FLOOD10167

• Designation Number: 299
• County: Costilla
• Community: Unincorporated Costilla County
• Basin: Rio Grande
• Title: Floodplain Information Report - for the Rio Grande, Trinchera Creek, Culebra Creek, Colstilla Creek, and Selected Tributaries in Costilla County
• Date: 3/1/1989
• Designation Date: 11/1/1989
• Floodplain - Doc Type: Floodplain Report/Masterplan

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5.0 INTERPRETATION AND USE OF REPORT

The floodplain information contained in tqis report
consists primarilY of flood discharges and floodplain
delineation maps. Both kinds o! information are useful for
evaluating flood risks and for performing engineering
analyses. They are also useful for guiding actions to reduce
flood damages. This chapter discusses the use of the
floodplain information for each of those purposes.

5.1 Flood Discharqes

The lOO-year flood event was used as the flood frequency
for this floodplain analysis. The 100-year frequency has been
selected by the State of Colorado and the Federal Emergency
Management Agency as the frequency to be used for floodplain
delineation and regulation. As a result. the flood discharges
listed in Table 7 should be used to regulate proposed
development in the delineated floodplain. For points other
than those listed in Table 7. the discharge-drainage area
relationship shown on Figure 5 should be used to compute a
discharge. There is one exception, From the gage that is
furthest downstream on each of the three major tributaries
downstream to the confluence of that tributary with the Rio
Grande. the flow at that gage should be used.

The above flows should also be used to develop revised
floodplain delineations for any portion of the study area .
whether to i11ustrate the effects of proposed floodplain
development or to take advantage of topographic or hydraulic
information that is more current or refined than the
information that was used for this study, Changes to the
discharges in this report must be approved by the Colorado
Water Conservation Board and the Costilla County Board of
Commissioners. The same requirements apply to proposed
discharges for stream reaches not included in this study.

5.2 Flooded Area Maps

The Flooded Area Maps in this report (Plates 2-22) show the
approximate boundary of the 100-year floodplain for the stream
reaches studied. Upon official approval of this report by the
Colorado Water Conservation Board the areas outlined by the
100-year flood boundary will be designated as floodplains and
may be regulated accordingly by Costilla county. Upon the
adoption of floodplain regulations by the county. all
development within the delineated 100-year floodplains will
require a floodplain development permit. Any engineering for
such permits will need to be based on the flood discharges
contained in. or derived from. this report. as described above.

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