Any consideration of the processes in the marine environment affecting MPAs must take into account the influence of sediments, including the causes and effects of these, together with any mitigation of their effects if necessary. In essence, the problem is fairly simple: sediments are transported by waves and currents into an area, where they may either reduce ambient light or settle to the bed (temporarily or permanently), creating a change in the character of the aquatic environment. This chapter is an attempt to describe the processes that cause this and other related phenomena to occur, and to offer some general principles regarding their effects in Marine Protected Areas. Some examples are given of instances where MPAs are or have been vulnerable to the effects of sediment transport, and some comments made on general management principles and recommendations for further research efforts.

The challenges associated with managing systems of shallow coastal lagoons along a rapidly evolving coastline are illustrated in a case study of small lagoon systems in Ghana where these important structures are relied on by a range of different stakeholders for a variety of different purposes including fishing, tourism and salt production. Results of some water quality measurements are presented, showing that these lagoons have poor ecological status where they experience either a lack of flushing by the tide, or large amounts of anthropogenic inputs, or both. A vulnerability assessment is applied to the lagoons in question and this reveals a varying degree of threat from climate change to the operation and use of the lagoons. Our understanding of these systems suggests that a set of 1D hydrodynamic models, underpinned by an understanding of the local coastal sediment transport in each case, is appropriate, and could then be used to inform stakeholders and management in decision making. Integrated, broad-ranging management strategies must adapt to the realities of climate change in order to allow the sustainable use of these lagoons in providing economic benefits, ecosystem services, and elements of coastline protection for the benefit of the local and regional population and its economy.

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The link between scientific understanding of the behaviour of estuarine sediments and their management is not well represented in the literature. This concluding article seeks to identify the key challenges for estuarine managers in terms of the issues related to safe and practical solutions for redistribution or disposal of sediments in macrotidal estuaries and tidal waters. The article concludes with some suggestions for future studies in this area and highlights the need for long term modelling studies.

Hydrodynamic and fine sediment transport characteristics of four major macrotidal Northern European estuaries are compared. The four estuaries (Weser, Seine, Scheldt, Humber) are amongst those key to navigation and shipping in that they are home to several major European ports (e.g. Hull, Antwerp, Le Havre). In particular, the characteristics and behaviour of the estuarine turbidity maximum are described for each system. While this is a complex topic that continues to benefit from ongoing research, some similarities exist between the estuaries in terms of the response of the turbidity maximum to changes in tidal range (during the neap–spring–neap cycle) and fresh water flow (due to seasonal variations in rainfall in the catchments). The hydrodynamics of the four estuaries are very similar, and are characterised by faster, shorter flood tide currents compared with longer, slower ebb tides. Under low fresh water flow conditions, the turbidity maximum is in each case moved upstream, while high fresh water flow conditions cause a net seaward movement of the turbidity maximum. While in general the concentrations of suspended sediment within turbidity maxima are no more than a few hundred milligrams per litre, the particular topography of the Humber estuary system leads to concentrations considerably higher than this.

A previously derived method (the tidal length—mean spring tidal range, TL-MSTR diagram) is used to predict the estuarine turbidity maximum (ETM) concentration and the residence time of the Thames Estuary. The predicted and observed residence time is 2 months. The predicted, depth-averaged ETM is 2.5 g l −1 of suspended particulate matter (SPM) at spring tides, which is much higher than that observed from surface sampling (<0.5 g l −1 ) and that simulated by recent models (approx. 0.6 g l −1 ), but is consistent with spring-tide concentrations measured throughout the water column over a tidal cycle. The observed locations of the surface 1-isohaline and 5-isohaline exhibit strong relationships with the logarithm of freshwater runoff. The observed ETM exhibits statistically significant relationships both with tidal range and the logarithm of runoff, and is generally located between the Millennium Dome and the Woolwich Reach. The apparent over-prediction of SPM afforded by the TL-MSTR diagram is unsurprising considering the removal of fine sediment by dredging and the removal of fine-sediment storage areas by embanking.

Reliable prediction of upstream and downstream depths in a hydraulic jump is essential for hydraulic design in open channels. A series of algorithms is proposed for estimating the ratio of conjugate depths in a hydraulic jump in a horizontal channel over a range of Froude numbers and for a range of different trapezoidal and circular sections running part-full. By solving the momentum equation using appropriate values for the depth of centroid below the free surface, an iterative approach is proposed that uses the Newton–Raphson method and produces satisfactory agreement with recent published experimental data. The resulting graphs of conjugate depth ratio y2/y1 against F1 were also used to form the basis of a series of equations of best-fit lines that could be used as first approximations for use in hydraulic design problems. The results obtained were also used to predict the energy loss in the hydraulic jump. It is envisaged that the algorithms described here could be incorporated into standard design spreadsheets for use by practitioners involved in civil engineering hydraulics design.

Mathematical models of solute mixing and sediment transport in estuaries rely heavily on the provision of good-quality field data. Observations of salinity, suspended sediment concentration and velocity at one of the tidal limits of a semi-enclosed tidal lagoon in Southern England (Pagham Harbour, West Sussex, UK) are presented, which illustrate how the natural processes of tidal incursion and solute mixing have been heavily modified as a result of the construction of sea walls dating back to the 18th Century. These observations, made immediately downstream of two parallel tidal flap gates by a conductivitytemperature-depth (CTD) profiler, and also using velocity sensors on bedmounted frames to measure the velocity at 2 fixed depths, have yielded a set of results covering 11 tidal cycles over the period 2002-2004. It is clear from the results obtained that over a typical tidal cycle the highest vertical salinity gradients occur in the 1-2 hours immediately after the onset of the flood tide, and that subsequently, energetic mixing acts to rapidly break down this stratification. Under moderate-to-high fresh water flows (>0.3 m 3 /s), the break-down in vertical salinity gradient is more gradual, while under low fresh water flows (<0.2 m 3 /s), the vertical salinity gradient occurs earlier in the tidal cycle. The data also show that most of the sediment transport is landward, and occurs during flood tides. These observations can help to provide information about the appropriate techniques for managing siltation and pollution, including nutrient transport from sewage effluent waters, in estuaries where hydraulic flap gates are used to control the entry of fresh water.

The design and operation of mathematical models of solute mixing and sediment transport in estuaries rely heavily on the provision of good-quality field data. We present some observations of salinity, suspended sediment concentration and velocity at one of the tidal limits of a semi-enclosed tidal lagoon in Southern England (Pagham Harbour, West Sussex, UK) where the natural processes of tidal incursion and solute mixing have been heavily modified as a result of the construction of sea walls dating back to the 18th Century. These observations, made immediately downstream of two parallel tidal flap gates by conductivity-temperature-depth (CTD) profiler, and also using bed-mounted sensor frames to measure velocity at 2 fixed depths, have yielded a set of results covering 11 tidal cycles over the period 2002-04. It is clear from the results obtained that over a typical tidal cycle, the greatest vertical salinity gradients occur in the 1-2 h immediately after the onset of the flood tide, and that subsequently, energetic mixing acts to rapidly break down this stratification. Under moderate-to-high fresh water flows (>0.5 m(3)/s), the breakdown in vertical salinity gradient is more gradual, while under low fresh water flows (<0.2 m(3)/s), the vertical salinity gradient is generally less pronounced. Estimates of Richardson number during the early flood-tide period reveal values that vary rapidly between <1 and about 20, with lower values occurring after around 1.5-2 h after low water. Observations of suspended sediment concentration vary widely even for similar tidal and fresh water flow conditions, revealing the possible influence of wind speed, the storage effects of the water in the lagoon downstream of the observation site, and the complexity of the hydrodynamics downstream of tidal flap gates. The data also show that most of the sediment transport is landward, and occurs during flood tides, with estimated total tidal landward flood tide flux of fine sediment of the order of 50-120 kg under low fresh water flow conditions. These observations, which reinforce the results presented in Warner et al. (2004) and elsewhere, can help to provide information about the appropriate techniques for managing sediments and pollutants, including nutrients from sewage effluent waters, in estuaries where hydraulic flap gates are used to control the entry of fresh water over the tidal cycle. (C) 2008 Elsevier Ltd. All rights reserved.

Results of nitrate and phosphate concentrations measured using hand-held ‘Hach’ monitors are presented, both over individual tidal cycles and over longer term deployments at Pagham Harbour, West Sussex, UK. This macrotidal lagoon (offshore tidal range 3.0 m neaps–6.5 m springs) is a site of key importance as a nature reserve and a home for several rare species of plants and animals. In particular, the effects of fresh water-salt water stratification over 4 tidal cycles at two tidal-fresh water boundaries is presented. It is shown that obtaining periodic vertical profile measurements during individual tidal cycles helps to quantify the transport mechanisms of nutrients from the tidal limits into the main body of the lagoon. Of key interest is the interaction between sediment-bound nutrients with the surrounding water in which the sediment is suspended during parts of the tidal cycle. Synthesis of these results with existing knowledge about sediment-water-nutrient interactions reveals how it is possible for nutrients to become trapped at the muddy tidal limits of the lagoon. In certain cases it is shown that nutrient-rich water from fresh water streams only gradually mixes with the denser, salt water of the incoming tide. Whilst a degree of salinity-induced stratification may be expected during the flood tide, these observations suggest that the water column is stratified with respect to both N and P, even well into the ebb tide. Thus at sites where stratification is important, there is a tendency for nutrients to remain preferentially near the water surface, and thus come into contact with fine, less mobile sediments near the surface of inter-tidal zones, which are themselves, in general, accreting. Since the overlying water is generally slow-moving during high water, it is postulated that saline-induced vertical stratification of estuarine water is an important mechanism in promoting nutrient build-up in muddy inter-tidal areas of this kind.

The Pevensey Levels is an area of reclaimed coastal wetlands located in East Sussex, UK. Agricultural and land-drainage activities dominate land use and have impacts on water quality within the Levels. The dense arterial ditch network which drains the levels suffers from nutrient enrichment, in particular orthophosphate PO34- and inorganic nitrogen compounds (NH4+, NO2- and NO3-). The primary drivers behind the increase in nutrient concentrations are agricultural intensification, conversion to arable farming and point source pollution (particularly from two nearby Sewage Treatment Works). This study describes water quality data from January 1994 to July 2005 in order to discern temporal and spatial nutrient trends. It is evident that water quality within the Pevensey Levels is degraded. Concentrations of NH4+% NO2- and PO34- throughout both major catchments are elevated, whilst concentrations of NO3- are lower than expected, indicating that many sites may also experience problems with low levels of dissolved oxygen. The Pevensey/Hurst Haven catchment was found to have significantly higher concentrations of all determinands, primarily as a result of effluent discharge from the Hailsharn. STWs. The Wallers Haven catchment was also found to experience water quality problems, but to a lesser extent. Over the period of observation, chemical P stripping was introduced at the Hailsham STWs, resulting in a significant decrease in recorded PO34- concentrations. However, although external nutrient loading has decreased, water quality recovery limited. Suggestions are made for ftirther research into the reasons for this lack of improvement.

A method is proposed for assessing the impact of rising sea levels on areas upstream of tidal flap gates. These devices, designed to allow drainage of surrounding land during low water and flood defence during high water, are commonly used in areas where tidal high water level is higher than the level of the land behind the sea wall. Studies were undertaken at Pagham Harbour, West Sussex, UK, where a number of tidal flap gates are used to control the flow of water from channels carrying drainage waters away from the nearby town of Chichester. On one of these channels, water level data were collected at 15-min intervals at three sites near the flap gate and analysed in order to obtain values over each tidal cycle of maximum and minimum water levels downstream of the gate, and the time of closure of the gate. Water level was also monitored at two locations upstream of the gate. By obtaining estimates of mean fresh water discharge for each tidal cycle, and combining these with peak tidal water level, a functional relationship (in the form of a three-dimensional plot) was obtained for the parameter tc, the length of time in hours for which the flap gate is closed during each tidal cycle. These values of tc were also used in conjunction with mean tidal fresh water discharge to produce another three-dimensional plot showing the effect on peak tidal water level upstream of the flap gate, thus providing an illustration of the sensitivity of local flooding to varying tc under different tidal conditions. Finally an estimate was made of the likely impact of a 300 mm rise in mean sea level on tc for the same set of fresh water flow data, using a set of ‘look-up’ tables based on the three-dimensional plots obtained. These indicated that the frequency of local flooding was likely to increase significantly for fresh water flows greater than 0·8 m3/s. Although the increase in local flooding illustrated here is not thought to be a cause for immediate concern, particularly in view of the recent construction of a further tidal flap gate adjacent to the existing one, nevertheless the methodology employed is applicable to similar systems.

Preliminary analysis of data collected at a macrotidal semi-enclosed lagoon (Pagham Harbour, UK) has revealed useful information about long-term patterns of siltation and some of the related mechanisms. Sediment surface-level measurements made over 2 years at different sites within Pagham Harbour have shown a steady siltation, in common with earlier measurements, which is moderated by seasonal effects due to erosion by locally generated waves. Furthermore, inspection of vertical profiles of salinity and turbidity over individual tidal cycles has revealed that the degree of sediment transport on the flood tide is related to the vertical salinity gradient. Thus, at the Ferry Pool site, which is characterised by episodic pumped discharges from a nearby sewage treatment plant, landward sediment transport is enhanced by the high degree of salinity stratification observed during the flood tide. The mobility of the sediment, and the greater distribution of softer, less well-consolidated sediment deposits, is greater here than at the other significant freshwater inflow at the Salthouse site, where the fresh water flow is instead moderated by a tidal flap gate. Preliminary analyses suggest that the higher the salinity stratification, the greater the landward sediment transport during the flood tide. Such analyses could help inform future policy on the methods of land drainage to macroticial lagoons, and on the potential for managed realignment at such sites.

The purpose of this research was to determine if fiber spacing for small fiber diameter fibro-porous meshes affected tissue response in vivo. Disk-shaped polyurethane meshes, with mean fiber diameters of 7.6 microm and fiber spacing between 6 and 68 microm, were implanted in rat subcutaneous dorsum for 5-week intervals and then prepared for light microscopy and morphological analysis. Results showed that implants with 12- to 68-microm spacing had no histologically apparent fibrous capsule around the perimeter, a result different from that for 6-microm spacing samples that had a capsule around a mean of 34.2% of the perimeter. For the 12- to 68-microm spacing range, a mean of 21.0% of individual fibers within the meshes were encapsulated. Qualitatively, it appeared that larger fibers were encapsulated more frequently than smaller ones. When nodeless or baggy meshes were implanted, cells tended to cluster three or more fibers into groups and then encapsulate each group. Over the 6- to 68-microm spacing range, cell nuclei volume fraction within the meshes increased from the 6- to the 29-microm spacing (p = 0.000) and then decreased from the 29- to the 68-microm spacing (p = 0.015). There was a trend of an increase in local vessel volume fraction with spacing over the 6- to 68-microm range, though the relationship was weak. The results indicate that the reason for the lack of encapsulation of small-fiber fibro-porous meshes is not exclusively a pore boundary explanation, as is proposed for small-pore porous meshes.

Abstract Prediction of wave energy distribution in coastal areas is necessary if an assessment of the likelihood of cliff collapse is to be undertaken. Use has been made of numerical modelling to predict relative wave heights along the chalk cliff coastline of East Sussex between Brighton and Eastbourne, UK. In this study, wave modelling has been undertaken using the University of Delaware REFDIF-1 software with a 100m mesh size to predict nearshore wave heights for boundary unit wave height conditions from a range of different incident directions. The results from this wave modelling have been combined with the frequency distribution of incident waves obtained from analysis of time series of 12 years of hindcast wave data in the English Channel, obtained from the UK Meteorological Office. The resulting distribution of nearshore wave heights is presented as a surrogate for the distribution of wave energy over the 12-year period. Some concern exists about the quality of the output data, in particular of the effect of the relatively coarse bathymetry grid used for the model. Some wave focusing is evident from the model output, caused by the presence of local shoals in the model grid, leading to a ‘banding’ effect in the model output. Some suggestions are made for the improvement of the modelling scheme, including the use of finer mesh size, bathymetric smoothing and the use of a spectral model such as REFDIF-S.

ABSTRACT Field investigations were undertaken to identify the mechanisms of fine‐sediment transport at a landward limit of Pagham Harbour. Which is a semi‐enclosed natural harbour in West Sussex, UK. Measurements of water level, velocity, salinity and turbidity were made during three tidal cycles between June and August 2002. Near‐bed measurements revealed that, for spring tides, the most significant transport occurs during the flood tide, with smaller turbidity peaks recorded at times of intermittent pumped discharges at low water. Vertical profiling revealed that the timing of these discharges acts as a control on the landward transport of fine sediment by increasing salinity stratification. The resulting graphs show that, while increased near‐bed velocity leads to increased turbidity and sediment transport, the degree of vertical salinity gradient is also linked with landward transport of fine sediment. These results help to explain the role of tides and fresh‐water flow in controlling the transport of fine sediment in natural harbours, emphasising the importance of taking stratification into account when using 2‐D depth‐averaged predictive numerical models.