Laserfiche WebLink
<br />, <br /> <br />. <br /> <br />that Colorado was in compliance with the Arkansas River Compact for 1997-99 without having to completely <br />resolve the differences between the Kansas and Colorado implementations of the Penman-Monteith method, He left <br />the resolution of several issues dependent on the conduct of further studies and the acquisition of additional data that <br />could support Colorado's position that the use of the Penman-Monteith method with currently available parameters <br />and data tends to overestimate the consumption of water by crops and therefore also overestimate the depletions <br />which Colorado well users must replace in order to comply with the Arkansas River Compact. <br /> <br />The impact of the Special Master's acceptance of the Penman-Monteith method is not limited to the well owners in <br />the Arkansas River Valley or the calculation of crop water use in the HI model. Now that the Special Master has <br />accepted the Penman-Monteith method as more accurate to calculate crop consumptive use, others will want to use <br />the Penman-Monteith method to determine the transferable consumptive use for changes of agricultural water rights <br />to municipal use in the Arkansas River Basin and elsewhere in the state, In addition, the use of the Penman- <br />Monteith method to calculate consumptive use in any basin where the use of water is apportioned on the basis of <br />consumptive use could result in determinations that higher amounts of water are being consumed in Colorado. <br />Therefore, water users throughout the state have an interest in determining whether the Penman-Monteith method <br />and the crop coefficients used by the Kansas experts are suitable to determine crop consumptive use in Colorado, <br /> <br />Summarv of Request <br />The four general areas containing tasks which are required to implement or support the [mdings of the Special <br />Master that require funding are: <br />I. Design, installation, and operation of weighing lysimeters at the Colorado State University Agricultural <br />Experiment Station at Rocky Ford, Colorado, ($300,000) <br />II. Enhancement of the CoAgMet Electronic Weather Station Network in the Lower Arkansas River Basin, <br />($130,000) <br />III, Monitoring of irrigation amount, timing and crop yield in the Lower Arkansas River Basin, ($220,000) <br />IV, Review of the H-I Model, after changes have been made by the State Engineer's Office, by Hydrosphere <br />Resource Consultants and Helton & Williamsen, ($100,000) <br /> <br />. <br /> <br />I. Installation of Lvsimeters <br />Install and operate a set (2) of monolithic continuous weighing (direct load cell, 2 to 3m x 2 to 3m x 2.5m deep) <br />lysimeters to accurately measure evapotranspiration of a reference crop and of production crops under a variety of <br />field conditions typical of the lower Arkansas River Valley in Colorado, Estimated cost of $300,000 over the three <br />year period July 1, 2004 - June 30, 2007, Detailed cost estimate attached, <br /> <br />The Special Master has ruled that the Penman-Monteith method will be used to predict crop water consumption or <br />evapotranspiration (ET) for use in the Hydrologic-Institutional (H-I) Model. The H-I Model will be used to <br />determine whether or not Colorado has complied with the Arkansas River Compact for the ten year period from <br />1997-2006, In order to use the Penman-Monteith method to predict ET, crop coefficients for the various crops <br />grown specifically in the Arkansas River Valley must be determined, This data is currently not available and has <br />been inferred from studies performed in Idaho and Texas, If Colorado is forced to continue to use this data, <br />Colorado's experts believe that the accuracy of the results produced by the H-I Model will be questionable and that <br />well users may have to purchase more water than actually needed for Colorado to comply with the Arkansas River <br />Compact. The weighing Iysimeter is the instrument used to accurately determine the crop coefficients needed by the <br />Penman-Monteith method to produce accurate ET data for use with the H-I Model. <br /> <br />. <br /> <br />In order to obtain the data and information needed to use the Penman-Monteith method for predicting ET at various <br />locations in the Arkansas River Valley, studies must be conducted at a location in the Arkansas River Valley to <br />determine crop coefficients for the various crops grown in the valley, Because of the recent adoption of the <br />Penman-Monteith method, studies of this type have not yet been conducted in Colorado and the crop coefficients <br />currently being used have been estimated using data obtained from studies conducted in Idaho and Texas, To obtain <br />accurate data for the H-I Model using the Penman-Monteith method, Colorado's experts testified that the results <br />produced using the Penman-Monteith method need to be adjusted for the less than ideal conditions that exist in most <br />agricultural settings when compared with the controlled and pristine conditions of an agricultural experiment station <br />where the crop coefficients used with the Penman-Monteith method are determined, Colorado's experts proposed <br />the use of an irrigation management factor and a salinity adjustment to modify the results obtained using the <br />Penman-Monteith method with accurately determined crop coefficients, Although the Special Master found that <br /> <br />7 <br />