Award Date


Degree Type


Degree Name

Master of Science (MS)


Water Resource Management

First Committee Member

Charalambos Papelis

Second Committee Member

Mark Stone

Number of Pages



The Colorado River system is one of the most heavily used river systems in the world and as such, accurate water accounting methods are vital. The U.S. Bureau of Reclamation (Reclamation) is charged with accounting for the Colorado River's water use. One tool Reclamation uses to accomplish this is the Lower Colorado River Accounting System (LCRAS). This system uses a combination of remote sensing (RS) and a crop coefficient method to calculate agricultural and phreatophyte evapotranspiration (ET), a crucial component to any water budget. In this study, ET was measured within an irrigated mixed vegetation field (sapling cottonwood and willow, alfalfa, and noxious weeds), within Cibola, AZ, using a Bowen-Ratio (BR) flux tower, from May 18, 2006 through January 9, 2007. In the same field, ET estimates were calculated using LCRAS methodology and three RS Vegetation Index (VI) techniques were tested using various regression analyses. In this study, a published regression technique for estimating ET from VI data was tested and a local regression equation was developed using data collected in the study field. Cost effectiveness analyses were completed assessing the use of all methods to estimate phreatophytic ET along the lower Colorado River; The accuracy of all ET estimates was determined by comparison with BR flux tower ET measurements. LCRAS ET estimates ranged from a root mean error (RME) of 1.1 -- 2.3 mm per day, while RS ET estimates ranged from a RME of 0.5 to 2.5 mm per day. This study found that: RS VI methods for estimating ET within complex phreatophyte communities had the potential to be more accurate than LCRAS ET estimates; ET estimates based on local data outperformed estimates based on regional data; and that the tested RS techniques were not sensitive to different VI but were sensitive to sensor resolution and local empirical calibration data. This research demonstrates that estimating ET using VI techniques shows promise within mixed vegetation environments, but the accuracy of such estimates is improved by the availability of local ET measurements.


Environment; Evapotranspiration; Irrigated; Methods; Mixed; Monitoring; Vegetation

Controlled Subject

Environmental sciences

File Format


File Size

2826.24 KB

Degree Grantor

University of Nevada, Las Vegas




If you are the rightful copyright holder of this dissertation or thesis and wish to have the full text removed from Digital Scholarship@UNLV, please submit a request to and include clear identification of the work, preferably with URL.


IN COPYRIGHT. For more information about this rights statement, please visit