Effects of Spatial Distribution of Prairie Vegetation in an Agricultural Landscape on Curve Number Values

Abstract

The curve number (CN) method is used to calculate runoff in many hydrologic models, including the Soil and Water Assessment Tool (SWAT). The CN method does not account for the spatial distribution of land cover types, an important factor controlling runoff patterns. The objective of this study was to empirically derive CN values that reflect the strategic placement of native prairie vegetation (NPV) within row crop agricultural landscapes. CNs were derived using precipitation and runoff data from a seven‐year period for 14 small watersheds in Iowa. The watersheds were planted with varying amounts of NPV located in different watershed positions. The least squares and asymptotic least squares methods (LSM) were used to derive CNs using an initial abstraction coefficient (λ) of 0.2 and 0.05. The CNs were verified using leave‐one‐out cross‐validation and adjustment for antecedent moisture conditions (AMC) was tested. The asymptotic method produced CN values for watersheds with NPV treatment that were 8.9 and 14.7% lower than watersheds with 100% row crop at λ = 0.2 and λ = 0.05, respectively. The derived CNs produced Nash‐Sutcliffe efficiency values ranging from 0.4 to 0.7 during validation. Our analyses show the CNs verified best for the asymptotic LSM, when using λ of 0.05 and adjusting for AMC. Further, comparison of derived CNs against an area weighted CN indicated that the placement of vegetation does impact the CN value. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.

Projecting hydrologic change under land use and climate scenarios in an agricultural watershed using agent-based modeling

“…For agricultural land, CN values are set to 82 for 100% row crops, and 72 for the prairie strips conservation practice (10% native prairie strips, 90% row crops) based on values found by Dziubanski et al (2017). Urban areas are set to a CN of 90 [based on standard values for residential areas with lot sizes of 0.051 hectares or less, soil group C, USDA-Natural Resources Conservation Service (USDA-NRCS), 2004].…”

Linking economic and social factors to peak flows in an agricultural watershed using socio-hydrologic modeling

“…For the agricultural areas, empirically derived CN values (Dziubanski et al, 2017) are used for native prairie strips; a CN of 82 is used for 100 % row crop production; and a CN of 72 is used for the conservation option implemented by the farmer agents. Urban areas are set to a CN of 90 which is derived from the standard lookup tables for residential areas with lot sizes of 0.051 ha or less (soil group C; USDA-NRCS, 2004).…”

“…The conservation option implemented by farmer agents is native prairie strips, a practice in which prairie vegetation is planted in multiple strips perpendicular to the primary flow direction upland of and/or at the farm plot outlet (Dziubanski et al, 2017;Helmers et al, 2012;Zhou et al, 2010). Either 10 % or 20 % of the total field size is converted into native prairie vegetation under this practice.…”

Featured Series Conclusion: SWAT Applications for Emerging Hydrologic and Water Quality Challenges

“…(), Dziubanski et al . (), and Almendinger and Ulrich () continue to add to this existing body of knowledge, but the study by Hanson et al . () shows SWAT also can be used to understand the potential effect of natural gas development on the hydrology and water quality in a watershed.…”