Tidal Duration Research Articles

Tidal asymmetry in a funnel-shaped estuary with mixed semidiurnal tides

Different types of tidal asymmetry (see review of de Swart and Zimmerman Annu Rev Fluid Mech 41: 203–229, 2009) are examined in this study. We distinguish three types of tidal asymmetry: duration and magnitude differences between flood and ebb tidal flow, duration difference between the rising and falling tides. For waterborne substance transport, the first two asymmetries are important while the last one is not. In this study, we take the Huangmaohai Estuary (HE), Pearl River Delta, China as an example to examine the spatio-temporal variations of the tidal asymmetry in a mixed semidiurnal tidal regime and to explain them by investigating the associated mechanisms. The methodology defining the tidal duration asymmetry and velocity skewness, proposed by Nidzieko (J Geophys Res 115: C08006. doi: 10.1029/2009JC005864, 2010) and synthesized by Song et al. (J Geophys Res 116: C12007. doi: 10.1029/2011JC007270, 2011), is utilized here and referred to as tidal duration asymmetry (TDA) and flow velocity asymmetry (FVA), respectively. The methodology is further used to quantify the flow duration asymmetry (FDA). A positive asymmetry means a shorter duration of low water slack for FDA, a shorter duration of the rising tide for TDA, and a flood dominance for FVA and vice versa. The Regional Ocean Modeling System (ROMS) model is used to provide relatively long-term water elevation and velocity data and to conduct diagnostic experiments. In the HE, the main tidal constituents are diurnal tides K 1, O 1 and semidiurnal tides M 2 and S 2. The interaction among the diurnal and semidiurnal tides generates a negative tidal asymmetry, while the interactions among semidiurnal tides and their overtides or compound tides result in a positive tidal asymmetry. The competition among the above interactions determines the FDA and TDA, whereas for the FVA, aside from the interaction among different tidal constituents, an extra component, the residual flow, plays an important role. The results show that the FDA exhibits a predominant tendency of shorter duration of low water slack, favoring the landward transport of fine sediment. The FVA demonstrates prevailing ebb dominance in the study period, favoring the seaward transport of coarse sediment. This ebb dominance is primarily induced by the interaction among the residual flow and the tidal constituents. The external TDA in the ocean experiences distinct cyclic variations with positive asymmetry when semidiurnal tides dominate and negative asymmetry during the periods when diurnal tides dominate. The funnel shape of the HE is advantageous for the development of positive tidal asymmetry as the semidiurnal tides are more amplified than the diurnal tides. The effect of river flow can enhance the ebb dominance, while the baroclinic effect is more complex. The existence of channel and shoals favors the development of residual pattern with seaward flow (ebb dominance) in the channel and landward flow (flood dominance) at the shoal when the tides are strong (semidiurnal tides dominate) and the residual pattern with landward flow (flood dominance) in the channel and seaward flow (ebb dominance) at the shoal when the baroclinic effect is dominant (diurnal tides dominate).

Application of geospatial models to map potential Ruditapes philippinarum habitat using remote sensing and GIS

This study applied geographic information system (GIS)-based models to map the potential Ruditapes philippinarum (Korean littleneck clam) habitat area in the Geunso Bay tidal flat, Korea. Remote-sensing techniques were used to construct spatial datasets of ecological environments, and field observations were undertaken to determine the distribution of macrobenthos. The mapping of potential habitat was completed and eight controlling factors relating to the distribution of tidal macrobenthos were determined. These were the tidal flat digital elevation model, slope, aspect, tidal annual exposure duration, distance from tidal channels, tidal channel density, spectral reflectance of the near-infrared bands, and surface sedimentary types, which were all generated from satellite imagery. The spatial relationships between the distribution of R. philippinarum and each control factor were calculated using a frequency ratio, logistic regression, and artificial neural networks combined with GIS data. Individuals were randomly divided into a training set (50%) to analyse habitat potential using the frequency ratio, logistic regression, and artificial neural network models, and a test set (50%) to validate the predicted habitat potential map. The relationships were overlaid to produce a potential habitat map with a R. philippinarum habitat potential (RPHP) index value. These maps were validated by comparing them to surveyed habitat locations such as those in the validation data set. From the validation results, the frequency ratio model showed prediction accuracy of 82.88%, while the accuracy of the logistic regression and artificial neural networks models was 70.77% and 80.45%, respectively. Thus, the frequency ratio model provided a more accurate prediction than the other models. Our data demonstrate that frequency ratio, logistic regression, and artificial neural networks models based on GIS analysis are effective for generating potential habitat maps of R. philippinarum species in a tidal flat. The results of this study will be useful for conserving and managing the macrofauna of tidal flats.

A method to identify the boundary between rocky and gaseous exoplanets from tidal theory and transit durations

AbstractThe determination of an exoplanet as rocky is critical for the assessment of planetary habitability. Observationally, the number of small-radius, transiting planets with accompanying mass measurements is insufficient for a robust determination of the transitional mass or radius. Theoretically, models predict that rocky planets can grow large enough to become gas giants when they reach ~10 MEarth, but the transitional mass remains unknown. Here I show how transit data, interpreted in the context of tidal theory, can reveal the critical radius that separates rocky and gaseous exoplanets. Standard tidal models predict that rocky exoplanets’ orbits are tidally circularized much more rapidly than gaseous bodies’, suggesting the former will tend to be found on circular orbits at larger semi-major axes than the latter. Well-sampled transits can provide a minimum eccentricity of the orbit, allowing a measurement of this differential circularization. I show that this effect should be present in the data from the Kepler spacecraft, but is not apparent. Instead, it appears that there is no evidence of tidal circularization at any planetary radius, probably because the publicly-available data, particularly the impact parameters, are not accurate enough. I also review the bias in the transit duration towards values that are smaller than that of planets on circular orbits, stressing that the azimuthal velocity of the planet determines the transit duration. The ensemble of Kepler planet candidates may be able to determine the critical radius between rocky and gaseous exoplanets, tidal dissipation as a function of planetary radius, and discriminate between tidal models.

A numerical study on the impact of tidal waves on the storm surge in the north of Liaodong Bay

A storm surge is an abnormal sharp rise or fall in the seawater level produced by the strong wind and low pressure field of an approaching storm system. A storm tide is a water level rise or fall caused by the combined effect of the storm surge and an astronomical tide. The storm surge depends on many factors, such as the tracks of typhoon movement, the intensity of typhoon, the topography of sea area, the amplitude of tidal wave, the period during which the storm surge couples with the tidal wave. When coupling with different parts of a tidal wave, the storm surges caused by a typhoon vary widely. The variation of the storm surges is studied. An once-in-a-century storm surge was caused by Typhoon 7203 at Huludao Port in the north of the Liaodong Bay from July 26th to 27th, 1972. The maximum storm surge is about 1.90 m. The wind field and pressure field used in numerical simulations in the research were derived from the historical data of the Typhoon 7203 from July 23rd to 28th, 1972. DHI Mike21 is used as the software tools. The whole Bohai Sea is defined as the computational domain. The numerical simulation models are forced with sea levels at water boundaries, that is the tide along the Bohai Straits from July 18th to 29th (2012). The tide wave and the storm tides caused by the wind field and pressure field mentioned above are calculated in the numerical simulations. The coupling processes of storm surges and tidal waves are simulated in the following way. The first simulation start date and time are 00:00 July 18th, 2012; the second simulation start date and time are 03:00 July 18th, 2012. There is a three-hour lag between the start date and time of the simulation and that of the former one, the last simulation start date and time are 00:00 July 25th, 2012. All the simulations have a same duration of 5 days, which is same as the time length of typhoon data. With the first day and the second day simulation output, which is affected by the initial field, being ignored, only the 3rd to 5th day simulation results are used to study the rules of the storm surges in the north of the Liaodong Bay. In total, 57 cases are calculated and analyzed, including the coupling effects between the storm surge and a tidal wave during different tidal durations and on different tidal levels. Based on the results of the 57 numerical examples, the following conclusions are obtained: For the same location, the maximum storm surges are determined by the primary vibration (the storm tide keeps rising quickly) duration and tidal duration. If the primary vibration duration is a part of the flood tidal duration, the maximum storm surge is lower (1.01, 1.05 and 1.37m at the Huludao Port, the Daling Estuary and the Liaohe Estuary respectively). If the primary vibration duration is a part of the ebb tidal duration, the maximum storm surge is higher (1.92, 2.05 and 2.80 m at the Huludao Port, the Daling Estuary and the Liaohe Estuary respectively). In the mean time, the sea level restrains the growth of storm surges. The hour of the highest storm tide has a margin of error of plus or minus 80 min, comparing the high water hour of the astronomical tide, in the north of the Liaodong Bay.

Tidal variations in the Sundarbans Estuarine System, India

Situated in the eastern coastal state of West Bengal, the Sundarbans Estuarine System (SES) is India’s largest monsoonal, macro-tidal delta-front estuarine system. It comprises the southernmost part of the Indian portion of the Ganga–Brahmaputra delta bordering the Bay of Bengal. The Sundarbans Estuarine Programme (SEP), conducted during 18–21 March 2011 (the Equinoctial Spring Phase), was the first comprehensive observational programme undertaken for the systematic monitoring of the tides within the SES. The 30 observation stations, spread over more than 3600 km2, covered the seven inner estuaries of the SES (the Saptamukhi, Thakuran, Matla, Bidya, Gomdi, Harinbhanga, and Raimangal) and represented a wide range of estuarine and environmental conditions. At all stations, tidal water levels (every 15 minutes), salinity, water and air temperatures (hourly) were measured over the six tidal cycles. We report the observed spatio-temporal variations of the tidal water level. The predominantly semi-diurnal tides were observed to amplify northwards along each estuary, with the highest amplification observed at Canning, situated about 98 km north of the seaface on the Matla. The first definite sign of decay of the tide was observed only at Sahebkhali on the Raimangal, 108 km north of the seaface. The degree and rates of amplification of the tide over the various estuarine stretches were not uniform and followed a complex pattern. A least-squares harmonic analysis of the data performed with eight constituent bands showed that the amplitude of the semi-diurnal band was an order of magnitude higher than that of the other bands and it doubled from mouth to head. The diurnal band showed no such amplification, but the amplitude of the 6-hourly and 4-hourly bands increased headward by a factor of over 4. Tide curves for several stations displayed a tendency for the formation of double peaks at both high water (HW) and low water (LW). One reason for these double-peaks was the HW/LW stands of the tide observed at these stations. During a stand, the water level changes imperceptibly around high tide and low tide. The existence of a stand at most locations is a key new finding of the SEP. We present an objective criterion for identifying if a stand occurs at a station and show that the water level changed imperceptibly over durations ranging from 30 minutes to 2 hours during the tidal stands in the SES. The tidal duration asymmetry observed at all stations was modified by the stand. Flow-dominant asymmetry was observed at most locations, with ebb-dominant asymmetry being observed at a few locations over some tidal cycles. The tidal asymmetry and stand have implications for human activity in the Sundarbans. The longer persistence of the high water level around high tide implies that a storm surge is more likely to coincide with the high tide, leading to a greater chance of destruction. Since the stands are associated with an amplification of the 4-hourly and 6-hourly constituents, storm surges that have a similar period are also likely to amplify more during their passage through the SES.

Hydraulics Characteristics of the Close Gap in Large-Scale Beach Reclamation Works in Radial Sandbanks

By the2-D tidal flow mathematical model, Calculation and analysis of hydraulics r Characteristics of the Longkou ine LV four port rcclamaiton project;and the relationship between the fill area and the width of of longkou. Research shows that, after the completion of an embankment, with the inning area fill, Longkou velocity gradually decreases. In I, II area harbor dam is formed, When the fill range from Longkou 1km ,and the Long kou width is reduced to 50m, I, II zone Longkou maximum velocity were 1.42m /s、1.54m / s, can meet the requirements of the closure gap.when III area harbor dam formed,if the fill maximum range from Longkou 1km, then closure-gap width at least to maintain 200m; for closure-gap width below 100m, then in the north and south area at the same time need to built bank. The ebb tide duration of the Longkou greater than the flood tidal duration;during the ebb tide, flow velocity basically stable, relatively small, Longkou closure should be selected during low tide and the low tide period.

Environmental Reviews and Case Studies: Restoring a Salt Marsh in a Highly Urbanized Environment of New York City: The Alley Park Restoration Project

The success of urban salt marsh restoration depends upon an understanding of the local tidal regime and hydrologic conditions. Reference wetland characteristics can provide biological and physical restoration baselines for a restoration design through the use of techniques such as bio-benchmarking and geomorphologic assessment. Reference site vegetation can be used as indirect indicators of local tidal elevations and duration of flooding of each tidal zone. Reference sites can also provide landscape allometry to generate geomorphologic ratios that can be applied to the restoration site. Through the use of field measurements, aerial photographs, and GIS technology, relationships can be identified for tidal channel width, depth, diurnal tidal prism, and marsh area. Calculating a hydrologic budget for freshwater is critical to estimate salinity concentrations and their effect on the restoration wetland. This information, along with field measurements of salinity, can be used to predict salinity ranges result...

Modeling the erosion of cohesive clay coasts

A model was developed to study the erosion of cohesive clay coasts in macro- to non-tidal environments. The model shares some of the characteristics of previous models, including the erosion of bare clay surfaces by wave generated bottom shear stresses, and of mobile, sediment-covered surfaces by abrasion. It differs from previous models, however, in several important ways. The morphodynamics of beaches with clay foundations, under different wave conditions, are based on a previously developed model for beaches on rocky shore platforms. Sediment thickness along a beach profile is calculated at regular intervals and compared with the maximum thickness that could be moved at that location under prevailing wave conditions. Wave friction factors are determined, where necessary, according to the occurrence and morphology of ripples on the bottom. In addition to abrasion and the effect of wave induced shear stresses on the clay bottom, erosion by stresses generated by wave impact at the bluff foot and on the intertidal platform is calculated using an expression derived from hard rock coastal models. Tides are represented by their computed tidal duration values, the amount of time each year that the water level falls within each 0.1 m vertical interval. Water depths are modified by wave setup and set-down conditions. Several preliminary model runs were made. The profiles were concave in the submarine zone and roughly linear in the intertidal zone. Equilibrium profiles developed which were maintained as they migrated landwards.

Impacts of the large amount of sand mining on riverbed morphology and tidal dynamics in lower reaches and delta of the Dongjiang River

The sand dredging and its impacts on riverbed evolution and tidal dynamic change in the lower reaches and delta of the Dongjiang River are examined in this paper. The large amount of sand, totally 3.32 billion m3 from 1980 to 2002, was mined from the riverbeds of the lower reaches and delta of the Dongjiang River. Increasing of the channel capacity, lowering of the average riverbed elevation, deepening of the water depth and decreasing of the longitudinal riverbed gradient are the main effects on the riverbed evolution brought by the large amount of sand dredging. Under the strong sand dredging and associated significant riverbed deformation, the notable changes of the tidal dynamic in the lower reaches and delta of the Dongjiang River occurred, including: (1) in the upper reaches of the Dongjiang River delta and lower reaches of the Dongjiang River, tidal level dropped apparently, tidal range widened, flood tidal duration became longer, amplitudes for major tidal components became bigger and tidal dynamics intensified; (2) tidal wave spread faster; and (3) the limits of the tidal level, tidal current and salt water moved upstream.

Nonchemical elimination of inspiratory motor output via mechanical ventilation in sleep.

In six dogs studied in nonrapid eye movement (NREM) sleep, we found that the frequency, volume, and timing of application of mechanical ventilator breaths had marked and sustained inhibitory effects on diaphragm electromyogram (EMG(di)). Single ventilator breaths of tidal volume (VT) 75-200% of control caused apnea (up to three times eupneic expiratory time [TE]) when applied during the initial 25-65% of expiratory time. When continuous controlled mechanical ventilation (CMV) was applied with ventilator frequency increased as little as 1 cycle/min > eupnea and Pa(CO(2)) and VT maintained at near eupneic control levels, EMG(di) was silenced and triangularis sterni EMG (EMG(ts)) became tonic within 2 to 5 ventilator cycles. On cessation of normocapnic CMV, apnea ensued with TE ranging from 1.2 to five times eupneic TE. The spontaneous VT and EMG(di) determined immediately after these prolonged apneas were also markedly reduced in amplitude. The larger the VT applied during the isocapnic CMV (120-200% of eupnea) and the longer the duration of the CMV (3-90 s), the longer the duration of the postventilator apnea. Significant postventilator apneas and postapneic hypoventilation also occurred even when end-tidal CO(2) pressure (PET(CO(2))) was raised 3-5 mm Hg > eupnea (and 7-10 mm Hg > normal apneic threshold) throughout CMV trials at raised frequency and VT. Our findings demonstrate that the increased frequency of CMV was critical to the elimination of inspiratory motor output and the onset of tonic expiratory muscle activity; furthermore, once EMG(di) was silenced, the tidal volume and duration of the passive mechanical ventilation determined the magnitude of the short-term inhibition of inspiratory motor output after cessation of CMV.

Reservoir Heterogeneity in an Estuarine Incised Valley-fill Reservoir, Sun Ranch Field, Wyoming: ABSTRACT

Abstract Incised valley-fill reservoirs containing sand derived primarily from the sea may contain significantly more barriers and baffles to flow than fluvially filled incised valleys. In choosing well locations, designing above ground handling capabilities and predicting economics of individual wells, it is important to recognize that the geometry, scale and type of barriers to flow are significantly different in these two types of valley fills. The tidal estuarine model developed primarily by Clifton for Pleistocene and modern estuarine deposits of Wilipah Bay, Washington, provides an excellent analog for deposits of Muddy (Cretaceous) sandstones at Sun Ranch field. Individual tidal valley-fill deposits may have several relatively continuous horizontal shaley beds which form baffles or barriers to vertical flow. These thin horizontal shales represent flooding events of more than the usual daily tidal duration. The beds are: (1) dominantly clay and fine sand and silts; (2) have very low porosity and permeability; (3) prevent or deter vertical flow between reservoir compartments and act as baffles to flow; (4) are the focus of diagenetic clay formation; and (5) are easily recognizable in core but not on most logs. Tidal and tidally-reworked fluvial valley fills may have significantly lower porosity and permeability and smaller port sizes than most fluvial fills. Detrital clay also occurs as drapes, clasts and grains within otherwise very sandy beds. Anomalously low log porosities may be calculated where clay occurs as clasts and clay drapes or ripples in otherwise high quality reservoir sandstones.

Tidal Inlet Equilibrium, in Relation to Cross-sectional Area and Sediment Transport Patterns

Equilibrium cross-sectional area is a crucial parameter in the assessment of the stability of tidal inlets; it has been related to tidal prism, through the empirical O'Brien method. Analyses presented here, based upon equations associated with equilibrium, show that other factors (i.e. not tidal prism alone) are also important: (1) flood and ebb tidal durations; (2) freshwater discharges; and (3) sediment transport through the entrance. Analytical approaches are suggested for evaluating tidal inlet equilibrium conditions. The method can be applied to analyse the equilibrium of individual inlets, reducing errors in the application of the O'Brien method. Equilibrium conditions for inlet systems at Langstone Harbour (southern England) and Yangpu Harbour (southern China) are compared, suggesting some deviation from the conclusion that maximum cross-sectional mean current speed for a stable inlet should be around 1·0 m s -1.

Steady-state ventilatory responses to expiratory resistive loading in quadriplegics.

Patients with quadriplegia have a limited capacity to recruit expiratory muscles and are deprived of respiratory-related feedback from the rib cage and abdominal wall. We wished to evaluate the compensatory strategies available to such patients during expiratory resistive loading (ERL) and to compare their responses with those of normal healthy individuals. In addition, to determine whether the quadriplegic subjects have a blunted sensory appreciation of added ERL, we also compared sensory detection thresholds (delta R50). Steady-state ventilatory responses to ERL (delta R = 12 cm H2O/L/s) were compared in seven quadriplegic patients (level of injury, C6, C7) and six age-matched normal subjects. Highly significant intergroup differences were evident in the extent of prolongation of expiratory time (TE) and total cycle duration (Ttot) during ERL; values of delta TE and delta Ttot in quadriplegics were, on average, 46% of those of normals (p < 0.001). Minute ventilation (VE) was defended to an equal or better extent in quadriplegics. ERL-induced changes in tidal volume, inspiratory duration, mean inspiratory and expiratory flows, and end-expiratory lung volume (EELV) were not significantly different. Average delta R50 in quadriplegics and normals were (mean +/- SD), 1.73 +/- 0.039 cm H2O/L/s and 1.62 +/- 0.4 cm H2O/L/s, respectively (p = ns). Quadriplegics, therefore, despite substantial sensory and motor deficits, defend ventilation and EELV as effectively as normal individuals and show no attenuation in the ability to detect an added expiratory resistance.

Role of lung inflation in control of air breath duration in African lungfish (Protopterus annectens).

Studies were conducted in the African lungfish (Protopterus annectens) to investigate the role of lung inflation on control of the duration of the lung breath. The studies were done in decerebrate spinalectomized animals. Two types of tests were performed: 1) a no-inflation test (airway occluded) in which the lungs were not inflated during an air breath, and 2) an inflation test in which the lungs were inflated at the onset of the lung breath to different levels of intrapulmonary pressure (2.5, 5.0, 7.5, and 10.0 cmH2O). Lung inflation shortened the duration of the lung breath. The relationship between intrapulmonary pressure and breath duration was curvilinear and similar to the relationship between tidal volume and inspiratory duration in mammals. Likewise, the relationship could be described by a hyperbola with a linear relationship between intrapulmonary pressure and the inverse of breath duration. This relationship was essentially not affected by changing the composition of the gas used to inflate the lungs: air, oxygen, or nitrogen. Vagotomy, however, largely abolished the effect of lung inflation on breath duration. Because there is such similarity between these results and effect of lung inflation on control of inspiratory time in mammals, it is postulated that neural circuits for control of respiratory timing were already developed and similar in the lungfish. Because the muscles used in the lungfish to ventilate the lung are totally different (buccal force pump) from those in mammals, the neural circuits for timing control and those for shaping the pattern of motor output appear to be separate.(ABSTRACT TRUNCATED AT 250 WORDS)

Inspiratory timing of heart-lung transplant recipients during progressive hypercapnia

The relationship between tidal volume (VT) and inspiratory duration (TI) displays biphasic characteristics during progressive hypercapnia in humans: an initial phase in which VT increases while TI remains constant (region I) and a subsequent phase with reciprocal decreases of TI as VT continues to increase (region II). Region II behavior is generally attributed, albeit inferentially, to lung volume-mediated inflation inhibition (Breuer-Hering reflex). To investigate this phenomenon, we compared CO2 responses of 10 heart-lung transplant recipients (HL) with normal pulmonary function tests and 13 normal controls. Despite pulmonary denervation, the HL exhibited region II behavior identical to controls. In four additional HL with pulmonary restriction, there were comparative decreases of the region II slope (P less than 0.05), but the absolute VT where the phase change between regions occurred was indistinguishable from the other groups. We conclude that TI shortening in humans during progressive hypercapnia occurs in the absence of pulmonary reflexes. The consistency of the VT associated with phase changes, despite pulmonary denervation, suggests that the stimulus for this behavior is volume displacement of extra-pulmonary respiratory structures.

Effect of slowly increasing elastic load on breathing in conscious humans

Because the detection of added loads is a function of the step change in load relative to background level of load (Weber's law), we reasoned that detection may be delayed if the load is increased in very small steps over a protracted period. This would permit the study of subliminal load responses over a greater range than would otherwise be possible. In 13 healthy males, an external elastic load (delta E) was added in very small steps (load increased every few seconds) such that delta E increased from zero to 6.0 cmH2O/l in 18 min. Each subject underwent a control study in which an identical protocol was followed but no load was added. Five subjects sensed the load after a variable period of load application. Their results were discarded. In the remaining eight subjects, there was no perception of increased load throughout the 18 min. By comparison with the control studies in the same subjects, there was a progressive reduction in tidal volume and breath duration with loading. To assess the response to an increase in load associated with perception, in five of the eight "nonsensers" the load was suddenly doubled (delta E = 6 cmH2O/l) at the end of the 18 min of progressive nonsensed loading. This evoked perception in all subjects and was associated with highly variable responses in tidal volume and breath duration. We conclude that tachypnea associated with elastic loading in conscious humans is a reflex response that is facilitated by consciousness but does not require perception.

Breathing and upper airway CO2 in reptiles: role of the nasal and vomeronasal systems

The ventilatory response of the garter snake, Thamnophis sirtalis, to 2% CO2 delivered to the upper airways (UA) was measured before and after the olfactory or vomeronasal nerves were transected. The UA (nasal cavities and mouth) were isolated from the gas source inspired into the lungs by inserting an endotracheal T tube into the glottis. CO2 was administered to the UA via a head chamber. The primary ventilatory response to UA CO2 was a significant decrease in ventilatory frequency (f) and minute ventilation. The decrease in f was caused by a significant increase in the pause duration. Tidal volume, expiratory duration, and inspiratory duration were not altered with UA CO2. The f response to UA CO2 was abolished with olfactory nerve transection, whereas vomeronasal nerve transection significantly increased the magnitude of the f depression. These results indicate that CO2-sensitive receptors are located in the nasal epithelium and that the olfactory nerves must be intact for the UA CO2 f response to be observed. In addition, the vomeronasal system appears to modulate the ventilatory response to UA CO2.

Improvement of data acquisition and analysis to evaluate regional ventilation.

To evaluate the regional ventilation using 133Xe under different conditions, the respiratory flow and the phase with image were measured simultaneously, and sequential frames were made breath by breath. The flow signal and phase signal were converted to pulse signals by a microcomputer and stored with image data in the same file. Thus, the tidal volume and duration of each breath were measured. From sequential frames compiled breath by breath, an activity breath-number curve was made in each pixel, and the half-clearance breath number (B1/2) was calculated. The changes in conventional half-clearance time (T1/2) and B1/2 were compared under different ventilatory conditions in normal subjects and in patients with chronic pulmonary emphysema. Values of B1/2 indicated the change of turnover rate more accurately than T1/2. It is considered that B1/2 is a better parameter than T1/2 for evaluating the change in regional ventilatory function under different conditions.

The Tidal Immersion Factor and Shore Platform Development: Discussion

In a series of recent papers it has been suggested that shore platforms are best developed at mid-tide level because tidal duration is greatest in this zone and, hence, beach processes operate for a proportionately longer time there. The present short paper demonstrates that, in fact, maximum tidal duration is associated with highand low-water zones rather than with mid-tide level. Since tidal level varies most rapidly at the mid-tide position wave action is least effective there. The implications of this are briefly considered. Recent papers by Trenhaile (1978, 1980) and Trenhaile and Layzell (1980, 1981) have discussed the development of shoreline platforms in various parts of the world. One aspect which has received attention is the 'tidal duration factor'. Figure 1 shows a 'tidal duration curve' redrawn from Trenhaile (1980) and Trenhaile and Layzell (1981). Without wishing to dwell on the semantics, what appears to be shown is a sea-level frequency distribution curve. Trenhaile and Layzell (1981) write: The tidal duration curves effectively express the role of fluctuating tidal levels in distributing wave energy within the tidal range. Each curve is characterized by a broad peak centred about mid-tide level, whose amplitude decreases with increasing tidal range. As these curves may be considered to represent the elevational frequency of storm wave attack within the tidal range, they demonstrate that storm wave action is much more likely to occur when still water is at mid-tide level, than when it is close to the tidal extremes. Unfortunately, the distribution depicted in Figure 1 is incorrect and this inevitably has a bearing on some of the conclusions on genesis and evolution stated in the various published papers. The Institute of Oceanographic Sciences is responsible for tidal predictions both in the area around the United Kingdom and at many sites throughout the world. The Institute also has a responsibility to process and archive tide-gauge records from associated coastal regions. Digitized hourly sea-level records are available for 3 out of the 6 locations quoted by Trenhaile and Trenhaile and Layzell. These are Swansea Dock (=Glamorgan); Margate (=Isle of Thanet); and Burnie (= Devonport, Tasmania). A figure based on similar criteria to Trenhaile's and Trenhaile and Layzell's figure is shown here as Figure 2 of this paper. There are 2 peaks in the frequency distribution and, except where these may be obscured by a very small tidal range, this will generally be the case. This is because the tide is composed principally of waves having Trans. Inst. Br. Geogr. N.S. 7: 240-45 (1982) Printed in Great Britain This content downloaded from 207.46.13.115 on Sat, 08 Oct 2016 04:48:22 UTC All use subject to http://about.jstor.org/terms The tidal immersion factor and shore platform development 241 4540Gasp6 35 >1' C 1 30 -Auckland 25E Tasmania Isle of Thanet . 0 20Uc Isle of Man----, . 0 15S10/ / 10 Glamorgan .10.1 S / . MS -5 -4 -3 -2 -1 0 1 2 3 4 5 Height (m) relative to MSL FIGURE 1. 'Tidal duration curves' for six areas: after Trenhaile (1980) and Trenhaile and Layzell (1981). MSL = Mean Sea Level diurnal and semi-diurnal frequencies which generate a sinusoid with still-stands at high and low water and a maximum rate of change at mid-tide level. There is a progressive change in tidal range between spring and neap tides, the extreme range occurring at equinoctial springs. In reality the tide is a composition of many harmonics which can have a complex mode of interaction including responses attributable to meteorological forcing. The net result, based on a year's actual observations for each site, is that depicted in Figure 2. While the same water level occurs at mid-tide height twice during each tidal cycle (i.e. on both rising and falling tides) the duration is not sufficient to eliminate the effect of the longer period over the 'high'and 'low'-water peaks. A more satisfying way of displaying all these data is in the Emersion Curves (Fig. 3) where it becomes clear that at a level roughly approximating to Lowest Astronomical Tide the site is permanently covered, while just above Highest Astronomical Tide it is always exposed. The cumulative frequency curves show the increasing rate of inundation (and exposure) at mid-tide level. Figure 4 depicts a plot of Mean Rate of Change for Swansea, South Wales. This demonstrates that the pattern for a falling tide is not quite identical with that for the rising tide and This content downloaded from 207.46.13.115 on Sat, 08 Oct 2016 04:48:22 UTC All use subject to http://about.jstor.org/terms

Shore Platform Morphology and the Tidal Duration Factor

A simple wave erosional model was used to simulate the profiles of shore platforms in eastern Canada, Australia, New Zealand, and Britain. The model assumes that the rate of intertidal erosion is determined by the time that still water level occupies each elevation within the tidal range (the tidal duration factor), by an erodibility factor related to wave energy and rock hardness, by platform gradient, and by the rate of submarine erosion. Simulated profiles were broadly similar to actual platforms in nearly all areas. All profiles eventually reached states of dynamic equilibrium, as the platforms assumed gradients which caused erosion rates to become equal at all points along their surfaces. Equilibrium was attained in periods which suggest that wave-cut platforms are essentially postglacial features. The model explains the effect of tidal range and erodibility on platform gradient and width, and the prominence of ramps and low tide cliffs in microand mesotidal environments, as well as identifying those factors which determine the elevation of platforms. The morphology characteristics of shore platforms are determined by a variety of morphogenic and geological factors. Bed dip, jointing, thickness, and other structural and lithological factors may be responsible for considerable variation in platform geometry within short distances along a coastline (Bird and Dent, 1966; Trenhaile, 1971). These local variations may be most marked along indented shorelines, and headland platforms are often quite different from those in the adjacent embayments; although few generalizations about the precise nature of these differences appear to be justified (Bartrum, 1935; So, 1965; Wright, 1970; Trenhaile, 1972). At the regional scale, however, differences in mean platform morphology between areas largely reflect differences in their morphogenic environments. The secondary role of geological factors at the regional scale is indicated by the relationship between aspects of platform geometry and a number of morphogenic factors (Wright, 1967, 1970; Trenhaile, 1972, 1974a, 1978, 1980). The geological contribution at the regional and larger scale is essentially limited to producing local deviations about morphological means which are determined by the morphogenic environments. Platform morphology also varies at the global scale. Davies (1964) has emphasized differences between the morphogenic environments of world shorelines, and Trenhaile (1974b) has applied this concept to shore platforms. The wave-cut platforms' in the storm wave, macrotidal environments of England and Wales, are generally wide, quasilinear surfaces, with gradients between 0-5 and 3'. They extend from a cliff-platform junction, generally close to high tide level, to low tide level or Trans. Inst. Br. Geogr. N.S. 6, 82-102 (1981) Printed in Great Britain This content downloaded from 207.46.13.146 on Tue, 23 Aug 2016 04:00:36 UTC All use subject to http://about.jstor.org/terms N .........iiiiiiiiiiiii!i!iii!!!i~~i~ii~~iiiii~iiiiii~~i . . . . . . . . . ...~iiiiiiiiiiiiiiiii~i~i~iiii!i~~ii~ i~iiiiiiiiiii!!iiiiiiiiiiiii~~ii~i!iiiiiii~ii~ ~~~~iliiiiiiiiii~iii~iii~ii~iii~iiiiiiiiiiiiilii~ i~i~i!i!ii~i~~iiiiii~iiiiiiii~iiiiiiiiiiiiiiiiiii~ i~ ~iiiiiii~iiiiiiiiiiiiiiii~iiiiiiii~i~i ii~i!ii!iiiiiii!i~ ~ii iii~ ~iiiiiiii~ ii~i~ iiii~iiiiiiiiiiiiii~ii~i~iiiii!iiii ii~ ~~~ii~i~ii~ii~iiiiiiiiiiiiiiiiiiiiiiiiiiiiii i i ii~ ~iiiiii~iiiiiiii~ii~iiiiiiiiii~iiii!!iii i iii~ii i~~iiiiiiiiiii~iiii~iiii!i!!!i~ ~iiiii~ iiiOW Nii~iii~i~i!~!iiiiiii~ii! i!!i! ii i iii% !i~!i~i!!!.!!.!%.l.i . ii.i.ii.i%.i.