SPDSS_Task58_Review Previous Estimates of Potential CU

• Title: SPDSS Task 58 - Review Previous Estimates of Potential CU
• Description: This memo reviews the methods used in the past to determine potential consumptive use.
• Decision Support - Doc Type: Task Memorandum
• Date: 8/5/2004
• DSS Category: Consumptive Use
• DSS: South Platte
• Basin: South Platte
• Contract/PO #: C153954
• Grant Type: Non-Reimbursable
• Bill Number: SB01-157, HB02-1152, SB03-110, HB04-1221, SB05-084, HB06-1313, SB07-122
• Prepared By: Leonard Rice Engineering

SPDSS Task 58 Memo
August 5, 2004
Page 14 of 22
pumping and supply data in SPGIS to determine CU impacts to the South Platte River. This tool
is available from http://www.ids.colostate.edu/index.html?/projects/idscu/.
IWR
Irrigation Water Requirements (IWR) is a Windows based crop consumptive use program
developed specifically for MRCS use in development of Consumptive Use Table for the new
MRCS Irrigation Guide. This program is available from the web site
http://www.wcc.nres.usda.~ov/nresirri /~ irrig-mkt-models.html. This program has seen extensive
use by the State Engineer's staff at the Division and main offices. Three consumptive use
methods are implemented in IWR: 1) Radiation Method developed by Doorenbos and Pruitt
(1977), 2) Temperature Method commonly referred to as the FAO-Blaney-Criddle method, and
3) SCS Blaney-Criddle Method as detailed in USDA-SCS TR21. The IWR program indicates an
elevation correction for SCS TR21 Blaney-Criddle is made based on 10% for each 1000 meters
above sea level (as recommended by W.O. Pruitt, one of the authors of the FAO document, and
others).
DWR TR21.xls
A spreadsheet model of the modified Blaney-Criddle Method was developed by Keith Vander
Horst of the State Engineers' Office and is in use by a number of the Division Engineers' Offices
as well as by SEO staff in Denver. In addition to the straight TR21 based calculation of
modified Blaney-Criddle estimates, the spreadsheet also allows a modified Blaney-Criddle
calculation with user inputted crop coefficients, with an altitude adjustment or a calculation of
lawn grass consumptive use based on the Pochop method (Pochop, Borelli, Burman, 1978). The
analysis allows for 12 months of climate data (usually average annual data entered). The default
altitude adjustment available in this spreadsheet is the same (10 percent for 1000 meters above
sea level) used in the IWR model though the user can enter a different altitude adjustment factor.
Ref-ET
Ref-ET was first created in 1990 by Dr. Rick Allen to serve as a companion computer program
to ASCE Manua170 (Jensen, 1990). This program provides computations of Reference
Evapotranspiration (ET) through methods such as FAO-56 Penman-Monteith, Standardized
ASCEPenrnan-Monteith or Hargreaves. This program is available for download from
http://www.kimberly.uidaho. edu/ref-et/.
The models briefly described above generally provide a reasonable basis for confirming many of
the new calculation processes for PCU to be implemented in SPDSS. For example, the IDSCU
and Ref-ET provide ET estimates for the Standardized ASCE P-M method that are basically
identical for a climate station on the lower South Platte. However, one should be cautious of
understanding the methods implemented in these models and check any new method
implemented in SPDSS between several models. An example of the need to exercise caution is
given the Hargreaves method implementation in IDSCU. Though the Hargreaves equations
appear to be properly implemented in IDSCU, the program allows one to apply alfalfa based