Announcements  Lab 1 due on Friday  No lab next week  Visit Seattle Aquarium  Pick up ticket before or after class  Monday (10/6) is last day to pick up ticket  Lab and Case Study posted  Due in class on Friday, 10/10 1

Do you really want to buy that beachfront house?  Recognize the different types of coasts  Describe the processes that change the shoreline  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 2

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

Beach: River of Sand  Describe the seasonal changes that occur on a beach? Explain the cause for the changes between winter and summer months.  What are “longshore currents”? What causes them?  Explain the role of submarine canyons in sediment transport.  List and explain two ways people can affect beaches.  How can breakwaters parallel to shore affect sediment transport or deposition? Can you illustrate your explanation with a diagram? STUDY QUESTIONS 4

Beaches: River of Sand Up to beach tank Minute 7 5

Seasonal Beach Changes The small waves of summer move sand from offshore to the beach and form a summer berm Summer Profile The high waves and storms of winter erode sand from the beach and store it in offshore bars. Winter conditions remove the summer berm, leaving only the winter berm on the beach. Winter Profile Fig

Sands shift with the seasons  Most beaches in WA consist of a shallow covering of sand or gravel over rocks  Winter:  Storms remove most of the sand, exposing cobbles and underlying rock  Summer:  Sand returns At South Whidbey State Park, sand bars cover the lower portion of the gravel beach. Sand moves with the seasons and storms, sometimes covering much of the beach, other times being drawn offshore 7

Beaches: River of Sand Up to N. America Map Minute 12 8

How do waves move sediments?  Wind = waves  Breaking wave = turbulence  Swash moves sediment onshore diagonally  Backwash moves sediment straight down beach  Swash + backwash = zigzag Fig Why do waves bend as they come onshore? 9

How do waves move sediment?  Winds blow, waves form  As a wave approaches shore, it feels the bottom (surf zone)  Speed changes, wave steepens and begins to break  The turbulence generate from the breaking wave tumbles beach material (beach absorbs some of the waves energy)  The “stronger” or more energetic a wave is, the more sediment it stirs up and tumbles  Waves moving toward shore transport sediment onshore (called onshore transport)  Wave angle results in the transport of sediment parallel to shore  Up-rush or swash from breaking waves moves sediment diagonally up and along beach in direction of longshore transport  Backwash moves sediment downslope 10

Sources & Sinks  Longshore transport is interrupted by obstacles  Natural - headlands, inlets, and sharp bends in the shore contours  Manmade obstacles – seawalls, jetties, groins, etc.  Shoreline divided into "drift sectors”  Pick-up (source) & drop-off points (sinks)  Sources?  Eroding bluffs, rivers, and streams  Sinks?  Spits, bars, tombolos, beaches (…can also be a source if supply is blocked or changes….) 11

In-class Activity 12  Write full name and section on a sheet of paper  Quickly sketch the shape of the coast on your paper  Label a) the area of accumulation and b) the area of erosion caused by the constructed groins  Indicate the direction of longshore transport with an arrow Groins are constructed perpendicular to coasts to prevent sand from drifting away from the beach. On the figure below, label a) the area of accumulation and b) the area of erosion caused by the constructed groins.

In-class Activity 13 Do you think the spit has grown or eroded since the construction of the groins?

Understanding Beach Evolution  Summer:  Waves tend to be gentle & transport sediment landward  Beaches widest  Winter:  Storms at sea produce larger waves that erode beaches & transport the sediment seaward  Longshore transport alters the shape and profile of a beach  Where wave action is strong, sediment is eroded and transported  Where wave action is reduced, sediment is deposited 14

Wave action and longshore transport can erode beaches and be a hazard to boat harbors People have taken measures to minimize those undesirable effects (with mixed results) 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 15

Beaches: River of Sand To end 16

Test your knowledge  Can you identify the “parts” of a beach?  Can you describe how a beach changes from summer to winter conditions?  Width?  Berms?  Slope?  Sediment type?  Can you describe how waves move sediment along the shoreline (longshore transport)?  Can you identify sources and sinks of sediment to a beach? 17