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1997 Toccoa Flood

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The 1977 Toccoa Flood
Report of Failure of Kelly Barnes Dam Flood and Findings

by Federal Investigative Board
December 21, 1977


GLOSSARY

abutment
A surface or mass provided to withstand thrust such as at the ends of a dam.
acre foot
A volumetric measure of water equivalent to one acre covered to a uniform depth of one foot.
alluvial
Pertaining to or composed of alluvium, or deposited by a stream or running water.
alluvium
A general term for clay, silt, sand, or gravel or similar material deposited during comparatively recent geologic time by a stream or other body of running water.
base line
A reference line used for measurements and surveys.
bedrock
Rock of relatively great thickness and extent in its native environment.
berm
A horizontal shelf or ledge built into an embankment or other sloping surface.
biotite gneiss
A metamorphic rock of coarse grain size, in which biotite is a predominant mineral.
bituminous coated
A tarry hydrocarbon substance sometimes used to coat metals to prevent oxidation.
borrow pit
An area from which earth is taken to be used in the construction of an embankment.
breach
An opening made by breaking down a portion of a solid body, such as a dike or embankment.
clay
A fine grained, natural, earthy material composed primarily of hydrous aluminum silicates.
compaction tests
Tests carried out to determine the relationship between unit weight and water content of a soil.
conduit
A pipe, tube, or tile through which water or other fluid passes or is conveyed.
core drilling
The process of obtaining natural or undisturbed samples of soil or rock by drilling.
datum
A point, line, or surface with reference to which elevations are measured.
dip
The angle at which a bed, stratum, or vein is inclined from the horizontal.
discharge
The rate of flow of water in a stream, conduit, or other channel, usually measured in cubic feet per second (cfs).
dispersive soil
A dispersive soil is a clay soil that behaves as a single grain soil and is highly erodable when subjected to water forces.
drainage area
The area of a drainage basin, or catchment area.
earth fill dam
A dam built of gravel, earth, broken rock, sand, or silt, and usually containing an impervious clay core or facing.
embankment
A structure, usually of earth or gravel, constructed above the natural ground surface and designed to hold back water.
factor of safety
The ratio allowed for in design, between the ultimate breaking strength of a material, to the force exerted against it. A factor of safety of one means a material will fail when the force exerted against it equals the ultimate breaking strength of the material.
field density tests
Tests carried out under site conditions to determine the density of soils.
flashboard
See stop log.
foundation cutoff
A wall, collar, or other structure intended to reduce percolation of water along otherwise smooth surfaces or porous strata.
freeboard
The vertical distance between water level and the crest of a dam or the top of a channel.
grout
A cementitious material of high water content, fluid enough to be poured or injected into spaces and thereby fill or seal them.
high-water mark
A wash line, seed line, mud line, trash line, or other debris line formed at the highest level reached by a stream or body of water.
hydrograph
A graph to show the relation with time of the level, flow, or velocity of water in a lake or stream.
internal drain
A means of draining water from the interior of an embankment to prevent water from entering the soil and causing it to soften and endanger the embankment.
invert
The bottom, or lowest part, of the internal cross section of a conduit or channel.
joint
A surface of actual or potential fracture or parting in a rock without displacement.
left or right
The direction designated as one faces in a downstream direction.
liquefaction
The process of becoming liquid; the sudden large decrease of the shearing resistance of a cohesionless soil.
metalurgical analysis
An analysis of the physical and mechanical properties of metal.
micaceous silt
Silt containing mica.
National Geodetic Vertical Datum
Reference level, equivalent to mean sea level datum, from which elevations are measured.
normal pool
The usual reservoir level during times not affected by drought or flood.
overtopping
Flow of water over the top of a dam or embankment.
penstock
A closed conduit for supplying water to a water wheel or turbine.
percolation
Flow of water, usually downward, through small openings in a porous material.
permeability
The property of a porous rock or soil medium for transmitting a fluid without impairment of the structure of the medium.
phreatic line
The upper free-water surface of the zone of seepage.
Piedmont province
A physiographical area lying along the southern and eastern base of the Appalachian Mountains.
pin hole dispersion tests
Tests to determine dispersive properties of soils.
piping
Erosion by percolating water in a soil resulting in caving and the formation of conduits, tunnels, or pipes through the soil.
plane-table survey
A method of surveying whereby the observations are plotted as the survey progresses. Used extensively in topographic surveys.
plasticity
In soil mechanics, a term used to define soils, usually clays, that are capable of deforming plastically at varying water contents.
Proctor
A method developed by R. R. Proctor for measuring the degree of compaction of a soil.
return period
The average period of time occurring between events.
right or left
The direction designated as one faces in a downstream direction.
rock crib dam
A dam constructed of interlocking sections of timber or concrete, forming cells which are filled with earth or broken rock.
routing
A computation technique whereby a streamflow hydrograph for a specific site can be transposed to another site.
runoff
That portion of rainfall that finds its way into streams as surface flow.
scarp
An escarpment, cliff, or steep slope along the margin of a plateau, terrace, or bench.
sediments
Solid material settled from suspension in a liquid.
seepage
The act or process involving the slow movement of water or other fluid through a porous material such as soil or rock.
seepage collar
A wall, collar, or other structure to reduce or prevent seepage of water along the outside surface of a conduit or pipe.
shear test
Tests to determine the shear strength of soils.
Shelby tube
A soil sampling device consisting of thin-wall tubing which is driven into a soil to obtain a sample.
sill
A horizontal structural member forming the bottom of a door, opening, or other entranceway, such as to a conduit or penstock.
silt
A fine grained sediment having a particle size intermediate between that of fine sand and clay.
sliding circle analysis
A method of analysis that allows the determination of the relative stability of a soil mass.
slope failure
The downward and outward movement of a mass of rock or unconsolidated materials as a unit.
spillway
A passage for surplus water over, around, or through a dam or similar construction.
stop log
A log, plank, cut timber, or steel or concrete slab or beam fitted into end guides between walls or piers to close an opening to the passage of water.
storage attenuation
A decrease in intensity or level of a flood wave as a result of water being stored in the channel or reservoir.
strike
The direction or bearing of a horizontal line in the plane of an inclined stratum, joint, fault, or other structural plane. It is perpendicular to the direction of dip.
sub-parallel
Nearly, but not exactly, parallel.
tension crack
A fracture that is the result of stresses that tend to pull material apart.
toe of dam
The base of an embankment, bank, bench, or slope.
topographic map
A map designed to portray an area to a certain scale, and that primarily depicts the relief of the area.
unit-hydrograph
A hydrograph of streamflow representing the flow resulting from one inch of rainfall excess occurring uniformly over a drainage basin in unit time.
void
An opening in a rock or soil not occupied by solid matter.

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