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ARS Home » Southeast Area » Tifton, Georgia » Southeast Watershed Research » Research » Publications at this Location » Publication #267418
Title: Rainfall Intensity Effects on Runoff and Sediment Losses From a Colorado Alfisol

Author
item Truman, Clinton
item Ascough Ii, James
item DAVIS, JESSICA - Colorado State University

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: 6/17/2011
Publication Date: 9/15/2011
Citation: Truman, C.C., Ascough II, J.C., Davis, J. 2011. Rainfall Intensity Effects on Runoff and Sediment Losses From a Colorado Alfisol. In: Ascough II, J.C. and Flanagan, D.C. (eds.), Proceedings of the International Symposium on Erosion and Landscape Evolution (ISELE), September 18-21, 2011, Anchorage, Alaska. American Society of Agricultural and Biological Engineers Publication No. 711P0311, St. Joseph, MI, p. 44. (Refereed Symposium Proceedings.) http://elibrary.asabe.org/azdez.asp?earch=1&JID=1&AID=39244&CID=isel2011&v=&i=&%-2&url.

Interpretive Summary: For the Front Range region of Colorado, quantifying rainfall partitioning under current and/or proposed farming practices and changing precipitation patterns is the first step to understanding how to efficiently conserve water and soil resources to meet crop water demands. We hypothesize that quantifying runoff, sediment, and agrichemical losses would be improved if rainfall intensity patterns derived from natural rainfall were used in rainfall simulations to evaluate runoff and sediment losses from intensively cropped Alifsols in the north-central region of Colorado. Our objective was to quantify effects of constant (Ic) and more realistic, observed variable rainfall intensity (Iv) patterns on runoff (R) and sediment (E) losses from a Fort Collins sandy clay loam cropped to conventional-till corn. Five intensity patterns were evaluated: 3 Ic patterns (20, 47, and 65 mm/h) and 2 Iv patterns representing the most frequent (Ivf) and most extreme (Ive) events occurring in the region. Field plots, 2 m wide by 3 m long, were established for each treatment, and each received simulated rainfall (Ic or Iv) for 60 min. For Ic events, increasing Ic 2.3-fold (20.3 vs. 47.3 mm/h) and 1.4-fold (47.3 vs. 65 mm/h) increased runoff 5.9- and 2.4-fold; sediment 4.9- and 4.1-fold; Rmax 5.8- and 1.9-fold; and Emax 3.1- and 3.9-fold, respectively. For Ivf vs. Ic (20 mm/h), runoff, Rmax, and sediment losses were similar. However, Emax values for Ivf events were 33% less than those for Ic events. Also, tRmax and tEmax for Ivf events were 40- and 33-min earlier than those for Ic (20 mm/h) events. For Ive vs. Ic (65 mm/h) events, runoff losses were similar. However, Ive events had 1.7-fold more sediment, 28% higher Rmax, and 2.9-fold higher Emax losses than those for Ic (65 mm/h) events. Also, tRmax and tEmax for Ive events were 32- and 28-min earlier than those for Ic (65 mm/h) events. For Ivf vs. Ive events, runoff, Rmax, sediment, and Emax values for Ive events were 11.7-, 16.1-, 36-, and 48-fold greater than corresponding values for Ivf events, respectively. Surface sealing increased 19-fold as Ic increased 3.3-fold. The Iv patterns had at least 52% more surface sealing than corresponding Ic patterns; Ive events had 3.1-fold more surface sealing than Ivf events. Our results show the pronounced effect of rainfall intensity patterns, particularly Iv patterns, runoff and sediment losses. A more accurate measure of rainfall partitioning, soil detachment, and sediment transport was obtained when Iv patterns derived from natural rainfall were utilized and evaluated.

Technical Abstract: For the Front Range region of Colorado, quantifying rainfall partitioning under current and/or proposed farming practices and changing precipitation patterns is the first step to understanding how to efficiently conserve water and soil resources to meet crop water demands. We quantified the effects of constant (Ic) and more realistic, observed variable rainfall intensity (Iv) patterns on runoff (R) and sediment (E) losses from a Fort Collins sandy clay loam cropped to conventional-till corn. We evaluated three Ic patterns (20, 47, and 65 mm/h) and 2 Iv patterns representing the most frequent (Ivf) and most extreme (Ive) events occurring in the region. Field plots, 2 m wide by 3 m long, were established for each treatment, and each received simulated rainfall (Ic or Iv) for 60 min. For Ic events, increasing Ic 2.3-fold (20.3 vs. 47.3 mm/h) and 1.4-fold (47.3 vs. 65 mm/h) increased runoff 5.9- and 2.4-fold; sediment 4.9- and 4.1-fold; Rmax 5.8- and 1.9-fold; and Emax 3.1- and 3.9-fold, respectively. For Ivf vs. Ic (20 mm/h), Emax values for Ivf events were 33% less than those for Ic events. Also, tRmax and tEmax for Ivf events were 40- and 33-min earlier than those for Ic (20 mm/h) events. For Ive vs. Ic (65 mm/h) events, Ive events had 1.7-fold more sediment, 28% higher Rmax, and 2.9-fold higher Emax losses than those for Ic (65 mm/h) events. Also, tRmax and tEmax for Ive events were 32- and 28-min earlier than those for Ic (65 mm/h) events. For Ivf vs. Ive events, runoff, Rmax, sediment, and Emax values for Ive events were 11.7-, 16.1-, 36-, and 48-fold greater than corresponding values for Ivf events, respectively. Surface sealing increased 19-fold as Ic increased 3.3-fold. The Iv patterns had at least 52% more surface sealing than corresponding Ic patterns; Ive events had 3.1-fold more surface sealing than Ivf events. Our results show the pronounced effect of rainfall intensity patterns, particularly Iv patterns, runoff and sediment losses. A more accurate measure of rainfall partitioning, soil detachment, and sediment transport was obtained when Iv patterns derived from natural rainfall were utilized and evaluated.