FLOOD08336

• County: Chaffee
• Community: Poncha Springs, Salida
• Stream Name: South Arkansas River
• Basin: Arkansas
• Title: Floodplain Information Report - Lower South Arkansas River
• Date: 4/1/1979
• Prepared For: Chaffee County
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The 1% chance flood flows may also be used for those planning and design

activities mentioned in connection with the 10- and 50-year flood flows. This

is particularly true where a lower risk of failure than the 10- or 50-year

flood is desired. The most important use of the 1% chance flood flow is for

the description of the floodplain and its land use regulation. The Colorado

state statutes consider the 1% chance flood as the flood event to be used in

designing and protecting improvements slated for human occupation. Also, the

land within this flood area may be delineated as an area of state interest as

set forth in H.B. 1041 (State's Land Use Bill). The 1% flood is almost accepted

nationally for the above mentioned purposes.

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The SOO-year flood event is useful in making the public aware that floods

greater than the 1% chance flood do occur, and those living above the water

surface elevations for such a flood event are not fully protected from flooding.

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Flood Elevations

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The water surface elevations for the 10-, 50-, 100-, and SOO-year floods

can be found in four different locations throughout this report, These loca-

tions include: (1) the flood frequency elevations presented in Table-3 for

the selected points along the river reaches; (2) the limits of the 100-year

and SOO-year flood in plan presented on Plates 3 through 13; (3) the flood

profiles shown on Plates 14 through 24; and (4) the water surface elevations

for the different frequencies at typical cross sections throughout the study

reach shown on Plates 25 through 28.

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The flood profiles may be used in areas where controversy arises over

the 1% flood boundary on the flooded area plates. Since the flood profiles

give the elevation and distance or stationing from a known point, the high

water elevations can be conveyed to the ground. Three control markers, iden-

tified as S-l, S-2, and S-3, have been established in the field for this

purpose. An example of the marker, consisting of a brass cap set in concrete,

is presented on the following page.

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Detail of Brass Cap.

Control Marker S-3

The locations of all control markers are shown on the index map on

Plate-2. The map coordinates, elevations, and general location of the monu-

ments are listed in Table-4. Additional survey notes and marker descriptions

are available for review at the Colorado Water Conservation Board.

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