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

I
'-.
I
I
I

II

,I
I
I
..
I
I
I
I
I
I
I
I.
I

Sub-Bed Material - Material underlying that portion of the stream bed which is
subject to direct action of the flow.

Subcritical anrl Supercritical Flow - Open channel flow conditions with F roude
number less than and greater than unity, respectively.

Synthetic Mattress, Mattinq or Tubinq - A grout, or sand-filled, manufactured,
semiflexible casing placed on a stream bank to prevent erosion.

Tetrahedron - Component of river-training works made of six steel or concrete
struts Fabricated in the shape of a pyramid.

I etrapod - Bank protection component of precast concrete consisting of four
legs joined at a central joint, with each leg making an angle of 109.5 degrees with
the other three.

Thalweq - The line extending down a channel that Follows the lowest elevation
of the bed.

Tidal Amplitude - Generally, half of tidal range.

Jidal Cycle - One complete rise and fall of the tide.

Tidal Inlet - A body of water with an opening to the sea, but otherwise enclosed.

Tidal Period - Duration of one complete tidal cycle.

Jidal Passaqe - A tidal channel connecting with the sea at both ends.

Tidal Prism - Volume of water contained in a tidal inlet or estuary, between
low and high tide levels.

Jidal Ranqe - Vertical difference between specified low and high tide levels.

Tides. Astronomical - Variations in sea level due to motion of heavenly bodies.

Jieback - Structure placed between revetment and bank to prevent flanking.

Timber or Brush Mattress - A revetment made of brush, poles, logs, or lumber
interwoven or otherwise lashed together. The completed mattress is then placed on
the bank of a stream and weighted with ballast.

Toe - 1 hat portion of a stream cross section where the lower bank terminates
and ftiechannel bottom or the opposite lower bank begins.

Joe -Fill - Break in slope between the bank and the overbank area.

Total Sediment Dischar'~ - 1 he sum of suspended-sediment discharge and
bedload dischar<Je or the sum of bed material discharge and washload discharge of a
stream.

Iv