Chapter 9: Water Erosion & Deposition

Aim: What affects runoff?

Factors that affect Runoff Runoff is water that doesn’t soak into the ground or evaporate, but flows across earth’s surface Factors that affect runoff Amount of rain Length of time Light rain over an hour has time to soak up Heavy rain over less than an hour will run off because it can’t soak into the ground fast enough

Slope of land Gravity causes water to move down slope Water moves quickly down steeper slopes Water moves slowly down gentler slopes Slower movement=water soaked up by ground Vegetation Plants slow down runoff and help prevent soil from being carried away Runoff will carry more soil and sediments in places lacking vegetation

Aim: What are the 4 types of water erosion? Create concept map

Aim: How do rivers and streams develop?

River System Development Streams are parts of river systems Can compare to a tree Water comes from rills, gullies and small streams Drainage basin is the area of land from which a stream or river collects runoff All the water in a river system flows to the trunk (main river)

Stream Development Stages depend on the slope of the ground over which the stream flows 3 classifications: Young Mature Old The stages of development do not always coincide with the actual age of the river

Young Streams Flows swiftly Slope is steep Has a rough bottom High level of energy Erodes bottom of stream faster than its side

Mature Streams Flows smoothly through its valley Rocks in the streambed over time are eroded by running water and sediments Erosion takes place more on the sides than the bottom This causes curves to develop called meanders

Old Streams Flow through broad, flat floodplains Drops load of silt near its mouth Dropping of sediments forms a delta A delta is an area of flat, fertile land extending into the ocean

Aim: How do deltas and alluvial fans form?

Deposition of Water As water moves through a river system it loses energy This lose of energy causes sediments to be dropped along the way Some sediments are carried a long way, while others only short distances When sediments are deposited as the water empties into an ocean or lake, a deposit called a delta forms Deltas are triangular or fan-shaped

When a river empties from a mountain valley into a flat plain, the deposit is called an alluvial fan

Aim: How do soil and rock permeability affect groundwater?

Groundwater Water that soaks into the ground collects in the pores and empty spaces in the soil or rock is called groundwater 14% of all water exists as groundwater Groundwater system has connecting pores Soil and rock are permeable if pores are connected and water can pass through them Water flows easily through Ex: sandstone-permeable rock

Impermeable rock or soil doesn’t have well connected pores or few pore spaces Water doesn’t flow easily through Ex: granite, clay Groundwater keeps going deeper into Earth’s crust until it reaches a layer of impermeable rock Zone of saturation is where all the pores in the rock are filled with water The upper surface of this zone is the water table

Aim: Why is the water table so important?

Water Table The amount of groundwater is limited Many people get their water from wells that have been drilled into the zone of saturation During a draught, the water table drops This is why it is important to conserve water

Wells A good well extends deep into the zone of saturation Groundwater flows into a well and a pump brings it to the surface If water is taken out of well faster than it can be replaced, wells can go dry If too much water is pumped out in area, the land can drop or sink Artesian well-doesn’t need a pump to bring water to the surface

Water in an artesian well rises to the surface due to pressure Are very rare because the aquifer needs to be located between 2 impermeable layers that are sloping Water enters at the high part of the slope and exits through a well at the low part of the slope due to the pressure created by the higher part of the aquifer

Springs Springs are found on hillsides where the water table meets a sloping surface Water flows out of the spring Source of freshwater Usually water comes to the surface as a cool temperature When water comes to the surface after being heated by hot rocks, it is called a hot spring

Geysers Is a hot spring that erupts periodically Groundwater is heated to high temperatures causing it to expand underground The expansion forces some of the water out of the ground Most of the water turns into steam Ex: Old Faithful, Yellowstone National Park

Aim: What are the causes of shoreline erosion?

Causes of Shoreline Erosion 3 forces shape shorelines Waves Crash against the shorelines Very powerful force Erode and move away large amounts of material Currents Longshore currents are created by waves that hit at a slight angle

Carry tons of loose sediments Tides Outgoing tides carry sediments away from the shore Incoming tides bring new sediments to the shoreline Work with waves to shape shorelines

Aim: What is the difference between rocky beaches and sandy beaches?

Types of Beaches Rocky Sandy Consist of rocks and cliffs Smooth, gently sloping beaches Made up of grains of quartz or shell fragments Fragments range from stones to fine sand Some beaches have different colored sands Ex: Hawaii-black, made of basalt Ex: Jamaica-white, made of coral and shell Consist of rocks and cliffs Waves and sediments slowly wear away rocks Rock parts that break off are carried away by longshore currents

Aim: How do barrier islands form?

Barrier islands Are sand depositions that lay parallel to the shore but are separated from the mainland Start out as underwater sand ridges Hurricanes and waves help form the islands Last only a few years to a few centuries Storms and waves also erode the barrier islands and cause erosion to beachfront developments