Separating preferential and matrix flows using subsurface tile flow data¹

Journal Paper No. J‐15847 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 2988. This work was supported in part by the Iowa Department of Natural Resources, U.S. Environmental Protection Agency, and The MSEA project funded by the USDA‐CSRS.

Abstract

Preferential flow is primary mechanism for faster movement of agricultural chemicals to groundwater. Subsurface tile flow data were used to quantify the contributions of preferential flow and matrix flow at the field scale over time. Tile flow hydrographs were constructed using hourly tile flow data related to rainfall events that were equal to or greater than 25.4 mm. A hydrograph separation technique was applied to separate preferential and matrix flow components of the subsurface tile flows. On the average, preferential flow was found to contribute about 13% of the total subsurface tile outflow for all the rain events, and an annual contribution of 10–20% is reasonable approximation. However, considerable spatial and temporal variability was observed, even among contiguous plots. Preferential flow for some rain storms was found to be as high as 60% of the total subsurface tile flow. This study also indicated that for storms greater than or equal to 25.4 mm, the subsurface tile outflow, on the average, was about 16% of the total rain water. However, it was observed that some of the subsurface tiles could drain as much as 80% of the rainfall depending upon the initial water table and soil moisture conditions.

Key words:

• Macropore
• preferential flow
• subsurface drain flows

Notes

Journal Paper No. J‐15847 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 2988. This work was supported in part by the Iowa Department of Natural Resources, U.S. Environmental Protection Agency, and The MSEA project funded by the USDA‐CSRS.