Geology of Groundwater Occurence Flashcards
The Philippines has complex geology owing to presence of:
various tectonic and structural formation
where does groundwater inevitably occur?
geologic formations
t or f: earth is heterogenous
T
groundwater studies of an area necessarily includes:
review of previous geological studies
t or f: groundwater is more abundant than surface water
T
a ______________ must be made along groundwater study
detailed geological study
concerned with the distribution of earth material as they affect porosity and hydraulic conductivity of the earth
hydrogeologist
amount of voids contained in a particular volume of rock mass
porosity
porosity ranges for sedimentary materials
soil
clay
silt
medium to coarse sand
uniform sand
fine to medium sand
gravel
sand and gravel
sandstone
shale
limestone
capacity of a porous rock or soil to transmit a fluid
permeability / hydraulic conductivity
t or f: large interconnected pore openings are associated with high permeability
t
three types of limestone bedrock
karstified, fissured, compact
t or f: in groundwater assessment, using large ranges of hydraulic conductivity is not safe
t
the water that cannot be pumped out of a well
specific retention (Sr)
specific retention is left as a _____ on the rock surface
film
the water that can be pumped from a well
Specific yield (Sy)
part of the water that would be drained under the influence of gravity
Specific yield
what is the material with highest specific yield by (heath 1983)?
soil
what is the material with lowest specific yield by (heath 1983)?
granite
dumoy aquifer is under what watershed?
Talomo-Lipadas watershed
Dumoy aquifer is of what material?
volcaniclastics
this watershed supplies 90% of the drinking water serviced by Davao City Water Districts
Talomo-Lipadas watershed
target areas of groundwater exploration (2):
fllodplain ; malayo sa dagat
t or f: air allows passage of electrical currents
F (air does not allow electrical passage)
probability of sinkhole may reflect a _______ (high/low) electrical resistivity
high
this allows one and two dimensional acquisition of resistivity values of subsurface and generate long signature
Vertical electrical sounding (VES)
estimate lateral and vertical variations in ground resistivity values (allows 2D and 3D)
Electrical Resistivity Tomography (ERT)
a gently sloping plain consisting of alluvium
alluvial valleys
a dry lake bed
playa
playas and floodplains are good prospects of groundwater exploration because they have
unconsolidated sediments
an aquifer where water is held in pore spaces between grains of sand, gravel, clays, or rock fragments
unconsolidated aquifer
alluvial valleys are normally delimited by _______ on either side that rise above the level of the valley to varying heights
uplands
t or f: the alluvial valley of a stream is the portion of its alluvial plain that is on the upstream of its deltaic plain
T
basins formed by faulting or erosion are both filled with ______________; coarse grained deposits form ______
unconsolidated deposits ; productive aquifers
t or f: lake mainit is a graben
t
t or f: marikina valley is a graben formed by fault
T
emptied oxbow lake, remnants of a meandering water channel
meander scar
A lake formed as a river finds a different, shorter, course
oxbow lake
t or f: many major valley systems are products of tectonic activities rather than of fluvial and glacial erosion
t
during mountain-building episodes, the uplift of mountain masses will result in _____________ being formed
intermontane basins
An alluvium-filled valley between mountain ranges, often formed over a graben
intermontane basin
major aquifers in intermontane basins are composed of _____________ that overlie _________ aged rocks
unconsolidated deposits ; pre-Miocene
are also created by down-dropping of large crustal pieces along faults
fault-block valleys
basins bounded by impermeable rock may form ________
local or single-valley flow systems
if the interbasin rock is permeable, __________ may form
regional flow systems
in closed basins, ground water discharges into _______
playas
playas are discharged by
evaporation and transpiration by phreatophytes
closed basins are also called
endorheic basins
much of the drainage in this basin occurs underground
cryptorheic basins
a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but drainage converges instead into lakes or swamps, permanent or seasonal, that equilibrate through evaporation
closed / endorheic basin
one of the most productive terrains for recovering groundwater
alluvial valleys
these form a large part of the stream alluvium
sand and gravel
likely to tap a good aquifer or series of aquifer
alluvial valleys
t or f: individual aquifers in alluvial valleys do not usually extend far
T
t or f: the number and depth of water-bearing sand and gravels change rapidly from place to place in an alluvial valley
t
t or f: lithified sedimentary rocks have lesser hydraulic conductivity
t
clastic sedimentary rocks are typically composed of
silicate, carbonate, or clay minerals
chemically precipitated sedimentary rocks are primarily
limestone, dolomite, salt, or gypsum
chemically precipitated sedimentary rocks that are good aquifers
limestone and dolostone
salt or gypsum can be a material that prohibit petroleum deposits from leaking out, also known as ______
petroleum caprocks
can also be considered to be sedimentary deposits with the original sediments being organic
coal and lignite
t or f: sedimentary rock sequences are formed with younger beds laid down upon older ones
t
t or s: sedimentary rocks can occur as single unit
T (but rarely)
t or f: horizontally dipping beds are not common in the Philippines
T
t or f: folded and faulted rocks are common in the Philippines
T
how many wells are needed to locate in order to determine groundwater flow?
at least 3
this is a very real hindrance to groundwater exploration
complex stratigraphy
can create a very complex hydrogeologic systems in which the determination of recharge and discharge zones and flow systems are confounded
faulting and folding
in addition to determining hydraulic characteristics of rock units and measuring of ground-water levels, _________ must also be evaluated
detailed geology
three steps in determining groundwater flow systems
-determine hydraulic characteristics or rock units
-measure groundwater levels in wells
-evaluation of detailed geology
t or f: structure may or may not help with the formation of groundwater, but often than not, they help by increasing porosity
t
t or f: silangan is composed of hard rocks but is highly fractured so it has high recharge rates
t
________ and _________ must be reconciled with the pre-existing geologic knowledge
logs of test wells and borings
hydraulic conductivity of clastic sedimentary rocks are based on _______
primary permeability
primary permeability of clastic sed rx is a function of:
grain size, shape, and sorting of original sediments
carbonate aquifers have _____ dissolution and ________ pore spaces
high dissolution ; interconnected
t or f: primary porosity of limestone and dolomite varies
t
can be zones of high primary porosity and permeability in carbonate rocks
bedding planes
why is drilling limestones or karst lithology not recommended?
-when drill bit reaches the cavity/hollow, it detaches
- it is unfeasible to develop if maglagay ng pebbles and casing
explain the stages of growth of a carbonate aquifer
a.) first, most joints in the recharge area undergo solution enlargement
b.) as the solution passes grow, they join and become fewer
c.) eventually, one outlet appears at the discharge zone
t or f: growth of carbonate aquifers starts in recharge area towards the discharge area
t
this make the best aquifer
coarse-grained unconsolidated sediments
search for groundwater starts with investigations of
non-indurated sediments
properties of unconsolidated sediment aquifers
- easy to drill / dig = rapid and cheap
- found in valleys = shallow groundwater level
- favorable locations = recharge from rivers
- permeabilities are much higher
good aquifers of consolidated sediments
coarse-grained rocks
permeability of consolidated sediments depends on the degrees of
compaction, cementation, and fracturing
these acts as impermeable beds in a consolidated sedimentary rocks
finer sediments
properties of consolidated sediment aquifers:
1.) good aquifers = often coarse grained
2.) permeability depends on degrees of compaction, cementation, and fracturing
3.) finer sediments act as the impermeable beds
___________ igneous rocks are preferred for groundwater
extrusive igneous rocks
igneous and metamorphic rocks conductivity depends on:
development of secondary porosity
conductivity of metamorphic rocks depends on
degree of metamorphism
type of metamorphism
for groundwater to occur on igneous and metamorphic rocks, there must be openings developed through:
fracturing, faulting, or weathering
volcanic rocks have __________ permeabilities
low to high
igneous rock that is originally not porous
plutonic
recent volcanic aquifers may have high permeabilities due to:
- development of gas bubbles (vesicles)
- fracture/joints caused by buckling, faulting
- development of leached zone by weathering
- sand and gravel trapped between flows
fractures of plutonic igneous rocks tend to close due to
compaction and crystallization of secondary minerals
in plutonic rocks, groundwater is present in ____________ by tectonic processes and in ___________ or ________
open fractures ; leached or weathered zone
what type of aquifer is metamorphic rocks
fractured aquifer
metamorphic rocks have very low permeability except:
marble
groundwater in metamorphic rocks occur and moves through
fractures and leached zones
t or f: porosity and permeability of metamorphic rocks decrease with rapid depth
t
porosity and permeability of metamorphic rocks decrease with rapid depth because of
weight of overlying material
this metamorphic rock could have well developed solution openings or even caverns where large groundwater flow occurs
marble
properties of metamorphic rock aquifer
1.) very low permeability (except marble)
2.) groundwater moves and occurs in fracture and leached zones
3.) porosity and permeability decreases with depth
4.) marble could have well-developed solution openigs or caverns
t or f: arid regions have presence of groundwater but are difficult to find
t
manifestation of groundwater in arid regions
presence of vegetation (oasis)
desert areas receive ________ of precipitation or less each year
10 (25 cm)
t or f: cold deserts can have great accumulations of water
t
why is it that there is often virtually no local ground-water recharge in warm deserts?
the potential evapotranspiration is many times greater than annual precipitation
t or f: bedrock and unconsolidated aquifers are known in desert areas
t
unconsolidated materials in desert areas are often rather _____ and ______
coarse and permeable
dry climate in arid regions promote ________ of rock
mechanical weathering
vast bedrock aquifers are known to occur in the sedimentary basins of ____, ______, and _______
Egypt, Jordan, and Saudi Arabia
The Sahara Desert is underlain by what aquifer?
Nubian aquifer
what rock makes up Nubian aquifer? and how thick is it?
sandstone ; 3000 ft (900m) thick
much of North Africa and Arabia have old groundwater exceeding ____________ years
35,000 radiocarbon years
t or f: coastal plain aquifers are common in the Philippines
t
they are regional features, bounded on the continental side by highlands and seaward by coastline
coastal-plain aquifers
where do coastal plains exist?
in areas of stable basement rock;
in areas where the basement is sinking
the coastal plain may include large areas of __________, and the geology of the coastal zone may be very similar to the ___________
former sea floor ; adjacent continental shelf
transition between fresh and salt water
zone of diffusion
t or f: aquifers located next to tidal bodies are subjected to short-term fluctuations in the head, due to the tide
T
much of the aquifers in Davao City are located in?
south (bajada, talomo)
t or f: Dumoy aquifer is a confined aquifer
t
t or f: dumoy aquifer has low susceptibility to subsidence because it is made of hard and competent rocks
t
