Running Water Day 1
Running Water • The single-most important erosional agent on earth is RUNNING WATER. • But where does the water come from, and how much of it is running, or moving on our planet?
Water Cycle • Water is EVERYWHERE • About 97.2 % is in the oceans • About 2.15 % is in glaciers and ice sheets • About 0.65 % is freshwater in lakes, streams, groundwater, and the atmosphere • Water constantly moves among the oceans, the atmosphere, the solid Earth, and the biosphere. This unending circulation of Earth’s water supply is the water cycle.
Water Cycle • How much of our planets water is fresh? • How does that affect life on our planet?
Water Cycle • You are already familiar with the Water Cycle - precipitation , evaporation, infiltration, runoff and transpiration. -Infiltration – the movement of surface water into rocks or soil through cracks and pore spaces. - Runoff – excess water that does not permeate into the land and flows over the surface instead Running water starts as precipitation and either infiltrates the surface to flow under ground, or becomes runoff and creates streams and rivers.
Running Water • When water falls to Earth it hits the ground running in the form of streams and rivers • Gravity influences how water makes its way to the sea – or base level.
Streams • Water that has become runoff creates streams. • The stream channel is the course that the water in a stream follows. • Streams have different features that will determine how much erosion it causes: • Gradient • Discharge • Stream profile • Base level • Let’s take a closer look at each of these features…
Streams - Gradient • Gradient is the slope or steepness of a stream channel. • Expressed as the vertical drop of a stream channel over a certain distance. • Which would move at a higher rate: • A stream with a high gradient, or • A stream with a low gradient? • Why?
Stream Profile • A stream’s profile is the cross-sectional view of a stream • From head (source) to mouth. • Where would a stream have the steepest gradient – near the head or near the mouth? • The stream would have a steeper gradient near the head.
Streams - Discharge • A streams discharge is how much water is flowing in the stream at a given point. • Discharge can vary with snowfall, snowmelt or drought. • **What do you think would happen to a streams discharge as it moves from the head to the mouth? • It would INCREASE! • What do you think would happen if a stream’s discharge is increased? • It would go faster: increased velocity • It would get wider: increased channel width • It would get deeper: increased depth
Streams – Base Level • A base level is the lowest point to which a stream can erode. • the level at which the mouth of the stream enters the ocean, a lake, or another stream • Two general types • ultimate—sea level • temporary, or local
Streams – Base Level • Streams mostly head down slope, ultimately reaching it’s final destination – the sea. • What would happen if you lowered the base level? • It will cause the stream to downcut.
Check In Questions • What is the single most important erosional agent on earth? • In the water cycle, what is infiltration in your own words? • What happens to a streams discharge as it moves from the head to the mouth? • Explain what happens when a stream’s discharge increases. • At which part of a stream would the gradient be steepest? • What would happen if you lowered the base level of a stream?
Brownie Ticket • The vertical drop of a stream channel over a certain distance is called: • Discharge • Channel roughness • Gradient • Runoff • What is the single most important erosional agent on earth? • Where is a streams discharge greatest? • A the mouth • At the source • During a drought • The same at the mouth and the source
Warm Up 9/5 • What would happen to a streams discharge as it moves from the source to its mouth? • Define the GRADIENT of a stream in your own words. Where is the gradient of a stream at its highest? • THINK: What factor(s) do you think would affect the ability of a stream to erode and transport materials?
Running Water Day 2
Objective • By the end of today, I will be able to: • Evaluate how materials are transported in a stream and how they are deposited. • Predict why floods happen and some methods of flood control.
Key Points • The ability of a stream to erode and transport material depends largely on its velocity. • Most streams carry the largest part of their load in suspension. • The suspended load of a stream usually consists of find sand, silt, and clay-sized particles. • A depositional feature that forms where a stream enters a lake or ocean is a delta. • In a stream channel, the heaviest particles are deposited first. - gravel, then sand, then clay. • Occasionally, deposition causes the main channel of a stream to divide into smaller channels called distributaries. • Major causes of floods include: rapid snow melt, heavy rain, decreased capacity of stream channels. • Flood control methods include artificial levees , sandbags and dams.
Stream Load • The ability of a stream to erode and transport material depends largely on its velocity. • What is velocity? • velocity = distancethestreamcovers/amount of time • What type of materials do streams carry? • Sand, dirt, clay, silt, salt, gravel… • How do streams carry material?
Streams • Streams generally erode their channels, lifting loose particles by abrasion, grinding, and by dissolving soluble material. • When the flow is turbulent enough, it can dislodge loose particles from the channel and lift them into the moving water. • The stronger the current, the more erosional power and more effectively water will pick up the particles.
Streams Sediment is transported by streams in 3 ways… 1. In solution (dissolved load) 2. In suspension (suspended load) 3. Scooting or rolling along the bottom (bed load)
Streams Sediment is transported by streams in 3 ways… • In solution (dissolved load) • What type of materials would dissolve in a stream? • Salt and other fine materials • How do these materials enter the stream? • Through groundwater and dissolving rock along the stream’s course
Streams Sediment is transported by streams in 3 ways… 2. In suspension (suspended load) • What does it mean if something is suspended? • It’s floating! • What types of materials are suspended? • Usually just sand, silt, and clay • This is where streams carry the largest part of their load
Streams Sediment is transported by streams in 3 ways… 3. Scooting or rolling along the bottom (bed load) • What type of material moves in the bed load? • Materials too large to be carried in suspension • The bed load moves only when the force of the water is large enough to move the larger particles
Depositional Features • When the materials carried in a stream stop moving they are DEPOSITED. • This creates several features that shape the landscape around the stream including: • Distributaries • Deltas • Natural levees
Depositional Features • Distributaries • Deposition in the main channel can sometimes cause the stream to divide into smaller channels called distributaries.
Depositional Features • In your notes label the head and mouth of this river and place a “D” next to the distributaries D D D Head Mouth
Depositional Features • Delta – an accumulation of sediment formed where a stream enters a lake or ocean. • Why does the sediment build up (accumulate) when a stream reaches a lake? • Because the velocity drops! • The current can no longer carry sediment!
Delta • What happens to the sediments when the stream reaches the ocean?
Depositional Features • Natural Levees – a natural build up of sediments that run parallel to a stream. • They form after the stream floods, leaving sediment behind. • This can naturally prevent future flooding
Flooding • What are some things that cause flooding? • Heavy Rain • Rapid Spring Snowmelt • Why are floods bad? • They cause damage • They can come without warning (flash floods) • They can hurt people • Cost a lot of money • What are some floods that you have heard of, why were they dangerous? – Discuss with a partner
Flooding • There are several methods used to help prevent flooding: • Artificial levees • Create Dams • Sandbags • Limit construction around areas known to flood • Mississippi Flooding • What caused the flood? • What caused the most damage during the Flood?
Recap • How materials are transported in a stream? • How they are deposited? • Why do floods happen? • What are some methods of flood control?
Check In Questions • The ability of a stream to erode and transport material depends on what? • Most streams carry most of their load in what way? • What is a delta in your own words? Why do they form? • What is a distributary? How do they change the course of a stream? • Why do floods form? • How could we prevent extreme flood damage, like during Hurricane Katrina?
Essay Preparation • How does climate affect erosion and shape our planet? • What climate is best for chemical erosion? • What climate creates the most soil? • What climate poses the greatest threat for mass movement? • How does climate influence the discharge of a stream?
Brownie Ticket • The ability of a stream to erode and transport material depends largely on its________________________. • Most streams carry the largest part of their load: • As dissolved material • In suspension • Along the stream’s bottom • As bed load • Occasionally, deposition causes the main channel of a stream to divide into several smaller channels called: • Oxbow lakes • Meanders • Distributaries • Deltas • Other than heavy rain, what else causes floods?