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<br />under some conditions, adjustments are made to reflect local conditions, he also found that in this case, a good deal
<br />more needs to be known about farm conditions in Colorado before an irrigation management adjustment should be .
<br />considered, The Special Master also noted that currently there are no standard publications showing a direct
<br />relationship between salinity and ET,
<br />
<br />The Special Master concluded that Colorado's recommended adjustments to the results of the Penman-Monteith
<br />method were not sufficiently supported, He concluded his [mdings with the statement "This is not to say that the
<br />Kansas values, as calculated with the Penman-Monteith equation and crop coefficients can never be changed, As
<br />more information is developed on conditions in the Arkansas River Valley, adjustments made in accordance with
<br />recognized professional procedures may be appropriate,"
<br />
<br />n. Enhance Coaemet Electronic Weather Station Network
<br />Enhance and improve the Colorado Agriculture Meteorological (CoAgMet) electronic weather station network in
<br />the Lower Arkansas River Basin and provide for its adequate operation and maintenance in order to provide accurate
<br />data for predicting evapotranspiration using the Penman-Monteith method, Estimated cost of $130,000 over the
<br />three year period July 1,2004 - June 30, 2007,
<br />
<br />In order to use the Penman-Monteith method to predict ET, accurate weather data must be obtained from
<br />representative locations in the Lower Arkansas River Basin, In his Fourth Report, the Special Master concluded, "If
<br />data from all of these stations should become an important factor in the operation of the H-I Model, I am confident
<br />that we can expect more complete and accurate weather measurements in the future," Experts for both Colorado and
<br />Kansas agree that accurate weather data that adequately covers the area represented in the H-I Model is an important
<br />factor in the operation of the model and the accuracy of its results,
<br />
<br />The course of action in complying with this recommendation necessitates dependable collection of electronic
<br />weather station data utilizing existing and new CoAgMet weather stations in the Arkansas Valley, To ensure that
<br />the most accurate crop consumptive use estimates can be obtained by this methodology, several issues regarding the .
<br />locations, siting, operation, and maintenance of the CoAgMet weather stations in the Arkansas Valley must be
<br />addressed, These are as follows:
<br />
<br />I) The number of stations and their locations are too few and not representative for the entire area from Pueblo to
<br />the Stateline, The Special Master's recommendation was made on the basis of only three stations located at
<br />Avondale, Vineland and Rocky Ford, Two new CoAgMet stations were installed at Lamar and Holly in 2001.
<br />However, usable data begin for the Holly station on 1/1/02 and for Lamar on 8/1/02, Spatial analyses of the
<br />available weather data have shown that the Avondale and Vineland sites are redundant of each other and weather
<br />stations are needed in up to three additional locations,
<br />2) To be suitable for reference ET and crop water use computations each station should be located in an irrigated
<br />area with irrigated crops in all directions to at least 3/4-mile radius and be situated over a plot of about 50 ft x 50 ft
<br />green vegetation, preferably grass, The Rocky Ford experiment station site is close to this ideal setting, The
<br />Avondale site needs to be planted to permanent drought tolerant grass cover, and occasionally watered, The Holly
<br />and Lamar stations are situated on dry ground and the sites are on the edge of irrigated areas that may have periods
<br />during the year when air movement across the station is from extensive areas of upwind dry, prairie fetch, To
<br />eliminate arguments about the need for data corrections caused by non-reference siting conditions, weather stations
<br />must be sited and maintained according to the prescribed reference siting conditions, If stations are located in a
<br />warmer and drier environment, the predicted crop ET will be biased to higher values, ultimately resulting in higher
<br />predicted streamflow depletion at the Stateline,
<br />3) The Colorado Climate Center at Colorado State University (CSU) currently operates and maintains the CoAgMet
<br />network, including data processing, data quality control checks, and posting of data and other weather products on a
<br />web site, Due to budget and staff limitations, field weather station sites receive a single annual maintenance visit.
<br />The consequence of these limitations is the inability to offer sufficiently reliable weather data to meet future
<br />demands in complying with the Arkansas River Compact. Examples of past problems with the CoAgMet weather
<br />station network as a direct result of budget and staff limitations has included incidences ranging from sensor
<br />calibration errors, gaps in data due to sensor failure to intermittent losses of data records for selected time periods.
<br />In order to reduce these risks the frequency of maintenance visits to check weather station equipment and replace .
<br />sensors for re-calibration needs to increase to at least semi-annually. Another significant change needed in the
<br />network's operation is routine site maintenance and sensor checks on at least a bi-weekly basis throughout the year
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