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<br />DEPARTMENT OF NATURAL RESOURCES <br />DIVISION OF WATER RESOURCES <br /> <br />Water Division 1 •••• Greeley <br />810 9th Street, Suite 200 • Greeley, CO 80631 • Phone: 970-352-8712 • Fax: 970-392-1816 <br />http://water.state.co.us <br /> <br /> <br /> <br /> <br />MEMORANDUM <br /> <br />TO: DAVID NETTLES, Division Engineer in Water Division 1 <br /> KEVIN REIN, Asst. State Engineer <br /> <br />FROM: DEAN SANTISTEVAN, Asst. Division Engineer in Water Division 1 <br /> <br />DATE: December 13, 2013 <br /> <br />SUBJECT: Issues with Selecting an Appropriate Crop Growth Stage Coefficient for <br />the SCS Modified Blaney-Criddle Equation <br />____________________________________________________________________________________ <br />EXECUTIVE SUMMARY <br /> <br />This memo stems from our involvement in Case No. 10CW2631 where the Applicant relied upon the <br />upper plains coefficients for pasture grasses in Task Memo 59.1 for their change of use analysis. The <br />Applicant defended their use by alleging that if an elevation adjustment to SCS Blaney-Criddle <br />coefficients was performed from sea level as referenced in Pochop2, the result would be the same. We <br />contested the use of the Task Memo 59.1 coefficients and argued that an elevation adjustment pursuant <br />to Pochop would not necessarily be from sea level. This memo addresses issues with selecting an <br />appropriate crop growth stage coefficient, and separates them into three parts. <br /> <br />Part I: Technical review of an elevation adjustment from Pochop (begins on p.2) <br />• For Kentucky Bluegrass and alfalfa, an elevation adjustment to the SCS Modified Blaney-Criddle <br />equation is appropriate from the elevation at which the coefficients were developed (during the <br />growing season). <br /> <br />o An elevation adjustment of around 10 percent per 1,000m was confirmed <br /> <br />Part II: Forensic Analysis of selected SCS TR-213 crop growth stage coefficients (begins on p.4) <br />• The source of SCS TR-21 crop growth stage coefficients are data published in ARS 12754 <br /> <br />• SCS TR-21 crop growth stage coefficients for “Pasture Grasses” may better describe a “lawn” <br />type grass, or Kentucky Bluegrass, at or near sea level (see pp.6-9) <br /> <br /> <br />Part III: Evaluation of “upper plains” calibrated coefficients in Task Memo 59.15 (begins on p.20) <br />• While the methodology in Task Memo 59.1 for a local calibration may be appropriate, the <br />published upper plains coefficients for “Pasture Grasses” are suspect to error and should not be <br />relied upon6 (see pp.22-23) <br /> <br />1 Perry Park Water & Sanitation District, Case No. 10CW263, Water Division 1 <br />2 Pochop , et al. (1984), herein referred to as “Pochop” <br />3 USDA-SCS (1967), rev. 1970 <br />4 Blaney and Criddle (1962) 5 Wilson, et al. (2005) 6 Testimony (deposition) from Ray Alvarado, Project Manager of SPDSS, in Case No. 10CW263 confirmed that the coefficients <br />should not be relied upon in a legal proceeding and noted that the disclaimer inTM59.1 (p.1) states the same