GEO - topic 5 hydrology and groundwater

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Created by: kit

HYDROLOGICAL CYCLE How is the worlds water stored?
- oceans, lakes, ice caps
- oceans, lakes, ice caps, groundwater
- oceans, surface land water, groundwater, icecaps
Which is an untrue statement about the hydrological cycle?
- water is present virtually everywhere in the ground in some some form
- the water table height may vary seasonally
- the majority of rainfall is sourced from land sources
- the height and water table, depth from surface vary within the ground
- the height of the groundwater generally follows the shape of the surface but may be influenced by other factors
- the water table can be found at the surface are well below the surface
The water in the ground comes from 3 main sources, which is not one?
- connate water
- juvenile water
- isolated water
- meteoic water
What is juvenile water?
- water seperated from magma during recent volcanic activity. Can often be contaminated with disolved minerals and gases.
- water trapped under ground in aquifers, has been under ground for extremely long periods of time
- water that follows underground through voids, due to this it is usually very mineral rich and clean. This type of water feeds springs.
Which best describes connate water?
- the water found in large limestone voids, very rare but significant water source. usually acidic and often hazardous to extract
- isolated water unground, typically very old. trapped in a manner similar to crude oil.
- the most common type of water, this water typically feeds springs. It is also high in mineral content due to its exposure to different minerals over time.
which best describes meteoic water?
- by far the most common type of water, comes from precipitation infiltrating the ground.
- water actually made in the crust, very little is known about this
- water formed when frozen meteorites melt deep underground
Which is not a type of precipitaion?
- rain
- snow
- dew
- transpiration
- hail
which is not a process returning h2o to the atmosphere?
- evaporation
- runoff
- transpiration
- juvenile h20
what is juvenile h2o?
- steam from volcanoes
- water evaporating from lakes
- h2o that is constantly in the air
- very humid and hot air rising
Which list, from surface down, describes the structure of the ground best?
- surface, zone of aeration, groundwater
- surface, zone of aeration, capillary fringe, groundwater
- surface, voids, ground water
what is the zone of aeration or vadose zone?
- the region between the surface and the water table
- the capillary fringe
- a totally dry section of the ground
What happens when water is on the surface?
- water flows under gravity to the saturation zone/water table, having infiltrated the ground.
- the water infiltrates the ground and is carried by underground currents away
- if it cannot run off fast enough it infiltrates
what is/where is the capillary fringe?
- betweem the surface and water table, allows water to move by capillary action.
- between the zone of aeration and water table, allows water to be held by capillary action, can hinder the downward flow of water due to suction forces
- a band of little tunnels and voids that quickly allow water to become level underground, this is under the zone of aeration and can be very deep depending on the areas precipitation
GROUNDWATER (and previous) where the water table meets the surface we can usually see ponds, lakes, streams and rivers. However a body of water on the surface can be either... which is wrong?
- Gaining or effluent, the body of water is feed by the water table, and precipation, found in humid areas, like lake district, without precipation the river flows normally at its baseflow.
- loosing or influent, the body of water feeds the water table, the body is only fed by precipation and can become dry during dry periods. Typical in deserts
- combination stream, the body supports and relies on the water table. A delicate balance.
Regarding a gaining or effluent stream, which is untrue?
- a gentle rain does not increase runoff, but infiltration raises the water table and increases the baseflow
- infiltration takes longer to affect streams than direct runoff because, this is due to underground obstacles
- the higher the gradient of the water table the greater the influence on the baseflow: the higher the gradient the higher the discharge
- because is is controlled by the water table the stream will not dry out
changes in the environment can cause stream types to changes, which is not one?
- flood, effluent to influent
- flood: influent to effluent
- drought, effluent to influent
Ground water is never static, it flows, due to gravity, to gaing/effluent surface water bodies. which is not a scale of system?
- local flow
- random flow
- intermediate flow
- regional flow
What influences goundwater flow?
- water flowing from high ground to low ground, high water table to low water table
- pressures under the surface
- the allignment of aquifers and aquitards underground
PORES AND VOIDS, Which is untrue?
- We can only get water in the ground if there is space, ie pores and voids
- rocks with high porosites, permeability and fractures are considered pervious. Or aquifers.
- rocks with low porosity and low permeability, no open fractures are known as aquitards.
- the amount of voids and pores influence the height of the watertable
- pores and voids can vary largely in size
- cannot be found in soilds due to effective stress and saturation relationship
PERCHED WATER TABLES Which is untrue regarding perched water tables?
- where there is a discontinuous layer or lens of impervious material, stopping water percolating down. The water then collects.
- Water is stored in a clay/rock basin that is impervious, these are fed by precipitation
- a geographic feature that is fed by the landscape but also drains, such as a tarn
Describe the process of a perched water table being formed. Which step does not belong?
- infiltrates can be stopped by clay
- the clay stops the water and the water builds up, making the perched water table
- the water table will eventually over flow and drain over the edges and continue to the main water table
- this run off may become a spring if run off is focused
- none its all in order
ARTESIAN GROUNDWATER Where a dipping aquifer is covered by an aquitard, the water is confined. Which is untrue?
- the piezometric head in the aquifer is higher than the actual water table, if this is the case it is said to be artesian.
- this water is pressurised and will rise if the aquitard is bored into
- pressure at the foot of the dip is so great the ground is lifted and voids are created
What is a flowing well?
- Where the top of the well is below the piezometirc surface, and consequently water flows out of the well
- where water rises to a level inside the aquitard, but outside of the aquifer
- a well that used to gather water, but due to lowering of the water table the well is dried up
How does ground water affect strength of soils? Which is untrue?
- Can strengthen soils
- can significantly reduce soil strength
- saturation can cause failure in rocks by inducing fractures
- effective stress = total stress - pore pressure
- if pore water pressure is great enough is forces seperates grains and causes quicksand
- saturation causes voids and pores to disappear once the water dries/leaves
EXCAVATIONS, engineering Why is it important to dewater the site if digging below the water table?
- Will eventually fill with water, pore water pressure reduces the strength and stability of rocks and soils. increasing the chance of collapse
- digging into the water table will permanently lower the water table
- leaving water near the excavation will cause voids and caves below the excavation to collapse, hazardous
How can dewatering be done? Which is not one?
- drilling boreholes and continuously pumping water out
- constructing barriers around the site
- freezing the surrounding ground
- tunnelling under the site and creating voids to lower the table
WATER SUPPLY In many parts of the world groundwater is used as a water supply. Which is untrue?
- Some wells are artesian, others need pumping?
- wells usually preferable when building resevoirs is difficult, or if increased supply is needed
- requires a suitable source, with suffcient supply
- wells drilled/dug/bored into a aquifer
- good aquifers to use are: sands, gravels, sandstones, deeply weathered igneous rock, some permeable limestones
- it is preferable to access deeper groundwater because it is cleaner generally
OVER DRAWING What can overdrawing permanently affect?
- the height of the piezometric head and the water table, in extreme cases the whole local hydrological cycle
- the amount of water that the ground can hold, voids collapse and pores become blocked
- the quality of the water extracted
What is subsidence and what causes it? Subsidence is...
- when the ground level lowers, due to water being removed. The water pore pressure may be literally supporting the ground surface
- when the ground level rises. The water pressure causes the ground level to rise. Occurs when there is an overlying aquitard.
- when water leaves the area due to excesses pumping, the water table lowers. However voids and pores remain, this causes the ground to be unstable
What is the opposite of subsidence?
- extra water in the ground cases the ground to become denser and sink
- when the drainage of water causes the ground to become less dense and for the surface to rise as a result
- the extra water in the ground causes the surface to rise as pressure increases
CONTAMINANTS Which is untrue about polluting ground water?
- polluted ground water is a very serious problem as it is difficult to clean
- a wide range of contaminants exist
- pollutants disperse and travel throughout groundwater networks
- clean up is difficult and expensive
- natural pollution occurs when sea water travels inland
- detecting pollutants can take a very long time, long since the pollution occured, this is due to the slow flow
Which is not a common contaminant?
- hydrocarbons - buried or surface fuel tanks leak
- landfill leachate - land fill seals fail
- leached chemicals - on surface chemicals disolved and infiltrated into the ground by infiltration
- Sulphur - sulphur bearing minerals exposed to water infiltrate into the ground
- saline water - from oil wells or ocean
- all of these, and sewage - from badly maintains sewer systems

GEO - topic 5 hydrology and groundwater

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