Technical and Special Reports
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Browsing Technical and Special Reports by Author "Anand, Shilpa"
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Item Hydrology, Salinity, and Salinity Control Possibilities of the Middle Pecos River: A Reconnaissance Report(Texas Water Resources Institute, 2008-05) Hatler, Will; Anand, Shilpa; Miyamoto, S.The Middle Pecos River between Malaga, New Mexico, and Girvin, Texas, is known for high salinity. Streamflow salinity during the last decade (1991-2000), for example, averaged 3,500 and 6,150 mg L-1 at Malaga and at the Red Bluff release, and upwards of 12,000 mg L-1 at Girvin. These high levels of streamflow salinity not only reduce the economic uses of the water, but also limit the biodiversity of aquatic and riparian species along the river. This report outlines the hydrology, geochemistry, and water management practices of the Middle Pecos River in order to explain the reasons for the high salinity, and to discuss the potential for salinity control. The main causes of high salinity between Malaga and Red Bluff are brine intrusion at Malaga Bend and Bottomless Lakes and a drastic reduction in flow since the late 1930s that does not adequately dilute the intrusion. The amount of salts entering the Pecos River from these two sites is estimated at 450,000 tons/year while freshwater flow at Malaga has decreased from 260 Mm3 (210,000 acre-ft) per year from 1929 through 1937 to 81 Mm3 (66,000 acre-ft) per year from 1959 through 2001. The causes of high salinity between Red Bluff and Girvin are saline water intrusion from both surface and subsurface sources, low runoff into the river, and the evaporative concentration of the stream. The amount of salts entering this reach is estimated at 250,000 tons/year, primarily from Salt Creek, Salt Draw, Toyah Creek, and shallow saline groundwater. The sources of the shallow saline groundwater which enters the Pecos River between Coyanosa and Girvin are suspected to be groundwater flow from adjacent areas, but details are yet to be investigated. Diversion for irrigation, high seepage loss above Pecos, and low runoff resulted in inadequate flow to prevent intrusion or to dilute saline water entering the Pecos below Coyanosa. The annual flow at Coyanosa decreases below 30 Mm3 (24,000 acre-ft) per year. There are interests to lower the salinity of the Middle Pecos River for preserving its biodiversity, protecting groundwater quality, and encouraging the regrowth of native riparian species after ongoing saltcedar control activities, besides increasing the economic value of this water for irrigation. A regional level of concern is its impact on Amistad International Reservoir, located downstream along the Texas/Mexico border. The salinity of this huge reservoir (6.8 billion m3 or 5.5 million acre-ft) has increased from 560 mg L-1 to about 1000 mg L-1, the upper limit of the Texas drinking water standard. The Pecos River accounts for nearly 30 percent of the salt loading into Amistad International Reservoir while providing about 10 percent of the flow, thus raising the background salinity of the reservoir. In addition, historical records from 1941 and 1942 indicate that a high precipitation event between Roswell and Red Bluff can cause the Pecos River to send enough saline water to Amistad to raise the salinity level of the reservoir well above the Texas drinking water standard. Since the potential for additional freshwater inflow from runoff appears to be limited, salinity management strategies must incorporate ways to reduce saline water intrusion and percolation losses from reservoirs and river beds. Streamflow salinity can be restored closer to the original level by reducing saline water intrusion roughly in proportion to the reduction in fresh water flow caused by diversion and percolation losses. Potential control options include saline water intrusion control upstream at Malaga Bend and Bottomless Lakes, and possibly in the segment between Pecos and Girvin. The methods of salt source control at each of these sites are yet to be addressed. Preliminary estimates show that salt source control at Malaga Bend and/or Bottomless Lakes will result in a significant reduction of salinity of Red Bluff Reservoir. The control of brine intrusion at Malaga Bend alone can lower salinity of the Red Bluff release from 6150 to 4800 mg/L, the level comparable to the level that existed shortly after the construction of Red Bluff Reservoir in 1936. However, its impact on Amistad International Reservoir is yet to be analyzed, and it requires good understanding of the hydrologic connection between the middle and the lower reaches. If the connection is weak, salt sources below Pecos should be evaluated for control as a part of the salinity control plan for Amistad International Reservoir. Streamflow salinity below Coyanosa can be lowered simply by reducing the percolation losses from the reservoir and river beds above Pecos, provided that the water saved is left in the river. However, this option will increase salt transport to the Lower Pecos River unless implemented in conjunction with salt source control. Impacts of water management and salt source control options on monthly or daily salinity of the middle and the lower reaches are yet to be evaluated.Item Influence of Tributaries on Salinity of Amistad International Reservoir(Texas Water Resources Institute, 2006-04) Anand, Shilpa; Yuan, Fasong; Miyamoto, S.Amistad International Reservoir is located at the Texas–Mexico border, and is fed by four main tributaries: the middle Rio Grande (MRG), the Pecos, the Devil’s, and the Rio Conchos from Mexico (Fig. 1). This reservoir is among the largest reservoirs in the western US, and it was built to hold 6.7 billion m3 (5.5 million acre-ft.) of water. The structure was completed in 1968, and the Reservoir was filled near its capacity by 1972 (Fig. 2b). The storage declined to 3.1 billion m3 by 1985, backed up to over 4.0 billion m3 for much of 1986 through 1992, then depleted to as low as 1.5 billion m3 during the last decade, following the drought which started in 1994. Salinity of the Rio Grande at Amistad prior to reservoir construction averaged 560 mg L-1 (Fig. 2a). Starting in 1975, salinity reached 700 mg L-1, and remained at that level through 1983. This was followed by a steep increase in salinity which peaked in 1988, and again in 1996. Salinity of the outflow increased to 945 mg L-1 during 1988, and during February of that year, it reached the federal secondary drinking water standard of 1,000 mg L-1. There is a concern that salinity may exceed the limit with a greater frequency in the future. This problem of salinity increase at Amistad was noted a decade ago (Miyamoto et. al., 1995). In the meantime, a reconnaissance survey was carried out for identifying salt sources entering the Pecos River (Miyamoto et al., 2005). The report indicates that the Pecos River had been salinized largely due to saline water intrusion and through the reduction in streamflow that is needed for diluting the saline water intrusion. The flow of the MRG below El Paso has also declined, and saline irrigation returnflow has deposited large quantities of salts in the reach between El Paso and Presidio. Consequently, bank salinity is extremely high in the MRG below El Paso. The Rio Conchos from Mexico has historically provided the largest inflow into Amistad. According to the data from the US Section, International Boundary and Water Commission (USIBWC), salinity of this flow when it enters the Rio Grande has been steadily increasing in the recent decades. These signs do not bode well for maintaining low salinity at Amistad. This study was conducted to identify the influence of tributaries on salinity fluctuation at Amistad Reservoir. This type of assessment may be useful for developing salinity control and water management strategies. The data shown in Fig. 2 indicate that the first salinity peak appeared during the high storage period under a seemingly normal inflow situation; and this will be the focus of this study. The second peak appeared in 1996 during a low flow and low storage period. In this instance, the increase in salinity is certainly drought-related.Item Reconnaissance Survey of Salt Sources and Loading into the Pecos River(Texas Water Resources Institute, 2006) Belzer, Wayne; Anaya, Gilbert; Hatler, Will; McDonald, Alyson; Anand, Shilpa; Yuan, Fasong; Miyamoto, S.The Pecos River of southeastern New Mexico and west Texas is among the saltiest rivers in North America with streamflow salinity regularly exceeding 7,000 mg L-1 at the New Mexico and Texas border, and eventually exceeding 12,000 mg L-1 at Girvin, Texas. It originates in northeastern New Mexico, flows through the semi-arid part of New Mexico and west Texas, and merges into the Rio Grande just below the historical town of Langtry (Fig. 1). The diversion from this river, estimated at 224 million m3 (180,000 acre-ft.) per year, is mostly above Red Bluff, mainly for irrigating an estimated 25,000 ha (60,000 acre) of crop lands in New Mexico. The water stored in Red Bluff is also used for irrigating comparatively small areas (less than 4,000 ha) in west Texas. The area irrigated with ground water is much greater. High salinity of the river has adversely affected stability and diversity of the riparian and aquatic ecosystem (e.g., Hart, 2004; El-Hage and Moulton, 1998; Davis, 1987) as well as the economic use of this water resource, especially in the reach below Red Bluff Reservoir. Degradation of ground water quality along the streamflow is also a concern, as the saline stream percolates through highly permeable alluvium (Boghici, 1999). In addition, one study shows that the flow of this river accounts for nearly one-third of salts entering Amistad International Reservoir located approximately 64 km (40 miles) south of Langtry (Miyamoto, 1996). Salinity of the Amistad Reservoir reached 1,000 mg L-1 (the upper limit of secondary drinking water standard) in February 1988, and there is a concern that such an incident may occur with greater frequency unless salinity control measures are implemented at some point. Several measures to lower salinity have been proposed. Pumping of saline seepage below Malaga, which otherwise enters the Pecos, is among the options tried (e.g., Hale et al., 1954). The saline water is saturated brine consisting of common salts (NaCl). The brine once pumped into a nearby depression was evaporated, but the leakage from the ponding area made this option ineffective or unattractive (Havens and Wilkins, 1979). Deep well injection was also considered, but was found to be costly and probably not sustainable (Cox and Kunkler, 1962). The latest effort has been to evaporate the brine and to harvest salts (Personal Communication with the Red Bluff District). Another attempt which has been implemented in recent years is the eradication of salt cedar which invaded the bank of the Pecos River (Hart, 2004). The idea is to maintain the flow by reducing the evapotranspiration, and hopefully streamflow salinity as well by lowering evaporative concentration of salts (Weeks, et al.,1987; Hart, 2004). This study was conducted for identifying additional sources of salts and river reaches where saline water sources are entering the Pecos River, and was proposed as Subtask 1.5. Identification of saline tributaries is covered under Subtask 1.4.Item A Simple Model for Estimating Water Balance and Salinity of Reservoirs and Outflow(Texas Water Resources Institute, 2010-08-23T19:58:42Z) Miyamoto, S; Yuan, F; Anand, ShilpaReservoir storage reduces fluctuation in streamflow salinity, yet increases outflow salinity because of water evaporation. These processes are highly relevant to developing water management strategy, yet the method to predict outflow salinity has not been adequately examined. The study reported here examined the water and salt balance in a reservoir using a two-layer model. This model assumes that inflow blends with the storage, but the water evaporation takes place from the surface layer, and the percolation losses from the subsurface. The thickness of the first layer where salinity increases with evaporation was estimated through calibration against the measured outflow salinity. The changes in salinity were computed using a moving average method on a monthly time step. This model was applied first to Red Bluff Reservoir of the Middle Pecos River, then to Elephant Butte, Amistad, and Falcon along the Rio Grande. The outflow salinity projected by the model was in good agreement with the measured, except under a few circumstances where mixing of inflow and reservoir storage was suspected to be incomplete. The accuracy of prediction can be improved by improving the estimate of initial salinity of reservoir storage, which is currently taken as being equal to outflow salinity at the onset of the simulation.Item Water Balance, Salt Loading, and Salinity Control Options of Red Bluff Reservoir, Texas(Texas Water Resources Institute, 2007-01) Yuan, Fasong; Miyamoto, S.; Anand, ShilpaRed Bluff is the main reservoir of the Pecos River in Texas, and its maximum storage capacity adjusted to sediment accumulation is estimated at 357 million m3 (289,600 acre-ft.). Aside from the shortage of water entering the reservoir, high salinity has been a concern. This report was prepared with three main objectives: i) to outline water balance of the reservoir, ii) to establish salt loading trends over the past several decades, and iii) to evaluate the impact of salt loading on salinity of the reservoir and its outflow. We also outlined the needs for salinity control, and briefly discussed salinity control options. The data used in this report were gathered through an EPA project entitled “Basin-wide Management of the Texas Pecos River”, and consisted of flow and salinity data from various agencies. Flow data are fairly reliable as the discharge is measured daily at a number of stations. Salinity data have been taken several times a month to several times a year, and may be considered “sketchy” at best. However, an effort was made to establish salinity and flow relationships, so that salinity measured under a certain flow condition can be extrapolated to the monthly flow. Flow and salt loading analyses were performed since 1959, and the water balance analyses from 1991 through 2001 during which a complete set of flow, storage, and salinity data was available. The analyses of flow balance indicate that the inflow into Red Bluff from 1991 through 2001 averaged 95 million m3 (77,000 acre-ft.) per year from the Pecos, and 31 million m3 (25,000 acre-ft.) from the Delaware River (DWR). These flow means are higher than the longterm (1959-2001) averages of 84 and 21 million m3 from the Pecos and the DWR, respectively. The reservoir storage during 1991-2001 fluctuated widely between 47 to 186 million m3 with a mean of 100 million m3 (81,000 acre-ft). The recorded annual surface outflow averaged 59 million m3, the estimated evaporation losses, 35 million m3, and the estimated percolation loss, 41 million m3 per year or 33% of the total inflow. About 8.7 of the 41 million m3 appears to be returning to the River above Orla. Ignoring the high percolation loss estimated in two out of eleven years, the seepage losses appear to have averaged 37 million m3 (30,000 acre-ft) per year. This estimate of percolation losses is subject to the reliability of reservoir outflow measurements. Salinity of the Pecos River at Malaga (NM) averaged 4100 mg L-1 in arithmetic mean, and 3320 mg L-1 in flow-weighted during 1959 to 2001. Since 1991, the flow-weighted mean at this location averaged 3500 mg L-1. Salinity of the DWR was estimated at 2600 mg L-1, and the flow-weighted salinity of the composite flow which enters Red Bluff was 4425 mg L-1 since 1991. Salinity of outflow from the reservoir since 1991 averaged 6150 mg L-1, thus registering an annual mean salinity increase of 1700 mg L-1 in flow-weighted, and 650 mg L-1 in arithmetic mean between the inflow and the outflow since 1991. Salt loading into Red Bluff averaged 478,000 tons per year since 1991, and is stable. The best loading estimate from the Pecos and the DWR combined is 560,000 tons per year or somewhat higher. Salt loading from Malaga Bend is estimated at 150,000 tons per year since 1991, as compared to the long-term mean of 172,000 tons/year. Salt load of the reservoir outflow since 1991 is estimated at 410,000 tons/year which includes seepage returning back to the river. Salinity of the reservoir release (6150 mg L-1 on the average) is too high for irrigated production of most crops, except for highly salt tolerant types, such as cotton and hay. It is not acceptable for poultry, and is marginal for livestock. It also limits biodiversity of both aquatic and riparian species. Salt loading from the Pecos measured at Langtry, (where the Pecos enters the Rio Grande) has averaged 429,000 tons per year since 1986. This accounts for 26% of salt loading (or 30% of gauged inflow) into Amistad, while providing only 9% of the total inflow into the reservoir. This is not an ideal situation as salinity of the Amistad International Reservoir located downstream is nearing 1000 mg L-1, the upper limit of drinking water standard in Texas. The proposed control of brine intrusion at Malaga Bend seems to be the most effective option for lowering salinity of the Pecos River entering Red Bluff. When this source is controlled, salinity of the reservoir outflow can be reduced to the salinity level reported during 1937 to 1940, which is 4710 mg L-1. Salinity can be lowered even more if saline water intrusion near Chain Lakes (east of Roswell, NM) is controlled. Saline water intrusion controls not only reduce salinity, but can also reduce salt load of the Pecos River entering the Rio Grande, then Amistad Reservoir. The reduction of seepage losses at reservoirs upstream should also help reduce salinity of the Pecos River downstream.