Water Model for Ark Basin Promoted

(March 10, 2006, as appeared in the Pueblo Chieftain)

A computer model to predict water quality changes from agricultural efficiency, urban water transfers and tamarisk removal is being refined and almost at the point where it can be applied to real-world decisions.

“This will allow us as a basin to look at not only the impact on flows in the river, but the quality of those flows as well,” said Tim Gates, Colorado State University professor of civil engineering.

Gates detailed the results of his ongoing study of salinity and water tables at the Southeastern Colorado Water Conservancy District’s Second Annual Water Users Meeting Thursday. About 80 people attended the meeting to learn more about research programs and projects the district is involved in.

Gates’ study of more than 250,000 irrigated acres of farmland is funded in part by the Southeastern District and Lower Arkansas Valley Water Conservancy District.

Gates began the study in 1998 to look at irrigation practices in the Lower Arkansas Valley. About 230 wells have been monitored along with surface water and soil testing. Over time, the study has been expanded to look at ways to improve agricultural efficiency and water quality on a regional scale.

The study also was expanded to look at impacts on the entire basin, which faces issues from salinity and selenium. Salinity refers to the amount of dissolved solids in the water, which increases with return flows east of Pueblo. Selenium is an element that leaches into the river as water flows over natural formations.

Preliminary findings include:

• More efficient irrigation techniques could lower water tables and salinity, increasing crop yields by at least 10 percent.
• Overall salinity loading in the Arkansas River could be reduced by 40 percent.

Water tables in the valley were high in the late 1990s, and began dropping during the drought of 2002, but not significantly. It’s rising again as the area slowly recovers from drought, Gates said.

The high water tables are actually a source of water loss, Gates explained.

With high water tables, water wicks to the surface and evaporates, soil salinity increases, crop yields drop and the water supply on nonproductive land for invasive species like tamarisk (also called salt cedar) increases.

“We’re seeing a sizeable impact of salinity on crop production,” Gates said.

This year, Gates is planning to do large-scale tests of polyacrylamide, or PAM, in three canal systems to measure the impact on reducing seepage. The tests on 5- to 20-mile stretches of canals will be the first large-scale experiment with the technique where baseline conditions can be compared.

“What we’re hoping to find is the right timing of application on the scale of a canal,” Gates said.

Lowered water tables would mean increased water in the river, helping to satisfy downstream demands and Colorado’s Arkansas River Compact obligations.

Tamarisk removal and agricultural techniques like drip irrigation would also increase the water supply in the river, Gates said.

Gates said water savings would raise other questions that need to be studied:

• Are options available to hold high-quality water in Lake Pueblo, while releasing water to mimic historic flows?
• How would proposed water leases and exchanges affect return flows and water quality?
• How would major changes on the river like the Southern Delivery System and the Preferred Storage Options Plan affect flows, timing and water quality?
• How would recovering “liberated” water affect the river?

Gates said more study is needed to answer those questions. He said he is working with state officials to coordinate his efforts with developing basin-wide water management databases. He also is relaying the results of the study to various farmers, ditch companies and agencies cooperating in the study.

Other speakers:

Water Division 2 Engineer Steve Witte reviewed the history of the winter water storage plan, which began 20 years ago and is now governed by a court decree. About 100,000 acre-feet of winter water has been stored this year, slightly less than last year and well below the long-term average.

Kevin Meador of Black & Veatch Engineering reviewed progress on the Arkansas River Conduit, a $300 million drinking water pipeline that will serve 42 communities and 50,000 people east of Pueblo.

Jean Van Pelt, Southeastern conservation outreach coordinator, talked about the district’s Water Wise Web site.

Donald Frick, water resource engineer for the Applegate Group, talked about using geographic information systems to map water rights.

Copyright 2006, Pueblo Chieftain