go to chapters:
1. Overview
2. Study Area Description
3. Geomorphology and Sediment Cones
4. Environmental Resources
5.Problems and Opportunities
6. Recommendations
7. References
8. Appendices
CHAPTER 2.0 STUDY AREA DESCRIPTION
2.1 Study Area Definition
2.2 Study Area Description and General Trends
2.2.1 Climate
2.2.2 Physiography and Geology
2.2.3 Soils
2.2.4 Watershed Stakeholders
2.1 Study Area Definition The study area was mainly limited to the United States side of the Rio Grande and its tributaries in the Forgotten River Reach, although some study was given to environmental conditions and tributaries on the Mexican side of the International Border. The study area begins approximately 13 miles downstream of Fort Quitman in Hudspeth County, Texas, to the north and approximately 6 miles upstream of Presidio, Texas, to the south at the Rio Conchos confluence with the Rio Grande.
The study area is contained within a 1.86 mile buffer extending on either side from the main channel centerline of the Forgotten River Reach of the Rio Grande from Fort Quitman to Presidio, Texas. Areas within the buffer zone determined to exceed the river channel base elevation level by 30.28 feet or more were eliminated from the study area.
2.2 Study Area Description and General Trends
2.2.1 Climate There are no weather stations within the project study area; thus, all climate data comes from the El Paso National Weather Service station, approximately 85 miles upstream of feet Quitman, the northern terminus of the study area. Rainfall, primarily in the form of brief but heavy local thunderstorms, averages 14-22 inches per year for the study area (depending on one degree quadrangle data from along the reach) (TWDB 2007), with 55 percent of this annual amount occurring in the months of July, August, and September. August is historically the wettest month and April the driest. Extremes include 1884, when a high of 18.29 inches of precipitation fell; and in 1891, when only 2.22 inches fell; all months except for July have experienced zero precipitation (NWS 2007). Rainfall varies from a number of intense storms per month to periods of no rainfall. Occasionally, the rainfall during a single month can exceed the average annual rainfall at that station. For the period 1879 through 2003, temperatures in the study area average 100 degrees Fahrenheit or higher for 14 days a year; however, in 1994, there were 62 days higher than 100 degrees. June and July are the hottest months, averaging maximum temperatures of approximately 95 degrees Fahrenheit and January being the coldest month with monthly lows of 33 degrees Fahrenheit. Prevailing winds are generally out of the west during February through May and then shift to the east-southeast during June and July, transitioning to the south in August and September, before originating from the north-northeast during October through January.
Evaporation rates average 56 inches per year (TWDB 2007). These high evaporation rates are the result of the high temperatures and low relative humidity, which is often as low as ten percent during the summer afternoons and occasionally as low as five percent.
2.2.2 Physiography and Geology The study area is located near the northeastern edge of the Mexican Highlands section of the Basin and Range Physiographic province. The region has a long history of extensive tectonic activity. A great deal of tertiary block faulting led to the formation of much of the present basin and range topography. In general the study area is composed of a number of southeast trending fault-block mountains with intervening basins and their sedimentary fills.
The canyon segments have steep to mildly sloping walls. The valley reaches display numerous but discontinuous areas of floodplain with some low depositional terrace remnants, tributary arroyo mouths and alluvial fans, intervening dissected pediment and bolson fill deposits (both of which are abandoned erosion surfaces of the more ancient Rio Grande), and isolated sand dune deposits.
NOTE: Bolsons are basins or structurally deep depressions partially filled with sediments from the surrounding highlands. In most cases, bolsons are formed by down-faulted blocks, while up-lifted or tilted blocks on either side separate the basins from one another.
Stratigraphically, the area contains sedimentary deposits or rocks of Permian to Holocene Age; and igneous rocks of Tertiary Age. In general, the mountains are composed of Permian or Cretaceous shale, sandstone, and limestone; and early Tertiary volcanic tuffs, ignimbrites, rhyolites, trachytes, andesites, and basalts. The mid-Tertiary and later basin fills consist principally of gravels, conglomerates and other sediments that are the basic materials of most of the pediments, terraces and older alluvial fans. In some places, close to the river, these basic materials are inter-bedded or overlain by the more recent Rio Grande sediments. The Pleistocene and Holocene, or recent deposits, are for the most part composed of the recent floodplain sediments which have probably been deposited within the last centuries; the lowest river and arroyo terraces; sand dunes; and a very thin veneer of sand or gravel on some of the older and higher surfaces.
The Forgotten River Reach valley width is typically 1,000 feet or less, but occasionally widens, with some areas as wide as 3,000 feet (Fullerton and Batts 2003). In contrast, the river also flows through several narrow canyons no more than 200 feet wide between Mayfield Canyon and Goat Canyon below Indian Hot Springs, and 2.5 river miles above the Hudspeth County line (The University Of Texas Center For Space Research [UTCSR] 2006).
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2.2.3 Soils The soils in the Rio Grande floodplain in Hudspeth County are of the Harkey-Glendale association of deep, nearly level, calcareous, loamy soil. The soils are used for irrigated cropland, pastures, and orchards.
In Presidio County, the Glendale-Anthony-Toyah association of deep, nearly level, light to dark colored, calcareous soils is used for rangeland and wildlife. Some areas along the Rio Grande are used for irrigated cropland.
Where these alluvial soils are heavy (clay-rich) they are often highly impregnated with soluble salts. This is especially true where irrigation practices coupled with an aggraded river channel have resulted in a high water table with poor drainage conditions.
In the tributary watershed area, the Reeves and Anthony series soils (gravelly) are found above the floodplain or overflow areas, on the pediment and terraces slopes and flats, and within most of the arroyos and their fan.
The Reeves series soils have light brown to ashy gray, calcareous, low organic content, surface soils underlain by light brown, yellow, or buff calcareous subsoils, which may consist primarily of igneous rock gravel, caliché or both. The texture of the Reeves soils varies from fine sand to clay with much included gravel. The Anthony series soils are light brown to grayish brown, friable, calcareous, generally well drained surface soils and subsoils which at a depth of several feet may rest on loose, rounded gravel.
Land use in the Forgotten River Reach of the Rio Grande is mainly limited to farming and ranching, due to the distance from major population centers. Ownership on the American side of the International Border with Mexico is 98% private, with approximately 2% owned by the state of Texas. Access to the study area is limited.
Fort Quitman, Texas, lies approximately eighty miles southeast of El Paso and twenty miles southeast of the site of present-day McNary in far southern Hudspeth County. During the Civil War, the post was intermittently garrisoned by Confederate and Union detachments and quickly fell into disrepair. Over the next decade companies and detachments of black soldiers of the Ninth Cavalry and the Twenty-fifth United States Infantry guarded the mails and scouted for hostile Native Americans. The post was abandoned in 1882, partly because it was not on a railroad. Fort Hancock (originally Fort Rice) was established in 1882 at a better site nearby. Today only a cemetery remains near the site of Fort Quitman.
Presidio is located on the Rio Grande in southern Presidio County, Texas. The surrounding area is the oldest continuously cultivated area in the United States. Farmers have lived at Presidio since 1500 B.C. By 1400 A.D., the area’s Native Americans lived in small, close-together settlements, which the Spaniards later called pueblos. The handful of Anglo settlers who came to the region was assimilated into the Hispanic population and their descendants are primarily Spanish speaking today.
In 1930, the Kansas City, Mexico and Orient Railway reached Presidio, and the town incorporated. The population grew from 96 in 1925 to 1,671 in 1988, but the number of businesses declined from 70 in 1933 to 22 in 1988. At the end of 1988, Presidio experienced a population boom due in part to previously undocumented aliens enrolled in the amnesty program. The population in 1990 was 3,422. Population reached 4,877 by 1998, and is expected to top 10,000 by the year 2013 at present growth rates.
2.2.4 Watershed Stakeholders The Rio Grande Compact is an interstate agreement to apportion equitably the water of the Rio Grande among Colorado, New Mexico, and Texas. A preliminary compact of February 12, 1929, provided for stream-gauging stations, for construction of a reservoir in Colorado, and for equitable dividing of the water of the river pending the signing of a permanent compact. The compact was signed at Santa Fe, New Mexico, on March 18, 1938, approved by the state legislatures, and approved by Congress on May 31, 1939. The compact worked out provided for Colorado and New Mexico to deliver water in accord with a formula based upon the flow of the Rio Grande and its tributaries at designated gauging stations above the state lines. A Rio Grande Compact Commission, consisting of one representative from each state, was established, the state engineers of Colorado and New Mexico serving ex officio and the Texas commissioner being appointed by the Texas governor. The United States designates a representative to sit with the commission.
Apportionment of water of the Rio Grande between the United States and Mexico is determined by various compromises and treaties made between 1904 and 1944. The first attempt at apportionment of the waters was the Compromise of 1904, which divided the waters above and below El Paso. In the treaty of 1906 the United States promised to deliver 60,000 acre-feet of water annually for irrigation in the Juarez Valley, peak period of delivery falling in April, May, and June. In return Mexico waived all claims for any purpose to the waters of the river between the head of the Mexican Canal and Fort Quitman, Texas. The 1944 treaty dealt with the Rio Grande between Fort Quitman and the Gulf of Mexico. The following order of preference in joint use of the international waters was set up: (1) domestic and municipal uses, (2) agriculture and stock raising, (3) electric power, (4) other industrial uses, (5) navigation, (6) fishing and hunting, and (7) any other beneficial use to be determined by the International Boundary Commission. Under Article IV of the 1944 treaty, Mexico received all of the waters of the San Juan and Alamo rivers; one-half of the flow in the main channel of the Rio Grande below the lowest major international storage dam; two-thirds of the flow in the main channel from the Conchos, San Diego, San Rodrigo Escondido, and Salado rivers and Las Vacas Arroyo, provided that the United States receive from these same six streams not less than 350,000 acre-feet annually as an average in five-year cycles, and one-half of all other flows not otherwise allotted, occurring in the main channel of the Rio Grande. Also under Article IV the United States was given all of the waters of the Pecos and Devils rivers, Goodenough Spring, and Alamito, Terlingua, San Felipe, and Pinto creeks; one-half of the flow in the main channel of the Rio Grande below the lowest major international storage dam; one-third of the flow reaching the main channel of the Rio Grande from the Conchos, San Diego, San Rodrigo, Escondido, and Salado rivers and Las Vacas Arroyo, provided that this be not less than 350,000 acre-feet annually as an average in five-year cycles, and one-half of all other flows not otherwise allotted, occurring in the main channel of the Rio Grande. The quantity of water allotted to the United States not only took care of existing needs but also permitted expansion of irrigated areas. In 1993, the 1944 treaty remained in effect.
State agencies with an interest in the Forgotten River Study include the TCEQ, Texas Department of Fish and Game, and the Texas Department of Agriculture. Federal agencies with interest in the study, or jurisdiction over properties in the watershed, include the International Boundary and Waters Commission (IBWC), The United States Border Patrol (USBP), the Department of Homeland Security, U.S. Fish and Wildlife Service, and the Natural Resource Conservation Service.
In the past, the Mexican government has indicated interest in sharing information regarding hydrology, geomorphology, and ecology as well as working with the United States in future restoration projects.
Private parties own large portions of the river and floodplain with divergent interests in the resources of the watershed. Non-governmental agencies, such as Environmental Defense Fund, World Wildlife Fund, and American Rivers have shown a willingness to assist in studies and work on projects within the Forgotten River Reach of the Rio Grande.
As part of the study’s public involvement process, a public workshop was held in Marfa and Sierra Blanca, TEXAS, on August 17, 2007. The workshop provided an opportunity for attendees to learn about the study process and to provide input as to what issues they felt to be important. The attendees were asked to review provided poster boards demonstrating the issues within the Forgotten River Reach of the Rio Grande Basin and to provide their opinions on what they felt could be done towards rehabilitation of the study area. The issues ranged from invasive species to surface water use and they covered large areas of the watershed. This information has been incorporated into the various analyses conducted under this study.
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go to chapters:
1. Overview
2. Study Area Description
3. Geomorphology and Sediment Cones
4. Environmental Resources
5.Problems and Opportunities
6. Recommendations
7. References
8. Appendices
