The Center for Research in Water Resources (CRWR) of the University of Texas at Austin in cooperation with several Mexican agencies is developing a binational dataset to build hydrologic information systems, which can be used to support hydrologic analysis and modeling in the Rio Grande/Bravo basin. This dataset consists of an ArcHydro-based Geographic Information System and relational data base containing hydrologic and hydraulic information from American and Mexican sides. It will assist in developing bi-national cooperation between Mexico and the United States concerning water in this basin, providing accurate and reliable data necessary for analysis and resolution of water resources issues. Information collected from both Mexican and American agencies did not have the same features and presented some errors, especially in the river system dataset. This information has been processed and reprojected in order to use the same characteristics for the whole basin, creating several feature classes contained into a geodatabase. The concept of regionalization was introduced in order to divide the basin into several hydrological subregions, so raster data were generated in smaller amount to avoid conflicts when the ArcHydro schema was applied. This geodatabase represents the first major attempt to establish a more complete understanding of the basin as a whole, using both Mexican and the U.S. data.

The Rio Grande/Bravo is a transboundary water source shared by the United States and Mexico.  At this time in Mexico there is limited capacity to develop efficient management plans for the water in the Rio Grande/Bravo basin, given the existing infrastructure and the methods of application and distribution of the water.  A continually increasing population, serious problems related to lack of sanitation and clean water, as well as regular high investments in infrastructures which are not achieving their objectives, are likely to force governments at various levels to search for alternative approaches, other than relying only on engineering solution through supply management alone. The institutions concerned have yet to fully realize that successful water resources management requires a long term planning process from technical, economic, political, social, and environmental viewpoints.

In addition, some decisions about water management are only partially supported, causing with it alterations in the global ecosystem.  For this reason it is necessary to improve the administration and management of water in this watershed.  This will require assessment of water availability and how to manage it appropriately for agriculture, industry and other services, also taking into account ecosystem preservation.

Recent drought conditions have increased tensions over water sharing in this basin.  Several areas of conflict and possible negotiated remedies have been identified, but there is a lack of data available to use in analysis of alternative solutions to these problems. The development of a watershed-scale database for the Rio Grande/Rio Bravo basin is fundamental. Minute 308 of the International Boundary Waters Commission (IBWC), June 28, 2002, states that it is very important to support projects that increase data exchange related to the management of hydrological information systems.  These systems should include information from both sides of the basin in a timely manner to enable the IBWC to adopt principles and understandings under which both Governments provide the highest priority to fulfilling their respective obligations under the 1944 Water Treaty. In part of this research project, the Center for Research in Water Resources (CRWR) of the University of Texas at Austin, the Texas Commission on Environmental Quality (TCEQ), the Mexican Institute of Water Technology (IMTA), and the National Water Commission (CNA) of Mexico are cooperating to develop the relational database containing hydrologic, hydraulic and related data for the basin.

The Rio Grande originates in the San Juan Mountains of southern Colorado. Flowing 858 kilometers from its headwaters and through the state of New Mexico, it enters Texas about 12 kilometers northwest of El Paso and then continues 2025 kilometers to the Gulf of Mexico. The figure 1 shows the total length of the river, as well as the political division of the Rio Grande/Bravo basin that includes the Hydrologic Unit Cataloging (HUCs) on the American side and Cuencas and sub Cuencas on the Mexican side; according to the Mexican government classification.

The Rio Grande is the fifth longest river in North America (2895 Km), and among the 20 longest rivers in the world. The river carries little water compared to other rivers of its length.  For this reason, it has been classified as an exotic stream, which means that it tends to shrink in size as it flows downstream. This is typical of rivers that pass through arid regions.  Most precipitation in the basin falls at either end of the river, as snow near its headwaters or as rain near its mouth.

The river collects rain, snowmelt and spring water from an area about 557,722 square kilometers including closed basins. The whole basin includes three states on the American side (Colorado, New Mexico, and Texas), and five states on the Mexican side (Chihuahua, Coahuila, Durango, Nuevo Leon, and Tamaulipas). From the basin area, 225,380 Km² lies on the Mexican side and 242,994 Km² on the American side, without considering closed basins.

Fig. 1. Political division of the Rio Grande/Bravo basin

The basin is divided in two sub basins, the Upper Rio Grande watersheds that include Colorado, New Mexico, and part of Texas, and the Lower Rio Grande Basin (LRGB) that includes parts of the Chihuahua, Durango, Coahuila, Nuevo Leon, Tamaulipas, and Texas states. The LRGB, from below Fort Quitman to the Gulf of Mexico and including the Rio Conchos and Pecos sub-basins, is used for the case study area, encompassing the drainage of all major tributaries downstream of El Paso and Ciudad Juarez. The portion of the basin that lies in this study area is known as Cuencas Del Rio Bravo del Norte by the Mexican agencies.

A part of the Rio Grande basin lies within North America’s largest desert, the Chihuahua Desert.  Mexico irrigates about 1.1 million acres in the basin, while the United States irrigates about 993,000 acres.  Only 98,000 acres of irrigated land lie upstream from Texas.  The Conchos, San Pedro, San Rodrigo, Alamos, and San Juan Rivers are the primary tributaries in Mexico.  The Pecos and Devil rivers are the principal tributaries to the river in Texas (Figure 2).   

The Rio Grande/Bravo basin is considered as an arid and semi-arid region, dominated by agriculture and with limited supplies of both surface and groundwater. Average rainfall in the basin ranges from 200 – 900 millimeters with the highest values in the upper basin of the Rio Conchos. The Rio Conchos enters to the Rio Grande/Bravo near Presidio, Texas, just upstream of Big Bend National Park and Ojinaga, Mexico; in a region of mountains and canyons. The basin ranges from arid and suitable for crops, to semi-arid and hospitable to some crops only. Along the entire river, water lost through evaporation exceeds water gained from precipitation. The Lower Valley serves as temporary or permanent home for hundreds of bird species, and the river contributes vital fresh water to its gulf estuary (Tate, 2002).

Figure 2. The primary tributaries in the Rio Grande/Bravo basin

Hydrological information was obtained from Mexican and U.S. agencies in this step of the project. The political boundaries, river network, water bodies and gauging stations on the Mexican side were collected from the National Water Commission (CNA), the Mexican Institute of Water Technology (IMTA), the University of Ciudad Juarez (UACJ), and the National Institute of Geography and Information (INEGI). The information for the American side was obtained from the U.S. Geological Survey (USGS), the Texas Commission on Environmental Quality (TCEQ), Texas Natural Resources Information System (TNRIS), among others agencies.  Some of this information was downloaded from Internet, as well as directly from the agencies’ offices. The data collected from the original sources are included in the table 1, as well as some of the data characteristics.

Several errors were found in the hydrological information such as wrong positions of some control points, disconnection in the river network, wrong location of some water bodies, etc. Part of the original information is shown in Figure 3. This information had to be edited using ArcMap 8.3, in order to fix these errors.

Table 1.  Summary of the original data collected for the Rio Grande/Bravo basin

Figure 3.   Cuencas, Sub Cuencas and original hydrography of the Rio Bravo basin on the Mexican side

The Mexican agencies usually use the Geographic Coordinate System and Lambert projection to create their geographic information. The Albers equal area projection was proposed for this project in order to preserve the areas. The Datum chosen was the Nad_Datum 1983; the Geographic Coordinate System corresponded to the GCS_North_American_1983, while the Central Meridian was located at -100.00 degrees.

The HUCs that make up the corresponding hydrological subregion were selected, including a 10 Km buffer around the HUCs called a BufferWatershed. All the Hydro Edges that lie within this buffer were selected and exported in order to create the WRAP Flowline feature class. After this step, the DEM to the buffered area was clipped and processed it using Terrain processing tool in Arc Hydro Toolset. The delineation of catchments for each stream segment of WRAP Flowline was made using the Delineate Watershed tool in WRAP Hydro toolset. This feature class was called WRAPCatchment. The DrainID of the delineated catchments was populated by the HydroIDs of the WRAP Flowline segment it is draining to. In order to create the HydroNetwork, the relief of the hydrography information had to be checked. Every stream should be connected and the flow direction assigned correctly. The river network must be edited to establish the appropriate connections among the rivers assigning the correct flow direction to them. The hydro network is an essential part of this data model, created from edges and the control points. The topological connections of its HydroEdges and control points in a geometric network enables tracing of water movement upstream and downstream through streams, rivers, and water bodies. Relationships built from the control points connect drainage areas and point features such as diversion points to the hydro network. This hydro network allows knowing the distance between any two points on a flow path.  

Figure 8 describes the comparison between the SubCuencas at the Rio Conchos basin defined by INEGI (continuously line) and the WRAPWatershed defined by the WRAPHydro Tools (polygons), as well as the connectivity among control points. The SubCuencas were defined using a topographic map 1:250K, while the WRAPWatershed feature considered a WRAPEdge 1:100K (from a digitalized map) and a DEM resolution of 30 m close to the border, and 90 m for the rest of the Rio Conchos sub basin. The points represent the related water rights and return flow control points.

Figure 9 shows the schematic network diagram for the whole basin. This schematic network is a simplification of the hydro network that consists of separate point and line feature classes called SchematicNode and SchematicLink, respectively. The schematic network is an abstract representation of the elements to which the hydrologic models are applied, and it provides a simplified view of the connectivity of the river network and the control points. This kind of networks are useful as a visual check to make sure that the hydrologic elements needed for a model are correctly linked in the landscape (Maidment, 2002)

A binational geodatabase was created that includes a relational database containing hydrologic, hydraulic and related data for the Rio Grande/Bravo basin. This geodatabase will be made available to Mexican and U. S. federal, state, and local organizations.  It will assist in developing bi-national cooperation between Mexico and the United States concerning water in the Rio Grande basin, providing accurate and reliable data necessary for analysis and resolution of water resources issues. The first part of this project was to collect the hydrologic information from both Mexican and American agencies. Unfortunately this information did not have the same characteristics and accuracy in both sides, so it had to be edited, reprojected, and fixed in order to get unified criteria for the geodatabase. Some watershed parameters, such as upstream area above each control point, average upstream curve number and annual precipitation, were calculated in the second part of this project, using the WRAPHydro tools developed by the CRWR. One of the most important contributions of this research was the regionalization of the basin in order to get the parameters mentioned above. For large watersheds such as the Rio Grande/Bravo basin, the data is too huge to be handled as one entity; this problem is dealt by subdividing the basins into parts. The results from each sub basin are merged on the vector side for determining parameters. This methodology helped us to verify the validity of dividing a basin for processing without compromising on the accuracy of the parameter values determined.

This research project was funded by the Texas Commission on Environmental Quality. I would like also to express my appreciation to the Mexican National Council for Science and Technology, who is supporting my PhD program at the University of Texas at Austin.

Csillag, F., 1996. Variation on hierarchies: toward linking and integrating structures. In: Goodchild, M.F. et al (Eds.), GIS and Environmental Modeling: Progress and Research Issues. GIS World Publication, Fort Collins, CO, pp. 433-437

Goodchild, M.F., 1993. Data models and data quality: problems and prospects. In: Goodchild, M. F., Parks, B.O., Steyaert, L.T., (Eds.), Environmental Modeling with GIS. Oxford University Press, New York, pp 8-15

Tate, Diane E., 2002. Bringing Technology to the Table: Computer Modeling, Dispute Resolution, and the Rio Grande. Master Thesis, University of Texas at Austin, TX.

Maidment, D. R., 2002. Arc Hydro: GIS for Water Resources. ESRI Press

Two ArcHydro training courses have been offered, one in English and one in Spanish, to the Texas Commission on Environmental Quality (TCEQ) and Mexican National Water Commission (CNA). You can have the lecture notes in the link shown below: