Coastal Engineering

Bioprotection and Disturbance: seaweed, microclimatic stability and weathering in the intertidal zone.

by Martin Coombes

MA. Coombes, LA. Naylor, HA Viles, RC Thompson (accepted). Bioprotection and Disturbance: seaweed, microclimatic stability and weathering in the intertidal zone. Geomorphology.

Plants, animals, and microorganisms can contribute to geomorphology and ecology through their direct or indirect... more Plants, animals, and microorganisms can contribute to geomorphology and ecology through their direct or indirect bioprotective roles, which can reduce weathering and erosion. For example, indirect bioprotection can operate via biotic influences on microclimate, whereby weathering processes associated with fluctuations in temperature and moisture are limited. As a consequence, bioprotective organisms moderate physical disturbance at a range of spatial and temporal scales. The microclimatic influence of organisms can also improve environmental conditions for other species, and thus acts as an agent of biodiversity maintenance.
In the intertidal zone, the spatial and temporal distribution of macroalgae (seaweeds) is patchy, related to physical and ecological conditions for colonization and growth, and the nature and frequency of disturbance (both natural and anthropogenic). We examined the influence of seaweed canopies (Fucus spp.) on near-surface microclimate and, by implication, on weathering and ecology. Monitoring on hard artificial coastal structures in South West England, UK built from limestone and concrete showed that both the range and maxima of daily summertime temperatures were significantly lower (by an average of 56% and 25%, respectively) in areas colonized by seaweed compared to experimentally cleared areas. Short-term microclimatic variability (minutes–hours) was also significantly reduced (by an average of 78% for temperature and 71% for humidity) under algal canopies during low tide events.
Using seaweed as an example, we develop a conceptual model of the relationship between biological cover and microclimate in the intertidal zone. Disturbance events which remove or drastically reduce seaweed cover mediate shifts between relatively stable and unstable states with respect to both weathering and ecological stress associated with heat and desiccation. In urbanized coastal environments, where disturbance may be frequent, facilitating the establishment and recovery of canopy-forming species on rocks and engineered structures may enhance the durability of construction materials as well as support conservation, planning, and policy targets for biodiversity enhancement.

Including Ecological Enhancements in the Planning, Design and Construction of Hard Coastal Structures: a process guide.

by Martin Coombes

Naylor, L.A., Venn, O., Coombes, M.A., Jackson, J., Thompson, R.C. (2011). Including Ecological Enhancements in the Planning, Design and Construction of Hard Coastal Structures: a process guide. Environment Agency, 66 pages.

Considering Ecological Enhancement for Hard Coastal Infrastructure in the Intertidal Zone: Initial guidance for Ports and Harbours.

by Martin Coombes

Naylor, L.A., Coombes, M.A., Venn, O. (2011). Considering Ecological Enhancement for Hard Coastal Infrastructure in the Intertidal Zone: Initial guidance for Ports and Harbours. Report for Portland Port Ltd., 62 pages.

Portland Port Rapid Appraisal: Physical Habitat Characteristics and Biotopes found on Selected Hard Structures at Portland Port Portland Port Ltd.

by Martin Coombes

Naylor, L.A., Coombes, M.A., Baldock, L., White, A. (2011). Portland Port Rapid Appraisal: Physical Habitat Characteristics and Biotopes found on Selected Hard Structures at Portland Port Portland Port Ltd., 38 pages.

Natural variability and anthropogenic effects on the morphodynamics of a beach-dune system at Montrose Bay, Scotland

by Fraser Milne

Numerical modelling of 3-D tidal currents and water quality indicators in the Bristol Channel

by Roger Falconer - Cardiff University

Paper 60:  Lin, B. and Falconer, R. A. 2001. Numerical modelling of 3-D tidal currents and water quality indicators in the Bristol Channel”, Proceedings of the Institution of Civil Engineers, Water and Maritime Engineering. 148(3), 155-166.

Abstract
Details are given of the principle processes of flow and contaminant transport in coastal, estuarine... more Abstract
Details are given of the principle processes of flow and contaminant transport in coastal, estuarine and inland waters and the application of computer models to predict these processes. A typical computer modelling approach is outlined, involving a finite difference solution of the three-dimensional equations of mass and momentum conservation and the advective-diffusion (or solute transport) equation. Examples are given of the application of the model to predict the spatial and temporal distributions of velocity components and water quality indicators in the Bristol Channel.

Modelling and assessment of water quality indicators in a semi-enclosed shallow bay

by Roger Falconer - Cardiff University

Paper 62:  Tao, J., Li, Q., Falconer, R. A. and Lin, B. 2001. Modelling and assessment of water quality indicators in a semi-enclosed shallow bay. Journal of Hydraulic Research, IAHR. 39(6), 611-618.

Abstract
Bohai Bay is a large, semi-enclosed shallow water basin located along the western region of the Bohai... more Abstract
Bohai Bay is a large, semi-enclosed shallow water basin located along the western region of the Bohai Sea in the north-eastern part of China. As a result of rapid economic development in the surrounding coastal hinterland, the water quality characteristics within Bohai Bay have been of growing concern in recent years. Details are given herein of an aquatic environmental assessment study undertaken to investigate the hydrodynamic and transport processes within the Bay using an integrated numerical modelling approach and tield measurements. 3-D numerical model was used to simulate the tide flow and 2 D model was deployed with moving boundary to simulate the water quality. In order to improve on the water quality characteristics in the near-shore coastal zone, an ocean disposal plan was also considered, with various scenarios being simulated using the 2-D model. From an analysis of data collected from the held measurements, it was found that both chemical and phytoplankton indicators were important in the assessment of the overall water quality of the Bay. The occurrence of red tides was also found to be closely linked to the composition of phytoplankton community.

Physical modelling of tsunami using a new pneumatic wave generator

by Ingrid Charvet

Flushing study assessment of a tidally active coastal embayment

by Roger Falconer - Cardiff University

Paper 71:  Hartnett, M., Gleeson, F., Falconer, R. A. and Finnegan, M. 2003. Flushing study assessment of a tidally active coastal embayment. Advances in Environmental Research. 7(4), 847-857.

Abstract
In this paper four existing techniques for performing flushing studies of coastal embayments are... more Abstract
In this paper four existing techniques for performing flushing studies of coastal embayments are applied to a small embayment and intercomparisons between the results carried out. Two of the methodologies employ detailed computer modelling whereas the other two rely on relatively simple flushing formulae. The underlying principles behind the techniques are briefly presented and their applicability to a particular coastal embayment is discussed. Flushing characteristics of an embayment on the West Coast of Ireland, Casheen Bay, were determined using each of the four techniques. Because the spatial extent of an embayment obviously directly affects the flushing characteristics, the embayment was subdivided into four segments and each method was applied to all four segments. The results of each analysis for each segment is presented and compared with the other similar analyses. A discussion of the results is presented, in which the suitability of the various methods is considered and the effects of subdividing the embayment into segments are highlighted. A summary of the work carried out and conclusions drawn is then presented and recommendations for future work in this field are made.

Modelling estuarine and coastal flows using an unstructured triangular finite volume algorithm

by Roger Falconer - Cardiff University

Paper 80:  Namin, M. M., Lin, B. and Falconer, R. A. 2004. Modelling estuarine and coastal flows using an unstructured triangular finite volume algorithm. Advances in Water Resources. 27(12), 1179-1197

Abstract
Details are given of the development and application of a numerical model for predicting free-surface... more Abstract
Details are given of the development and application of a numerical model for predicting free-surface flows in estuarine and coastal basins using the finite volume method. Both second- and third-order accurate and oscillation free explicit numerical schemes have been used to solve the shallow water equations. The model deploys an unstructured triangular mesh and incorporates two types of mesh layouts, namely the ‘cell centred’ and ‘mesh vertex’ layouts, and provides a powerful mesh generator in which a user can adjust the mesh-size distribution interactively to create a desirable mesh. The quality of mesh has been shown to have a major impact on the overall performance of the numerical model.
The model has been applied to simulate two-dimensional dam break flows for which transient water level distributions measured within a laboratory flume were available. In total 12 model runs were undertaken to test the model for various flow conditions. These conditions include: (1) different bed slopes (ranging from zero to 0.8%), (2) different upstream and downstream water level conditions, and (3) initially wet and dry bed conditions, downstream of the dam. Detailed comparisons have been made between model predicted and measured water levels and good agreement achieved between both sets of results. The model was then used to predict water level and velocity distributions in a real estuary, i.e. the Ribble Estuary, where the bed level varies rapidly at certain locations. In order to model the whole estuary, a 1-D numerical model has also been used to model the upper part of the estuary and this model was linked dynamically to the 2-D model. Findings from this application are given in detail.

Modelling the fate of faecal indicators in a coastal basin

by Roger Falconer - Cardiff University

Paper 92:  Kashefipour, S. M., Lin, B. and Falconer, R. A. 2006. Modelling the fate of faecal indicators in a coastal basin. Water Research. 40(7), 1413-1425

Abstract
The paper describes a modelling study of near-shore coastal waters, undertaken to assess the impact of... more Abstract
The paper describes a modelling study of near-shore coastal waters, undertaken to assess the impact of various bacterial input loads on the receiving waters in a coastal basin in the UK. Total and faecal coliforms, used as the indicators for bathing water quality under the European Union (EU) Bathing Water Directive, were numerically modelled using a 2D depth integrated hydro-environmental model. Details are given of the governing equations and solution methods used in the numerical model, together with a discussion of the recent development in faecal bacterial indicator modelling. Details are also given of a field data collection exercise, which involved initially collecting existing information on effluent input loads and followed by an intensive field survey. Using the water quality model, the mortality rate of the pathogen bacteria was investigated. Three methods were used to represent the relationship between the decay rate and the level of solar radiation including: a constant decay rate, day- and night-time decay rates and a solar radiation related time varying decay rate. Relatively close agreement between model predicted and measured total and faecal coliform concentration distributions were obtained for different day- and night-time decay rates and time varying decay rates. No significant differences were found in the optimum decay rates for total and faecal coliform levels. Finally, the impact of the individual inputs on the bathing water quality of the basin was also statistically and numerically investigated. Results showed that the River Irvine was the most significant input during high river flows, and that under these conditions the bathing waters were likely to fail to comply with the European Union Bathing Water Directive. For base river flow conditions the Meadowhead effluent input was found to be critical for both total and faecal coliform level predictions.

Scaling tidal channel geometry with marsh island area: A tool for habitat restoration, linked to channel formation process

by Greg Hood

Hydraulic geometry and related analyses are often used to investigate tidal channel geometry and evolution and inform... more Hydraulic geometry and related analyses are often used to investigate tidal channel geometry and evolution and inform marsh restoration. An alternative approach is presented that avoids calculating tidal prism and allows analysis of additional
channel metrics. It relies on scaling relationships between marsh island surface area and various metrics of the set of tidal channels draining each island. In the Skagit Delta marshes (Washington, United States), total channel surface area and length and surface area of the largest channel draining an island scaled disproportionately with island area, suggesting restoration of a 100-ha site would be preferable to restoration of 10 separate 10-ha sites to maximize channel length and area. A model of channel formation through random island conglomeration replicated observed scaling patterns, linking channel scaling to blind channel evolution from river distributaries. Channel size and complexity varied spatially,
with significant deficits in an eroding marsh isolated from river distributaries and riverine sediments.

A conceptual model of depositional, rather than erosional, tidal channel development in the rapidly prograding Skagit River Delta (Washington, USA)

by Greg Hood

The origin and growth of blind tidal channels is generally considered to be an erosional process. This paper describes... more The origin and growth of blind tidal channels is generally considered to be an erosional process. This paper describes a contrasting depositional model for blind tidal channel origin
and development in the Skagit River delta, Washington, USA. Chronological sequences of historical maps and photos spanning the last century show that as sediments accumulated at the river mouth, vegetation colonization created marsh islands that splintered the river into distributaries. The marsh islands coalesced when intervening distributary channels gradually
narrowed and finally closed at the upstream end to form a blind tidal channel, or at mid-length to form two blind tidal channels. Channel closure was probably often mediated through gradient reduction associated with marsh progradation and channel lengthening, coupled with large woody debris blockages. Blind tidal channel evolution from distributaries was common in the Skagit marshes from 1889 to the present, and it can account for the origin of very small modern blind tidal channels. The smallest observed distributary-derived modern blind tidal channels have mean widths of 0·3 m, at the resolution limit of the modern orthophotographs. While channel initiation and persistence are similar processes in erosional systems, they are different processes in this depositional model. Once a channel is obstructed and isolated from distributary flow, only tidal flow remains and channel persistence becomes a function of tidal prism and tidal or wind/wave erosion. In rapidly prograding
systems like the Skagit, blind tidal channel networks are probably inherited from the antecedent distributary network. Examination of large-scale channel network geometry of such
systems should therefore consider distributaries and blind tidal channels part of a common channel network and not entirely distinct elements of the system. Finally, managers of tidal
habitat restoration projects generally assume an erosional model of tidal channel development. However, under circumstances conducive to progradation, depositional channel development may prevail instead.

Indirect Environmental Effects of Dikes on Estuarine Tidal Channels: Thinking Outside of the Dike for Habitat Restoration and Monitoring

by Greg Hood

While the most obvious effects of dike construction and marsh conversion are those affecting the converted
land... more While the most obvious effects of dike construction and marsh conversion are those affecting the converted
land (direct or intended effects), less immediately apparent effects also occur seaward of dikes (indirect or
unintended effects). I analyzed historical photos of the Skagit River delta marshes (Washington, U.S.) and compared
changes in estuarine marsh and tidal channel surface area from 1956–2000 in the Wiley Slough area of the South Fork
Skagit delta, and from 1937–2000 in the North Fork delta. Dike construction in the late 1950s caused the loss of 80 ha
of estuarine marsh and 6.7 ha of tidal channel landward of the Wiley Slough dikes. A greater amount of tidal channel
surface area, 9.6 ha, was lost seaward of the dikes. Similar losses were observed for two smaller North Fork tidal channel
systems. Tidal channels far from dikes did not show comparable changes in channel surface area. These results are
consistent with hydraulic geometry theory, which predicts that diking reduces tidal flushing in the undiked channel
remnants and this results in sedimentation. Dikes may have significant seaward effects on plants and animals associated
with tidal channel habitat. Another likely indirect dike effect is decreased sinuosity in a distributary channel of the South
Fork Skagit River adjacent to and downstream of the Wiley Slough dikes, compared to distributary channels upstream
or distant from the dikes. Loss of floodplain area to diking and marsh conversion prevents flood energy dissipation over
the marsh surface. The distributary channel has responded to greater flood energy by increasing mean channel width
and decreasing sinuosity. Restoration of diked areas should consider historic habitat loss seaward of dikes, as well as
possible benefits to these areas from dike breaching or removal. Habitat restoration by breaching or removal of dikes
should be monitored in areas directly affected by dikes, areas indirectly affected, and distinct reference areas.

Case History of Bodega Harbor, California

by Lawrence B. Karp

Rock warming and drying under simulated intertidal conditions, Part II: Weathering and biological influences on evaporative cooling and near-surface micro-climatic conditions as an example of biogeomorphic ecosystem engineering

by Martin Coombes

Martin A. Coombes and Larissa A. Naylor 2012. Rock warming and drying under simulated intertidal conditions, part II: weathering and biological influences on evaporative cooling and near-surface micro-climatic conditions as an example of biogeomorphic ecosystem engineering. Earth Surface Processes and Landforms 37(1), p100-118.

The way in which rocks and engineering materials heat-up and dry-out in the intertidal zone is of relevance to both... more The way in which rocks and engineering materials heat-up and dry-out in the intertidal zone is of relevance to both weathering and ecology. These behaviours can be measured in the laboratory under controlled conditions designed to replicate those occurring in the field. Previous studies have demonstrated differences in thermal behaviours between rock types and changes through time as a result of soiling in terrestrial environments, but the influence of weathering and colonization on rock behaviours in the intertidal zone has not been previously assessed.

We measured the warming and drying of blocks of rock (limestone and granite) and marine concrete during ‘low-tide’ events simulated in the laboratory, before and after a period of exposure (8 months) on rock platforms in Cornwall, UK. As well as differences between the material types, temperatures of control (unexposed) and field-exposed blocks differed in the order of 1–2 °C. Drying behaviours were also different after field exposure. Differences during the first few hours of exposure to air and heat were attributed to discolouration and albedo effects. Over longer periods of time, changes in the availability of near-surface pore water as a result of micro-scale bioerosion of limestone and the development of bio-chemical crusts on marine concrete (observed using SEM) are suggested as mechanisms enhancing and reducing, respectively, the efficiency of evaporative cooling. The retention of moisture by epilithic biofilms may also influence thermal and drying behaviours of granite.

These observations represent one of the first examples of cross-scalar biogeomorphic linkages in the intertidal zone. The significance of the results for the subsequent efficiency of weathering, and near-surface micro-climatic conditions experienced by colonizing organisms is discussed. The involvement of microorganisms in the creation of more (or less) ecologically stressful conditions through alteration of substratum geomorphic properties is suggested as an example of ‘biogeomorphic ecosystem engineering’. Copyright © 2011 John Wiley & Sons, Ltd.

Rock warming and drying under simulated intertidal conditions, Part I: Experimental procedures and comparisons with field data

by Martin Coombes

Martin A. Coombes 2011. Rock warming and drying under simulated intertidal conditions, part I: experimental procedures and comparisons with field data. Earth Surface Processes and Landforms 36(15) 15, p2114–2121.

The wetting-drying and warming-cooling behaviours of rock and stone are known to influence the nature and rate of... more The wetting-drying and warming-cooling behaviours of rock and stone are known to influence the nature and rate of weathering. The way materials warm-up and dry-out also influences their suitability as biological substrata. While thermal behaviours have been measured under controlled laboratory conditions, previous experiments have largely been restricted to simulating terrestrial conditions due to practical constraints. Where efforts have been made to simulate intertidal conditions, expansion and contraction of rocks or rates of breakdown (i.e. sediment production and weight loss) have been measured, while detailed observations of thermal and drying behaviours have rarely been made.

A simple, semi-automated procedure is described that enabled measurement of surface temperatures and desorption (evaporative water loss) of different material types (rock and concrete) under simulated semidiurnal tide conditions. Some preliminary results are presented illustrating the types of data that were obtained, and comparisons are made with temperature data collected on a rock platform in the UK to assess the ability of the procedure to adequately represent field conditions. Copyright © 2011 John Wiley & Sons, Ltd.

Avulsion in action: Reconstruction and modelling sedimentation pace and upstream flood water levels following a Medieval tidal-river diversion catastrophe (Biesbosch, The Netherlands, 1421–1750 AD)

by Kim Cohen

M.G. Kleinhans, H.J.T. Weerts & K.M. Cohen (2010) Geomorphology. In press. Online 24-12-2009. doi:10.1016/j.geomorph.2009.12.009

Deltaic land inundated by storm surges may reform by sedimentation from natural or human-induced river diversions.... more Deltaic land inundated by storm surges may reform by sedimentation from natural or human-induced river diversions. This is a well-known trigger mechanism for creation of new channels in coastal plains and deltas, which may develop into main channels and lead to abandonment of older (avulsion), particularly in the downstream parts of deltas that host tidal rivers. These new channels develop as part of deltaic splay complexes that heal initial diversion scars and fill up flooded basins at a certain pace.

We study a case with excellent historical and geological data of a diversion of the river Rhine following catastrophic inundations (1421–1424 AD) into medieval reclaimed land. Numerical modelling of deltaic splay and channel development is combined with reconstructions from historical maps and geological data. This yields detailed insight in pacing of splay sedimentation and changing hydrodynamics in the channel upstream of the diversion in the two centuries following the inundation.

The equivalent of the full sand budget of the river Rhine was effectively trapped in the developing splay. The tidal-avulsion splay evolution on aspects is similar to that of fluvial crevassing into flood basins documented for settings lacking ‘downstream’ tidal control. The typical small-scale delta-lobe avulsion cycles: mouth bar formation, backward sedimentation, upstream avulsion, channel progradation and mouth bar formation are reproduced in the splay-modelling. The pacing of splay development, however, is relatively fast due to the presence of tides and the water depth in the receiving basin. The diversion had a strong upstream impact, in particular on water levels in the feeding river channel at stages of peak flow. For two centuries levels were significantly raised, because bifurcation-imposed reduced transport capacity and associated sedimentation at the diversion site increased hydraulic roughness and hampered flow.

These findings have implications regarding flood mitigation for presently-planned lower-delta engineered diversions. Furthermore, they elucidate the differences between upstream fluvial avulsion and downstream tidal-river avulsion that are important to recognise if we want to understand how deltaic distributary-networks are maintained.

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Link to the full paper is found here: http://dx.doi.org/10.1016/j.geomorph.2009.12.009

The academia download is my new geological cross-sections of the Biesbosch area in mini-poster format; supplementary material to the paper.

Biogeomorphology of Coastal Structures: Understanding interactions between hard substrata and colonising organisms as a tool for ecological enhancement

by Martin Coombes

Martin A. Coombes 2011. Biogeomorphology of Coastal Structures: Understanding interactions between hard substrata and colonising organisms as a tool for ecological enhancement. PhD Thesis, University of Exeter in Cornwall.

Urbanisation is increasingly recognised as a major ecological pressure at the coast. By 2035, the Department for... more Urbanisation is increasingly recognised as a major ecological pressure at the coast. By 2035, the Department for Environment, Food and Rural Affairs will have to spend £1 billion each year on flood defence and erosion control infrastructure if current levels of protection are to be sustained in England and Wales; this represents a substantial commitment to building new hard structures. Ecological research has shown that structures like seawalls, breakwaters, and harbour and port infrastructure are poor surrogates for undisturbed rocky shores. This, alongside substantial international policy drivers, has led to an interest in the ways in which structures might be enhanced for ecological gain. Virtually all of this research has been undertaken by ecologists, while the contribution of geomorphological understanding has not been fully recognised. This thesis presents an assessment of the two-way interactions between colonising organisms and the materials used to build hard coastal structures under a framework of biogeomorphology. The influence of material type and small-scale surface texture on early colonisation is assessed alongside detailed observations of the ways in which biota are involved in the alteration of substratum properties and behaviours through weathering and erosion in the intertidal zone. The research demonstrates that biotic (organisms) and abiotic (material substrata) components of coastal structures are inherently linked at various spatial and temporal scales through complex biogeomorphic interactions and feedbacks. Importantly, these interactions have consequences for the subsequent operation of ecological and geomorphological processes that are of relevance to urban marine ecology, weathering and rock coast geomorphology, and engineering. This thesis demonstrates the considerable potential to manipulate substratum-biota interactions on artificial structures for ecological gain, both directly and indirectly. More broadly, the explicitly interdisciplinary methodological approach adopted shows the value and necessity of integrated research for achieving useful, applied outcomes.

Short communication: Engineering properties of wetland plants with application to wave attenuation

by Ricardo J. Colón-Rivera

Journal of Coastal Engineering 2011

This technical note presents empirically-derived values for biophysical attributes of several commonly
occurring... more This technical note presents empirically-derived values for biophysical attributes of several commonly
occurring wetland plant species, including plant stem diameter and tapering, plant clump and stem spacing
statistics, biomass, Young's modulus of elasticity, and bending strength. These parameters can be used to more
realistically configure plant canopies in numerical and laboratory studies to further our understanding of
wave attenuation by wetlands.