Lecture 12: Hydrologic Cycle

Question 1

What is the chemistry of the water molecule?

Answer 1

• 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)

Question 2

What are the phases of water?

Answer 2

• Ice
• Liquid Water
• Water Vapour

Question 3

What transitions between phases absorb energy?

Answer 3

Evaporation, Melting, Sublimation

Question 4

What transitions between phases release energy?

Answer 4

Condensation (water vapour to liquid water), Freezing, Condensation (water vapour to ice)

Question 5

Latent heat

Answer 5

The energy absorbed or released by a body or thermodynamic system during a constant-temperature process.

Question 6

Properties of liquid water

Answer 6

Due to its polarity, it:

• Has a high surface tension
• Is an excellent solvent

Question 7

Properties of ice

Answer 7

• Lower density than liquid water due to an open crystal lattice
• Floats in liquid water
• Expansion of freezing water can cause physical weathering

Question 8

Evaporation

Answer 8

Solar energy causes water to evaporate from large bodies of water, moving it into the atmosphere.

Question 9

Transpiration

Answer 9

The water vapour that is given off by plants.

Question 10

Condenses

Answer 10

Water vapour condenses into clouds

Question 11

Precipitation

Answer 11

The water falls back to land or the ocean as precipitation; rain, hail, or snow.

Question 12

Infiltration

Answer 12

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.

Question 13

Runoff

Answer 13

Some of the moisture flows back to the sea as surface runoff, while a small amount is captured by the biosphere.

Question 14

Hydrologic reservoirs

Answer 14

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

Question 15

Residence time

Answer 15

The average amount of time that a water molecule stays in a particular reservoir

Question 16

Flux

Answer 16

The rate at which water moves between reservoirs

Question 17

The residence time of Earth’s reservoirs

Answer 17

• Atmosphere: days
• Rivers and lakes: months to years
• Shallow groundwater: decades to centuries
• Oceans: thousands of years
• Antarctic ice: tens of thousands of years

Question 18

Hydrologic balance

Answer 18

The relationship between flux, reservoir size, and residence times.
-relatively small water reservoirs can have high fluxes because the residence time is short

Question 19

Overland flow

Answer 19

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.

Question 20

Stream flow

Answer 20

Once the flow of water occurs in an establishmed channel

-Overland flow becomes channelized due to erosion, typicaly over relatively short distances.

Question 21

Surface runoff

Answer 21

When stream flow and overland flow together they create surface runoff.

Question 22

What are the two major sources for the flow of water in streams?

Answer 22

1. Overland flow contributions

2. Baseflow

Question 23

Baseflow

Answer 23

The input of groundwater through the bed of a river, contributing to its flow.

Question 24

River systems

Answer 24

• Streams organize into river systems

- Small streams (tributaries) typically merge downstream

Question 25

Drainage basin

Answer 25

Area drained by a major river and tributaries

Question 26

Drainage divides

Answer 26

Separate drainage basins

Question 27

Continental-scale basins

Answer 27

Topographic highs, such as continental divides typically separate water drainage basins the flow into different oceans

Question 28

What controls river behaviour?

Answer 28

The width, depth, gradient, velocity, and discharge of the river.

Question 29

Does the width and depth of a river increase or decrease downstream?

Answer 29

Increases, as tributaries join together.

Question 30

Does the gradient of a river increase or decrease downstream?

Answer 30

Decreases, steep mountain down to flat plains.

Question 31

Does velocity increase or decrease downstream?

Answer 31

Increases

Question 32

Does discharge increase or decrease downstream?

Answer 32

Increase

Question 33

What is discharge and how is it determined?

Answer 33

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.

Question 34

Dissolved load

Answer 34

Major ions in rivers. Primarily comes from dissolution of minerals.

Question 35

Suspended load

Answer 35

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

Question 36

Bed load

Answer 36

Comprised of typically larger particles in a river system that are transported by moving along the bed.

Question 37

Different forms of transportation in bed load

Answer 37

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.

Question 38

Hydrographs

Answer 38

A record of river discharge at one point in the river continuously over many years.

Question 39

Trends in river mass transport

Answer 39

• Faster flow velocity moves large particles
• Large particles deposit near their source
• Smaller particles deposit further downstream
• Dissolved load is typically carried to sea