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Unformatted text preview: Effects of Waves and Tides Effect Tidal Range & Tidal Currents Tidal
• Microtidal TR < 2.0 m • Mesotidal 4.0 m > TR > 2.0 m • Macrotidal TR > 4.0 m Formation of Tidal Currents
B ay Ocean
H ig h S la c k W a t e r A B Time 3 Time 2 Bay A Ocean B F lo o d in g T id e ( f lo w in t o B a y ) E b b in g T id e ( f lo w o u t o f B a y ) Time 4 Time 1 Land L o w S la c k W a t e r Tidal Currents Produced due to Constriction of Tidal Wave
-entrance to a bay -tidal inlets -funnel-shaped embayments Tidal Currents are Bi-Directional
1. Flood Currents- flow landward into bay during the rising tide 2. Ebb Currents- flow out of bays & inlets during falling tide 3. Slack Water- no currents, occur at low & high tides ocean and bay water levels are equal Tide Curve Recording of water levels Tides can be separated into 3 time periods: 1/3 high tide, 1/3 low tide, 1/3 rising or falling What Tidal Currents Do: What
• Transport sand onshore and offshore
• Keep tidal channels open and flushed of sediment • Form flood & ebb-tidal deltas What Waves Do: What
Angular Wave Approach LONGSORE TRANSPORT LSC Produce Currents that flow along shore Longshore Currents together with Wave Suspension of sand transports sand along the underwater beach Results of Longshore Sand Transport Re Formation of Spits Elongation of Barriers Dumps sand into Tidal Inlets Tectonic Setting
Collision Coast Trailing-Edge Coast Continental Crust
After Davies, 1973 Oceanic Crust • D i s tr i b u ti o n o f b a r r i e r i s la n d s a n d la g o o n s • N o te c o r r e s p o n d e n c e b e tw e e n b a r r i e r a n d t e c to n i c s e tti n g Coastal Morphology: A Function of Waves and Tides
W a v e s v er s u s T id es Controls Coastal Morphology
Barriers, Bays, Lagoons, Tidal Inlets, Marshes, Tidal Deltas MIXED ENERGY 1. Wave-Dominated 2 . M i x e d E n e rg y Wave-Dominated Coast L o n g b a r r ier isla n d s Few tidal inlets Poorly developed ebb tidal delta Well developed flood tidal delta N a r r o w m a r sh es E x a m p les: L o n g I sla n d , N . N ew J er sey, D ela w a r e a n d Maryland, North Carolina, Florida, Texas, Denmark Wave-Dominated Coast
• L o n g lin ea r b a r r ier is la n d s • • • • • • F e w ti d a l i n l e ts W e ll-d e v e lo p e d F -T -D P o o r ly d e v e lo p e d E -T -D B a r r ier s b a ck ed b y b a ys & l a g o o n s M a r s h es fr in g e m a in la n d & b a r r ier s W a sh o v er s co m m o n Outer Banks of North Carolina Wave-dominated barriers Wave-dominated barriers Plymouth Bay W a v e -d o m i n a te d T i d a l I n l e t Ebb-tidal delta is small or absent Washovers W a sh o v e rs Flood Tidal Delta Often storm-generated Storm waves transport large amounts of sand into inlet Storm produces large storm surge, which increase flood currents and sand transport into back barrier F-T-D Why are Ebb-Deltas Poorly Developed at Wave-Dominated Coasts? Waves push E-T-D sand back onshore
Poorly formed E-T-D F-T-D Former Flood deltas Mixed Energy Barriers Short stubby barriers Numerous tidal inlets Barriers backed by marsh and tidal creeks Well formed E-T-D F-T-D maybe present Delmarva Peninsula
• S h o r t s tu b b y b a r r i e r s • B a c k e d b y m a r s h & ti d a l c r e e k s • N u m e r o u s ti d a l i n l e ts • W e l l d e v e l o p e d e b b -ti d a l d e l ta s Southern New Jersey Barriers north of Charleston, SC Barriers Backbarrier Marsh and Tidal Creeks
Backbarrier Mainland Barrier Island Intercoastal Waterway Price Inlet, SC W e ll-d e v e lo p e d E b b -ti d a l d e l ta Denmark North Sea Tidal ﬂats and tidal creeks Why do Mixed-Energy barrier coasts have Why backbarrier consisting of marshes? Greater Tidal Prism and number of inlets allows more sediment influx L a r g er T id a l R a n g e p r o d u ces m o r e z o n e fo r m a r sh d ev elo p m en t Marsh Tidal Flat Tidal Range Isles of Shoals Hampton R. Estuary Merrimack R. Estuary Parker R. Estuary Essex R. Est. C ape A nn -T-D F-T-D Backbarrier marsh and tidal creek system Drumlin Tidal Inlet Ebb-tidal delta Tidal Inlet Flood tidal delta Importance of Continental Shelf Width Narrow shelf—large waves, small tidal range Wide shelf—small waves, large tidal range
Width of Shelf NC NC GA GA North Carolina - Wave Dominated Georgia - Mixed Energy Outer Banks, NC Microtidal TR = 0.5 – 1.0 m Tide-dominated Coasts
Tide-dominate coasts contain no barriers. Sand is transported offshore into linear sand shoals. Onshore consists of tidal ﬂats and expansive marshes. Large tidal ranges Funnel-shaped embayments Riverine Sand is transported offshore into linear sand shoals (tidal ridges) Funnel-shaped embayment with a macrotidal range in the Bering Sea Summary of Geomorphic Characteristics Tide Dominated Mixed Energy Wave Dominated wavedominated mixed energy (meso-tidal) wave-dominated (micro-tidal) mixed energy (meso-tidal) wave-dominated (micro-tidal) ...
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This note was uploaded on 04/14/2011 for the course GEO 142 taught by Professor Fitzgereld during the Spring '11 term at BU.
- Spring '11