Temporal trends in amount and placement of conservation practices in the South Fork of the Iowa River watershed

Authors: Moorman, Thomas; James, David; Van Horn, Jessica; Porter, Sarah; Tomer, Mark

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2019
Publication Date: 5/12/2020
Citation: Moorman, T.B., James, D.E., Van Horn, J.D., Porter, S.A., Tomer, M.D. 2020. Temporal trends in amount and placement of conservation practices in the South Fork of the Iowa River watershed. Journal of Soil and Water Conservation. 75(3):245-253. https://doi.org/10.2489/jswc.75.3.245.
DOI: https://doi.org/10.2489/jswc.75.3.245

Interpretive Summary: There is interest in assessing the effectiveness of conservation practices on water quality. Conservation practices (CP) for erosion prevention include contour buffers, terraces, grassed waterways, water and sediment control basins and ponds. To assess the potential effectiveness of these practices we used GIS mapping techniques and aerial photography to document installation and removal of these practices from the 1930’s to 2016. The study was performed in the South Fork of the Iowa River in central Iowa as part of the Conservation Effects Assessment Program (CEAP). Installation of CP increased in each decade from the 1930’s to 2002 and then increased only slightly from 2002 to 2016. Grassed waterways were the most numerous and treated the largest area within the watershed. In the 1980’s through 2010 some grassed waterways were removed as water and sediment control basins were installed. The mean duration of grassed waterways was 21.5 years and the duration of WASCOBS averaged 24 years, suggesting that farmers are making long-term commitments to these CP. Different land areas were treated by these CP among the 8 HUC12 sub-watersheds. Treated areas tended to be greater in HUC12 sub-watersheds where erosion risk was greater. A comparison of the land areas treated by these CP tended to match areas identified for these CP by the Agricultural Conservation Planning Framework (ACPF) tool, although the ACPF tended to identify areas where additional CP could be installed. Mapping of conservation practices and the land areas treated illustrates some of the potential utility of these techniques at the watershed scale. These results inform local conservation practitioners, farmers, and policy analysts.

Technical Abstract: Conservation practices (CP) for erosion prevention include contour buffers, terraces, grassed waterways, water and sediment control basins and ponds. To assess the potential effectiveness of these practices we used GIS mapping techniques and aerial photography to document installation and removal of these practices from the 1930’s to 2016. The study was performed in the South Fork of the Iowa River in central Iowa as part of the Conservation Effects Assessment Program (CEAP). Installation of CP increased in each decade from the 1930’s to 2002 and then increased only slightly from 2002 to 2016. Grassed waterways were the most numerous and treated the largest area within the watershed. In the 1980’s through 2010 some grassed waterways were removed as water and sediment control basins were installed. The mean duration of grassed waterways was 21.5 years and the duration of WASCOBS averaged 24 years, suggesting that farmers are making long-term commitments to these CP. Different land areas were treated by these CP among the 8 HUC12 sub-watersheds. Treated areas tended to be greater in HUC12 sub-watersheds where erosion risk was greater. A comparison of the land areas treated by these CP tended to match areas identified for these CP by the Agricultural Conservation Planning Framework (ACPF) tool, although the ACPF tended to identify areas where additional CP could be installed. Mapping of conservation practices and the land areas treated illustrates some of the potential utility of these techniques at the watershed scale.