| Title: | Simulating hydrologic responses to alternate grazing management practices at the ranch and watershed scales |
| Authors: | Park, J.Y., S. Ale, W.R. Teague and S.L. Dowhower |
| Year: | 2017 |
| Journal: | Journal of Soil and Water Conservation |
| Volume (Issue): | 72(2) |
| Pages: | 102-121 |
| Article ID: | |
| DOI: | 10.2489/jswc.72.2.102 |
| URL (non-DOI journals): | |
| Model: | SWAT |
| Broad Application Category: | hydrologic only |
| Primary Application Category: | BMP and/or cropping system assessment |
| Secondary Application Category: | calibration, sensitivity, and/or uncertainty analysis |
| Watershed Description: | 763 km^2 Clear Creek, located in north central Texas, U.S. |
| Calibration Summary: | |
| Validation Summary: | |
| General Comments: | |
| Abstract: | Grazing management practices affect watershed hydrology by altering vegetation
cover and soil properties. Long-term success of grazing management depends on how
well increased forage harvest efficiency is balanced with the need to maintain soil aggregate
stability. The overall objective of this study was to assess the impacts of alternate grazing
management practices including the light continuous (LC), heavy continuous (HC), adaptive
multipaddock (MP) grazing, and no grazing (EX; exclosure) on hydrological processes at the
ranch and watershed scales in a rangeland-dominated (71% rangeland) Clear Creek watershed
(CCW) in north central Texas using the Soil and Water Assessment Tool (SWAT).
Measured data on vegetation, soil physical and hydrological properties, and grazing management
at four study ranches within the watershed (two under MP and one each under LC and
HC grazing management) were used to parameterize the SWAT model. The SWAT model
was calibrated and validated using the measured standing crop biomass and soil moisture data
at the study ranches, and streamflow data at the watershed outlet over a 34-year period from
1980 to 2013. At the ranch scale, when the management was changed from the baseline MP
grazing to HC grazing, the simulated average (1980 to 2013) annual surface runoff increased
within a range of 106% to 117% and water yield increased within a range of 39% to 53%.
While surface runoff was found to be a major contributor (52% to 67%) to streamflow under
the HC grazing, baseflow was the dominant (55% to 66%) component of streamflow under
the MP and EX practices. At the watershed scale, shifting grazing management from the
baseline HC grazing to the improved MP grazing decreased surface runoff by about 47%,
increased infiltration by 5%, and decreased streamflow by 29.5%. In addition, improvements
to grazing decreased the simulated highest annual streamflow over the 1980 to 2013 period
from 8.3 m3 s–1 ([293.1 ft3 sec–1] baseline scenario) to 6.2 m3 s–1 ([219 ft3
sec–1] MP grazing). This reduction in the maximum flow has a potential to reduce the risk of flooding downstream.
However, these hydrologic responses vary according to the extent of grazing lands in
a watershed. Overall, the MP grazing was found to be the best grazing management practice
in terms of water conservation, vegetation regrowth, and the potential to reduce flood risk. |
| Language: | English |
| Keywords: | continuous grazing, exclosure, multipaddock grazing, rangeland management, Soil and Water Assessment Tool (SWAT), water balances |