Ch 15 and 16-River Systems
and Groundwater
• Objectives
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Stages of the water cycle
Factors that affect a water budget
List approaches to water conservation
Summarize how a river develops
Describe the parts of a river system
Explain factors that affect the erosive ability of a river
Describe how erosive factors affect the evolution of a river
channel
Explain the types of stream deposition
Describe advantage and disadvantage of living in floodplain
Identify the methods of flood control
Describe the life cycle of a lake
Movement of Water on Earth
• Water vapor-water that occurs as invisible gas in
atmosphere
• Water cycle-continuous movement of water between the
atmosphere, land, oceans
• Evapotranspiration-total loss of water from an area
– Evaporation-liquid water changes into water vapor. Where does
the most evaporation take place at?
– Transpiration-plants release water vapor
• Condensation-gas to liquid
– Water on outside of glass
– Tiny liquid water droplets and forms clouds
• Precipitation-water falls from clouds
– 75% falls on oceans
– Examples
Water Budget/Use
• Water budget established by water cycle
– Factors that affect it include; temperature,
vegetation, wind, and amount and duration of
rainfall. How are these factors?
• Average person uses 95,000 L each yr.
What is it used for? 90% of water used in
cities, returned to rivers and oceans as
wastewater
– Some may contain harmful materials
Water Conservation
• What is water conservation?
– The wise use of water resources
– How can people conserve water?
• How can governments conserve?
– Enforcing conservation laws and antipollution laws
that prohibit dumping of waste into bodies of water
– Finding alternative ways to obtaining fresh water
• Desalination-process of removing salt from
ocean water
– Expensive and impractical
Stream Erosion
• How does a river develop?
– Soil collects water, runoff begins from excess water,
erodes rock and soil, forms narrow ditch. Precipitation
and erosion form valley w/ permanent stream
• Parts of River System
– Tributaries-feeders streams into main stream
– Watershed-land that is drained by river system
– Divides-ridges or elevated regions, separate water
sheds
– Channel-narrow depression stream follows downhill
– Banks-edges of stream above water level
– Bed-the part of stream channel below water level
Channel Erosion
• Stream Load-materials other than water
carried by stream
– Suspended load, bed load, dissolved load
• Stream Discharge-volume of water that
flows w/in given time
• Stream Gradient-change in elevation over
given distance. Velocity depends on
gradient
Evolution of River Channels
• As the stream’s load, discharge, and gradient
decrease, the erosive power of the stream
decreases
• Channels erode, become wider and deeper=rivers
• Meander- one of the bends, twists, or curves in lowgradient stream or river.
– More energy directed to banks than beds.
– Faster on outside of curve, sediment deposited to form
sand bars
– Oxbow Lake-the meander becomes isolated from river
• Braided Streams-multiple channels, divide or rejoin
around sediment bars
– Large sediment load, coarse sand and gravel
– Build up on channel floor
Oxbow Lake
Stream Deposition
• Types of stream deposition
– Deltas-fan shaped mass of rock material
deposited at mouth of stream
• Waves, tides, offshore depths, sediment load
– Alluvial fan-fan shaped mass of rock material
deposited by stream when slope of land
decreases sharply
• Form when streams flow from mts to flat land
Floodplains
• What is a floodplain?
– Area along river that forms from sediments deposited
when river overflows its banks
– Natural levees
• Advantage
– Convenient access to river for shipping, fishing,
transportation
– Rich soils, good for farming
• Disadvantage
– Swampy areas
– Flooding homes
Flood Control
• Name some things that could prevent
flooding
– Forest and soil conservation measures
– Artificial structures
– Dams
– Artificial levees, artificial lakes
– Permanent overflow channels or floodways
Life Cycle of Lake
• Most lakes located in high latitudes and
mountainous areas
• What are some sources of lakes?
– Springs, rivers, runoff
– Most comes from precipitation and melting of
ice and snow
– Short in geologic terms. Why?
Properties of Aquifers
• Groundwater-water beneath the Earth’s surface, fills
fractures and cavities in rock
• What is an aquifer?
– Body of rock or sediment in which large amounts of water can
flow and be stored
– Factors that affect flow of water-porosity and permeability
• Porosity
– Percentage of total volume of a rock or sediment that consists of
open spaces
– Sorting, particle packing and grain shape
• Permeability
– Ability of rock or sediment to let fluids pass through its open
spaces or pores
– Size and sorting, open spaces must be connected
Zones of Aquifers
• Zone of saturation-layer of aquifer in which the pore
space is completely filled w/ water
• Zone of aeration-lies between the water table and
Earth’s surface
– Top layer holds soil moisture
– Bottom region above water table is capillary fringe
– Dry area in between fills w//water when it rains
• Water table-upper surface of underground water
• Recharge zone- anywhere that water from the
surface can travel through permeable rock to reach
an aquifer
Wells and Springs
• Well-hole that is dug to below level of water table and
through which groundwater is brought to Earth’s surface
• Cone of depression- water table lowers below the well, it
goes dry
• Spring-Natural flow of groundwater to Earth’s surface in
places where ground surface dips below water table
• Artesian formation-sloping layer of permeable rock
sandwiched between 2 layers of impermeable rock and
exposed at surface
– Source of water for some springs
• Artesian well-well through which water flows freely w/out
being pumped
Hot Springs and Geysers
• Hot springs-groundwater is heated when it
passes through rock that has been heated
by magma
– At least 37 deg C and rises to surface before
cooling
• Geysers-hot springs that periodically erupt
from surface pools or through small vents
– Narrow vent that connects 1 or more
underground chambers w/ surface
Results of Weathering by
Groundwater
• Caverns-large cave that may consist of many smaller
connecting chambers
– Carbonic acid slowly dissolves the limestone and enlarges
cracks in the rock
• Stalactites-suspended cone-shaped deposit of calcite
on ceiling of cavern
• Stalagmites-upward pointing cone of calcite on floor of
cavern
• Sinkholes-circular depression that forms at the surface
when rock dissolves, when sediment is removed, or
when caves or mines collapse
• Natural bridges-uncollapsed rock between each pair of
sinkholes forms an arch of rock