FLOOD06421

• County: Statewide
• Basin: Statewide
• Title: Highways in the River Environment
• Date: 2/1/1990
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Lower Bank - That portion of a streambank having an elevation less than the
mean water level of the stream.

Mathematical Model - ^ symbolic representCltion of a flow situation using
mathematical equations.

Mattress - A covering of concrete, wood, stone or other material used to
protect a streambank against erosion.

Maximum Probable Flood - A very rare flood discharge value computed by
hydro meteorological methods, usually in connection with major hydraulic structures.

Meander Loop - An individual loop of a meandering or sinuous stream lying
between inflection points with adjoining loops.

Meanderinq Channel - A channel exhibiting a characteristic process of bank
erosion and point bar deposition associated with systematically shifting meanders.

Meander Scrolls - I_ow concentric ridges and swales on a floodplain, marking
the successive positions of former meander loops.

Meanderinq Stream - A stream having a sinuosity greater than some arbitrary
value, herein placed at 1.',0. The term also implies a moderate degree of pattern
symmetry, imparted by regularity of size and repetition of meander loops.

Measured Scour - The measured depth to which a surface is lowered by scour
below a reference elevation.

Median Diameter - The particle diameter at the 50 percentile point on a si;:e
distribution curve such that half of the particles (by weight for samples of sand, silt
or clay and by number for samples of gravel) are larger and half are smaller.

!Y1id -Channel Bar - A bar lacking permanent vegetal cover that divides the flow
in a channel at normal stage.

Middle Bank - That portion of a streambank having an elevation approximately
the same as that of the mean water level of the strear.l.

Miqration - Change in position of a channel by lateral erosion of one bank and
simultaneous accretion of the opposite bank.

Miqration (of bed forms or meanders) - Systematic shifting in the direction of
flow.

Mud - A soft, saturated mixture mainly of silt and clay.

Natural Levee - A low ridge along a stream channel, formed by deposition
during floods, that slopes gently away from the channel.

Nominal Sediment - [qui valent spherical diameter of a hypothetical sphere of
the same volume as a given stone.

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