Skip Links

USGS - science for a changing world

Scientific Investigations Report 2009–5126

National Water-Quality Assessment (NAWQA) Program

Identifying Hydrologic Processes in Agricultural Watersheds Using Precipitation-Runoff Models

By Joshua I. Linard, David M. Wolock, Richard M.T. Webb, and
Michael E. Wieczorek

Abstract

Thumbnail of and link to report PDF (1.57 MB)

Understanding the fate and transport of agricultural chemicals applied to agricultural fields will assist in designing the most effective strategies to prevent water-quality impairments. At a watershed scale, the processes controlling the fate and transport of agricultural chemicals are generally understood only conceptually. To examine the applicability of conceptual models to the processes actually occurring, two precipitation-runoff models—the Soil and Water Assessment Tool (SWAT) and the Water, Energy, and Biogeochemical Model (WEBMOD)—were applied in different agricultural settings of the contiguous United States. Each model, through different physical processes, simulated the transport of water to a stream from the surface, the unsaturated zone, and the saturated zone. Models were calibrated for watersheds in Maryland, Indiana, and Nebraska. The calibrated sets of input parameters for each model at each watershed are discussed, and the criteria used to validate the models are explained.

The SWAT and WEBMOD model results at each watershed conformed to each other and to the processes identified in each watershed’s conceptual hydrology. In Maryland the conceptual understanding of the hydrology indicated groundwater flow was the largest annual source of streamflow; the simulation results for the validation period confirm this. The dominant source of water to the Indiana watershed was thought to be tile drains. Although tile drains were not explicitly simulated in the SWAT model, a large component of streamflow was received from lateral flow, which could be attributed to tile drains. Being able to explicitly account for tile drains, WEBMOD indicated water from tile drains constituted most of the annual streamflow in the Indiana watershed. The Nebraska models indicated annual streamflow was composed primarily of perennial groundwater flow and infiltration-excess runoff, which conformed to the conceptual hydrology developed for that watershed. The hydrologic processes represented in the parameter sets resulting from each model were comparable at individual watersheds, but varied between watersheds. The models were unable to show, however, whether hydrologic processes other than those included in the original conceptual models were major contributors to streamflow. Supplemental simulations of agricultural chemical transport could improve the ability to assess conceptual models.

First posted July 8, 2009

For additional information contact:

Director,
USGS Colorado Water Science Center
Box 25046, MS 415
Denver, CO 80225

Or visit the Colorado Water Science
Center Web site at:
http://co.water.usgs.gov/

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.


Suggested citation:

Linard, J.I., Wolock, D.M., Webb, R.M.T., and Wieczorek, M.E., 2009, Identifying hydrologic processes in agricultural watersheds using precipitation-runoff models: U.S. Geological Survey Scientific Investigations Report 2009–5126, 22 p.



Contents

Abstract

Introduction

Purpose and Scope

Precipitation-Runoff Models

Methods

Performance of the Models

Performance of Initial Models

Performance of Calibrated Models

The Maryland Watershed

The Indiana Watershed

The Nebraska Watershed

Hydrologic Processes in Agricultural Watersheds Identified Using Precipitation-Runoff Models

Limitations of Study and Needs for Future Research

Summary and Conclusions

References Cited


Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/sir/2009/5126/
Page Contact Information: GS Pubs Web Contact
Page Last Modified: Thursday, January 10, 2013, 07:32:27 PM