BOARD00637

• Board Meeting Date: 1/25/2005
• Description: Flood Section and WSP Section - Bureau of Reclamation Colorado Snowpack Estimation Project for Colorado's Major River Basins, Informational Presentation
• Board Meetings - Doc Type: Memo

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STATE OF COLORADO

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Colorado Water Conservation Board

Department of Natural Resources
13 13 Sherman Street, Room 721
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
www.cwcb.state.co.lls

MEMORANDUM

Bill Owens
Governor

To:
From:

Colorado Water Conservation Board Members
Larry Lang, Chief, Flood Protection Program
Joe Busto, Flood Protection Program & Weather Modification Program
Michelle Garrison, Water Supply Protection Program
January 11,2005
Agenda Item 6: Bureau of Reclamation Colorado Snowpack Estimation
Project for Colorado's Major River Basins; Informational presentation

Russell George
Executive Director

Rod Kuharich
CWCB Director

Date:
Re:

Dan McAuliffe
Deputy Director

Background

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The CWCB chairs both the Drought and Flood Task Forces and desires improved forecasts of timing and
volume of stream flows from snowmelt in Colorado's Rivers, for both water supply and flooding issues.
A major limitation in these forecasts has been a lack of detailed knowledge of the spatial and temporal
evolution of the snowpack's snow water equivalent (SWE) in the mountains_ In June 2004 the CWCB
contracted with the U.S. Bureau of Reclamation (USBR) to develop a spatial snowpack assessment
project to benefit water management in Colorado.

Project Overview

Snowfall monitoring and flood warning systems have traditionally relied on precipitation gauges to
measure precipitation. There are several difficulties with precipitation gauges:
. Both rainfall and snowfall gauges provide sparsely distributed point measurements that may not
accurately reflect actual conditions across entire basins, particularly in mountainous areas.
. Snowfall gauges (SNOTEL and snow course) are very few in number.
. It is difficult to measure snow versus rain.
. Even if snowfall is accurately measured, it is still a challenge to track melt and sublimation of the
snowpack and its SWE.

Data sparseness leads to coarse and sometimes erroneous spring snowmelt and runoff forecasts. Since
snowmelt contributes, on average, around 80% of water storage in Western reservoirs, such forecasts can
be very problematic for water management. Not knowing how much snowmelt will enter the reservoirs
can lead to inappropriate releases of water from dams, causing floods or reduced conservation pool
storage and water delivery (volumes).

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The Snow Data Assimilation System (SNODAS) is a recent model operated by the National Operational
Hydrologic Remote Sensing Center (NOHRSC). It incorporates SNOTEL and snow course data, satellite
data, radar data and a numerical weather model to estimate snowpack spatially at a I-kIn resolution for the

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