Shoreline Processes Sediment Transport

Do you really want to buy that beachfront house?  Describe the processes that generate coasts  Beach anatomy  Seasonal changes  Longshore transport  How do the structures we build change the shoreline This week we will study the types of coasts and beaches and the natural processes that create and maintain them

Here today, gone tomorrow: sediment transport and beach evolution The shore takes on many forms along the WA coast and Puget Sound Weather, waves and gravity continue to shape the shorelines Beaches are dynamic

Major Zones  Coastal area: land edge that borders the sea  Width varies  geography  climate  vegetation  Shore: outer limit of wave action on the bottom to the limit of the waves’ direct influence on land  Beach: accumulation of sand or gravel that occupies part of the shore Coastal areas are regions of change in which the sea acts to alter the shape and the configuration of the land

Anatomy of a beach  Berm: ledge or terrace with flat tops  formed by wave-deposited material  Beach face: seaward slope, dependent on sediment type and wave energy  Troughs and bars run parallel to beach  Change seasonally Fig. 12.6

Seasonal Beach Changes Summer Profile Winter Profile

How do waves move sediments?  Wind = waves  Breaking wave = turbulence  Swash moves sediment onshore diagonally  Backwash moves sediment straight down beach  Swash + backwash = zigzag  related related Fig

Materials on the move A constant river of sand and gravel flows along beaches. Shore drift or longshore drift can move materials from eroding bluffs and streams to shorelines miles away. Weather and waves pick up particles in one area and drop them off in another area.

Sources & Sinks  Sources along the WA coast and Puget Sound include eroding bluffs, rivers, and streams  Sinks appear as spits, bars, tombolos, beaches (…can also be a source if supply is blocked or changes….)

Sink or Source? Source: Sink: Direction of drift or longshore transport: bluff spit

Wave action and longshore transport can erode beaches and be a hazard to boat harbors Human intervention in natural beach evolution  Build structures to stop beach erosion and stabilize beaches  jetties, groins, seawalls  Build structures to protect harbors  Breakwaters  Building dams

Beaches: River of Sand The end