In case of dune retreat dynamic equilibrium is assumed at annual scale. This means that dune retreat is assumed to be restored the same year in a natural manner. The deposited sand will be transported back to the dunes in a natural way. Structural erosion can be restored by sand nourishment. The damage to societal activities is influenced by these preventive maintenance measures like sand nourishment. Preventive maintenance measures result in a reduction of the probability of damage, but introduces maintenance costs on the other hand. Preventive maintenance costs and economic benefits have an important role in the relation between physical processes, societal activities and sand nourishment.
02 Coastal Stabilization And Alternative Solutions
COASTAL STABILIZATION AND ALTERNATIVE SOLUTIONS including Geosystems IN INTERNATIONAL PERSPECTIVE <ul><li>Krystian Pilarczyk, The Netherlands; email@example.com </li></ul>
Getting older I understand more and more how little I know (how little my knowledge is) Therefore I have to disappoint you I have more to say on What we do not know than What we do know Why What How COASTAL STABILIZATION AND ALTERNATIVE SOLUTIONS What I do know <ul><li>Krystian Pilarczyk </li></ul><ul><li>(former) Rijkswaterstaat/Public Works Dpt., Delft, NL </li></ul><ul><li>HYDROpil Consultancy; firstname.lastname@example.org </li></ul>(see also CEM 2002)
Example of coastal erosion: Typhoon Damrey 27Sept’05 Vietnam
Disappearing beaches: engineering solutions <ul><li>Humans are very clever at finding technical solutions to environmental problems but they seldom remove the causes of such problems. When trying to protect the land from the sea, they underestimate how powerful the sea can be, because large storms do not occur often enough. </li></ul>Dr J Floor Anthoni (2000) www.seafriends.org.nz/oceano/beacheng.htm
<ul><li>Line in the sand Beaches and dunes have natural periods of growth and erosion. Many people believe that we do not give our beaches enough space to wax and wane naturally. Once property is threatened, the beach is lost. </li></ul><ul><li>Renourishment When the beach erodes and the sand disappears, people's first reaction is to bring new sand in from elsewhere. Little attention is paid to the reasons why the sand disappeared, and beach erosion continues. </li></ul><ul><li>Beach drainage By draining the beach, the sand is able to dry and the sea wind is able to re-create a dry beach. It is a cheap and effective way for beaches whose sand cannot dry easily </li></ul><ul><li>Sea walls Where beach erosion appears unstoppable, sea walls are built to protect property, business and life, but the natural beach disappears. </li></ul><ul><li>Groynes Beaches strung between headlands are less prone to erosion from long-shore currents. Groynes (groins) are artificial headlands between which sand accumulates. But they cause problems too and look ugly. </li></ul><ul><li>Jetties Jetties are long dams jutting out in the sea, designed to keep the entrances to harbours open and navigable. They also cause serious beach erosion </li></ul><ul><li>Breakwaters Breakwaters are artificial barriers erected parallel to the shore. Sand gets trapped behind them. But extreme events destroy them. A new fad is the breakwater for surfing. </li></ul><ul><li>Sand mining Sand is bountiful in the sea but mining it attracts opposition, but is it really damaging the beaches?. With our newly found insights, we can support mining in certain places and conditions. </li></ul>
Problem analysis Restored cross section: sand nourishment Cross section after coastal recession Cross section eroded: sand nourishment on dune and/or beach
<ul><li>‘ Soft’ measures </li></ul><ul><li>artificial beach nourishments </li></ul><ul><li>shoreface nourishments </li></ul><ul><li>Nourishments: </li></ul><ul><li>have to be repeated </li></ul><ul><li>no lee-side effects </li></ul><ul><li>look so ‘soft’, but are a very good solution </li></ul><ul><li>at the end: rather cheap </li></ul><ul><li>argument: “we are a developing country, so we can’t afford beach nourishments” , is not a strong argument </li></ul>
Initial considerations Environmental conditions Functional pre-design alternative Selection of preferred scheme Detailed design In the design process one has to distinguish between functional design and structural design. Functional design concerns the impacts and performance of the coastal alternative with respect to coastal protection, improvement of recreational conditions and conservation of natural living resources. Structural design concerns the resistance of the coastal structure to the actions of waves and currents BASIS PRINCIPLES Design Starting Points www.delos.unibo.it
Interference with sediment transport To resolve a structural erosion problem (dS x /dx ≠ 0) with the help of structures (‘hard’ solution), the structures must interfere in the existing sediment transports. If we apply beach nourishments: we must nourish the ‘Loss’ J. Van der Graaff, TUDelft
<ul><li>Seawalls / revetments </li></ul><ul><li>initial erosion occurs always in this case (under water) </li></ul><ul><li>With revetment: </li></ul><ul><li>loss from dunes is physically prevented; lowering of beaches in front of revetment; loss of beaches </li></ul><ul><li>with time: heavier and more frequent attack to revetment; damage of revetment at the end of the day </li></ul><ul><li>large problems; high costs; angry people </li></ul><ul><li>(shame for our profession) </li></ul>
GROINS . Background and definitions. Groins are the oldest and most common shore-connected, beach stabilization structure. They are probably the most misused and improperly designed of all coastal structures. They are usually perpendicular or nearly at right angles to the shoreline and relatively short when compared to navigation jetties at tidal inlets. As illustrated schematically in Figure , for single and multiple groins (groin field) the shoreline adjusts to the presence of the obstruction in longshore sediment transport. Over the course of some time interval, accretion causes a positive increase in beach width updrift of the groin. Conservation of sand mass therefore produces erosion and a decrease in beach width on the downdrift side of the groin. The planform pattern of shoreline adjustment over 1 year is a good indicator of the direction of the annual net longshore transport of sediment at that location. http://www.ce.ufl.edu/~mcdougal/CEM/Part_V_Coastal_Project_Planning_and_Design/V-3_Shore_Protection_Projects.pdf
Tombolo: L s /X > 1.0 /(1-K t ) Andrew, 1997 (field data) L s /X >0.65 islands and reefs or X/L s < 1.0 (1-K t ), Salient: L s /X < 1 /(1-K t ) L s /X <1.0 - islands (assume K T = 0 for islands and 0.5 for reefs) L s /X <2.0 - reefs or X/L s > 1 (1-K t ), For salients where there are multiple breakwaters: GX/L s 2 > 0.5(1-K t ) (G= gap width) Where L s is the length of a breakwater and X is the distance to the shore, G is the gap width, and the transmission coefficient K t is defined for annual wave conditions. Transmission coef. in Tombolo-Salient relations (proposed by Pilarczyk as an example) Existing criteria (a choice from many):
Comment on functional design Use 2- or 3D numerical models for functional design
Burger/Delft 1995 Structural design Stability: Comparison (Delos/Aalborg * is lower limit) Design diagram for start of damage using rock
Artificial reefs Reef Balls http://www.artificialreefs.org/ Aquareef Japan
USACE demonstration program http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=PROGRAMS;3 its objectives are to provide state-of-the-art coastal shoreline protection A variety of shore protection devices and methods are being constructed, administered, and evaluated at a number of sites throughout the United States with diverse shoreline morphologies. These shore protection structures must have scientific support for projected performance and must not affect the aesthetic appeal of the area. Both patented devices and nonproprietary methods are permissible. Example: http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=PROJECTS;48 http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=PUBLICATIONS;50 National Shoreline Erosion Control Development and Demonstration Program (Section 227) Cape May Point, New Jersey Section 227 Demonstration Site Cape May Point, NJ - Evaluating a prefabricated submerged breakwater and double-T sill for beach erosion prevention
http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=ARTICLES;349 Cape May Point, New Jersey Section 227 Demonstration Site
Some other systems <ul><li>DRIM distorted ripple mat </li></ul><ul><li>Beach drainage </li></ul><ul><li>Gravel beaches </li></ul><ul><li>Geosystems </li></ul><ul><li>Etc. </li></ul>
ALTERNATIVES IN COAST PROTECTION DRIM Retaining Beach Sand by a Distorted Ripple Mat The Distorted Ripple Mat (DRIM) is a low cost shore protection method. It is made of precast concrete with a plastic sheet underlay. The DRIM works by controlling the movement of sand whilst causing little impact on the hydraulic and ecological conditions. Various test have been carried out on the design in order to find the optimum working conditions. The results of the laboratory and field tests are detailed in the paper. The DRIMs were found to work and a set of limiting criteria were identified. In addition the DRIM is able to control bottom currents within specific boundaries, even in unfavourable conditions. The combination of these function’s means that DRIMs can be used not only for beach retention, but in other circumstances as well. For example, reducing shoaling in navigation channels.
DISTORTED RIPPLE MAT (Japan) Concept of DRIM mat
Gravity drainage Japan http:// www.pari.go.jp / bsh / ky-skb / hyosa / hpj / english /02menb/ yana / yana.htm
Gravel beaches Granular materials are still the most popular materials / systems
Geosystems Geomattresses Geobags Geotubes Geocontainers Geocurtains Artificial seaweed Etc.
Geosystems have been devised as an alternative to traditional breakwater designs. A high strength synthetic fabric is cast into bags, mattresses, tubes or containers which are then filled with sand or mortar. They are used in the following ways: Mattresses applied as slope or bed protection; Bags are suitable for slope protection, retaining walls, toe protection, and in the construction of groynes, perched beaches or offshore breakwaters; Tubes and Containers are mainly used for the construction of groynes, perched beaches or offshore breakwaters, and bunds in reclamation projects. Geosystems have to date been commonly used as temporary measures due to limitations, including low resistance to waves and currents and low durability to vandalism and UV. The sand-filled variety can now be used as permanent structures and offer a number of advantages over traditional breakwaters, mainly: reduction in cost, quick installation, minimal impact on the environment, low skilled labour, use of local materials and equipment. As with most options it has its advantages and disadvantages, but geosystems have greatly improved since their early beginning. However, further work on improving designs and the need for testing under various conditions is still required.
Conclusions on Geosystems Remaining questions: - durability - execution - damage and repair - quality control In general it can be said that geosystems as well as all engineering systems and materials have (some) advantages and disadvantages which should be recognized before a choice is made. There is not one ideal system or material. Each material and system has a certain application at certain loading conditions and specific functional requirements for the specific problem and/or structural solution.
CONCLUSIONS on selection of protection measures: It is difficult to make the scoring and some of the scores can be discussed, however, the tendency is quite clear. • Dune/cliff stabilisation can provide some coast and slope protection, but at the expense of preservation of the coastal dynamics. • Coast protection by coastline structures can provide coast protection, but most often at the expense of shore degradation and downstream erosion, aesthetics and coastal dynamics. • Mixed solutions can be very attractive providing both coast and shore protection, but most often at the expense of downstream erosion, aesthetics, safety, bathing water quality and coastal dynamics. • Shore protection by nourishment can be attractive, providing some coast protection and good shore protection with even positive downstream effects, but at the expense of aesthetics and coastal dynamics. • Beach drain provides good protection against seasonal beach variations and high groundwater table. • Beach construction provides both coast and shore protection with improvements of aesthetics, safety and bathing water quality. • Management solutions concentrate on re-establishing the coastal dynamics for the benefit of also the downstream shoreline and the general aesthetics but at the expense of coast and slope protection. • Sea defence by a dike protects against flooding, but at the expense of coastal dynamics and biodiversity. Sea defence by artificial dunes or foreland restoration provides only mild protection against flooding, but does preserve/enhance coastal dynamics and bio-diversity.
Conclusions There is certainly a future for alternative structures - erosion control - reduction of wave loading The author does not intend to provide the new design rules for alternative structures. However, it is hoped that this information will be of some aid to designers looking for new sources, who are considering these kinds of structure and improving their designs.
Research and practical design in the field of Low-crested structures is also the focus of the “Artificial Reefs Program” in New Zealand ( www.asrltd.co.nz ), the International Society for Reef Studies (ISRS) ( www.artificialreefs.org ), and the European Project DELOS (Environmental Design of Low Crested Coastal Defence Structures, 1998-2003) ( http:// www.delos.unibo.it ). Continued research, especially on submerged breakwaters and alternative systems, should further explore improved techniques to predict shore response and methods to optimise functional and structural design.
The more intensive monitoring of the existing structures will also help in the verification of new design rules. International cooperation in this field should be further stimulated . These new efforts will bring future designers closer to more efficient application and design of these promising coastal solutions. Continued research, especially on submerged breakwaters and alternative systems, should further explore improved techniques to predict shore response and methods to optimise functional and structural design.
Conclusions/end remarks <ul><li>A number of concepts still need further elaboration to achieve the level of design quality comparable with more conventional solutions and systems. </li></ul><ul><li>A number of uncertainties can be solved in the scope of graduation works and doctoral dissertations. However, for a number of systems more practical experience is also still needed under various hydraulic conditions. </li></ul><ul><li>The realization of this need is only possible if manufacturers, clients and researchers cooperate closely. </li></ul>
Information sources (some websites) http://chl.erdc.usace.army.mil/%5CMedia/3/5/2%5Ccoas_19_202_684_722.pdf http://chl.erdc.usace.army.mil/CHL.aspx?p=s&a=ARTICLES ;349 Prefabricated breakwaters See also: Silvester, R. and Hsu, J.R., 1993, Coastal Stabilization, Prentice Hall Inc., Englewood Cliffs. ALTERNATIVE SHORELINE STABILIZATION DEVICES http:// www.env.duke.edu/psds/docs.htm http://www.coastal.crc.org.au/coast2coast2002/proceedings.html http://www.cne-siar.gov.uk/minch/coastal/coastal1-06.htm#P1407_126482 http:// www.beachdrainage.com / www.ieindia.org/publish/cv/1103/nov03cv3.pdf http://coastal.tamug.edu/capturedwebsites/cepraconference/glo_coastal_presentations/samplejay/sld001.htm http:// www.scourcontrol.co.uk/academic.html ; http:// www.scourcontrol.co.uk/index.html http://www.artificialreefs.org/ www.delos.unibo.it See also References and Websites in the paper
Thank you engineered solutions for an innovative world
(never) good enough !!??? The knowledge is in continue development/transition; we have to follow these developments
COASTAL STABILIZATION AND ALTERNATIVE SOLUTIONS including Geosystems IN INTERNATIONAL PERSPECTIVE Krystian Pilarczyk (former) Rijkswaterstaat/Public Works Dpt., Delft, NL HYDROpil Consultancy [email_address]