Quantification and simulation of surface runoff from fescue grassland watersheds
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Authors: D. S. Chanasyk, E. Mapfumo, and W. Willms
Date: 2003
Journal: Agricultural Water Management
Volume: 59
Number: 2
Pages: 137-153
Summary of Methods: Surface runoff and soil erosion, as well as non-point source (NPS) pollutants carried with them, are a concern in watershed management. A study was conducted at Agriculture Canada Stavely Range Substation, located approximately 100 km south of Calgary, to determine runoff and soil loss from fescue grassland watersheds under three grazing intensities; ungrazed (control), heavy (2.4 AUM haâ»Â¹) and very heavy (4.8 AUM haâ»Â¹). Three watersheds were carefully selected for similarities in slope, aspect, shape, area, and elevation. Actual runoff data was collected for 1998-2000 and total surface runoff, due to snow melt, was measured in March of 2000. The SWAT model was calibrated from 1998 runoff with adjustments made to simulate observed surface runoff. The SWAT model was then evaluated using observed climatological data; daily air temperature, solar radiation, precipitation and runoff data, as well as soils, land use, and vegetation data. SWAT model was used to calculate surface runoff for 1999 and 2000.
Article Summary / Main Points: Surface runoff over the entire study period was very small when compared to total precipitation. Surface runoff hydrographs indicated larger summer storm runoff for heavy grazed sites and larger snow-melt runoffs for heavily grazed sites. In all three years, the average rainfall runoff was less than 10 percent of the average daily precipitation for all three grazing intensities. Runoff due to snow melt resulted in 0.07 mm, 8.5 mm, and 3.7 mm for ungrazed, heavily grazed, and severely grazed watersheds, respectively accounting for 78, 96, and 92 percent of the total annual runoff from ungrazed, heavy, and severely grazed watersheds respectively. The Soil Water Assessment Tool (SWAT) under-predicted surface runoff in both years (1999 and 2000).
Vegetation Types: All Grasslands
MLRA Ecoregions: Not Applicable
Agrovoc Control Words: Grazing Rangelands Watersheds
Article Review Type: Peer Reviewed
Article Type: Experimental Research
Keywords: grazing, surface runoff, watershed, statistical evaluation, soil water assessment tool (swat), snow
Annotation: The SWAT model under predicted the runoff despite being calibrated. Other studies have found the use of SWAT model to be inadequate with severe snow-melt and are better suited for longer simulation periods (Peterson and Hamlett, 1998). Others suggest instability can be linked to model interactions with extreme low flow conditions (Shirmohammadi et al 2001). Testing of the model with larger datasets is needed.
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