FLOOD10328

• County: Boulder
• Community: Lyons
• Stream Name: North Saint Vrain and Saint Vrain Creeks
• Title: Floodplain Information Report, North Saint Vrain Creek, Saint Vrain Creek, Floodplain Update, Town of Lyons, Boulder County, Colorado
• Date: 6/1/1998
• Prepared For: Lyons
• Prepared By: BRW, Inc
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Floodplain Information Report
K\35600\004\FLOODPLAIN INFORMATION REPORT.doc

35

June

998

Floodplain Information Report
K:\35600\004\FLOODPLAIN INFORMATION REPORTdoc

36

June

1998

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Floodplain. An area in and adjacent to a stream, which is subject to flooding as the result of the
occurrence of a 100-year flood and which area thus is so adverse to past, current, or
foreseeable construction or land use as to constitute a significant hazard to public health
and safety or to property.

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Flood Peak. The maximum instantaneous discharge of a flood at
occurs at or near the time of the flood crest.

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a given

Flood Fre (See Probabilityo) The average recurrence interval
water stages which cause flooding.

locationo

of specific discharges of

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usually

Watershed. The drainage area situated above a specified point on a stream including the area
drained by tributary streams, which enter the main stream above this point.

100-Year. A type of flood, including the water surface elevation 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
statistical one percent chance of being equaled or exceeded during anyone year. The
term is used interchangeably with a one- percent flood or Intermediate Regional Flood
(see definition of Intermediate Flood).

elevation

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Flood

Crest. The
locationo

maXImum

stage or

reached by

the

water

of

a

flood

at

a

gIven

Any natural channel or depression through which water flows either continuously,
intermittently or periodically, including any artificial modification of the natural channel
or depression.

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Streamo

Runoff. The quantity of rainfall which flows over the surface
volumeo The difference in quantity between rainfall
infiltration and interception

stream or water course,

to enter the stream as discharge
and runoff represents losses in

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Flood

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Normally a flood is considered as any temporary rise in stream flow or stage, but not the
ponding of surface water, that results in significant adverse effects 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 material sin stream channels
during flood recessions, use of groundwater coincident with increased stream flow, and
other problemso

Right Bank.

Reference Point. A numbered point identifying a specific location for correlating
shown in various forms throughout the report.

The bank on the right side of a river,

looking downstreamo

Recurrence Interval. The average number of
equaled or exceededo

the data

Probabilityo The annual chance of occurrence of specific hydrologic events, such as rainfall over
a specified area or peak discharge at a specified location expressed in percent, eogo 5%
representing one change in 20 of the event occurring in any year or an average
recurrence of once in 20 years.

years

within which a given flood event

will

be

Flood. An overflow on lands not normally covered by water and that is used or usable by mano
Floods have two essential characteristics; the inundation of land is temporary; and the
land is adjacent to and inundated by overflow from a river of stream or an ocean, lake or
other body of standing water.

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Bank. The bank on the
downstream.

Intermediate Regional Floodo A type of flood, including the water surface elevation 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
statistical one percent chance of being equaled or exceeded during anyone yearo The
term is used interchangeably with a one- percent flood or 100-year flood (see definition
for 100-year flood).

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ated Floodplaino The area designated as
County Commissioners or City Council
Water Conservation Board.

a floodplain by official action of the Board of
with the prior concurrence of the Colorado

Left

left side of a river, stream or

water course as

the observer looks

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Desi

Cloudburst.
short
wind

A sudden and extremely heavy downpour of rain that is small in areal extent;
duration; and may be accompanied by lightning, thunder, and strong gusts

of
of

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

Flood Stage. 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 measured.

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Backwater Effect.
of an obstruction

The rise in surface elevation of flowing water upstream
to flow 0

from and as a result

Flood Profileo A graph showing the relationship of water surface elevation to location, the latter
generally expressed as distance 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.

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North St. Vrain & St.
Floodplain Update

Vrain Creeks

GLOSSARY

Town of Lyons

North St. Vrain & St.
Floodplain Update

Vrain Creeks

Town of Lyons