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 2 of 22
In Water Divisions on the West Slope (Divisions 4, 5, 6, and 7), PCU estimates were made for
the CDSS based on the SCS Blaney-Criddle method as outlined in SCS TR-21. CDSS estimates
of PCU in the Gunnison River Basin (Water Division 4) have been further refined through use of
high altitude coefficients, derived from lysimeter studies, for a monthly form of the original
Blaney-Criddle method. For the incorporation of Rio Grande Basin (Water Division 3) in the
CDSS, PCU estimates were prepared through 1) application of a Modified Hargreaves approach
in recent years (typically 1980-1998) in which temperature, wind and radiation data were
available to allow the calculation, 2) application of the SCS TR21 Blaney-Criddle method using
temperature data for the same years, 3) development of adjustment factors to the SCS TR21
results consisting of the ratio of the estimated PCU based on the Modified Hargreaves to the
estimated PCU based on SCS TR21 method, and 4) application of those adjustment factors to
PCU values calculated for a long historic study period (i.e. 1950-1998) with SCS TR21 method.
This method employed for the Rio Grande Basin results in a form of "local calibration" of the
SCS TR21 method based on the more detailed PCU estimates derived from the Modified
Hargreaves method.
Task 58, of the SPDSS consumptive use tasks, was initially designed to research information that
would allow an understanding of consumptive use applications made in the SPDSS study area
for support (verification and comparison) of estimates to be developed for SPDSS. These
investigations have been expanded into methods employed
in other parts of the state. The purpose of this memo is to Table of Contents Page
Introduction 1
convey results of these investigations and lay a foundation Approach 3
for the upcoming 1) review of lysimeter studies in Task 59, Results 4
2) review of existing high altitude crop coefficients in Task Traditional Calculations 4
60, 3) review of methods to estimate the effectiveness of Other Methods 7
precipitation in Task 61, 4) develop a plan for coexistence State Statute Review 9
Lysimeter Data 10
of SPDSS consumptive use tools with other tools in the Climate Station Networks 12
South Platte study area in Task 62, and 5) perform Computer Models 12
calibration of PCU for the SPDSS study area in Task 73. Regional Studies 14
This memo describes the approach taken in our Summary/Conclusions 16
investigations and the results of our investigations of References 19
Appendix
consumptive use methods and applications employed in the
State.
The results section of this memorandum is divided into seven categories as follows:
1. Traditional Calculations. Summarizes methods historically used to calculate PCU in
Colorado.
2. Other Methods. Identifies methods that are gaining favor or being used in current analyses.
3. State Statute Review. Summarizes a review of Colorado State Statutes for defined use of
PCU methods.
4. Lysimeter Data. Identifies studies documenting lysimeter-measured PCU.
5. Climate Station Networks. Identifies climate stations that report PCU data on a daily basis.
6. Computer Models. Discusses models commonly used in Colorado to calculate PCU.
7. Regional Studies. Provides a review of previous PCU estimates.