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121.
A variable mesh finite element model of the Irish and Celtic Sea regions with/without the inclusion of the Mersey estuary is used to examine the influence of grid resolution and the Mersey upon the higher harmonics of the tide in the region. Comparisons are made with observations and published results from finite difference models of the area. Although including a high resolution representation of the Mersey had little effect upon computed tides in the western Irish Sea it had a significant effect upon tidal currents in the eastern Irish Sea. In addition the higher harmonics of the M2 tide in near-shore regions of the eastern Irish Sea particularly the Solway and Mersey estuary together with Morecambe Bay showed significant small scale variability. The Mersey was used to test the sensitivity to including estuaries because high resolution accurate topography was available. The results presented here suggest that comparable detailed topographic data sets are required in all estuaries and near-shore regions. In addition comparisons clearly show the need for an unstructured grid model of the region that can include all the estuaries. Such an unstructured grid solution was developed here within a finite element approach, although other methods in particular the finite volume, or coordinate transformations/curvilinear grids and nesting could be applied. 相似文献
122.
123.
Flocculation has an important impact on particle trapping in estuarine turbidity maximum (ETM) through associated increases in particle settling velocity. To quantify the importance of the flocculation processes, a size-resolved flocculation model is implemented into an ocean circulation model to simulate fine-grained particle trapping in an ETM. The model resolves the particle size from robust small flocs, about 30 μm, to very large flocs, over 1000 μm. An idealized two-dimensional model study is performed to simulate along-channel variations of suspended sediment concentrations driven by gravitational circulation and tidal currents. The results indicate that the flocculation processes play a key role in generating strong tidal asymmetrical variations in suspended sediment concentration and particle trapping. Comparison with observations suggests that the flocculation model produces realistic characteristics of an ETM. 相似文献
124.
Carl L. Amos G. Umgiesser C. Ferrarin C.E.L. Thompson R.J.S. Whitehouse T.F. Sutherland A. Bergamasco 《Continental Shelf Research》2010
The stability of cohesive sediments from Venice lagoon has been measured in situ using the benthic flume Sea Carousel. Twenty four stations were occupied during summertime, and a sub-set of 13 stations was re-occupied during the following winter. Erosion thresholds and first-order erosion rates were estimated and showed a distinct difference between inter-tidal and sub-tidal stations. The higher values for inter-tidal stations are the result of exposure that influences consolidation, density, and organic adhesion. The thresholds for each state of sediment motion are well established. However, the rate of erosion once the erosion threshold has been exceeded has been poorly treated. This is because normally a time-series of sediment concentration (C) and bed shear stress (τ0(t)) is used to define threshold stress or cohesion (τcrit,z) and erosion rate (E). Whilst solution of the onset of erosion, τcrit,0, is often reported, the evaluation of the erosion threshold variation through the process of erosion (eroded depth) is usually omitted or not estimated. This usually leads to assumptions on the strength profile of the bed which invariably has no credibility within the topmost mm of the bed where most erosion takes place. It is possible to extract this information from a time-series through the addition of a step in data processing. This paper describes how this is done, and the impact of this on the accuracy of estimates of the excess stress (τ0(t)–τcrit,z) on E. 相似文献
125.
Dr. D. B. Prior 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):45-48
Prior, D. B., 1973: Coastal landslides and swelling clays at Røsnæs, Denmark. Geografisk Tidsskrift, 72: 45–48. København, September 30, 1973. The landslide morphology of the Røsnæs area has been examined and materials involved in active landsliding analysed. 相似文献
126.
Rui Zhang Li Zhou Fan Zhang Yingjun Ding Jinrong Gao Jing Chen Hongqiang Yan Wei Shao 《Marine pollution bulletin》2013
The heavy metal inventory and the ecological risk of the tidal flat sediments in Haizhou Bay were investigated. Results show that the average concentrations of heavy metals in the surface sediments exceeded the environment background values of Jiangsu Province coastal soil, suggesting that the surface sediments were mainly polluted by heavy metals (Cd, Cr, Cu, Mn, Pb and Zn). In addition, the profiles of heavy metals fluxes can reflect the socio-economic development of Lianyungang City, and heavy metals inputs were attributed to anthropogenic activities. Cr, Cu, Pb and Zn were mainly present in the non-bioavailable residual form in surface sediments, whereas Cd and Mn were predominantly in the highly mobile acid soluble and reducible fractions. The ecological risk of the polluted sediments stemmed mainly from Cd and Pb. According to the Sediment quality guidelines (SQGs), however, the adverse biological effects caused by the heavy metals occasionally occurred in tidal flat. 相似文献
127.
A tracer study in an Alaskan gravel beach and its implications on the persistence of the Exxon Valdez oil 总被引:2,自引:0,他引:2
Despite great efforts including bioremediation, the 1989 Exxon Valdez oil spills persist in many gravel beaches in Prince William Sound, Alaska, USA. To explore this mystery, a lithium tracer study was conducted along two transects on one of these beaches. The tracer injections and transports were successfully simulated using the 2-dimensional numerical model MARUN. The tracer stayed much longer in the oil-persisting, right transect (facing landwand) than in the clean, left transect. If the tracer is approximately regarded as oils, oils in the upper layer would have more opportunities to enter the lower layer in the right transect than in the left one. This may qualitatively explain the oil persistence within the right transect. When the tracer is regarded as nutrients, the long stay of nutrients within the right transect implies that the oil persistence along the right transect was not due to the lack of nutrients during the bioremediation. 相似文献
128.
The hydrodynamics of a small tributary channel and its adjacent mudflat is studied in Willapa Bay, Washington State, USA. Velocity profiles and water levels are simultaneously measured at different locations in the channel and on the mudflat for two weeks. The above tidal flat and channel hydrodynamics differ remarkably during the tidal cycle. When the water surface level is above the tidal flat elevation, the channel is inactive. At this stage, the above tidal flat flow is predominantly aligned along the Bay axis, oscillating with the tide as a standing wave with peak velocities up to 0.3 m/s. When the mudflat becomes emergent, the flow concentrates in the channel. During this stage, current velocities up to 1 m/s are measured during ebb; and up to 0.6 m/s during flood. Standard equations for open-channel flow are utilized to study the channel hydrodynamics. From the continuity equation, a lateral inflow is predicted during ebb, which likely originates from the drainage of the mudflat through the lateral runnels. Both advective acceleration and lateral discharge terms, estimated directly from the velocity profiles, play a significant role in the momentum equation. The computed drag coefficient for bottom friction is small, due to an absence of vegetation and bottom bedforms in the channel. Sediment fluxes are calculated by combining flow and suspended sediment concentration estimated using the acoustic backscatter signal of the instruments. A net export of the sediment from the channel is found during ebb, which is not balanced by the sediment import during flood. When the mudflat is submerged, ebb-flood asymmetries in suspended sediment concentration are present, leading to a net sediment flux toward the inner part of the Willapa Bay. Finally, a residual flow is detected inside the channel at high slack water, probably associated with the thermohaline circulation. 相似文献
129.
Crissy Field Marsh (CFM; http://www.nps.gov/prsf/planyourvisit/crissy-field-marsh-and-beach.htm) is a small, restored tidal wetland located in the entrance to San Francisco Bay just east of the Golden Gate. The marsh is small but otherwise fairly typical of many such restored wetlands worldwide. The marsh is hydraulically connected to the bay and the adjacent Pacific Ocean by a narrow sandy channel. The channel often migrates and sometimes closes completely, which effectively blocks the tidal connection to the ocean and disrupts the hydraulics and ecology of the marsh. Field measurements of waves and tides have been examined in order to evaluate the conditions responsible for the intermittent closure of the marsh entrance. The most important factor found to bring about the entrance channel closure is the occurrence of large ocean waves. However, there were also a few closure events during times with relatively small offshore waves. Examination of the deep-water directional wave spectra during these times indicates the presence of a small secondary peak corresponding to long period swell from the southern hemisphere, indicating that CFM and San Francisco Bay in general may be more susceptible to long period ocean swell emanating from the south or southwest than the more common ocean waves coming from the northwest. The tidal records during closure events show no strong relationship between closures and tides, other than that closures tend to occur during multi-day periods with successively increasing high tides. It can be inferred from these findings that the most important process to the intermittent closure of the entrance to CFM is littoral sediment transport driven by the influence of ocean swell waves breaking along the CFM shoreline at oblique angles. During periods of large, oblique waves the littoral transport of sand likely overwhelms the scour potential of the tidal flow in the entrance channel. 相似文献
130.