FLOOD06420

• County: Costilla
• Stream Name: Rio Grande, Trinchera, Culebra, Costilla Creeks
• Basin: Rio Grande
• Title: Floodplain Information Report
• Date: 3/1/1989
• Prepared For: Costilla County
• Prepared By: CWCB
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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and on to Texas. From the vicinity of El Paso it forms the
border between Texas and Mexico. The flow that remains after
irrigation diversions and reservoir storage enters the Gulf of
Mexico near Brownsville. Texas.

The Rio Grande is large enough that it is well defined
throughout the county. At the north end of the county, as it
flows south from Alamosa County. the river is broader and
flatter with a very wide floodplain, on the order of two or
three miles wide. Then in a stream distance of about two or
three miles the floodplain narrows substantially, to a width of
about 500 feet. Further south. the valley turns into a canyon
that is about 80 feet deep as the river enters New Mexico. On
the Rio Grande there are a few buildings in the northern part
of the county. Otherwise, to the south, very widely spaced
bridges are the only obstruction.

2.5 Trinchera Creek Basin

Trinchera Creek originates in the Sangre de Cristo
Mountains of northern Costilla County. Elevations are as high
as 14,345 feet. It flows generally to the west and southwest.
At its confluence with the Rio Grande the elevation is about
7,500 feet.

In the eastern part of the Trinchera Creek basin streams
are narrow and steep. Development in the floodplain has
consisted primarily of roads and bridges. In Fort Garland and
a few miles to the west several tributaries gradually join
Trinchera Creek to form a single major drainage. As Trinchera
Creek and its tributaries emerge from the foothills of the
Sangre de Cristo Mountains onto the alluvial plain of the
eastern San Luis Valley, the individual stream valleys become
broader and flatter.

Urbanization, mostly in and around Fort Garland. and
agricultural uses have led to streets, roads, houses,
commercial facilities. agricultural buildings and facilities,
and irrigation structures in and adjacent to Trinchera Creek
and its tributaries. This is the area where there is the most
extensive encroachment into the floodplain of Trinchera Creek
and its tributaries.

Finally, in the western part of the Trinchera Creek basin.
the single creek flow through agricultural areas or currently
undeveloped areas. The main channel and side channels are
poorly defined, and sometimes human activity has obliterated
them. Aside from highways, roads, bridges, and culverts, there
are few obstructions.

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