4.2 Earth Resources and Engineering Flashcards
What does a hydrogeologist have to do in order to ensure a reliable supply of water?
- asses geological factors affecting siting of reservoirs and dams
- identify underground supplies of water in aquifers
When water reaches the surface as rain, what can happen to it?
- run off over surface
- evaporate into atmosphere
- percolate downwards as groundwater
What factors does the passage of water into rocks depend on?
- porosity
* permeability
When is a rock porous?
If its grains have spaces between them that can hold water, or if there are other features in which water can be held
What type of rock is usually more porous?
Sedimentary
When is a rock permeable?
If water can travel freely from its upper surface to its lower surface
What type of rock is usually more permeable?
Sediments with larger, not so compacted grains
Texture of conglomerate rock?
- individual grains - clastic
- poorly sorted
- rounded, coarse grains
Texture of granite?
- crystalline
* coarse grained
Texture of desert sandstone?
- clastic - medium grained
- well sorted
- well rounded clasts
Texture of oolitic limestone?
- crystalline and clastic (individual oolites)
* medium sized oolites - well sorted
Practical to investigate porosity?
- weigh rock
- rock put into container and water poured over
- rock removed from water and weighed again - difference is amount of water it has absorbed
- rock put into 200cm3 water - record difference for volume
How to calculate percentage porosity?
Percentage porosity = (difference in weight / volume of water rise) x 100
Which rocks are more porous; clastic or crystalline?
Clastic
Factors for a good dam location?
- high rainfall
- flow of water into reservoir
- steep sided valley
- low construction cost
- impermeable rock to prevent water loss downwards
- little/no faulting to cause weaknesses
- stable slopes to prevent landslides
- no earthquake activity
What is the easiest way of storing water?
Building a dam and letting streams and rivers fill up the area behind the dam to form a reservoir
Is shale permeable?
No, it is impermeable
What is the water table?
The boundary between the saturated (where porous rocks have become totally saturated with water) and unsaturated rocks
What does the water surface come to the surface of the earth in the form of?
Rivers, springs and lakes
What is an aquifer?
A layer of porous rock saturated with water and underlain by an impermeable layer
What is a cuesta?
A hill with one steep side and one gentle side
What happens if too much water is taken from an aquifer?
The wells may dry up, or the water level in them might fall significantly
How is a cone of depression formed?
From taking too much water from a well
What is an artesian basin?
Where water is obtained under pressure from the porous rock lying between the impermeable rock - water rises automatically to the surface due to the pressure it is under from the overlying rocks