Water Resources Professional Project Reports

Belle T. Rehder

Document Type

Technical Report

Publication Date

6-7-2013

Abstract

Found approximately in the geographic middle of New Mexico, Socorro County is an agricultural community that relies on the Rio Grande as the major source of water for irrigation. The Rio Grande is used throughout the region for agricultural, industrial, domestic-municipal consumption, recreation and riparian vegetation, as well as for the protection of endangered species found in the environment. Salinity, a concern for all users, has been studied throughout the Rio Grande from Colorado to the Mexico border. Previous research suggests that salinity may increase through irrigation practices, municipal and industrial uses, evapotranspiration, climatic changes, and natural geologic processes and weathering of minerals. This study examines salinity variability in river and irrigation water through the Socorro region, from late February to November; within the time that irrigation water is diverted by the Middle Rio Grande Conservancy District, and delivered to agricultural lands through a series of canals and diversions. The study reach extends from the San Acacia Diversion Dam, north of Socorro, where irrigation for agriculture is supplied by the surface and groundwater return flows from the Unit 7 Drain and runs south for approximately 44 kilometers to San Antonio, NM, near the Bosque Del Apache National Wildlife Refuge. The Low Flow Conveyance Channel (LFCC) is found directly west of the river and is hydrologically connected through ground water seepage to the river in areas where the river bed is higher than the valley floor, and through diversions to the drain and irrigation systems. The Riverside drain is found west of the LFCC, between the irrigation canals and farms, and LFCC, drawing off excess water from agricultural fields. Salinity of the Rio Grande, LFCC, drains, and the irrigation canal flows were measured semi-monthly, both preseason and throughout the irrigation season from February 28 to November 10, 2011. Regional flows of the Rio Grande, within the Socorro region between San Acacia and San Antonio, NM, were compared to associated salinity within this time frame. Seasonality accounted for the greatest salinity variations. Electroconductivity (EC), as well as alkalinity, in general, rose over time along the study reach. For example, the EC at any given point in early spring (April 18) was between 590 and 861 μs/cm, while by the later part of the irrigation season ranged from 812 and 967 μs/cm (October 28). During the same time period, the alkalinity of samples (as CaCO3) ranged from 105-156 mg/L (April 18) to 176-209 mg/L (October 28). As expected, in most cases, salinity increased further south down river. Alkalinity and streamflow showed a positive correlation. Salinity increased in the river and associated channels when there was less streamflow. The salinity of the Rio Grande at San Acacia on April 7 was 537 μs/cm compared to San Antonio at 605 μs/cm on the same day. In addition, irrigation water, in general, had higher EC and alkalinity than the Rio Grande, except for periods in late summer when the river was at its lowest stream flow or had no flow at all. For instance, San Antonio irrigation was higher over the course of the season (average 868 μs/cm), than the river water EC average (715 μs/cm) at San Antonio. The major ions were primarily calcium and sodium cations and carbonate, and to a lesser degree sulfate anions. The river and irrigation samples showed similar ionic compositions through time, while the drain and LFCC water samples showed less calcium and sodium carbonates.

Language (ISO)

English

Keywords

Irrigation water--Environmental aspects--New Mexico--Socorro County., Stream salinity--New Mexico--Socorro County., Soils, Salts in--New Mexico--Socorro County.

Comments

A Professional Project Report submitted in partial fulfillment of the requirements for the degree of Master of Water Resources, Water Resources Program, University of New Mexico.

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