.

Impact of sea level rise on tidal range in Chesapeake and Delaware Bays

AbstractCoastal inundation is affected not only by rising mean sea level but also by changing tides. A numerical model is developed to investigate how sea level rise and coastline changes may impact tides in two coastal‐plain estuaries, Chesapeake Bay and Delaware Bay. Despite their different tidal characteristics, the two estuaries display similar responses to the sea level rise and shoreline management scenarios. When hypothetic sea walls are erected at the present coastline to prevent low‐lying land from flooding, tidal range increases, with greater amplification in the upper part of the two estuaries. When low‐lying land is allowed to become permanently inundated by higher sea level, however, tidal range in both estuaries decreases. Analyses of the tidal energy budget show that the increased dissipation over the shallow water and newly inundated areas compensates for the reduced dissipation in deep water, leading to smaller tidal range. The changes in the tidal range are not proportional to the changes in the mean sea level, indicating a nonlinear tidal response to sea level rise. The ratio of tidal range change to sea level rise varies between −0.05 and 0.1 in Chesapeake Bay and between −0.2 and 0.25 in Delaware Bay. The model results suggest a potential adaptation strategy that uses inundation over low‐lying areas to reduce tidal range at up‐estuary locations.

Relative sea-level trends in New York City during the past 1500 years

New York City (NYC) is threatened by 21st-century relative sea-level (RSL) rise because it will experience a trend that exceeds the global mean and has high concentrations of low-lying infrastructure and socioeconomic activity. To provide a long-term context for anticipated trends, we reconstructed RSL change during the past ~1500 years using a core of salt-marsh sediment from Pelham Bay in The Bronx. Foraminifera and bulk-sediment δ13C values were used as sea-level indicators. The history of sediment accumulation was established by radiocarbon dating and recognition of pollution and land-use trends of known age in down-core elemental, isotopic, and pollen profiles. The reconstruction was generated within a Bayesian hierarchical model to accommodate multiple proxies and to provide a unified statistical framework for quantifying uncertainty. We show that RSL in NYC rose by ~1.70 m since ~575 CE (including ~0.38 m since 1850 CE). The rate of RSL rise increased markedly at 1812–1913 CE from ~1.0 to ~2.5 mm/yr, which coincides with other reconstructions along the US Atlantic coast. We investigated the possible influence of tidal-range change in Long Island Sound on our reconstruction using a regional tidal model, and we demonstrate that this effect was likely small. However, future tidal-range change could exacerbate the impacts of RSL rise in communities bordering Long Island Sound. The current rate of RSL rise is the fastest that NYC has experienced for >1500 years, and its ongoing acceleration suggests that projections of 21st-century local RSL rise will be realized.

Drivers of Holocene sea-level change in the Caribbean

Abstract We present a Holocene relative sea-level (RSL) database for the Caribbean region (5°N to 25°N and 55°W to 90°W) that consists of 499 sea-level index points and 238 limiting dates. The database was compiled from multiple sea-level indicators (mangrove peat, microbial mats, beach rock and acroporid and massive corals). We subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on RSL. We account for the local-scale processes of sediment compaction and tidal range change using the stratigraphic position (overburden thickness) of index points and paleotidal modeling, respectively. We use a spatio-temporal empirical hierarchical model to estimate RSL position and its rates of change in the Caribbean over 1-ka time slices. Because of meltwater input, the rates of RSL change were highest during the early Holocene, with a maximum of 10.9 ± 0.6 m/ka in Suriname and Guyana and minimum of 7.4 ± 0.7 m/ka in south Florida from 12 to 8 ka. Following complete deglaciation of the Laurentide Ice Sheet (LIS) by ∼7 ka, mid-to late-Holocene rates slowed to

Spatial and Temporal Variability in Tidal Range: Evidence, Causes, and Effects

Tidal range is one factor in determining the vertical location of local mean sea level, and it is also a contributor to total water levels and coastal flooding. It is therefore important to understand both the spatial distribution of tidal range and the temporal variation in tidal range, over a wide range of scales. Knowledge of historic tidal range is obtained both through observations and through modeling. This paper reviews numerous observational and modeling studies of historic tidal range variations on decadal to millennial timescales. It also discusses many of the physical processes that are responsible for these variations. Finally, this paper concludes with discussion of several modeling studies that seek to constrain future changes in tidal range in coastal environments.

Small-scale benthos distribution modelling in a North Sea tidal basin in response to climatic and environmental changes (1970s-2009)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 551:13-30 (2016) - DOI: https://doi.org/10.3354/meps11756 Small-scale benthos distribution modelling in a North Sea tidal basin in response to climatic and environmental changes (1970s-2009) A. Singer1,2,*, U. Schückel1, M. Beck3, O. Bleich4, H.-J. Brumsack3, H. Freund3, C. Geimecke5, K. A. Lettmann3, G. Millat6, J. Staneva5, A. Vanselow3, H. Westphal7, J.-O. Wolff3, A. Wurpts7, I. Kröncke1 1Senckenberg am Meer, Dept. for Marine Research, Südstrand 40, 26382 Wilhelmshaven, Germany 2INTERCOAST Research Training Group, University of Bremen, Leobener Strasse, 26359 Bremen, Germany 3Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany 4Fraunhofer Institute for Wind Energy and Energy System Technology, Am Seedeich 45, 27572 Bremerhaven, Germany 5Helmholtz-Centre Geesthacht (HZG), Max-Planck-Straße 1, 21502 Geesthacht, Germany 6National Park Administration Wadden Sea Lower Saxony (NLPV), Virchowstraße 1, 26382 Wilhelmshaven, Germany 7Coastal Research Station - Lower Saxony Water Management, Coastal Defence and Nature Conservation Agency (NLWKN), An der Mühle 5, 26548 Norderney, Germany *Corresponding author: anja.singer@senckenberg.de ABSTRACT: We used small-scale species distribution models to predict the past and present spatial distribution of 7 characteristic macrofauna species in response to climatic and environmental changes that have been recorded for the Jade Bay (German Wadden Sea) over the last 4 decades (1970s to 2009). Four presence-absence modelling algorithms (RF, MARS, GLM, GBM) were merged within the ensemble forecasting platform ‘biomod2’. The present spatial distribution (representing 2009) was modelled based on statistical relationships between species presences, true species absences and 7 high-resolution (5 m) environmental grids. The past spatial distribution (representing the 1970s) was then hindcast in response to climate change-induced (1) sea-level rise, (2) water temperature increase and (3) seagrass recovery due to de-eutrophication. The past distribution scenario was evaluated using independent historical macrofauna data from the 1970s. Present ensemble prediction maps accurately captured the potential ecological niches of the modelled species throughout Jade Bay (i.e. good to excellent true skill statistic [TSS] and area under the receiver operating characteristic curve [AUC] evaluation measures). The predicted present macrofauna distribution correlated most significantly with hydrodynamic conditions (submergence time, shear stress) and sediment characteristics (mud content). The past distribution scenario revealed significant changes in small-scale spatial distribution patterns of the characteristic modelled species (1970s to 2009) and showed a very good match with historical macrofauna data. Climate change-induced sea-level rise and its local implications for Jade Bay (changes in topography, tidal range and submergence time), and water temperature increase explained the potential macrofauna distribution shifts over the last 4 decades. KEY WORDS: Ensemble models · Hindcasting · Sea-level rise · Water temperature increase · Wadden Sea World Heritage Site · Seagrass recovery · Marine ecosystems · Benthos Full text in pdf format Supplementary material PreviousNextCite this article as: Singer A, Schückel U, Beck M, Bleich O and others (2016) Small-scale benthos distribution modelling in a North Sea tidal basin in response to climatic and environmental changes (1970s-2009). Mar Ecol Prog Ser 551:13-30. https://doi.org/10.3354/meps11756 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 551. Online publication date: June 09, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Relative sea-level change in northeastern Florida (USA) during the last ∼8.0 ka

An existing database of relative sea-level (RSL) reconstructions from the U.S. Atlantic coast lacked valid sea-level index points from Georgia and Florida. This region lies on the edge of the collapsing forebulge of the former Laurentide Ice Sheet making it an important location for understanding glacio-isostatic adjustment and the history of ice-sheet melt. To address the paucity of data, we reconstruct RSL in northeastern Florida (St. Marys) over the last ∼8.0 ka from samples of basal salt-marsh sediment that minimize the influence of compaction. The analogy between modern salt-marsh foraminifera and their fossil counterparts preserved in the sedimentary record was used to estimate paleomarsh surface elevation. Sample ages were determined by radiocarbon dating of identifiable and in-situ plant macrofossils. This approach yielded 25 new sea-level index points that constrain a ∼5.7 m rise in RSL during the last ∼8.0 ka. The record shows that no highstand in sea level occurred in this region over the period of the reconstruction. We compared the new reconstruction to Earth-ice models ICE 6G-C VM5a and ICE 6G-C VM6. There is good fit in the later part of the Holocene with VM5a and for a brief time in the earlier Holocene with VM6. However, there are discrepancies in model-reconstruction fit in the early to mid Holocene in northeastern Florida and elsewhere along the Atlantic coast at locations with early Holocene RSL reconstructions. The most pronounced feature of the new reconstruction is a slow down in the rate of RSL rise from approximately 5.0 to 3.0 ka. This trend may reflect a significant contribution from local-scale processes such as tidal-range change and/or change in base flow of the St. Marys River in response to paleoclimate changes. However, the spatial expression (local vs. regional) of this slow down is undetermined and corroborative records are needed to establish its geographical extent.

Sea-level change and subsidence in the Delaware Estuary during the last ∼2200 years

We produced eight new sea-level index points that reconstruct a ∼2.5 m relative sea-level (RSL) rise at Sea Breeze in the Delaware Bay from ∼200 BCE to 1800 CE. The precision of our reconstruction improved upon existing data by using high-resolution surveying methods, AMS radiocarbon dating of in-situ plant macrofossils collected immediately above the basal contact between pre-Holocene sand and salt-marsh sediments, foraminifera as sea-level indicators, and by accounting for tidal range changes through time. Our new data were combined with a database of 65 sea-level index points available for the Delaware Bay to estimate the rate of RSL rise in the upper (1.26 ± 0.33 mm/yr) and lower bay (1.30 ± 0.36 mm/yr) using a spatial-temporal model. Correction for changes in tidal range through time removed the disparity in rate between the upper and lower Delaware Bay that had previously been postulated. After paleotidal correction, the rates of RSL rise estimated for the Delaware Bay (1.25 ± 0.27 mm/yr) correlate with the ∼1.3 mm/yr rate reported for New Jersey, Maryland, and Virginia, and confirm that the maximal ongoing forebulge collapse along the U.S. Atlantic coast is focused on the mid-Atlantic.

Global secular changes in different tidal high water, low water and range levels

AbstractTides exert a major control on the coastal zone by influencing high sea levels and coastal flooding, navigation, sediment dynamics, and ecology. Therefore, any changes to tides have wide ranging and important implications. In this paper, we uniquely assess secular changes in 15 regularly used tidal levels (five high water, five low water and five tidal ranges), which have direct practical applications. Using sea level data from 220 tide gauge sites, we found changes have occured in all analyzed tidal levels in many parts of the world. For the tidal levels assessed, between 36% and 63% of sites had trends significantly different (at 95% confidence level) from zero. At certain locations, the magnitude of the trends in tidal levels were similar to trends in mean sea level over the last century, with observed changes in tidal range and high water levels of over 5 mm yr−1 and 2 mm yr−1, respectively. More positive than negative trends were observed in tidal ranges and high water levels, and vice versa for low water levels. However we found no significant correlation between trends in mean sea level (MSL) and any tidal levels. Spatially coherent trends were observed in some regions, including the north‐east Pacific, German Bight and Australasia, and we also found that differences in trends occur between different tidal levels. This implies that analyzing different tidal levels is important. Because changes in the tide are widespread and of similar magnitude to MSL rise at a number sites, changes in tides should be considered in coastal risk assessments.

Global changes in mean tidal high water, low water and range

ABSTRACT Mawdsley, R.J., Haigh, I.D., Wells, N.C., 2014. Global changes in tidal high water, low water and range. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 343–348, ISSN 0749-0208. Impacts of extreme sea levels are increasing as the population and infrastructure in coastal zones increases. Extreme high sea levels generally increased at a similar rate to mean sea level through the twentieth century at most sites around the world, suggesting that the same mechanisms are driving both increases. However, the simplicity of this conclusion belies the fact that many mechanisms known to act on the different components of sea level, have been observed to change in local and regional studies. Using a ‘quasi-global’ dataset of sea level records, this paper investigates changes in the tidal component of sea level and shows that changes in mean high and low waters, and hence tidal range, are...

Effects of Entrance Constriction and Ocean Forcing on Waterlevels in an Unregulated Tidal Inlet

Long period waterlevel variations, from 14 d to 1 yr, are examined for Hamanako, a tidal inlet on the Pacific coast of Honshu, Japan. Eleven years of records, prior to the regulation of the entrance to the inlet, are analyzed. At all the frequencies examined there were substantial fluctuations, some periodic and some irregular. Dominant features were abrupt changes in mean waterlevel and tidal range, and regular 14 d and 28 d cycles in most years. These cycles have been related to the role of the entrance constriction in generating spring-tidal pumping (STP). The rapid changes in tidal amplitude and mean waterlevel are explained in terms of changes in the hydraulic resistance of the entrance and have been correlated with outflows from the tidal lagoon caused by typhoons and catchment runoff. An annual cycle of amplitude 12.5 cm has been explained in terms of the annual cycle of the Kuroshio. Novel features of this study are the extensions to conventional time series analysis, and showing that the 14 d periodic fluctuations were caused by STP and that this process also contributed to the 28 d fluctuations. STP is invariably present in estuaries with a shallow inlet but is rarely identified; this paper shows methods to evaluate it and other long period components of the waterlevel record.