Comparing Agricultural Conservation Planning Framework (ACPF) practice placements for runoff mitigation and controlled drainage among 32 watersheds representing Iowa landscapes

Authors: Tomer, Mark; Van Horn, Jessica; Porter, Sarah; James, David; NIEMI, JARAD - Iowa State University

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2019
Publication Date: 7/6/2020
Citation: Tomer, M.D., Van Horn, J.D., Porter, S.A., James, D.E., Niemi, J. 2020. Comparing Agricultural Conservation Planning Framework (ACPF) practice placements for runoff mitigation and controlled drainage among 32 watersheds representing Iowa landscapes. Journal of Soil and Water Conservation. 75(4):460-471. https://doi.org/10.2489/jswc.2020.00001.
DOI: https://doi.org/10.2489/jswc.2020.00001

Interpretive Summary: Precision conservation planning tools can use high-resolution data to identify conservation practice placement options for watershed improvement plans. Comparisons from using these planning tools across multiple watersheds could help to identify regional conservation strategies, which might help conservation action agencies target conservation programs more effectively. This study evaluated practice-placement options identified by the Agricultural Conservation Planning Framework (ACPF) ArcGIS® tools for four practices, including controlled drainage (CD), contour buffer strips (CBS), water and sediment control basins (WASCOBs), and grassed waterways (GWWs) across 32 headwater HUC12 watersheds in Iowa. The watersheds represented three Major Land Resource Areas (MLRAs) and four Agro-Hydrologic Landscape (AHL) classes. Differences among these classes were found that led to nuanced interpretations. The AHL classes captured differences in practice placement frequencies that could be attributed to slope steepness, but slope shape and convergence is also important in siting conservation practices and these were best captured by MLRA, which distinguishes Iowa landforms based on landscape age and stream dissection. Grassed waterway placements showed minor differences among MLRAs but also enabled guidance to better inform the choices that users must make when running the ACPF-GWW tool. Landscape classifications and precision planning tools could facilitate the development of effective regional conservation strategies, because results indicate densities at which different practices can be sited in different landform regions. This information is of greatest interest to those involved with conservation of agricultural watersheds from planning, policy and research perspectives.

Technical Abstract: Precision conservation planning tools can use high resolution data to identify conservation practice placement options for watershed improvement plans. Use of these tools across multiple watersheds could help to identify regional conservation strategies. This study evaluated practice-placement options, determined using the Agricultural Conservation Planning Framework (ACPF) ArcGIS® tools for controlled drainage (CD), contour buffer strips (CBS), water and sediment control basins (WASCOBs), and grassed waterways (GWWs) across 32 headwater HUC12 watersheds in Iowa. The watersheds represented three Major Land Resource Areas (MLRAs) and four Agro-Hydrologic Landscape (AHL) classes, with four watersheds randomly chosen from each of eight combined MLRA-AHL landscape classes. Placement options for the practices were quantified by watersheds as densities (km km-2 of cropland) of GWWs, counts of proposed practice locations per km2 for CBS and WASCOBs, and as fractions of tile drained land for CD. The influence of landscape-region classes on practice-placement densities among watersheds was tested using analysis of variance and contrast comparisons. Significant differences were found that led to nuanced interpretations. Differences attributed to slope steepness were captured by AHL classes, while differences attributed to slope shape and convergence were best captured by MLRA, which better separated landforms based on landscape age and stream dissection. Grassed waterway placements showed minor differences among MLRAs but provided data to better inform the choices that ACPF users can make when running the GWW tool. The MLRA/AHL landscape classifications could be used together to develop effective regional conservation strategies using precision planning tools.