This map identifies the potential suitability of land in the Upper Midwestern United States for subirrigation. Data sources are the 2018 gSSURGO data from the United States Department of Agriculture Natural Resources Conservation Service and the 2011 National Land Cover Database. Field assessment of any site is needed when evaluating a potential project.
The map layers can be accessed in three ways:
- The online tool at https://transformingdrainage.org/tools/subirrigation-suitability-tool/
- Downloadable data by state for those interesetd in conducting their own analyses, at https://purr.purdue.edu/publications/3263/1
- REST map service at https://mapsweb.lib.purdue.edu/arcgis/rest/services, under the "Ag" folder.
Specific criteria are explained below, and in the related publication Feng, Y., Frankenberger, J., Ackerson, J., and Reinhart, B., Transactions of the ASABE. In Review.
Suitability Criteria Used
Flat topography: To maintain a uniform depth from the surface to the water table, the surface topography should be nearly level to avoid excessive variation of the depth to water table, which increases the cost of the practice. 1% and 2% were used to define the slop suitability criterion in this study.
Hydraulic conductivity: Rapid horizontal conductivity allows the tile drains to be at economical (i.e. wide) spacing and still maintain the water table during periods of high evapotranspiration. The hydraulic conductivity criterion rated soils as suitable if the average hydraulic conductivity between 20 and 40 inches depth was greater than 1 foot/day (0.5 inch/hour).
Restrictive layer: The soil must have a restrictive layer that limits deep seepage losses and allows the water table to be maintained at the desired depth, but this information is not directly available from SSURGO. Drainage class was used as a proxy for depth to restrictive layer. Drainage classes of poorly and very poorly drained were considered highly suitable, and somewhat poorly drained soils were partially suitable. In addition, subirrigation is only beneficial on soils that have or would benefit from subsurface drainage, and this is also assessed using drainage class criteria.
Onsite investigations would be required to determine the feasibility of implementing subirrigation at any specific site, and this analysis identified areas where such investigations should be directed, to be most likely to identify suitable locations. Conversely it may help save time and money by showing where subirrigation is not likely to be successful. Agronomic and economic feasibility, as well as the availability of a water source (groundwater or surface water) and suitable outlet also need to be considered in site-specific feasibility analysis.
This suitability analysis used the most appropriate data that was widely available, but there are limitations with this approach. One is that although the presence of a water -restricting soil layer is a key requirement for land to be suitable for subirrigation, SSURGO data does not provide information on restrictive layers below the soil profile and therefore an indirect indicator, drainage class, was used for this criterion.