Water Is Everywhere Oceans, glaciers, rivers, lakes, air, soil and living tissue
The Water Cycle The unending circulation of the Earth’s water supply ◦ Works because water readily changes states
The Water Cycle Vocabulary Precipitation ◦ Rain and Snow Evaporation ◦ Water changes into gas in atmosphere Infiltration ◦ Movement of surface water into rock or soil ◦ Runoff Rate of rainfall exceeds Earth’s ability to absorb precipitation Transpiration ◦ Plants release water into atmosphere
Reading Checkpoint Looking at the graph on page 158 ◦ What percentage of Earth’s water is not held in its oceans? ◦ What percent of Earth’s water is in freshwater lakes and streams combined? Looking at Figure 2 on page 159 ◦ In which three ways does precipitation return to oceans? What is infiltration?
Earth’s Water Balance Balance means the average annual precipitation over Earth equals the amount of water that evaporates. ◦ There are local imbalances Precipitation exceeds evaporation over continents Evaporation exceeds precipitation over oceans
Streamflow The ability of a stream to erode and transport materials depends largely on its velocity. Velocity affected by ◦ Gradient ◦ Shape, size and roughness ◦ Discharge
Streamflow Look at Figure 3 on page 160 Along straight stretches the stream velocity is highest at the center of the channel What a stream curves, its zone of maximum speed shifts toward the outer bank How does velocity change with depth in the middle of the stream?
Gradient The slope or steepness of a stream channel Expressed as vertical drop over specified distance Varies over stream’s length Varies from one stream to the next Refer to Figure 4 on page 160 ◦ Where is the steepest gradient? ◦ How does the gradient change as the stream reaches the ocean?
Channel Characteristics Stream Channel ◦ The course the water in a stream flows Friction affects water from sides and bottom of channel ◦ Boulders will slow stream down ◦ Larger channels flow faster because a smaller proportion of water is in contact with the channel surfaces
Discharge Volume of water flowing past a certain point in a given amount of time ◦ Measured in cubic meters/second ◦ Changes with rainfall and snowmelt Higher discharge causes the stream channel to widen and deepen ◦ Less friction – flows faster Human Interference ◦ Building near streams increases runoff ◦ During dry times streams dry up because less water soaked in during rainy times
Reading Checkpoint The ____________ of a stream is the volume of water flowing past a specific point in a specific amount of time. What factors determine the velocity of a stream? Trivia ◦ What is the longest river in the US?
Changes from Upstream to Downstream Stream Profile ◦ Cross sectional view of stream from source to mouth Gradient decreases between a stream’s headwaters and mouth but discharge increases ◦ More tributaries enter main channel
Base Level Lowest point to which a stream can erode its channel ◦ Where mouth of stream enters ocean, lake or another stream Two Types ◦ Ultimate – sea level ◦ Temporary – lakes, resistant layers of rock and main streams that are base for tributaries
Base Level Meanders ◦ Bends in the stream ◦ Sometimes stream in broad, flat-bottomed valley is near base level ◦ Then the base level changes (dropped or stream uplifted by land) ◦ Now the stream has ◦ more energy and ◦ channel gets downcut
6.1 Assessment How is the earth’s water cycle balanced? What factor most influences the power of a stream to erode and transport material? How do gradient and discharge change between a stream’s headwaters and its mouth? What would happen if evaporation exceeded precipitation over the continents and the oceans? How does the development of urban areas along streams and rivers affect discharge during periods of heavy rainfall?
6.2 The Work of Streams Most important agents of erosion ◦ Downcut channels ◦ Erode channels ◦ Transport sediments produced by weathering ◦ Create depositional features
Erosion Lift loose particles by ◦ Abrasion ◦ Grinding ◦ Dissolving soluble material Stronger current = more erosion
Sediment Transport Three ways to transport sediment ◦ Dissolved load In solution ◦ Suspended load In suspension ◦ Bed load Scooting or rolling along the bottom
Dissolved Load Usually enters through groundwater ◦ Can also enter when rock is dissolved along course of stream Amount depends on climate and geological setting Measured in parts per million (ppm) ◦ Average dissolved load is 115-120 ppm
Suspended Load Most common type of transport Usually sand, silt and clay ◦ During floods can transport larger materials because of increased velocity
Bed Load Sediment too large to be carried in suspension ◦ Move along bottom ◦ Only moves when force of water is great ◦ Grinding action erodes stream channel
Competence and Capacity Ability to carry load depends on these two things Competence ◦ Measures the largest particles it can transport ◦ Increases with velocity Capacity ◦ Maximum load it can carry ◦ Related to discharge ◦ More water in stream = more capacity
Deposition Happens when stream slows down Heavier particles fall out first (sorting) Alluvium ◦ Sorted material deposited by stream
Deltas An accumulation of sediment formed where a stream enters a lake or ocean When it grows outward the velocity of the stream goes down ◦ Channel becomes blocked ◦ Stream finds new way to base level
Natural Levees River occupies valley with broad, flat floor Successive flooding causes ridge made of coarse sediments that parallel the river When river overflows its banks the velocity slows down so large particles get deposited
Stream Valleys Narrow Valleys ◦ V-shaped ◦ Stream downcutting towards base level ◦ Rapids and waterfalls Uneven erosion
Stream Valley Wide Valleys ◦ After stream gets close to base level erosion switches from downward to side to side ◦ Produces flood plain ◦ Streams begin to meander ◦ Erosion occurs on cut bank Outside of the meander Debris deposited at point bars Inside of meanders
Stream Valley Erosion more effective downstream of meander because of slope ◦ Bend gradually travels down the valley When bend reaches resistant portion of floodplain it quits moving and gets overtaken by next meander upstream Neck narrows and gets cut off Abandoned bend = Oxbow lake
Floods and Flood Control Flood ◦ Discharge of stream exceeds the capacity of its channel and overflows its banks ◦ Caused by rapid spring snow melt or storms that bring heavy rains
Floods and Flood Control Flash flood ◦ Little warning ◦ Caused by Rainfall intensity and duration Surface conditions Topography ◦ Common in urban and mountainous areas ◦ Human interference increases chances Building dams and levees
Artificial Levees Mounds of earth built along bank of river Increase volume channel can hold Causes sediments that otherwise would have been dropped in floodplain to be dropped in channel ◦ Over time channel holds less water ◦ Levees have to be raised
Flood Control Dam Store floodwater and let it out slowly Used for irrigation and hydroelectric power Consequences ◦ Trap sediment so deltas and floodplains downstream begin to erode ◦ Build up of sediment means volume of water goes down so flood control is problem again ◦ Ecological damage
Limiting Development Trend is to preserve floodplain in natural state ◦ No development ◦ Allows water to be absorbed without harming homes and businesses
Drainage Basins The land area that contributes water to a stream AKA – Watershed Divide – imaginary line that separates drainage basins of one stream to another
6.2 Assessment How do streams erode their channels? What causes floods? What is the relationship between a stream and a drainage basin? How do streams transport sediment? How does urban development interfere with the natural function of floodplains?
6.3 Water Beneath The Surface Underground water in US ◦ Drinking water for 50% of population ◦ 40% of irrigation ◦ 25% industrial
Distribution Near surface ◦ Belt of soil moisture ◦ Water drops stick to soil particles Zone of saturation ◦ Water fills all open spaces in sediment and rock ◦ Groundwater here ◦ Upper limit known as water table Zone of aeration ◦ Not saturated
Movement Porosity ◦ Percentage of total volume of rock or sediment that consists of pore spaces Permeability ◦ Ability to release a fluid Groundwater moves by twisting and turning through interconnected small openings ◦ Moves more slowly when pore spaces are small
Movement continued Clay ◦ Has high porosity Holds a lot of water ◦ Impermeable Pore spaces are too small for water to move through Aquitard ◦ Impermeable layer that prevents movement Aquifer ◦ Permeable rock layers or sediments that transmit groundwater freely ◦ Source of well water
Springs Flow of groundwater that emerges naturally at the surface Forms when the water table intersects the ground surface ◦ Aquitard blocks downward movement so water has to move laterally
Hot Springs Has to be 6*C – 9*C warmer than mean annual air temperature Over 1000 in US Most found in Western US Heated by cooling igneous rock Mudpot ◦ Hot acidic groundwater mixes with minerals from adjacent rock forming thick, bubbling mineral springs
Geysers Intermittent hot spring or fountain in which water shoots up with great force at various intervals ◦ Shoots water 30-60meters ◦ When water stops steam rushes out Old Faithful ◦ Erupts about every hour
Geyser Eruption Cycle Groundwater seeps into fractures in hot igneous rock Water heated to near boiling Water expands – so some is forced out at surface Loss of water reduces pressure and lowers boiling point Water then flashes to steam Rapidly expanding steam forces hot water out to form geyser Chambers now empty Refill with water and process starts over
Wells Bored hole in Zone of Saturation Used mostly for agricultural purposes Must penetrate below water table Cone of Depression ◦ Forms when large amounts of water are pumped at once
Wells continued Artesian Well ◦ Groundwater rises on its own under pressure ◦ Two conditions: Water must be in aquifer that is tilted so one end is exposed at surface Must be aquitard both above and below to keep water from escaping elsewhere ◦ Pressure from weight of water above forces water to rise when well is drilled
Environmental Problems Associated With Groundwater Two biggest issues: ◦ Overuse ◦ Contamination
Treating as Nonrenewable Resource Supplies are finite Can’s always replace water as fast as it is being pumped out ◦ Causes ground to sink ◦ Pores in sediment empty so sediment gets packed together ◦ Some places would take thousands of years to replenish
Groundwater Contamination Sewage from septic tanks Farm wastes Inadequate or broken sewers Depending on composition of aquifer contaminated water might be filtered ◦ If aquifer is too permeable then water doesn’t get filtered and is dangerous to drink
Contamination Continued Fertilizers, pesticides and highway salt Leakage from pipelines, storage tanks, landfills and holding ponds ◦ When rainwater oozes through it dissolves contaminants ◦ If it reaches the water table then groundwater is contaminated Heavy use of wells near coasts deplete aquifers which then refill with saltwater
Contamination Continued Must abandon water supply ◦ Allows pollutants to flush out gradually ◦ Least costly ◦ Easiest ◦ Takes years for pollutants to filter away Speed up process by pumping out and treating polluted water ◦ Aquifer can refill on its own or can pump treated water back in
Caverns Naturally formed underground chamber Limestone rock soluble in water with small amounts of carbonic acid ◦ Formed when rain in atmosphere combines with carbon dioxide that naturally occurs in atmosphere
Caverns continued Erosion forms most caverns at or below the water table in the zone of saturation ◦ Acidic groundwater follows lines of weakness in rock Leaves behind depositional stone formations ◦ Calcium carbonate = travertine ◦ Dripstone is in zone of aeration Happens when streams cut their valley deeper
Dripstone Features Stalactites ◦ Icicle-like pendants that hang from ceiling ◦ Form when water seeps through cracks in ceiling, water reaches air in cave, dissolved carbon dioxide from water is released and calcite separates out, deposition occurs as ring around edge of water droplet, drop falls and leaves calcite behind
Dripstone Features Stalagmites ◦ Develop on floor and reach up ◦ Water supplying calcite falls from ceiling and splatters over surface of cavern floor ◦ No central tube ◦ More massive ◦ More rounded
Karst Topography Area where landscape has been shaped largely by the dissolving of groundwater Have irregular terrain with many sinkholes ◦ Depression produced in a region where groundwater has removed soluble rock Common in Kentucky, Tennessee, Alabama, southern Indiana and central northern Florida
Sinkhole Formation Gradual ◦ Downward seeping rainwater dissolves limestone ◦ Can go years without physically disturbing the rock ◦ Usually shallow with gentle slopes Suddenly ◦ Roof of cavern collapses ◦ Steep-sided and deep
Karst Characteristics Pockmarked with sink holes Lack of surface drainage (streams) Runoff quickly funneled below ground through sinkholes – flows in cavern until it reaches water table If a stream does exist it is usually short Sinkholes become plugged with clay or debris to create small lakes or ponds
6.3 Assessment In which zone is groundwater located? How does water move underground? What are some environmental threats to groundwater supplies? How and where do most caverns form? What landforms are common in an area of karst topography? What is the difference between stalactites and stalagmites? How is groundwater a nonrenewable resource? Explain why caverns form in the zone of saturation, while dripstone features form in the zone of aeration.