Louisiana Administrative Code › Title 56 - PUBLIC WORKS › Part III - Flood Control and Water Management › Subpart 1 - Water Resources and Flood Control › Chapter 7 - Dam Safety Program › Subchapter A - Dam Safety › Section III-705 - Glossary

Current through Register Vol. 50, No. 6, June 20, 2024
Abutments
- those portions of the valley
						sides which underlie and support the dam structure, and are usually also
						considered to include the valley sides immediately upstream and downstream from
						the dam.
Auxiliary
or
Emergency
						Spillway
- a secondary spillway designed to operate only during
						unusually large storm events. Louisiana's Dam Safety Program defines "unusually
						large storm events" as being equal to the 100 year storm event or
						larger.
Baffle Blocks
- blocks constructed in a
						stilling basin to dissipate the energy of fast flowing water.
Berm
- a horizontal step in a sloping
						profile. The berm is usually constructed with a slight slope for drainage
						purposes. The berm is often referred to as a seepage or stability berm.
Blanket Drain
- a horizontal pervious
						zone located downstream of the impervious core. This zone is often referred to
						as a sand blanket.
Breach
- an eroded opening through a dam
						that drains the reservoir. A controlled breach is an intentionally constructed
						opening. An uncontrolled breach is an unintentional opening that allows
						uncontrolled discharge from the reservoir.
Chimney Drain
- a vertical pervious zone
						located just downstream of the impervious core. The chimney drain is usually
						constructed with a sand material.
Cofferdam
- a temporary structure
						enclosing all or part of the construction area so that the construction can
						proceed in the dry.
Conduit
- a closed channel to convey
						discharges through or under a dam. The conduit can be a reinforced concrete
						pipe, a corrugated metal pipe or a single or multi-barrel reinforced concrete
						box culvert.
Crest Length of Dam
- the length of the
						top of dam. This length includes the spillway(s) and other appurtenant
						structures. The crest length of dam is basically the length from where the top
						of dam terminates on one abutment to a similar point on the other
						abutment.
Cutoff Trench
- an impervious barrier
						built into the foundation to reduce seepage under the dam. A cutoff wall or
						slurry wall could be used as a seepage barrier. The slurry wall is relatively
						thinner in the horizontal direction when compared to a clay core cutoff
						trench.
Dam
- any artificial barrier, including
						appurtenant works, which does or will impound or divert water or any other
						liquid substance.
Downstream Slope
- the inclined surface
						of an embankment dam that faces away from the reservoir.
Drawdown Structure
- a low-level outlet
						which can be used to lower the reservoir below normal pool stage. This may be
						necessary for lake management purposes, routine repairs or dam safety
						purposes.
Earthfill Dam
- a dam constructed
						predominantly of fine-grained material. Earthfill dams are also known as rolled
						fill dams where material is placed in layers and compacted by using rollers or
						rolling equipment.
End Sill
- the area at the upstream and
						downstream end of the stilling basin base slab.
Foundation of Dam
- the natural material
						on which the dam is placed.
Heel of Dam
- the junction of the
						upstream slope with the foundation. The heel of the dam is often referred to as
						the upstream toe.
Impervious Core
- a zone of low
						permeability material. This zone is the water or seepage barrier and is often
						referred to as the clay core.
Intake Structure
- the structure placed
						at the beginning of an outlet works waterway. The intake structure establishes
						the ultimate drawdown level of the reservoir by the position of its opening(s)
						to the outlet works. Intake structures may be vertical or inclined towers (drop
						inlets).
Maximum Cross Section of Dam
- cross
						section of a dam at the point where the height of the dam is at it's
						maximum.
Maximum Storage Capacity
- the capacity
						at maximum storage is the volume in the reservoir in acre-feet when the level
						in the reservoir is at top of dam elevation.
Non-Overflow Wall
- a wall which is
						usually constructed parallel to the spillway crest at an elevation equal to the
						top of dam elevation. This wall is not designed to be overtopped and are often
						referred to as a closed dam section.
Normal Pool Stage
- the water level at
						the dam to which water may rise under normal operating conditions and for
						uncontrolled spillways is defined as the lowest crest elevation of the
						principal spillway. This does not include flood surcharge.
Outlet Gate
- a gate on the drawdown
						structure or spillway which is used to control the outflow of water.
Piping
- the progressive internal erosion
						of an embankment, foundation, or abutment material. The erosion (piping) begins
						on the downstream side and progresses upstream.
Primary
or
Principal
						Spillway
- the first used spillway during flood flows.
Probable Maximum Flood (PMF)
- the flood
						that may be expected from the most severe combination of critical meteorologic
						conditions that are possible in the region.
Retaining/Training Walls
- walls which
						are usually constructed perpendicular to the spillway crest. Retaining walls
						are walls which support an overturning load. Training walls are walls which
						confine or guide the flow of water. In many instances, these walls serve both
						purposes and can be referred to as either a retaining or training wall.
Riprap
- a layer of large uncoursed
						stones, broken rock or precast blocks placed in a random fashion on the
						upstream slope of the dam and stilling basin outlets. Riprap is a flexible type
						of slope protection which will deform if material is displaced from
						beneath.
Riser
- a type of drop inlet spillway
						with a vertical section of metal or concrete pipe that allows the reservoir to
						rise to a predetermined level before water flows into the pipe.
Slope Protection
- protection against
						wave action or erosion. The two most common types of slope protection, are
						riprap and soil cement.
Sluice
- a low-level opening for
						releasing water from a dam.
Soil Cement
- a well compacted mixture of
						soil, portland cement and water that produces a hard pavement. Soil cement is
						usually placed in horizontal layers. Soil cement is a rigid type of slope
						protection which attempts to span voids.
Spillway Crest
- the overflow section or
						top of weir section of the spillway.
Stilling Basin
- a basin constructed to
						dissipate the energy of fast flowing water. The stilling basin area is located
						just downstream of the spillway crest between the training/retaining
						walls.
Structural Height
- the distance between
						the lowest point in the excavated foundation and the top of the dam.
Surcharge/Flood Surcharge
- the volume or
						space between normal pool and the maximum design water level.
Tailwater
- the level of water
						immediately downstream of the dam.
Toe of Dam
- the junction of the
						downstream slope with the foundation. The toe of the dam is often referred to
						as the downstream toe.
Top of Dam/Crown
- the uppermost surface
						of the dam. The top of dam can also be referred to as the crest of the dam.
						When the term "crest" is used, it must be specified that it is the "crest of
						the dam" and not the "crest of the spillway."
Uncontrolled
or
Ungated
						Spillways
- spillways where the flows over the spillway crest are
						controlled only by the elevation of the spillway crest. This type of spillway
						is often referred to as a fixed crest spillway.
Normal Pool
						Stage
for uncontrolled spillways is defined as the lowest crest
						elevation of the principal spillway.
Upstream Slope
- the inclined surface of
						an embankment dam that is in contact with the reservoir.
AUTHORITY NOTE:
						Promulgated in accordance with
						R.S.
						38:24.