| Aquifer |
Rock or sediment in a formation, group of formations,
or part of a formation, which is saturated and sufficiently permeable
to transmit economic quantities of water to wells and springs. |
| Aquifer, confined |
An aquifer that is overlain by a confining bed. The confining
bed has a significantly lower hydraulic conductivity than the aquifer. |
| Aquifer, perched |
A region in the unsaturated zone where the soil or rock may be
locally saturated because it overlies a low-permeability layer. |
| Aquifer, unconfined |
An aquifer with no confining beds between the saturated zone
and the surface. There is a watertable in an unconfined aquifer. |
| Asphalt |
A hard surface lining formed by the spreading of asphalt on the
subgrade of the channel to form a hard surface and seal the channel. |
| Bank remodelling |
The remediation method by which a bank is at least
partially rebuilt. |
| Bank re-profiling |
A channel construction step by which work in the
channel alters the channel cross-section, especially the slope
of the banks. |
| Bentonite |
Bentonite is a natural clay-like substance formed
from the deposition of volcanic ash in seawater.
Bentonite-soil blanket - A liner constructed by uniformly spreading
powdered bentonite over the surface area of a dry channel. The
powder is then mixed into the top layer of soil using a rotary
type mixer and compacted to form a 50 to 100mm thick blanket over
the channel section.
Bentonite-buried membrane - A liner constructed by uniformly spreading powdered
bentonite, 20 to 50mm thick, over a smooth, firm and dry channel subgrade. This
layer is covered by at least 300mm of stable earth and compacted.
Bentonite-sediment sealant - Dry, high swell bentonite in granular form is spread
over the channel water surface. This material sinks to form a seal at the base
of the channel. |
| Biological treatment |
Biologica19/10/07 agents to the either the channel water or soil layer, which assist
in reducing the seepage from the channel. There is also the potential
for additional ecological benefits in using biological treatments. |
| Capillary fringe |
The zone immediately above the watertable, where water is drawn
upwards by capillary tension. |
| Channel bed conductance |
The conductance (conductivity divided by thickness)
of the naturally forming channel lining (largely due to the depositing
of suspended sediment in the water) or, in the event of the removal
of this lining, the surface layer resistance. |
| Channel leakage |
Loss of water through the banks and base of a channel
via macro-pores. |
| Channel seepage |
Loss of water from a channel via infiltration through
micro-pores and soil processes (i.e. not via preferential flow
through macro-pores). Seepage as measured in pondage tests includes
a leakage component. Generally the term channel seepage refers
to both seeped and leaked water, as the two are not easily separated. |
| Compacted clay |
Compacted clay or a compacted earth lining consists
of importing (and compacting) soils which have better soil characteristics
than the in-situ soils (i.e. low permeability and high resistance
to erosion). |
Compaction of soils
in-situ |
This involves the enhancement of in-situ soil characteristics
such as stability and permeability using standard compaction techniques. |
| Concrete (reinforced, unreinforced, precast, cast
in situ) |
A hard surface lining formed by the construction
of concrete channel sections either in-situ or elsewhere, which
are placed onto the surface of the channel subgrade to form a hard
surface and seal the channel. |
| Constant head permeameter |
A device for measuring the saturated hydraulic conductivity
of soils. A constant head of water is maintained in a shallow auger
hole and the rate of leakage from the apparatus to maintain this
constant head (once saturated conditions have been reached) is
proportional to the saturated hydraulic conductivity (or permeability)
of the soil. |
| Core trenching |
A mechanism for reducing the seepage from channels
by excavating a trench either side of the channel and filling the
trench with an impervious substance. |
| Covered flexible membrane |
The construction of a lined channel using a geomembrane
to reduce seepage where the geomembrane is covered with a non-erosive
material that protects the geomembrane. |
| DamSeal |
Proprietary product - spray applied modified bituminous
polymer over a geotextile fabric base |
| Electromagnetic survey (EM) |
Measurement of the apparent conductivity of the
sub-surface by recording the response of a secondary electrical
field induced by the pulsing of a current
through a fixed or mobile loop. |
| Exposed flexible membrane |
An uncovered or exposed geomembrane lined channel
is constructed by placing the material on the subgrade of the channel. |
| Flexible membrane (geomembranes or flexible synthetic
liners) |
A geomembrane is a thin flexible impermeable liner,
which combined with the strength of the base soil, can be used
to reduce seepage. There are two distinct ways of constructing
channels using geomembranes: |
| Geophysics |
Section of earth science that employs the principles
and methods of physics to measure the physical properties of soil
and rock for the purpose of inferring composition and structure. |
| Groundwater |
The water contained in interconnected pores located
below the watertable in an unconfined aquifer, or located in a
confined aquifer. |
| Groundwater interventions |
Methods of seepage reduction which intercept seepage
flow outside of the channel prism. Includes core trenching, tile
drains, groundwater pumps and tree plantations |
| Grouted fabric matts |
Two layers of a woven or punched geotextile fabric
connected together at regular intervals and pneumatically filled
with concrete to form a hard liner that conforms to the channel
profile |
| Hydraulic head |
The hydraulic head is the sum of the elevation head,
the pressure head, and the velocity head at a given point in an
aquifer. |
| Infrared |
The band of wavelengths within the electromagnetic
spectrum between red light of the visible band at 0.7mm and microwaves
at 1000mm. Most remote sensing techniques for channel seepage
detection are based on the differences in the infrared reflection/absorption
properties of moist and dry soils, and between healthy and stressed
vegetation. |
| Isotope |
A particular atom of an element that has the same
number of electrons and protons as the other atoms of that element,
but a different number of neutrons, i.e. the atomic numbers are
the same but the atomic weights differ. Isotopes have essentially
the same chemical properties as other atoms of the same element. |
| Liquid Boot |
Proprietary product - spray applied modified bituminous
polymer over a geotextile fabric base. |
| Macro-pores |
Visible cracks or fissures in soil |
| Micro-pores |
Porosity of soil matrix (ie, 'natural' porosity,
not due to cracking or fissuring) |
Modified soil mix
(lime, gypsum,
cement, chemicals) |
To improve the slope stability, erosion resistance
and permeability of the soil being used in the channel construction
(in-situ or imported), soil may be treated or mixed with relatively
small quantities of substances such as lime, cement, gypsum, and
certain chemicals to overcome their natural deficiencies. |
| Permeability |
The measure of the ability of a rock, soil or sediment
to transmit a fluid. The magnitude of the permeability depends
largely on the porosity and the connectedness of pore spaces. |
| Piezometer |
A non-pumping well, generally of small diameter,
that is used to measure the elevation of the watertable or potentiometric
surface. A piezometer generally has a short well screen through
which water can enter. |
| Pondage test |
A water balance approach to measuring channel seepage
within an isolated reach of channel. A section of channel is blocked
off with embankments and the section filled with water. The seepage
rate is calculated from the rate of water decline after corrections
are made for evaporation and rainfall. |
| Potentiometric surface |
A surface that represents the level to which water
will rise in tightly cased wells. The watertable is a particular
potentiometric surface for an unconfined aquifer. |
| Remote sensing |
Any kind of data recording by a sensor which measures
energy emitted or reflected by objects located at some distance
from the sensor (i.e. no direct ground contact. |
| Resistivity survey |
A geophysical technique used to measure the apparent
resistivity of the sub-surface by applying a direct current to
the ground and measuring the resultant ground potential and current
in the vicinity of the applied current. |
| Saturated zone |
The zone in which pores in the rocks or soil are
filled with water at a pressure greater than atmospheric. The watertable
is the top of the saturated zone in an unconfined aquifer. |
| Seepage meter |
Covered cylindrical infiltrometer modified for use
under water. Seepage meters are used for spot measurements of seepage
in channels without artificial lining. The best known seepage meter
is the Idaho Meter. |
| Seepage plume |
The horizontal and vertical extent of groundwater
that has been mixed with channel seepage water. |
Shotcrete
(with/without fibres) |
A hard surface lining formed by the spraying of
a concrete that dries in place onto the surface of the channel
subgrade to form a hard surface and seal the channel. |
| Soil sealants |
Soil sealants are either natural or artificially
processed materials that can be either injected into water, mixed
into the soil, sprayed onto the soil or injected into the subsoil
to reduce the channel seepage losses and increase soil stability. |
| Terminal seepage rate |
The constant rate of seepage attained once the groundwater
mound caused by channel seepage rises to the elevation of the water
surface in the channel. |
| Unsaturated zone |
The zone between the land surface and the watertable.
The pore spaces contain water at less than atmospheric pressure,
as well as air and other gases. |
| Waterlogging |
Process of soil becoming saturated with water, generally
for an extended period. |
| Watertable |
The surface in an unconfined aquifer or confining
bed, at which the pore pressure is atmospheric. It can be measured
by installing shallow wells extending a few metres into the saturated
zone and then measuring the water level in those wells. |
| Watertable, perched |
The surface in a perched aquifer at which the pore
pressure
is atmospheric. |
