The Lower Rio Grande Border Region
The Rio Grande is the fifth largest river in North America. It runs North-South from its source in the Colorado Rocky Mountains to El Paso, Texas. From there it turns South-East and, for over 800 miles, serves as the border between Mexico and Texas. Due to intensive human development and water use in Colorado, New Mexico and West Texas, the Rio Grande runs dry South of El Paso during much of the year. As a result, the Rio Grande/Río Bravo below Fort Quitman, Texas to the Gulf of Mexico has effectively become a separate watershed. Its climate is arid to semi-arid, and vegetation and wildlife consist of Taumalipan scrub and chapparal desert ecosystems.

In the watershed below Fort Quitman, two tributaries — the Río Conchos from Mexico, and the Pecos River from the United States — are the main sources of inflow into the mainstem of the Rio Grande/Río Bravo. Runoff in general results from a temporary surfeit of water at the surface exceeding the watershed losses of infiltration and evaporation. Because of the dry, desiccated state that is normal for the Rio Grande watershed, most rainfall events are absorbed by the watershed without creating any appreciable increase in streamflow in the mainstem of the Rio Grande. By some accounts, less than four percent of the precipitation that falls on this watershed reaches the Rio Grande (Espinoza, 1995). Only for the very large events (or closely timed occurrence of several smaller events) does there result a storm hydrograph in the river. These events are mainly derived from mid-latitude storms and tropical disturbances, both of which typically diminish in rainfall amounts with distance from the Gulf of Mexico. For the Rio Grande, as for any river that derives its flow from deep-convection precipitation, the flows are "flashy", a series of sharp rises followed by recessions of stage. Because of the semi-arid climate of the Rio Grande, these spikes of rainfall are widely spaced in time. Water absorption on the watershed filters most of these spikes from appearing in the runoff. Thus, at the largest scale, the long-term river hydrograph of the Lower Rio Grande is characterized by long periods of low flow punctuated by very high flow events on an interval of several years.

Figure 1-1 - Map of the Study Region
Figure 1-1: Map of the Study Region
The tandem international reservoir system comprised of Falcon and Amistad reservoirs allows for the capture and storage of the runoff from these large, infrequent meteorological events, providing protection against floods a well as a more reliable water supply for users downstream. For each reservoir, the occurrences of such infrequent, high flow events play a major role in filling the reservoir, which otherwise is in a general state of drawdown. Operation of the two reservoirs by the International Boundary and Water Commission (IBWC) was formalized by the Treaty of 1944, which authorized construction of the international reservoirs, and provides for the division of stored waters between the two countries.

The reservoir management is a complex process involving not only the hydrological state of the reservoirs and demands from downstream users, but also judgment weighing the risk of flood versus drought and the political positions of the two countries. Generally, Falcón is drawn down first. This is hydrologically prudent since it maximizes the available storage downstream, so that rainfall events can be captured whether they occur on the Amistad or Falcón watershed. The entire Rio Grande/Río Bravo watershed, from below Fort Quitman to the Gulf of Mexico and including the Conchos and Pecos sub-basins, is the hydrological region that needed to be included in the study. In contrast, the project's primary study area is much smaller. This region, which we refer to as the Lower Rio Grande/Río Bravo Border Region (LRGB), receives the bulk of its water from the larger hydrological region.

Figure 1-2 - Map of the Texas Lower Rio Grande Valley
Figure 1-2: Map of the
Texas Lower Rio Grande Valley

Figure 1-3 - Map of the Tamaulipas Border Region
Figure 1-3: Map of the Tamaulipas Border Region
The Lower Rio Grande/Río Bravo Border Region (LRGB) comprises the final 150 miles of the river and the surrounding watershed below Falcon Reservoir (see Figure 1-2). It includes six Texas counties — Cameron, Hidalgo, Starr, Webb, Willacy and Zapata (see Figure 1-2) — and ten municipios from the state of Tamaulipas — Matamoros, Valle Hermoso, Río Bavo, Reynosa, Gustavo Diaz Ordaz, Camargo, Miguel Alemán, Mier, Guerrero, and Nuevo Laredo (see Figure 1-3). We refer to the Texas portion of the LRGB as the Texas Lower Rio Grande Valley (TV) in keeping with the local terminology for the region, while the Mexican portion is known as the Tamaulipas Border Region (TBR). Any thorough study of the LRGB must also include the city of Monterrey and surrounding metropolitan area in state of Nuevo Leon, which borders Tamaulipas to the south. Although the Monterrey Metropolitan Area (MMA) is not physically part of the primary study region, it is highly interconnected with the LRGB. The San Juan River, a Mexican tributary of the Rio Grande/Río Bravo, provides a hydrological tie between the MMA and the LRGB area. Monterrey does not receive its municipal water from the Rio Grande, but the economic and cultural ties between the LRGB and Monterrey are close. They are important in terms of geography, movement of goods and people, and investment. The reciprocal ties of the LRGB with the MMA are thus included in our analyses.

The Lower Rio Grande/Río Bravo Border Region represents a rich mix of cultures, traditional lifestyles and rural and urban communities. It is characterized by intensive irrigation; rapid population growth and urban development; significant and increasing industrial maquiladora production; large flows of binational trade in goods and services; high incidence of poverty, illiteracy, infant mortality, and water-born diseases; and significant ecological degradation.

The local reference to the "The Valley" is misleading; the area is actually a river delta, surrounded by semi-arid Tamaulipan brushland. In its natural state, the Lower Rio Grande/Río Bravo river channel is bounded by a dense riparian flood forest thicket. Plant communities in the surrounding area are a unique mixture of plants found in the deserts to the west, coastal areas to the east, the temperate zone to the north and tropical and subtropical regions to the south. The climate of the LRGB is that of a tropical to subtropical desert, and is generally, hot, windy and sunny. The LRGB experiences irregular rainfall patterns with average annual precipitation varying between about 38 to 75 cm and often coming in the form of torrential rains from tropical storms. The region is subject to frequent droughts and occasional floods.

The hydrology of the Lower Rio Grande/Río Bravo basin is dominated by operation of the Amistad and Falcón reservoir system. Releases from Falcón are the major component of the river's flow, providing this segment of the river with more than 95 percent of its water. The river channel itself serves as the conduit for delivery of these released flows to their ultimate users. The reliable water supply provided by the Falcon-Amistad system supports intensive agriculture in the area, and is essential to the growth of the region's municipalities and industries. These users comprise the bulk of the demand for waters from the International Reservoir system. As water is diverted from the river channel to various users in both Mexico and the U.S., the remaining flow in the channel is concomitantly reduced. The river flows at Brownsville/Matatmoros are typically reduced to 20 percent or less of the flow measured immediately below Falcón Reservoir, and essentially dropped to zero during the drought of record. Yet the instream flow of the Lower Rio Grande/Río Bravo is necessary to achieve dilution of wasteloads discharged to the river channel, to extrude salinity intruding up the channel from the Gulf of Mexico, and to maintain various ecosystems in and along the river. Groundwater is generally of poor quality, with high levels of salinity, nitrates, and sediments, and is currently not used widely.

Economically, the interdependence between Mexico and the United States is a defining characteristic of the LRGB, and may be greater in this region than elsewhere along the joint border (Zepeda Miramontes, 1996). For Mexico, this region is of paramount national economic importance, involving issues such as foreign direct investment (be it maquiladora-related or not), trade, employment, and migration (legal and illegal). For the United States, the region represents a major challenge since it is among the poorest in the nation, yet it is also a focal point for trade with Mexico. The LRGB thus represents a dynamic region of strategic importance for both countries.

As growth and development continue, both in the LRGB and in the watersheds above Falcon and Amistad Reservoirs, the need for water treatment to maintain adequate water quality is pressing. On both sides of the border, many people live in substandard housing. Poor water quality and lack of sewage and potable water, especially in Mexico and the colonias in Texas, have been linked to gastrointestinal diseases such as shigellosis, hepatitis A, cholera, and possibly birth defects such as anencephaly (Finley 1993). Toxic discharges have been documented downstream from population centers in the Lower basin and are most prevalent near the maquiladora industrial parks (assembly plants) (IBWC 1994; TNRCC 1994). As a result of the NAFTA Treaty and the environmental companion agreements between Mexico and the United States, construction of new water treatment facilities has received much attention in recent years. Important treatment plants are coming on line or are in the planning stage. EPA has invested much effort, including substantial financial funds, in helping Mexico to end conditions under which waste water from border communities is released with no or minimal treatment into the Rio Grande. EPA officials predict that most communities will be served by modern treatment facilities by 2010. To date, the two national as well as the various state governments in the region, have not given similar attention to the issue of secure water supply. We believe that this will become a critical concern in the LRGB in the next few years. If the current severe, prolonged drought continues, this may happen even faster.

Population and economic growth, irrigated agriculture and reservoir construction have had a significant impact on the region's ecology. Less than five percent of the original 8,000-square mile Tamaulipan brushland ecosystem remains along the binational downstream corridor (Jahrsdoerfer and Leslie 1988). The original grasslands and brush of the region have been largely cleared. Palm groves and wetlands are also threatened. Agricultural production has generated environmental impacts that include decreased water quality and eutrophication, salinization, soil modification, health hazards and the destruction of habitat (Mikesell 1992; Gleick 1993).

The existing natural plant communities support a wide variety of native wildlife which use these habitats for feeding, nesting and for protection. Nearly 700 species of wildlife have been documented from the study area (Jahrsdoefer and Leslie 1988); of these, more than 86 vertebrate species are either already listed by governmental organizations as Endangered or Threatened or are considered target species (candidates) which may require immediate protection (Malstrom and Jordan, 1994).

As elsewhere along the Mexico-U.S Border, water management in the Lower Rio Grande/Bravo is complex, involving international, federal, state and municipal institutions. Within the two countries, water management differs significantly. In accordance with the International Treaty of 1944 the Falcon and Amistad international reservoirs are operated jointly by the International Boundary and Water Commission (IBWC) in coordination with Mexican and Texas water agencies, and serve the dual functions of water storage and flood control. Electricity is produced at both dams, but as a secondary function. While the Treaty of 1944 establishes a quantitative allocation of river water between Mexico and Texas, no such agreement exists to deal with the binational aspects of water quality, minimum instream flow for ecosystem maintenance, and other environmental issues. Despite the regular occurrences of drought, no formal binational mechanism for drought management exists.

Because of the growing population and regional economy, the limited water resource available to the region, and the institutional context within which water management is currently carried out, there exists an array of potential conflicts in the basin: between agriculture and industry, between economic development and preservation of environmental quality, between rural and urban areas, and between Texas and Mexico. Indeed, during the 1990s drought, political conflict over water has escalated between Texas and Mexico, and between municipal and rural interests in the Mexican states of Tamaulipas and Nuevo Leon. The availability and quality of water resources will determine future development in the LRGB, and for both nations, management of the water resources within the basin is a central concern.