FLOOD07967

• Designation Number: 181
• County: Larimer
• Community: Loveland
• Stream Name: Big Thompson River
• Basin: South Platte
• Title: Floodplain Information Report - Big Thompson River, Loveland
• Date: 10/1/1981
• Designation Date: 12/1/1981
• Floodplain - Doc Type: Floodplain Report/Masterplan

GLOSSARY

Backwater effect. The rise in surface elevation of flowing water upstream
from and as a result of an obstruction to flow.

Channel. A natural or artificial watercourse of perceptible extent with
definite bed and banks to confine and conduct continuously or periodically
flowing water.

Cloudburst. A sudden extremely heavy downpour of rain that is 5mall in
areal extent; of short duration; and may be accompanied by lightning,
thunder, and strong gust5 of wind.

Conveyance capacity.

s. Channel conveyance capacity is the rate of discharge, in cubic
feet per second, which can flow in a water course with the water
surface not greater than the height of the channel banks.

b. Floodway conveyance capacity is the rate of discharge in the
overflo'o' purtiou uC the flood'o'ay which c"a pass through a
apecified area at depths and velocities governed by the hydraulic
dimensions of the floodway.

Designated flood plain. Thc area designated as a flood plain by official
action of the board of county commissioners or city council with the prior
cOncurrence of the Colorado Water Conservation Board.

Flood. An overflow on lands not normally covered by water and that are
used Or usable by ..an. Floods have two essential characteristics--the
inundation of lsnd is temporsry; and the land is adjacent to and inundated
by overflow from s river or stream or an ocean, lake. or other body of
~t"nding water.

Normally a flood is considered as any temporary rise in streamflow or
stage, but not the ponding of surface water, that results in significant
adverse effccts in the vicinity. Adverse effects may include damages from
overflow of land areas, temporary backwater effects in sewers and local
drainage channels, creation of unsanitary conditions or other unfavorable
situations by deposition of m.~terials in stream channels during flood
recessions, use of ground water coincident with increased streamflow, and
other problems.

Flood. lOa-year. A type of flood, including the water-surface clevation
and territorial occupation thereof, which can be expected to occur at any
time in a given area based upon recorded historical precipitation and other
valid data, but with an average statiatical one pcreent chance of being
equaled or exceeded during anyone year.

flood crest. Ihe maximum stnge or elevation reached by tn" ~aters of a
flood at a given location.

Flood frequency (see Probability).
specific discharges or water stages

recurrence interval of
flooding.
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The average
which cause

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flood peak, Thc maxi~um instantancou6 discharge of a flood at a given
location. It usually occurs at or near the time of the flood crest.

Flood frin~c. That portion of the flood plain betwcen the floodway
district boundary and the upper limits of thc ba5e flood. The flood fringe
is the portion of a drainway channel or watercourse outside the floodway
portion.

Flood profile. A graph showing the relstionship of water-aurface elevation
to lcoation, the latter generally expressed as di~tance above mouth for a
stream of water flowing in an open channel. It is generally drawn to show
surface elevation for the crest of a specific flood, but may be prepared
for conditions at a given time or stage.

Flood sta~e. The stage or elevation at which overflow of the natural banks
of a stream Or body of water begins in the reach Or area in which the
elevation is mcasurcd.

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Floodway. The channel of a river or other watercourse in the adjacent land
areas that must be reserved in order to discharge the bsse flood without
cumulstively increasing the water surface more than 0.5 feet.

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Left bank.
the observer

The bank on the left
looks upstream.

side of a river, stream or watercourse as

PrObability. The annual chance of ocCurrence of specific hydrologic ents,
such as rainfall over a 5pecified area or peak discharge at a specified
location expressed in percent, e.g., 5 percent represents 1 chance in 20 of
the event occurring in any year or sn average recurrence of once in 20
years.

Reference point. A numbered point identifying n specifiC location for
correlating the data shown in various forms throughout the report.

Right bank. The bank on the right side of a river, stream or watercourse,
looking upstream.

Runoff. The quantity of rainfall which flows over the surface to enter the
stream as discharge volume. Ihe difference in quantity between rainfall
and runoff represcnts losses to infiltration and interception.

Sheet flow.
to 2 feet in

Broad,
depth.

shallow overland flood flows varying from a few inches

Stream. Any natural channel or depression through whiCh water flows either
continuously, intermittently or pcriodically, including sny ~rtificial
modification of the natural channel or depresaiQn.

'.Iatershc<l. The drainage area situ.otio.. above a ~l'ec1fi"d point on a "t,e,,",
including the area drained by tributary streams Which ent~r the main stream
~bove th1a point.

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