Susan. Lecture 1 Flashcards
What is meant by the residence time of water molecules?
Average amount of time tat a water molecule resides in a reservoir before transfer to another
Compare the residence time in the atmosphere and in the ocean
Atmosphere - small reservoir with large flux so short - 10 days Ocean - huge reservoir with larger flux so variable - 4000 years
Briefly describe the three forms of groundwater
Meteoric water - originated as precipitation
Connate water - porewaters trapped during sedimentation
Juvenile water - water formed chemically within the Earth and brought to the surface Quantitatively the most important is meteoric
Briefly describe this image
The pore water gradually inceases with depth however at the capilliary fringe this begins to increase much faster
The percentage of pore space fillled by water increases exponentially until it reaches the cappilliary fringe where it reaches full saturation (100%)
What is an aquifer?
A saturated geological unit. It will transmit singificant quantities of water under ordinary hydraulic gradients. Aquifers are layers typically tapped by water supply cells and transmit most of the flow in a given location.
What is an aquitard?
An aquitard is a saturated permeable geological unit that has a lower ‘K’ (Hydraulic conductiivity) than nearby units and thus may limti flow
What is an aquiclude?
An aquiclude is a rock that can be saturated, but will not allow water to move through it under normal hydraulic conditions. It has such a low ‘K’ that it precludes flow
What is an unconfined aquifer?
An aquifer that is exposed at the surface, bounded by the water table. Generally follows topographic contours of the land.
What is meant by a confined aquifer?
Bounded on the upper surface of the aquifer by a low permeability layer (e.g. clay), confining the groundwater under pressure. The aquifer will be saturated throughout its full thickness. The groundwater is under pressure and thus will rise up a borehole drilled into the aquifer. This is called an ‘artesian well’.
Memorise the process schematic
What are the equations for porosity and void ratio?
Porosity - Volume of voids/Volume of material
Void ratio - Volume of voids/Volume of mineral solids in a given volume of material
What is the difference between primary and secondary porosity?
Primary Porosity - present when deposited
Secondary Porosity - created after rock forms
What is meant by effective porosity?
The proportion of pores part of an inter-connected network
What is meant by permeability?
Connectivity of pores in a rock influencing its ability to transmit water
When is water density greatest?
Water density is at its highest at 4 degrees celsius at 1g/cm3. Lowering or increasing temperature at this point will decrease the density.
