Watershed Protection Plan - Lower Rio Grande Valley Development ...

THE ARROYO COLORADO
WATERSHED
The Arroyo Colorado is located in the Lower Rio
Grande Valley of South Texas and fl ows through the
middle of Hidalgo and Cameron counties. The lower
16 miles of the Arroyo Colorado form the boundary
between Cameron and Willacy counties (Figure 5).
The Arroyo Colorado drainage area (i.e., watershed)
is a sub-watershed of the Nueces-Rio Grande Coastal
Basin, also known as the Lower Laguna Madre
Watershed (Hydrologic Unit Code 12110208).
The streams of the Nueces-Rio Grande Coastal
Basin, including the Arroyo Colorado, drain to the
Laguna Madre, which is considered to be one of the
most productive hypersaline lagoon systems in the
world (TPWD 2006a). The Rio Grande River is the
largest fl uvial system of the lower coast of Texas
and forms the border between the United States and
Mexico. The Lower Rio Grande Valley comprises the
northern part of the Rio Grande Delta, a broad fl uviodeltaic
plain laid down over tens of thousands of years
by the ancestral Rio Grande. The Arroyo Colorado is
thought to have been an ancient channel of the Rio
Grande that became isolated from the main fl ow of the
river during one of many fl ood events that caused the
river to change its course. Just as the Rio Grande is the
major source of fresh water for the Lower Rio Grande
Valley, the Arroyo Colorado System serves as the main
drainage stream for this area of Texas.
Arroyo Colorado Watershed
Characteristics
The Arroyo Colorado Watershed is approximately
1,828 square kilometers (706 square miles). It is
bounded on the west and south by the drainage divide
to the Rio Grande, on the north by the drainage divide
to the North Floodway and on the east by the Lower
Laguna Madre.
The Arroyo Colorado is part of the United States
International Boundary Water and Commission’s
(IBWC’s) Lower Rio Grande Valley Flood Control
Project, a fl ood control system that consists of interior
fl oodways including the Banker, Main, North and
Arroyo Colorado Floodways. In its uppermost reaches,
the Arroyo Colorado is the pilot channel for the Main
Floodway (Figure 1). The fi rst major tributary to the
Arroyo Colorado in Hidalgo County is the Banker
Floodway. The North Floodway branches off of the
Main Floodway at the Llano Grande, a shallow lake
located southwest of the city of Mercedes. Beyond
Figure 5. Arroyo Colorado Watershed and Lower Laguna Madre Drainage Basin (Hydrologic Unit Code HUC 12110208)
STARR
WILLACY
LAGUNA MADRE
HIDALGO
Texas
¯
Mexico
South Laguna Madre HUC
Arroyo Colorado
CAMERON
0 5 10 20 Miles Data Source: Census 2000 - TIGER Files
Map Source: Texas Coastal Watershed Program
www.Urban-Nature.org
Arroyo Colorado Watershed Protection Plan 22 January 2007