FLOOD07275

• County: Costilla
• Community: Costilla County
• Stream Name: Trinchera Creek, Costilla Creek
• Basin: Rio Grande
• Title: Floodplain Information Report
• Date: 3/1/1994
• Prepared For: Costilla County
• Prepared By: CWCB
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

incorporated in this study. The delineations for Culebra Creek
and Rito Seco have been replaced by the new CWCB delineations
for those streams.

2.0 STlJDY AREA

2.1 Location

A Flood Hazard Boundary Map for the Town of San Luis was
prepared on December 24. 191& by the l"ederal Insurance
Administration. It showed flood hazard areas in San Luis for
Rito Seco and Culebra Creek. The map has not been revised
since 1976. On September 1. 1967 that map was used as the
basis for converting San Luis from the Emergency Phase to the
Regular Phase of the National Flood Insurance Program.
A report entitled Master Drainaqe Study. Town of San Luis.
Colorado was prepared for the Town of San Luis, the Colorado
Department of Local Affairs. and the Colorado Water Conservation
Board by WRC l'lngineering. Inc. in December 1988. That report
included detailed floodplain delineations and water surface
prOfiles for Rito Seco in the Town Of San Luis and vicinity.
It also inclUded recommendations for alleviating surface and
subsurface drainage prOblems in the town. The information in
that report supercedes the 1976 ~lood Hazard Boundary Map for
San Luis. The floodplain delineations from that 1986 report
have been incorporated in this study.

Costilla County is located in southern Colorado. immediately
north of the New Mexico state line. It lies between the Sangre
de cristo Mountains on the east and the Rio Grande on the west
(see figures land 2).

Besides the Rio Grande. which forms the county'S western
boundary, there are three major drainage basins in Costilla
County. They are Trinchera Creek in the northern part of the
county, Culebra Creek in the central part of the county, and
Costilla Creek in the southern part of the county (see figure
3). Each of these creeks is tributary to the Rio Grande.
Trinchera Creek and Culebra Creek have their headwaters in
the Sangre de Cristo Mountains in Colorado. flow qenerally to
the west. and ultimately join the Rio Grande in Colorado.
Costilla Creek originates in the Sangre de Cristo Mountains of
northern New Mexico and southern Colorado. flows westerly in
New Mexico, turns northwesterly to flow into Colorado, turns
more westerly in Costilla County. then turns southwesterly to
eventually join the Rio Grande in northern New Mexico.

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The western part of Costilla County is very dry. From
somewhete near the middle of the county downstream to the west
all three of the major drainages are basically dry most of the
time. Only heavy snowmelt or rainstorms will generate surface
f10w~ in those portions of the drainaqes. In the eastern part
of the county mountain snowpack and mountain rainstorms assure
a more or less continuous flow of water in the major drainages
and some tributaries. As one continues west. the Channels are
dry under most conditions due to extensive irriqation for
ag.ciculture. the sandy soils which absorb much of the runoff.
the very low annual precipitation. and the lack. of significant
tributary flow.

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Figure 1 shows the location of Costilla County within
COlorado. Figure 2 shows the county's location within the Rio
Grande drainage basin.

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