BOARD02080

• Board Meeting Date: 7/25/2006
• Description: WSP Section - Consumptive Uses and Losses and High-Altitude Crop Coefficients
• Board Meetings - Doc Type: Memo

;

STATE OF COLORADO

Colorado Water Conservation Board

Department of Natural Resources
1313 Shennan Street, Room 721
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
www.cwcb.state.co.us

MEMORANDUM

Bill Owens
Governor

TO:

Colorado Water Conservation Board Members

Russell George
Executive Director

FROM:

Ray Alvarado, Andy Moore
Water Supply Protection Section

Rod Kuharich
eweB Director

Dan McAuliffe
Deputy Director

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 Iysimeter-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.

Backl!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-21 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 Iysimeters 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.

Colorado Water Conservation Board
Flood Protection. Water Supply Planning and Finance. Stream and Lake Protection
Water Supply Protection. Conservation and Drought Planning