Topic 7: Water - Sources, Volume, & Flow

Question 1

Define volume and flows of water

Answer 1

• Volumes: the amount and quality of water stored in parts of the water cycle
• Flows: connectivity and movement of water through the water cycle, involving many physical connections and driven by processes

Question 2

Describe water catchment

Answer 2

A catchment is when water is bounded or captured by a natural landscape.
Term catchment used interchangeably with watershrd, river basin, sub-catchment

Question 3

Identify and describe different categories of water

Answer 3

• Blue water: available in streams, rivers, lake reservoirs, and pumped from ground water
  + For human consumptions
  + Supports aquatic and terrestial life
  + Supplement for irrigated agriculture
• Green water: accumulates in the soil because rain infiltrates in
  + Available to plants and microbes in soil
  + Flows through simple being, transpiration, and evaporation
• Grey water: required to assimilate pollutants, ensure water quality
  + Point-source pollution discharged to freshwater
  + Indirect sources: leaching through soil, runoff, diffuse sources

Question 4

What is virtual water?

Answer 4

Virtual water, or hidden water, is the water used throughout the process of value chain producing many products, services, or processes that people purchase and consume.

Question 5

Describe infiltration, evapotranspiration and how they are related

Answer 5

Infiltration is the process of water entering the soil.
Evapotranspiration refers to water being evaporated into the atmosphere through lands and plants.
+ Evaporation rate should be smaller than transpiration rate –> make sure that the water is going through plants
+ If evapotranspiration rate is higher than rainfall, most of the water from the surface will be lost.

Question 6

Explain the concept of water footprint

Answer 6

Water footprint of a person is the water consumption of that person as well as the amount of water hidden in the products or services that person purchase or use.

Question 7

Why do we need some runoff?

Answer 7

Although we do want to minimize surface runoff and allow most of the water to supply plants and soil, we also don’t want to suffocate the plants and we need to replenish rivers and streams.

Question 8

How to maintain a balance in the water storage and movement?

Answer 8

There must be a balance between how much rainfall as precipitation, the evapotranspiration rate, and runoff within the catchment.
Also, we need to account for all inflows and outflows in the water cycle.

Question 9

Why do we need some drainage?

Answer 9

We don’t want the pores in soil to completely filled with water. Also, if too much water is deposited, salt will be deposited to making soil too saline.
So we need to some drainage for some air spaces.

Question 10

Briefly describe water allocation

Answer 10

Water allocation is a state problem in which bulk water supply from precipitation will be allocated differently along the flow path to different states.
This water will be allocated differently to individual irrigators who decide what to do with that water. They can also use carryovers from previous year for annual allocation.
The irigator may use the water for agriculture or trade for other people.

Question 11

Explain soil/surface sealing

Answer 11

The destruction of soil surface due to impermeable materials, preventing water to infiltrate into the soil which is essential for soil health, life of microbes and quality of crops/plants.
Also, soil already used for infrastructure is isolated from the carbon sequestration system.

Question 12

Differences between confined and unconfined groundwater

Answer 12

• Unconfined: not under pressure, flow between streams and rivers, connecting to the surface
• Confined: under pressure, can be tapped into for extract, artisan water

Question 13

Advantage and disadvantage of groundwater

Answer 13

• A reliable water supply during dry seasons and droughts. major reservoir that can be always be tapped into
• Less dynamic than surface water –> slow to recharge –> can be overused

Question 14

What is capillary fringe?

Answer 14

Capillary fringe is a layer right above the water table which is saturated by the rise of water due to capillary tension, providing moisture in the soil at which some salts and carbonate can build up. If too much salts build up or the level of water table rise, it can cause damage to the plants.

If the pore size is small, capillary fringe may fill up to several meters above the water table. If the pore size is larger, this layer may be just few inches.

Question 15

How can soil water be determined?

Answer 15

• How much water can infiltrate
  + Depend on porosity and surface condition
  + In agriculture, we want infiltration to be higher than irrigation –> water can go into soil
  + If no pores, cracks, or surface is sealed; most water will be in runoff.
• How much can be stored
  + Depend on aggregation and texture (sand vs clay)
• How much drainage

Question 16

Why does clay holds more water than sand?

Answer 16

Clay has a higher maximum porosity, thus more void spaces that can be filled with water.

Question 17

Which type of soil is best for agriculture and why?

Answer 17

Loamy soil because sandy soil cannot hold as much water as clay but it doesn’t hold water as tightly as clay so plants can access the water in the soil more easily and vice versa for clay soils.

Question 18

Describe hygroscopic, capillary, and gravitational water; wilting point and field capacity

Answer 18

• Hygroscopic water: below wilting point, water adheres to the soil particles –> plants don’t have enough energy to suck any more water
• Capillary water: water held in micropores because surface tension exceeds gravity and that is available to plants to use
• Gravitational: above field capacity, mostly in macropores, flows/drains quickly right through the aggregates due to gravity