groundwater
any water drawn from below the water table
origin of groundwater (2)
precipitation;
infiltration of rainfall into the soil and sediment/bedrock.
infiltration capacity
rate at which water is absorbed into soils, sediments, rock
the rate of infiltration also depends on
the ground slope, types of vegetation, and existing soil-moisture conditions; the limiting infiltration capacity is the hydraulic conductivity of the soil;
in general, groundwater moves slowly through
the pore spaces of Earth materials
groundwater moves fastest through
the central area of a material's pore space
groundwater can move upward against the force of gravity, and moves from areas of
high pressure toward areas of low pressure
overland flow
when rainfall exceeds the infiltration capacity of the soil,
the result of overland flow
s ponding or water flowing across the surface (runoff) to lower elevations to stream channels
throughflow is
the sporadic horizontal flow of water within the soil layer
throughflow normally takes place when the soil is? and then proceeds?
is completely saturated with water
This water then flows underground until it reaches a river, lake, or ocean.
Rates of water movement via throughflow are usually
low
Rates of maximum flow occur on
steep slopes and in pervious sediments
The lowest rates of flow occur in
soils composed of heavy clays
Rates of throughflow in these sediments of clay can be less than
1 millimeter per day
3 sources of water
1. meteoric - precipitation
2. connate - water trapped during sediment deposition
3. juvenile - water released by igneous activity
% of Earth's water is fresh rather than salt water
3%
% of the Earth's water is unavailable or unsuitable for beneficial human use because of its salinity (seawater), or form and location (icebergs, glaciers).
99%
% of the world's total water supply exists as uncontaminated fresh water on or close to the surface and readily available for human use
0.003%
leads the world in the amount of water withdrawn from the Earth
United States
The single greatest use of groundwater in the United States is? in %
65%
% of groundwater withdrawn in the United States is not replenished.
25%
groundwater transports
dissolved mineral matter, sediment, heat, gases, and microorganisms;
water is a what kind f molecule? And possesses what kind of unique property?
dipolar
having its solid form (ice) less dense than its liquid form
cohesion
attraction of dipolar water molecules toward each other
groundwater occurs in two major regions beneath the Earth's surface:
zone of aeration (vadose zone)
zone of saturation (phreatic zone)
zone of aeration (vadose zone) consists of
the uppermost zone of soil moisture, intermediate zone; this zone is one in which the pore spaces are occupied partly by air
zone of saturation (phreatic zone) is the boundary between?
the vadose and phreatic zone is the water table; this boundary may be a capillary fringe; all pore spaces are filled with water in this zone
capillary rise in soils, sediments, and porous and/or fractured rock is due to:
adhesion and surface tension
adhesion is
water molecules attracted to a solid surface (wetability)
surface tension is
water molecules are much more attracted to each other than to molecules of air
he capillary fringe can range in
thickness from a few centimeters thick coarse sand to several meters in clay deposits
The capillary fringe fits neither into the zone of aeration nor the zone of saturation because ? Region is called?
the pores there are saturated but the pressure heads are less than atmospheric.
tension-saturated zone
groundwater movement is also called
laminar flow
hydraulic conductivity
ability of water to move through a particular material (measured in meters per day);
hydraulic conductivity is the function of
the properties of a fluid (viscosity, density) and properties of the material (particle diameter, size of pores, how interconnected the pore spaces are);
with units of velocity (meters/day), hydraulic conductivity characterizes
the capacity of the medium to transmit water
groundwater discharge
groundwater flows into a lake or river, or is a flowing artesian well or spring
influent stream
stream which flows above water table and adds water to the ground (found typically in arid regions); streams are intermittent or ephemeral
effluent stream
stream fed by groundwater (found typically in humid, temperate regions); streams tend to be perennial
% of the streamflow in the United States is supplied by groundwater that emerges as springs or other seepages along the stream channel (base flow).
30%
Base flow is
the component of stream flow derived from groundwater and is responsible for the low flow or dry season flow of perennial streams.
porosity (n)
amount of void space in soil, sediment, or rock expressed as a percentage
effective porosity (e)
percentage of interconnected pore space
permeability
ability of material (rock, soil, sediment) to transmit a fluid
permeabilty, with units of L2 (cm2 or m2) characterizes the capacity of the medium to transmit water but only in terms of
the properties of that material and not the properties of the fluid
well
any opening bored into the zone of saturation
water table well
well that extends into the zone of saturation in an unconfined aquifer
drawdown
the difference in height between the bottom of a cone of depression and the original height of the water table
aquifer
a saturated, permeable geologic unit that can transmit significant quantities of water under ordinary hydraulic gradients;
the water-well industry defines an aquifer as a geologic unit permeable enough to yield
economic quantities of water to wells
The fluid pressure in the saturated zone of an aquifer increases with depth and is greatest at
base of the aquifer
The fluid pressure at the water table surface is what to atmospheric pressure?
equal
Saturated material above the water table in the capillary fringe has a fluid pressure what than atmospheric pressure?
less than atmospheric pressure (negative pressure)
Capillary rise in sediments and rock fractures is due to
water adhesion and water surface tension
The water table is best defined as the surface on which the fluid pressure in the pores of a porous medium is? the location is at the level?
exactly atmospheric
which water stands in a shallow well open along its length and penetrating the surficial deposits just deeply enough to encounter standing water in the bottom.
A perched water table
a local water table separated from the regional groundwater table below.
good aquifers can be found in
sandstone, conglomerate, fractured rocks such as basalt, and cavernous limestone
aquiclude
a saturated, geologic unit that is incapable of transmitting significant quantities of water under ordinary hydraulic gradients
unconfined aquifer
no confining layer restricting the upper surface of the zone of saturation at the water table;
water table wells are developed in the zone of
saturation
confined aquifer
aquifer overlain by a confining layer and bounded below by a confining layer resulting in groundwater flowing under pressure
requirements for a confined aquifer include (3)
1. confined permeable strata, 2. tilted strata, and 3. recharge area
water in a confined aquifer is produced additionally by? Result is?
compression of the aquifer matrix during pumping of a well as well as by expansion of the water as pressure decreases;
result, the aquifer remains saturated even during heavy pumping
artesian
condition in an aquifer where an aquiclude is present
the water below the aquiclude is under or over pressure?
under
two conditions are required to form an artesian system
1. groundwater is confined to an inclined aquifer that is recharged at only one end, and 2. the aquifer is confined by aquicludes
spring
water table intersects the Earth's surface where a natural flow of groundwater results;
a localized discharge point; this point could be a
fault, cave mouth, joints intersecting the land surface, water discharge along the top surface of an impermeable rock
cone of depression
cone-shaped depression in the water table immediately surrounding a well
artesian well
water that flows under pressure; any situation in which groundwater under pressure rises above the level of the aquifer
perched water table
local water table separated from regional groundwater table below
Darcy's law :
Q = KIA
Q is a volumetric flow rate
in L3/T;
K is the hydraulic conductivity and is a coefficient that depends on
the permiability of the material, the acceleration of gravity, and viscosity of water
Q = KIA, I stands for
hydraulic gradient;
Q = KIA, A stands for
is the cross-sectional area of flow
hydraulic gradient is obtained
dividing the vertical difference between the recharge and discharge points (head) by the length of the flow between those points; hydraulic gradient must exist for flow to occur:
hydraulic gradient (I) equation
(h2 - h1) / length (l)
velocity equation?
[K(h2 - h1)] / length (l) = q (specific discharge) = Q / A
specific discharge is directly proportional to
hydraulic conductivity, hydraulic gradient, and hydraulic head drop along the flow path
hydraulic head decreases in
the direction of flow and can vary in three dimensions
piezometer
pipe in which the elevation of a water level can be determined for the purpose of measuring hydraulic head
equipotential lines
connects points where the value of the movement potential is constant; that is, these are lines of equal hydraulic head
flow lines
paths that the groundwater will follow in a system
flow net
set of intersecting flow lines and equipotential lines
groundwater always moves from an area of
high hydraulic head to an area of lower hydraulic head