Coaste_valuri
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MEDII COSTIERE CONTROLATE DE ACTIUNEA VALURILOR
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OBIECTIVUL CURSULUI
Prezentarea si discutarea principalelor tipuri de medii
costiere
controlate de valuri si a proceselor asociate
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CUPRINSUL CURSULUI
• Tarmuri erozionale
• Insule bariera
• Plaje
• Dune litorale
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TARMURI STANCOASE
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Procesele de eroziune implicate: • Presiunea hidraulica• Evorsiune• Abraziune• Dezagregare• Alterare• Eroziune chimica
Eroziunea marina cea mai intensa se manifesta in proximitatea nivelului marii. In prezenta mareelor eroziunea marina se produce in principal in zona intertidala.
Eroziunea este rezultatul unei balante intre agentii de modelare (valuri, curenti, maree) si fortele de rezistenta (tipul de roca)
MECANISMUL DE EROZIUNE A TARMURILOR STANCOASE
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Cei mai importanti trei factori care afecteaza morfologia tarmurilor stancoase sunt:• Climatul valurilor: nivel energetic (H,T) si variabilitate• Geologie: litologie si structura • Morfologia pre-existenta: din anterioarele intervale glaciare/interglaciare
Stacks
Arc (Portal)
Firide De tip notch
Platforma de tarm
Faleza
ELEMENTELE
TARMURILOR INALTE
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Morfologia falezelor depinde in primul rand de balanta dintre procesele marine si procesele subaeriene. In plus aceasta balanta este afectata de climatul valurilor si de geologie. Morfologia mostenita joaca de asemenea un rol important.
SISTEMUL MORFODINAMIC AL FALEZELOR
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SISTEMUL MORFODINAMIC AL PLATFORMELOR DE TARM
Platf. cvasiorizontala Platf. inclinata
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BARIERE
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SUBMEDIILE BARIERELOR
Barrierele sunt principalele forme depozitionale ale coastelor dominate de valuri. Acestea pot fi separate de continent printr-o laguna (insule bariera), pot inchide partial un estuar (bariere estuariene), pot fi legate direct de continent (spit bariera) sau pot desparti complexe deltaice de acvatoriul marin (bariere deltaice).
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FORMA IN PLAN A BARIERELOR
Sunt doua tipuri majore:• Aliniate de swash tarmurile sunt aliniate de refractia valurilor• Aliniate de curenti tarmurile sunt aliniate de curentii longitudinali de tarm (driftul de tarm)
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COASTE ALINIATE DE SWASH (refractie)
Plaje de golf (pocket beach) Golf de echilibru
Tombolo
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COASTE ALINIATE DE CURENTI
Spit
Camp de creste de plaja
Bariere crescentice
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RASPUNSUL BARIERELOR LA
CRESTEREA NIVELULUI MARII
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PLAJE
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GRADIENTUL PLAJEIFactorii care afecteaza panta plajei:• Granulometria sedimentelor: panta plajei creste odata cu dimensiunea granulelor de nisip• Inaltimea valurilor: panta descreste odata cu inaltimea valurilor• Inaltimea mareelor: gradientul descreste odata cu inaltimea mareelor
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ELEMENTE MORFOLOGICE
ALE PLAJELOR
Berme de plaja Ripple-marksuri Caspuri de plaja
Curenti de tip rip
Bare ancorate
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CURENTII DIN ZONA DE
SURF
Alaturi de miscarea de du-te vino indusa de valuri (swash), trei tipuri de curenti apar in zona de surf:• Curentii longitudinali de tarm indusi de valurile oblic-incidente• Curentii de retur de pe fund (bed return flow) indusi de miscarea rezultanta catre larg produsa in proximitatea fundului in zona de surf• Curentii de tip rip sunt de asemenea indusi de transportul general catre larg datorat valurilor deferlante
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FORMAREA BERMEI/BAREIMorfologia plajelor cuprinde in general schimbari sezoniere:• Furtunile cauzeaza transportul sedimentelor catre larg si implicit formarea barelor submerse.• Conditiile de calm marin (energie marina joasa) impun deplasarea sedimentelor dinspre larg catre plaja, avand drept rezultat formarea reverelor fetei plajei din a caror juxtapunere rezulta bermele de plaja (furtuna/hula, bara submersa/berma de plaja si profil de iarna/vara).
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FACTORII CARE AFECTEAZA MORFOLOGIA
PLAJELOR
Cei mai importanti trei factori care afecteaza morfologia plajei sunt:• Valurile• Mareele• Granulometria sedimentelorAcestea pot fi cuantificate prin doi parametrii:
Indicele maree-val (relative tide range): RTR = MSR/Hb
Indicele vitezei de cadere a sedimentelor (dimensionless
fall velocity): = Hb/wsT
unde:
MSR = inaltimea mareelor de sizigii (mean spring tide range) (m)
Hb = inaltimea valurilor deferlante (m)
ws = viteza de cadere a sedimentelor (m/s)
T = perioada valurilor (m)
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CLASIFICAREA PLAJELOR
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TARMURI REFLECTIVE• RTR < 3 si < 2• Regim micromareic, valuri mici si medii (inclusiv de hula) cu nisip grosier si pietris • Plaje inclinate, frecvent cu caspuri de plaja supraimpuse• Zona de surf in general lipseste valurile spargandu-se direct pe fata plajei
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TARMURI INTERMEDIARE• RTR < 3 si 2 < < 5• Regim micromareic, valuri de inaltime medie si sedimente nisipoase• Plaje moderat inclinate cu morfologie de bare submerse si canale de rip • Conditii intermediare ale zonei de surf cu valuri de tip plunging• Curenti longitudinali de tarm si curenti rip
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TARMURI BARATE DISIPATIVE• RTR < 3 si > 5• Regim micromareic, valuri medii si inalte (furtuni), sedimente fine nisipoase• Plaje slab inclinate cu morfologie de bare si santuri submerse• Zona de surf disipativa: zona de surf foarte lata si valuri deferlante de tip spilling si plunging• Curenti longitudinali de tarm puternici si curenti de retur de fund (bed return flow)
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TARMURI CU TERASA DE MAREE JOASA RTR > 3 si < 2• Regim mezo si macromareic, valuri mici, nicip grosier sau pietris• Plaja inalta este puternic inclinata frecvent cu morfologie de tip caspuri• Terasa de maree joasa este cvasiorizontala (apar curenti rip in timpul furtunilor)• Zona de surf inregistreaza un comportament reflectiv la mareea inalta (valuri deferlante de tip surging/plunging)• Zona de surf inregistreaza un comportament disipativ la mareea joasa
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PLAJE CU BARE SI CURENTI RIP LA
MAREEA JOASA 3 < RTR > 7 si 2 < < 5• Regim mezo/macromareic, valuri mari, sedimente nisipoase• Plaja cu panta mica in sectorul intertidal cu morfologie de tip bare si santuri de curenti rip la mareea joasa• Sistemul de curenti rip este activ in timpul mareei joase
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TARMURI ULTRADISIPATIVE• RTR > 3 si > 5• Regim mezo/macromareic, valuri mari cu sedimente nisipoase fine• Plaje cu panta mica incllinand uniform fara subunitati• Zona de surf inregistreaza un comportament disipativ in timpul ciclului mareic
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DUNE LITORALE
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STRUCTURA MORFOLOGICA
A DUNELOR LITORALE
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STADII IN FORMAREA DUNELOR LITORALE
Vegetatie pioniera Dune embrionare
Fordune tinere Cordon de fordune
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Formarea campurilor de creste de plaja (beach ridge
plain)
Formarea de cordoane dunicole
paralele
Dezvoltareafordunelor
Erodarea fordunelor
Procese de overwash
BUGETUL PLAJEI
BU
GE
TU
L F
OR
DU
NE
LO
R
RELATII IN BUGETUL SEDIMENTAR PLAJA/DUNE
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Cel mai vechi cordon de dune
Cordonul de fordune
20 - 70 ani vechime
Al doilea cordon de dune
150 ani vechime
Al treilea cordon dunicol
200+ ani vechime
EVOLUTIA DUNELOR LITORALE