BOARD00039 ‎(2)‎

• Board Meeting Date: 9/20/2006
• Description: WSP Section - Consumptive Uses and Losses and High-Altitude Crop Coefficients
• Board Meetings - Doc Type: Memo

Agenda Item 21
September 19-20, 2006 Board Meeting
Page 3 of6

.

MEMORANDUM

TO: Colorado Water Conservation Board Members

FROM: Ray Alvarado, Andy Moore
Water Supply Protection Section

DATE: July 10,2006

SUBJECT: Agenda Item 10, July 24-26, 2006 Board Meeting-
Consumptive Uses and Losses and High-Altitude Crop Coefficients

Introduction

Lysimeter studies have shown that at higher altitudes (e.g., greater than 6500 feet) pasture grass
consumes significantly more water than at lower altitudes. CWCB decision support system (DSS) staff
has utilized lysimeter-derived, high-altitude crop coefficients for calculating consumptive use (CU) in
appropriate areas in Colorado, using the StateCU model. The next step for staff is to work with the US
Bureau of Reclamation (USBR) in getting this methodology incorporated into their consumptive uses
and losses reporting.

.

Back!!:round

The modified Blaney-Criddle method, as outlined in the SCS publication Irrigation Water
Requirements Technical Release No. 21 (TR-2l), is commonly used for estimating CU in Colorado.
However, general crop coefficients from TR-2l may not be as accurate as locally calibrated crop
coefficients for more specific situations, such as for higher altitude irrigation.

DSS staff has progressively utilized locally calibrated crop coefficients for high-altitude CU
calculations in Colorado. The Upper Gunnison Water Conservancy District (UGWCD) has been using
StateCU, the DSS consumptive use model, to calculate depletions as part for their subordination
agreement with the USBR. Because of the operation of lysimeters in the upper Gunnison basin, the
UGWCD requested that locally calibrated crop coefficients from these lysimeters be available in
StateCU to more accurately reflect crop consumption in this area. After evaluation by the DSS staff,
these coefficients were added to StateCU. Additionally, in the development of the Rio Grande
Decision Support System (RGDSS), locally calibrated crop coefficients were used for calculating crop
CU.

.

For the South Platte Decision Support System (SPDSS), Leonard Rice Engineers (LRE) investigated
using locally calibrated Blaney-Criddle crop coefficients, as derived from lysimeters, for calculating
consumptive use. The following table is adapted from their SPDSS Task 59.1 memo from February

Flood Protection. Water Project Planning and Finance. Stream and Lake Protection
Water Supply Protection. Conservation Planning