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Exploring the Extent of Artificial Agricultural Drainage using GIS Tools (Soil and Water Conservation Society)
Citation:
Christensen, J. Exploring the Extent of Artificial Agricultural Drainage using GIS Tools (Soil and Water Conservation Society). 2019 Annual Conference of the Soil and Water Conservation Society, Pittsburgh, PA, July 28, 2019.
Impact/Purpose:
Artificially draining agricultural lands through ditches and pipes is an important management tool for farmers but drainage may also lead to poor water quality downstream. Despite its importance, where drainage has occurred is poorly known. I used soil data, land use and crop productivity data to estimate drained lands and compared it to county level census estimates. I estimate that more than 30.5 million hectares are drained and found good agreement with census estimates (R-squared of 0.88). These results which are also summarized at the 12-digit HUC can be used to inform water quality models and aid water quality managers as they tackle eutrophication concerns.
Description:
Artificial agricultural drainage (i.e. surface ditches or subsurface tile) is an important agricultural management tool that allows for timely fieldwork and adequate root aeration allowing for higher crop yields. This practice is widespread throughout many regions of the United States, especially in flat, poorly-drained yet fertile regions like the glaciated Midwest. While beneficial for crop yields, agricultural drains can also alter watershed storage and hydrology and increase conveyance of nutrients into natural water bodies. Despite the importance of drainage to agricultural production and water quality, the spatial extent of artificial agricultural drainage is poorly known. Data from the agricultural census, soil surveys, crop productivity indices and crop-specific land cover were used to create estimates of potential agricultural drainage across the United States, with a focus on the eastern two-thirds of the contiguous US. Estimated agricultural drainage extent is likely across over 30 million hectares of agricultural land, covering greater than 80% of available land for 164 12-digit HUCs. Agricultural drainage is widespread in the upper Midwest Corn Belt as well as in other concentrated areas in the Mississippi Alluvial Valley and the Carolina Coastal Plain. When summarized at the county scale, GIS estimates align well with county census data. Estimated drainage values for numerous counties indicate that even moderately well drained soils are subject to artificial drainage in some portions of the country. Overestimations of GIS drainage estimates were present in areas that are dominated by crops other than corn/soybean or have specific geological features that discourage widespread adoption of drainage practices. The use of GIS tools to provide spatial estimates of artificial drainage is promising and can be used to support agricultural, hydrological and nutrient modeling within agricultural watersheds.
