Lecture 12: Hydrologic Cycle Flashcards
-Properties of Water -Water Cycle and Balance -Water on the Land's Surface
What is the chemistry of the water molecule?
- formed by the covalent bonding of two hydrogens to and oxygen
- Bent (104.5º)
- Polar (more negative charge near the oxygen, more positive near the hydrogens)
What are the phases of water?
- Ice
- Liquid Water
- Water Vapour
What transitions between phases absorb energy?
Evaporation, Melting, Sublimation
What transitions between phases release energy?
Condensation (water vapour to liquid water), Freezing, Condensation (water vapour to ice)
Latent heat
The energy absorbed or released by a body or thermodynamic system during a constant-temperature process.
Properties of liquid water
Due to its polarity, it:
- Has a high surface tension
- Is an excellent solvent
Properties of ice
- Lower density than liquid water due to an open crystal lattice
- Floats in liquid water
- Expansion of freezing water can cause physical weathering
Evaporation
Solar energy causes water to evaporate from large bodies of water, moving it into the atmosphere.
Transpiration
The water vapour that is given off by plants.
Condenses
Water vapour condenses into clouds
Precipitation
The water falls back to land or the ocean as precipitation; rain, hail, or snow.
Infiltration
Some of the water infiltrates the ground, where it joins the ground-water reservoir and may eventually be locked up in the lithosphere in the form of the hydrous mineral.
Runoff
Some of the moisture flows back to the sea as surface runoff, while a small amount is captured by the biosphere.
Hydrologic reservoirs
Places in the water cycle where water is stored.
- Nearly all the Earth’s water resides in the oceans
- 75% is locked up as ice at the poles
- Freshwater and surface water bodies comprise less than 3% of the total water on Earth
Residence time
The average amount of time that a water molecule stays in a particular reservoir
Flux
The rate at which water moves between reservoirs
The residence time of Earth’s reservoirs
- Atmosphere: days
- Rivers and lakes: months to years
- Shallow groundwater: decades to centuries
- Oceans: thousands of years
- Antarctic ice: tens of thousands of years
Hydrologic balance
The relationship between flux, reservoir size, and residence times.
-relatively small water reservoirs can have high fluxes because the residence time is short
Overland flow
The initial sheet-like movement of water downhill with gravity.
- Some of the rainfall and meltwater on the landscape begins to flow across the surface once the soil is saturated.
Stream flow
Once the flow of water occurs in an establishmed channel
-Overland flow becomes channelized due to erosion, typicaly over relatively short distances.
Surface runoff
When stream flow and overland flow together they create surface runoff.
What are the two major sources for the flow of water in streams?
- Overland flow contributions
2. Baseflow
Baseflow
The input of groundwater through the bed of a river, contributing to its flow.
River systems
- Streams organize into river systems
- Small streams (tributaries) typically merge downstream
Drainage basin
Area drained by a major river and tributaries
Drainage divides
Separate drainage basins
Continental-scale basins
Topographic highs, such as continental divides typically separate water drainage basins the flow into different oceans
What controls river behaviour?
The width, depth, gradient, velocity, and discharge of the river.
Does the width and depth of a river increase or decrease downstream?
Increases, as tributaries join together.
Does the gradient of a river increase or decrease downstream?
Decreases, steep mountain down to flat plains.
Does velocity increase or decrease downstream?
Increases
Does discharge increase or decrease downstream?
Increase
What is discharge and how is it determined?
Discharge is the flux of water moving through the river at any given point.
It is determined by calculating the cross-sectional area of a river (width x depth), then multiplying that area by the velocity of the river
-This gives the units of discharge in units of volume per time.
Dissolved load
Major ions in rivers. Primarily comes from dissolution of minerals.
Suspended load
Comprised of particulate matters that remains in suspension in a river of stream.
- Smaller particles settle more slowly than larger ones, and so are transported farther
- Causes water to appear cloudy and opaque
Bed load
Comprised of typically larger particles in a river system that are transported by moving along the bed.
Different forms of transportation in bed load
Roll - rotate along the bed without leaving it.
Slide - move along the bed without leaving it.
Saltation - hopping along the bed, leaving it for short periods of time.
Hydrographs
A record of river discharge at one point in the river continuously over many years.
Trends in river mass transport
- Faster flow velocity moves large particles
- Large particles deposit near their source
- Smaller particles deposit further downstream
- Dissolved load is typically carried to sea
