Navigational charts are a valuable data source for the study of morphological change in estuaries, as they provide bathymetric information of many estuaries, and span a vast period of time. Charts are suitable for studying patterns of morphological change, such as shoal and channel migration. In addition, sequential bathymetric charts or bed surveys can be used to calculate sedimentation and erosion rates. However, a number of problems arise when using these data to identify morphological change. Sources of error and uncertainty are associated with surveying techniques used, density of depth sampling points, interpolation and averaging during compilation of the chart. Large systematic errors may stem from the non-uniformity or poorly defined levels to which the depths on the charts are reduced. Errors propagate in spatiotemporal operations using such charts. Analysis of historical bathymetric charts from the Ribble estuary (north-west England) illustrates the difficulties involved in assessing morphological change in a quantitative manner. The pattern of morphological development within the Ribble estuary over the last 150 years was clear, and a significant long-term net accretional trend was found. However, temporal variations in the rate of sedimentation on a decadal scale were generally not significant. 相似文献
Whilst the measurement of radiation emissions from a surface is relativelystraightforward, correct interpretation and proper utilization of the informationrequires that the surface area `seen' be known accurately. This becomes non-trivialwhen the target is an urban surface, due to its complex three-dimensional form andthe different thermal, radiative and moisture properties of its myriad surface facets.The geometric structure creates shade patterns in combination with the solar beamand obscures portions of the surface from the sensor, depending on where it is pointing and its field-of-view (FOV). A model to calculate these surface-sensor-sun relations (SUM) is described. SUM is tested against field and scale model observations, and theoretical calculations, and found to perform well. It can predict the surface area`seen' by a sensor of known FOV pointing in any direction when placed at any pointin space above a specified urban surface structure. Moreover, SUM can predict theview factors of the roof, wall and ground facets `seen' and whether they are sunlit orshaded at any location and time of day. SUM can be used to determine the optimalplacement and orientation of remote sensors to study urban radiation emissions; ifthe facet temperatures are known or modelled it can calculate the average temperatureof the system, and it can determine the directional variation of temperature (anisotropy) due to any particular surface-sensor-sun geometric combination. Thepresent surface geometry used in SUM is relatively simple, but there is scope to makeit increasingly realistic. 相似文献
A radiation and diffraction boundary value problem is investigated. It arises from the interaction of linear water waves with a freely floating rectangular structure in a semi-infinite fluid domain of finite water depth with the leeward boundary being a vertical wall. Analytical expressions for the radiated potentials and the diffracted potential are obtained by use of the method of separation of variables and the eigenfunction expansion method. The added masses and damping coefficients for the structure heaving, swaying and rolling in calm water are obtained by use of the corresponding radiated potentials and the wave excitation forces are calculated by use of the diffracted potential. To verify the correctness of the method, a boundary element method is used. A comparison of the analytical results with those obtained by the boundary element method is made and good agreement is achieved, which shows that the analytical expressions for the radiated and diffracted potentials are correct. By use of the present analytical solution, the added mass, damping coefficients, wave excitation force, together with the hydrodynamic effects of the draft, width of the structure and the clearance between the structure and the sidewall are also investigated. 相似文献
Egmont Key is a small, elongate island located on the huge ebb-tidal delta at the mouth of Tampa Bay, FL, USA. The multiple sets of intersecting beach/dune ridges that comprise the low-lying island indicate several periods of growth spaced between periods of erosion. The island has experienced considerable expansion and erosion during recorded history. The oldest of these ridges represents accumulation that took place about 1000 years before the present. Over the past century of well-documented change, there has been a general reduction in the area of the island as the result of extended periods of erosion punctuated by short accretion periods. The net change during this period has been a loss of approximately 40% of the area of the island. A 1-year, time-series monitoring of the Egmont shoreline during 1996–1997 showed sediment loss of 26 500 m3, while the annual average over the period of 1877–1996 was only 3360 m3. A single storm is responsible for most of this loss leading to the conclusion that the island is storm-dominated. Inferences from time intervals during which hurricanes took place support this conclusion. This island provides a major contrast in its coastal location, development and stratigraphy as compared to typical barrier islands. There is no underlying sediment deposited in shallow, paralic environments. The development of the island was lateral rather than having a vertical component through time, partly because of its relatively young age but also because of its position on a thick, ebb-tidal delta sand body. 相似文献
Abstract. The Adriatic brown macroalga Fucus virsoides (DON.) J. Ac (Fucales, Phaeophyceae) was investigated with particular respect to basic physiological features such as photosynthesis, dark carbon fixation, and respiration. Values obtained are expressed in various reference systems. Chemical composition of the fronds and physiological activity (photosynthesis/dark fixation along with the respective carboxytating enzymes (ribulose-1,5-bisphophate carboxylase and phosphoenol-pyruvate carboxykinase) show longitudinal profiles. Temperature characteristics of photosynthesis in long-term adapted specimens indicate reduced productivity at temperatures exceeding 20 °C. Photosynthesis during atmospheric exposure is markedly increased under moderate desiccation. Photosynthetic rates steadily decline under reduced salinity of the incubation medium, while respiration is stimulated. Net primary productivity of a F. virsoides stand at 15 °C ambient average temperature, tidal exposure for maximally 2–3 hours and light-dark regime = 12: 12 is calculated as 4.8-5.4 g C m-2d-1. Culture experiments with polluted incubation media provide evidence that excessive nutrients including nitrate and phosphate as well as high concentrations of heavy metals (Zn, Co, Mn) cause severe growth-rate reduction which may account for the steady decrease of F. virsoides in its natural habitat. The results are discussed with emphasis on the autecology of F. virsoides and its relationships to Atlantic representatives of the genus. 相似文献
Abstract. The population of Laminaria ochroleuca in the current swept Straits of Messina was investigated regarding its age structure and photosynthesis. Age structure appears to be determined by sporadic recruitment and the limitation of growth due to peak currents decapitating older plants, which is corroborated by drag force resistance calculations. The calculation of a carbon budget from measurements of photosynthesis and dark respiration both in the laboratory and in situ shows that L. ochroleuca cannot satisfy its carbon demands for growth and respiration at 50 m depth and no satisfactory explanation can be given for its rapid growth between 50 and 100 m. 相似文献
Analysis of high-resolution seismic reflection profiles and sediment samples has revealed the evolution and sediment budget of the southeastern Yellow Sea mud belt (SEYSM) along the southwestern Korean Peninsula. The SEYSM, up to 50 m thick, over 250 km long and 20–55 km wide, can be divided into three stratigraphic units (A1, A2, and B, from oldest to youngest). Unit A1, overlying the acoustic basement, comprises the northern part of the SEYSM. Unit A2 comprises the southern part of the SEYSM; much of unit A2 is exposed at the seafloor. Unit B completely covers unit A1 and pinches out southward.
14C data suggest that evolution of each unit is closely related to the postglacial sea-level changes. Unit A1 consists of estuarine/deltaic or shallow-water muds deposited during the early to middle stage of postglacial sea-level rise (ca. 14,000–7000 yr B.P.). Unit A2 corresponds to relict muds deposited during the last, deceleration stage of sea-level rise (ca. 7000–3.500 yr B.P.). Unit B consists of shelf muds deposited during the recent sea-level highstand (ca. <3500 yr B.P.).
Very low background activities of 210Pb of the surface sediment of unit A2 suggest that the present-day sediment accumulation is negligible in the southern SEYSM. On the other hand, 210Pb excess activity profiles in unit B yield an average sediment accumulation rate of 3.9 mm/yr, indicating active sediment accumulation in the northern SEYSM. The annual sink (3.0×107tons/yr) of fine-grained sediment in unit B is about an order of magnitude greater than can be explained by the sediment input from the Korean rivers alone. We propose that reworking of unit A2 has provided large volumes of muds to unit B, resulting in excessive sediment accumulation in the northern SEYSM. Much of unit A2, in turn, is likely to have originated from erosion of unit A1 in the north. This rather unique erosional/depositional regime of the SEYSM is probably owing to the tidal and regional currents characteristic in the southeastern Yellow Sea. 相似文献