text stringlengths 59 1.12k |
|---|
notably, gravel can support a steep gradient typically of the order of 1 in 8 with a tendency to form a near vertical berm towards the high water mark and a step at the wave break point. Swell wave conditions promote onshore accretion in the swash zone, with storm conditions promoting rapid offshore erosion. Despite th... |
at the high water mark of the beach below which is a beach face of uniform slope, which ends in the step feature at the low water mark. Cusp formation on gravel beaches is another distinctive feature. They can form rapidly when the wave approach is near normal, but are also washed out rapidly when the wave approach cha... |
the literature, two dominant models of cusp formation are recognised, namely edge wave forced and swash circulation/self organisation modes. However, cusp formation on gravel beaches has not been discussed very much in the literature . |© A. J. Chadwick| The steep beach gradient allows waves to progress much closer ins... |
of infra-gravity waves. Even during storms, a wide surf zone is rare. An important consequence of this is that the swash zone can be of similar width to the surf zone and hence the sediment transport within the swash zone is of considerably more significance than on sand beaches. A second effect of the steep beach grad... |
to a narrower zone than is experienced on a sand beach, with the result that refraction is often observed to be incomplete and the waves arrive at the beach face with some considerable angle, resulting in significant longshore transport. Gravel beaches are also much more reflective than sand beaches, with reflection co... |
of gravel which, compared to a sand beach, increases the potential for infiltration during the swash uprush and exfiltration during the swash downrush. This induces a downward, stabilising force on sediment movement during the uprush and a lift force during backwash. Conversely, there is a thinning of the boundary laye... |
backwash, leading to deceased shear stress on the bed. This latter effect is thought to predominate. On a gravel beach the backwash volume can also be considerably reduced, lowering the backwash velocities (see Elfrink and Baldock (2002) for a detailed review). It is these processes that lead to the formation of the hi... |
common geomorphological feature across the world, many of which are composed of gravel. Their essential features comprise a narrow, elongated ridge of sand or gravel existing slightly above the high tide level. The ridge generally extends parallel to the shore, but is separated from it by a wetland, lagoon or a tidal f... |
wetlands and lagoons formed behind barrier beaches provide shelter for many coastal habitats and are therefore of considerable environmental significance. One explanation of their formation is that they have been formed by landward migration of submerged sand/shingle banks with rising sea levels since the last ice age.... |
barrier beaches are related to local wave and current climate, tidal variations, frequency and magnitude of storm events, barrier geometry and type of beach sediment and permeability. Over longer terms, the primary factors for change and modification of barrier beaches are sea level rise, longshore sediment transport a... |
can respond to these factors by landward or seaward migration, reshaping and re-alignment and crest breakdown or build-up . The episodic processes of over-washing, over-topping and associated breaching are the primary phenomena behind long term evolution. Understanding the processes of sediment transport on gravel beac... |
still rely on one-line models since, as yet, 3D morphodynamic models are restricted to short- and medium-term predictions and none have been validated against coarse-grained field data. Most one-line models make use of empirical total longshore transport equations. Hence, the formulation of a reliable estimate of longs... |
port extensions, derivation of sediment budgets for coastal areas and the appraisal of long term beach stability. To some extent, the mechanisms associated with the longshore transport of gravel may be differentiated from that of sand. Generally, for a sand seabed the oscillatory force due to the passage of a (breaking... |
to the longshore current can then transport the sand. On gravel beaches the sediment normally moves as bedload and is largely confined to the swash zone. As the flow in the uprush is perpendicular to the wave crest and in the backwash is perpendicular to the beach contours, the gravel describes a 'sawtooth', or zig-zag... |
rates is extremely difficult on a gravel beach. Direct measurement of longshore transport has been attempted using a variety of techniques, such as deposition of a tracer material (radioactive, dyed or artificial sediment) or installation of traps (see Van Wellan et al. (2000) for a review). |all pictures: © A. J. Chad... |
or aerial surveys. If surveys are carried out over several years a trend for accretion or depletion may be discernible. This is not necessarily a direct measure of the longshore transport rate along the coast. Rather it is an indication of any imbalances in the supply of sediment from one point to another. However, whe... |
from further up the coast, comparisons of beach volumes before and after construction can give some indication of the longshore transport rates. |all pictures: © A. J. Chadwick| The most widely used formula for calculating longshore transport is the CERC equation (US Army Corps of Engineers, 1984). The equation was der... |
formula is intended to include both bedload and suspended load and is usually given in the form of: is the immersed weight sediment transport rate is the longshore component of wave power where E is wave energy, is group wave speed, θ is wave approach angle, subscript b refers to wave break point and where K is a dimen... |
transport rate, , is related to by: where where ρs is sediment density, ρ is sea water density, e is voids ratio. There is no direct inclusion of the influence of grain size in the CERC equation, other than via the coefficient, K. It should be noted that for random waves, the choice of wave height used in the CERC equa... |
Hs or root mean square wave height, Hrms) must be correlated with the K value. Much confusion can arise, as some authors have used Hs and others Hrms without explicitly stating which one. For Rayleigh distributed waves, the K value using Hrms is twice that using Hs. A suggested value for K using Hrms is 0.77 for sand s... |
(1989) data suggested a K value of 7% of that for sand (K=0.053). This was later found to work well at another beach site, Slapton Sands, Devon,UK (see Alegria-Arzaburu & Masselink (2010) ). Chadwick (1991) also developed a numerical model to predict longshore transport on gravel beaches. The hydrodynamic module uses t... |
velocities throughout the surf and swash zones. These are combined with a sediment transport module based on Bagnold's stream power concept. Instantaneous transport rates across the surf and swash zones are subsequently summed in space and time to determine the total longshore transport rate. Thus, this model specifica... |
importance on shingle beaches. The model required calibration of only the friction coefficient, which was determined from field data. Subsequently, an algebraic formula (the Chadwick-Van Wellen formula) was derived from the numerical model results given by: This equation was specifically designed for application to gra... |
other longshore transport equations, applicable to gravel beaches, see Van Wellen et al (2000) . Large scale experimental studies |© A. J. Chadwick| More recent work on coarse grained beaches was undertaken by the EU project “Large Scale Modelling of Coarse Grained Beaches” which was undertaken between March-May 2002. ... |
small scale models. The measurements included not only the wave field and resultant equilibrium profile development, but also detailed measurements of pore water pressures under the swash face. The experimental results of this work may be found in López de San Román-Blanco et al (2006) . This experiment was used to dev... |
in more detail in this article. Subsequently another large scale experimental study of gravel barrier beaches was undertaken in BARDEX (Barrier Dynamics Experiment) in the Delta wave flume, the Netherlands, during June and July 2008. One unique aspect of this work was the inclusion of the effects of a back barrier lago... |
Engineering has been devoted to papers resulting from this work (see Turner and Masselink (2012)) . These include details of the observations, the effect of the lagoon water level on the beach profile, new measurements of and prediction techniques for wave friction factors, new predictive techniques for assessing barri... |
evolution and the morphological effect of washover. Parametric models for equilibrium profiles The prediction of the expected profile for a gravel beach is very different from the concepts used for equilibrium profiles on a sand beach. The problem was first comprehensively addressed by van der Meer (1988) and Powell (1... |
case and large and small scale with gravel in van der Meer’s case). Powell’s work resulted in the development of a parametric profile model, which described the profile as a set of three curves: from the crest to the still water level, from the still water level to a transition point and from the transition point to th... |
found to work well using the data from the GWK experiment ). Parametric models for barrier stability Bradbury (2000) carried out a series of 3-D mobile bed laboratory tests on barrier crest response to hydrodynamic conditions and initial barrier geometry. Based on the model investigations, several categories of barrier... |
raised by overtopping, crest lowered due to undermining of crest but with no overtopping, crest raised by over-washing with roll-back, crest lowered by over-washing with roll-back and finally, no change to the crest elevation with profile contained to seaward of the barrier crest. He developed an expression for an over... |
steepness (Hs/Lm), barrier free board (Rc) and barrier cross-sectional area Ba (above the still water line), given by: The expression was validated against field data gathered at Hurst Spit, UK and found to be consistent with the field data. In addition, a conceptual model for barrier over-washing was formulated. Accor... |
the critical barrier inertia is exceeded then the crest will be lowered by over-washing. Modelling cross shore profile development |Picture courtesy of A. Pedrozo-Acuna| The first of several recent deterministic process based models for predicting the profile response of coarse grained beaches was developed by Lawrence... |
formulation were a useful approach for process-based modelling of gravel beach profile evolution. This model was subsequently extended to model the sediment transport of grain size fractions and thus to predict sediment sorting across the beach face . However, it was found that this numerical model scheme was not stabl... |
that the two principle sediment parameters of friction (f) and sediment transport efficiency (C) were controlling the shape of the gravel beach profile. With f and C as constant values, accurate prediction of the profile evolution was not possible. The use of bigger friction factors in the uprush slightly improved the ... |
in the uprush compared to the backwash, better predictions of the beach profile resulted. The physical processes which dictate the differences between the predicted and measured profiles were hypothesised as being related to infiltration effects on the flow above the beach face and more accelerated flow in the uprush. ... |
time. The more recent results reported by Jamal et al (2010) and Williams et al (2012) indicate that including this process leads to significant improvements in prediction. Pedrozo et al (2010) have also highlighted the importance of the impulsive pressures induced by plunging breakers on gravel beach sediment transpor... |
gravel and mixed beaches offers much opportunity to enhance our knowledge. Longshore transport prediction is still imprecise and cross shore processes very complex and not completely understood. Current parametric design methods leave much to be desired. Further field and large scale experimental studies remain a prima... |
heads of the previously mentioned studies. Numerical modelling tools can still benefit greatly from improved process representation, including infiltration/exfiltration, interactions with groundwater flows, impulsive pressure forces, the incorporation of grain size fractions and the prediction of sediment sorting acros... |
average, 160 metres wide. The height of the beach is typically 11 metres above mean sea level. The beach stabilised close to its present position around 5000 years ago. A rent research paper concerning the internal structure of Chesil beach (Bennett et al (2009)) also contains a good summary of the extensive historical... |
rise on barrier migration and its susceptibility to over-washing and overtopping, inter alia. It was found that the processes at work on the Slapton shoreline included: |© A. J. Chadwick| - Short-term changes in beach profile due to storms, acting over a period of several days. These storms cause cut-back of the seawar... |
Overtopping, in which wave action throws water and sediment onto the crest. - Overflowing, or overwashing, where extremely high water levels coincident with wave action cause water to flow over the crest of the ridge. This can cause significant changes to the crest and backslope of the ridge. - Medium-term changes in b... |
of months or several years. - Long-term landward retreat; the barrier beach responds to sea level rise by “roll-over” and by increasing its crest height. This process involves overwashing, transferring sediment from the shore-face to the back barrier area. This is an episodic rather than a continuous process. - Planfor... |
(Strete and Torcross), landward retreat results in a gradual increase in both curvature and length. In a later comprehensive field study of this site, Alegria-Arzuburu and Masselink (2010) used an ARGUS video system to monitor short and medium term changes. This study confirmed many of the conclusions reached in the Ch... |
shore processes which affect beach erosion and accretion. An up to date and comprehensive review of gravel beaches and barriers may be found in Anthony (2008) . Gravel beach dynamics are reviewed by Buscombe and Masselink (2006) . Stripling et al (2008) present a good review of barrier beaches and their management. Fin... |
beach monitoring and maintenance, evaluation of the state and performance of a beach, design, procurement, execution and the after-care of beach improvement schemes. It also includes case studies to illustrate popular management techniques and draws from experience of existing management approaches. - Risk and coastal ... |
to Coastal Zone Management (ICZM) - Natural causes of coastal erosion - Human causes of coastal erosion - Coastal defense techniques - Natural barriers - Relative sea level - Shore nourishment - ↑ 1,0 1,1 Buscome D., Masselink G. (2006). Concepts in gravel beach dynamics. Earth science Reviews 79 33-52. - ↑ Fuller, R. ... |
UK. Classic conflicts in coastline management. Biological conservation. - ↑ 3,0 3,1 Powell, K. A. (1990). Predicting short term profile response for shingle beaches. HR Wallingford Report SR 219. - ↑ Diserens, A. P. & Coates, T. T. (1993). UK South Coast shingle beach study: storm response of shingle beaches. HR Wallin... |
Elfrink B, Baldock T. (2002) Hydrodynamics and sediment transport in the swash zone: a review and perspectives. Coastal Engineering, 45, 149–167. - ↑ Orford, J.D., Carter, R.W.G., Jennings, S.C. and Hinton, A.C. (1995). Processes and time scales by which a coastal gravel dominated barrier respond geomorphologically to ... |
R.W.G., Forbes, D.L., Jennings, S.C., Orford, J.D., Shaw, J. and Taylor, R.B., (2003), Barrier and lagoon coast evolution under differing relative sea level regimes-examples from Ireland and Nova-Scotia, Marine Geology, 88, Issue 3-4, pp.221-242. - ↑ 11,0 11,1 Ruiz de Alegria-Arzaburu, A., Masselink, G. (2010). Storm r... |
A J. (1991). An unsteady flow bore model for sediment transport in broken waves Part 1: The development of the numerical model. Proc. Instn. Civ. Engrs. Part 2, 1991, 91, Dec. 719 - 737. - ↑ Chadwick, A J. (1991). An unsteady flow bore model for sediment transport on broken waves Part II: The properties, calibration an... |
Civ. Engrs. Part 2, 1991, 91, Dec., 739-753. - ↑ 14,0 14,1 López de San Román-Blanco, B., Coates, T., Holmes, P., Chadwick, A. J., Bradbury, A., Baldock, T., Pedrozo-Acuña, A., Grüne, J. (2006). Large scale experiments on gravel and mixed beaches: experimental procedure, data documentation and initial results. Coastal ... |
A.J. (2006). On the cross-shore profile change of gravel beaches. Coastal Engineering, 53 (4), 335-347. - ↑ Ian L. Turner, Gerd Masselink (2012). Coastal gravel barrier hydrology — Observations from a prototype-scale laboratory experiment (BARDEX). Coastal engineering, 63, 13-22 - ↑ Van der Meer J. (1988) Rock slopes a... |
Predicting breaching of shingle barrier beaches- recent advances to aid beach management, 35th MAFF (DEFRA) Conf of River and Coastal Engineers. - ↑ Lawrence, J, Chadwick, A J and Fleming, C A. (2001). A phase resolving model of sediment transport on coarse grained beaches. In: Billy L Edge (ed) Coastal Engineering 200... |
↑ Jon J. Williams, Amaia Ruiz de Alegría-Arzaburu, Robert T. McCall, Ap Van Dongeren (2012). Modelling gravel barrier profile response to combined waves and tides using XBeach: Laboratory and field results. Coastal engineering, 63, 62-80 - ↑ Pedrozo-Acuña, A., Torres-Freyermuth, A., Zou, Q., Hsu, T.-J., Reeve, D.E. (20... |
Bennett M. R., Cassidy N. J., Pile J. (2009). Internal structure of a barrier beach as revealed by ground penetrating radar (GRP) Chesil beach, UK. Geomorphology 104, 218-229. - ↑ Chadwick, A. J., Karunarathna, H., Gehrels, R, Massey, A. C.,O’Brien, D. ,Dales, D.(2005). A New Analysis of the Slapton Barrier Beach Syste... |
A.H. and Cope S.N. (2008) Understanding Barrier Beaches Joint DEFRA/EA Flood and Coastal Erosion Risk Management R&D Programme. Technical Report FD1924/TR Please note that others may also have edited the contents of this article. |
At Walmart, we talk a lot about learning from one another and working in partnership to create global change. A recent report, “Smart Moves,” examines some of the best practices by companies working to cut emissions from transportation. Emissions from freight transportation are no small problem. The report’s author, Ja... |
out, the report is loaded with statistics about shipping emissions as well as examples of smart moves by companies that reduced emissions and saved money at the same time. Here’s what he highlighted about Walmart: Wal-Mart: Direct shipment Wal-Mart worked with Minute Maid to eliminate one stop in the chain used to deli... |
product moves directly from a production facility in Florida to Wal-Mart distribution centers. Eliminating delivery to Minute Maid’s own distribution centers slashed CO2 emissions by 1,500 metric tons annually and added six days to the shelf life of the orange juice. |
What is Rainwater Harvesting? Rainwater harvesting is an ancient practice of catching and holding rain for later use. In a rainwater harvesting system, rain is gathered from a building rooftop or other source and is held in large containers for future use, such as watering gardens or washing cars. This |
practice reduces the demand on water resources and is excellent during times of drought. Why is it Important? In addition to reducing the demand on our water sources (especially important during drought), rainwater harvesting also helps prevent water pollution. Surprised? Here’s why: the success of the 1972 Clean Water... |
has meant that the greatest threat to New York’s waterbodies comes not from industrial sources, but rather through the small actions we all make in our daily lives. For example, in a rain storm, the oil, pesticides, animal waste, and litter from our lawns, sidewalks, driveways, and streets are washed |
down into our sewers. This is called non-point source (NPS) pollution because the pollutants come from too many sources to be identified. Rainwater harvesting diverts water from becoming polluted stormwater; instead, this captured rainwater may be used to irrigate gardens near where it falls. In New York City, keeping ... |
out of the sewer system is very important. That’s because the city has an old combined sewer system that uses the same pipes to transport both household waste and stormwater to sewage treatment plants. During heavy rains, the system overloads; then untreated sewage and contaminated stormwater overflow into our rivers |
and estuary, with serious consequences: Who is Harvesting Rainwater in New York City? Back in 2002, a drought emergency pushed many community gardens to the brink of extinction. For the first time in twenty years, community gardeners were denied permission to use fire hydrants, the primary source of water for |
most community gardens. This crisis led to the formation of the Water Resources Group (WRG), an open collaboration of community gardening and environmental organizations. With help from the WRG, rainwater harvesting systems have now been built as demonstration sites in twenty NYC community gardens. At community gardens... |
rain is diverted from the gutters of adjacent buildings and is stored in tanks in the gardens. A 1-inch rainfall on a 1,000-square-foot roof produces 600 gallons of water. The tanks are mosquito proof, so the standing water does not encourage West Nile virus. Because rainwater is chlorine free, it |
is better than tap water for plant growth, meaning healthier plants. And it’s free! What are Other Cities Doing? Many cities have adopted creative, low-cost ways to stop wasting rainwater by diverting it from their sewage systems and putting it to use where it falls. Here are some examples: What |
Can I Do? Spread the word! Educate those around you on the importance of lifestyle decisions. Tell people not to litter, dump oil down storm drains, or overfertilize their lawns. Install a rainwater harvesting system at your home, school, business, or local community center. Contact your local elected officials, and |
Students at a local college walked around campus Tuesday without shoes on and it was all for a good cause. Bowling Green Technical College held a "One Day Without Shoes" event. It's meant to raise awareness for the millions of |
children around the World who don't have proper footwear and are therefore, exposed to disease and injuries. Students and community members walked over a gravel pathway barefoot at the event. "People are not really aware that kids go daily without |
shoes. Roughly, 30,000 children just in the area are going without shoes," says John Rose, one of the event's coordinators. "I think it's a good awareness and it shows people what kids go through every day," says Haley Womac, a |
student at BGTC. Those who took part also got the chance to get pedicures. Organizers say the Philippines and Kenya are just two of the countries where many children go without shoes. |
What is Morbid Obesity? Obesity becomes "morbid" when it reaches the point of significantly increasing the risk of one or more obesity-related health conditions or serious diseases (also known as co-morbidities) that result either in significant physical disability or even death. As you read about morbid obesity you ma... |
of the same condition and can be used interchangeably. Morbid obesity is typically defined as being 100 lbs. or more over ideal body weight or having a Body Mass Index of 40 or higher. According to the National Institutes of Health Consensus Report, morbid obesity is a serious disease and must be treated as such. It is... |
What Your Cholesterol Level Means How’s your cholesterol? Time to get it checked!?? Keeping your cholesterol levels healthy is a great way to keep your heart healthy – and lower your chances of getting heart disease or having a stroke. Cholesterol can be tricky to understand, though, because not all is bad for you. Som... |
you can do as a first step is to know your cholesterol numbers by getting your cholesterol tested. Here are some easy ways for you to understand what the testing involves, how it can help you and ways to improve your health by improving your cholesterol.?? The American Heart Association endorses the National Cholestero... |
adults age 20 or older should have a fasting lipoprotein profile — which measures total cholesterol, LDL (bad) cholesterol, HDL (good) cholesterol and triglycerides — once every five years. This test is done after a nine- to 12-hour fast without food, liquids or pills. It gives information about total cholesterol, LDL ... |
test report will show your cholesterol levels in milligrams per deciliter of blood (mg/dL). To determine how your cholesterol levels affect your risk of heart disease, your doctor will also take into account other risk factors such as age, family history, smoking and high blood pressure.?? A complete fasting lipoprotei... |
Save money with properly inflated tires (NewsUSA) - Tire pressure monitoring systems (TPMS) are now a standard safety feature on all new cars in the United States. TPMS automatically monitors tire pressure and alerts the driver when the pressure in one or more tires becomes significantly low -- and potentially |
dangerous. Still, conducting monthly tire pressure checks is one of the smartest driving moves you can make. Not only are properly inflated tires critical for vehicle safety, they also increase fuel efficiency and reduce carbon dioxide emissions. Increase Fuel Efficiency According to the U.S. Department of Energy, 3.56... |
of gasoline are wasted every day due to incorrectly inflated tires. The good news is you can improve gas mileage just by keeping tires inflated to the proper pressure. In fact, one study showed that if gas costs $3 per gallon, proper tire pressure can save you up to $432 |
at the pump each year. Reduce Carbon Dioxide Emissions According to the U.S. Environmental Protection Agency, the typical car in the United States releases more than five tons of carbon dioxide into the atmosphere each year. By keeping tires properly inflated, you can reduce your vehicle's "carbon footprint" by an |
average of 327 pounds per year. Because a tire can lose up to half its air pressure without appearing to be under-inflated, you cannot rely on a tire's appearance to determine whether it's properly inflated or not. Tire Pressure Tips To help ensure your tires are properly inflated year-round, here |
are some tips from Schrader, a manufacturer of TPMS: * Check the pressure in all four tires -- and the spare tire -- monthly with an accurate tire gauge, and always check tire pressure before a long road trip. * The "right" pressure for your vehicle's tires can be found |
in the vehicle's manual or on the driver door edge, glove box or fuel door. Do not follow the information listed on the tire sidewall. * For the most accurate reading, tires should be checked when they are cool. * Always remember to replace the valve cap. Distributed by Internet |
Streptococcus, Group B It is possible that the main title of the report Streptococcus, Group B is not the name you expected. Please check the synonyms listing to find the |
alternate name(s) and disorder subdivision(s) covered by this report. - Group B Streptococcal Septicemia of the Newborn - Lancefield Group B Streptococcus - Sepsis of the Newborn - Streptococcus Agalactiae |
- Infant Early-Onset Streptococcus, Group B - Infant Late-Onset Streptococcus, Group B - Adult Onset Streptococcus, Group B Group B streptococcus (group B strep) is a type of bacteria that |
causes infection among newborns, pregnant women or women after childbirth, females after gynecologic surgery, and older male and female patients with other serious diseases. Group B strep remains the most |
common cause among newborns (neonates) of infection of the blood (septicemia) and of the brain (meningitis). The responsible bacterium, usually S. agalactiae, may be found most often in the vagina |
and rectum of females and may be transmitted sexually, as well as to a fetus as the infant passes through the birth canal. Group B strep infection of newborns may |
be prevented by giving pregnant women who are carriers antibiotics through the vein (intravenously) during labor. The U.S. Centers for Disease Control and Prevention (CDC) recommend that any pregnant woman |
who has had a baby with group B strep disease in the past, who has a bladder (urinary tract) infection caused by group B strep, or who tests positive for |
group B strep during pregnancy should receive antibiotics during labor. Prevention and prompt treatment are important because group B strep infections may become life-threatening among newborns. GBS disease is said |
to be early onset if it is obvious within the first week of life. It is said to be late onset if the disease is evident after the first week |
of life and before the end of the first three months. Those at greatest risk of GBS disease are newborn children of infected mothers, women after childbirth, females after gynecologic |
surgery and older male and female patients with other serious diseases. Group B Strep Association P.O. Box 16515 Chapel Hill, NC 27516 Center for Disease Control and Prevention 1600 Clifton |
Road NE Atlanta, GA 30333 NIH/National Institute of Allergy and Infectious Diseases Office of Communications and Government Relations 6610 Rockledge Drive, MSC 6612 Bethesda, MD 20892-6612 MUMS National Parent-to-Parent Network |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.