Agricultural Return Flow Dynamics on a Reach of the East River, Colorado, as Assessed by Mass Balance

Open-File Report 2024-1075
Prepared in cooperation with Upper Gunnison River Water Conservancy District
By:  and 

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Abstract

The U.S. Geological Survey, in cooperation with the Upper Gunnison River Water Conservancy District, studied historical streamflow in a reach of the East River, Colorado, to gain a preliminary understanding of return flow dynamics. Return flow is agricultural irrigation water that is not consumed by evapotranspiration and instead reaches streams by surface and subsurface flow paths. The study reach had a contributing area of 50 square miles and contained 5.23 square miles of pastures irrigated with water diverted from the East River and its tributaries. By comparing upstream inflows to downstream outflows, the net water balance of the study reach from 1994 to 2023 was assessed.

Two general hydrologic conditions for the study reach were identified. One hydrologic condition was characterized by a net loss or consumption of water, termed here as general deficit. This general deficit condition extended about 16 years, from 1997 to 2012. During general deficit years, there was usually a notable net loss of streamflow from April through July, and a small net gain, possibly related to return flows, occurred in August about 75 days after the minimums for losses. The second hydrologic condition was characterized by a net gain of water, termed here as general surplus. This second condition extended about 10 years, from 2014 to 2023. During general surplus years, two separate transitions from net loss to net gain commonly occurred during June through August. Losses during general surplus years were smaller than losses during general deficit years, the respective gains were larger, and times between losses and gains were about 18 and 22 days.

Differences between the two hydrologic conditions could reflect interactions among irrigation water, available capacity to store additional shallow groundwater, and streamflow. However, deciphering the causes for the shifts between the two general hydrologic conditions was beyond the scope of this report.

Suggested Citation

Bern, C.R., and Gidley, R.G., 2024, Agricultural return flow dynamics on a reach of the East River, Colorado, as assessed by mass balance: U.S. Geological Survey Open-File Report 2024–1075, 10 p., https://doi.org/10.3133/ofr20241075.

ISSN: 2331-1258 (online)

Study Area

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Table of Contents

  • Abstract
  • Introduction
  • Methods
  • Agricultural Return Flow Dynamics
  • Summary
  • Acknowledgments
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Agricultural return flow dynamics on a reach of the East River, Colorado, as assessed by mass balance
Series title Open-File Report
Series number 2024-1075
DOI 10.3133/ofr20241075
Year Published 2024
Language English
Publisher U.S. Geological Survey
Publisher location Reston VA
Contributing office(s) Colorado Water Science Center
Description Report: iv, 10 p.; Database
Country United states
State Colorado
Other Geospatial East River basin
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details