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.
