Final Flashcards
(38 cards)
Define Area of Influence
The land surface overlaying the cone of depression.
Define Artesian Aquifer
occurs when there is positive hydraulic head in the aquifer, when an aquifer’s recharge area is higher in elevation than the drainage point. This allows the porous aquifer to have a positive pressure and possibly even flow water to the ground.
When an aquifer is confined by an impermeable bed, a well penetrating this aquifer will have a water level higher than the aquifer, reflecting the pressure within the aquifer which is > than atmospheric
Define Bail Test
The removal of water from a well at regular timed intervals, using a long cylindrical container or bailer.
Define Baseflow
Steady input of groundwater that sustains streamflow over long periods of time.
Define Bedrock
A common term for consolidated rock underlaying soils and subsoils, a relatively solid rock or rick with significant contrast in hydraulic conductivity.
Define Capacity
The rate at which a well can produce on a continuous long-erm basis.
Define Cave
A natural underground space, created by the movement of groundwater.
Define Capillary Fringe
The subsurface layer in which groundwater seeps up from a water table by capillary action to fill pores. Pores at the base of the capillary fringe are filled with water due to tension saturation. Height of the capillary fringe is related to pore size.
Define Catchment
An area over which water falling on the surface will drain into a river or lake. Refers only to surface waters.
Define Condensation
an air mass is not 100% saturated with water vapour, but as the air temperature drops and the concentration of the air mass reaches 100% (the dew point), water will condense and drop out of the air (precipitation).
Define Compaction
to the process by which a sediment progressively loses its porosity due to the effects of loading. This forms part of the process of lithification. When a layer of sediment is originally deposited, it contains an open framework of particles with the pore space being usually filled with water. As more sediment is deposited above the layer, the effect of the increased loading is to increase the particle-to-particle stresses resulting in porosity reduction primarily through a more efficient packing of the particles and to a lesser extent through elastic compression and pressure solution.
Define Cone of Depression
The lowering of the water table near a well, an inverted cone-shaped surface of the water levels in the vicinity of a pumping well, caused by a decrease in pressure in the aquifer due to pumping.
Define Darcy’s Law
Flow rate is proportional to the rate of change in hydraulic head.
Define Differential Subsidence
When a subsiding rock unit has varying mechanical properties, portions of the unit may subside more quickly relative to the rest of the unit.
Define Drainage Basin
An area over which water falling on the surface will drain into a river or a lake, refers only to surface waters.
Define Drawdown
The lowering of the water level (hydraulic head) in the well due to pumping
Define Funicular Groundwater
Water that is maintained in the vadose through the adhesive property of water, i.e. the water is adhering to the individual grains of soil or clasts of sediment.
Define Hydraulic Conductivity
The permeability of soil for water. A property of both fluid and porous media.
Define Hydraulic Head
elevation + pressure head
is a specific measurement of liquid pressure above a geodetic datum (sea level)
It is usually measured as a liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer.
In an aquifer, it can be calculated from the depth to water in a piezometric well given the information of the piezometer’s elevation and screen depth.
Hydraulic head can similarly be measured in a column of water using a standpipe piezometer by measuring the height of the water surface in the tube relative to a common datum.
The hydraulic head can be used to determine a hydraulic gradient between two or more points.
The distribution of hydraulic head through an aquifer determines where groundwater will flow. Where the hydraulic head is constant, there is no flow. However, if there is a difference in hydraulic head from the top to bottom, the water will flow downward, due to the difference in head, also called the hydraulic gradient
Define Piezometer
Any device used to measure hydraulic head.
Define Residence Time
The average time required to replace an entire volume with new water.
Define Slug Test
A controlled field experiment in which water level in a control well is caused to change (rise or fall) instantaneously and the subsequent water-level response (displacement or change from static) is measured in the control well and one more surrounding observation wells through time.
Define Stratigraphic log
The description of the nature and thickness of geologic formations penetrated by a borehole.
Define Subsidence
The motion of a surface as it shifts downward relative to a datum such as sea-level. This may be a response to groundwater removal, e.g. San Joaquin Valley
