Evaluating the Potential for Drainageways to Serve as Test Sites for Innovative Grass Waterway Designs

Date: 
Aug 2019

Issue

Grass waterways, a common conservation practice used to reduce gully erosion throughout much of Iowa, are typically located where surface runoff water is concentrated. They are often planted with sod-forming grasses to reduce runoff, sediment transport and gully formation by slowing water flow. As a surface erosion-prevention practice, the benefits of grass waterways are well understood. However, the subsurface characteristics and potential nutrient reduction benefits of these systems have not been well investigated. Schilling et al. (2013) noted that drainageways in the region are typically filled with organic-rich alluvium and post-settlement materials and have high water tables and anaerobic conditions that could serve as natural bioreactors for nitrogen (N) reduction. Most first-order drainageways are tile drained, a recommended grass waterway design practice as it prevents long-term buildup of excessive wetness, maintains the vegetative cover, prevents formation of gullies and facilitates accessibility of farm equipment into fields. However, tiling beneath drainageways results in groundwater nitrate-N concentrations bypassing denitrification hot spots, increasing nitrate-N export from the landscape.

Objective

Researchers will study the potential to alter drainageway tiles to reconnect upland groundwater with organic-rich drainageway deposits for N reduction, which could allow them to better function as “natural bioreactors” on the landscape. In many cases, drainage tiles are installed on the edges of and run parallel to grass waterways. At a concept scale, we believe that these tile drains could be reconfigured (similar to saturated buffer designs) to allow tile water to reconnect with the organic-rich waterway soils for N treatment. This project represents a first step toward developing a new grass waterway design by characterizing potential candidate sites for testing at the Kirkwood Community College farm in Cedar Rapids, Iowa, at the largest two-year agricultural department in the nation.

Approach

This project will:

  • use soil mapping and LiDAR, along with the Agricultural Conservation Planning Framework (ACPF) tool to identify current and potential grass waterways located at the Kirkwood farm;
  • characterize the alluvium contained within the grass waterways and collect soil samples to verify the characteristics of the deposits;
  • install shallow wells to document water table depths and biogeochemical conditions in the alluvium;
  • rank the suitability of the current and potential grass waterways to serve as a test site for evaluating new grass waterway designs; and
  • develop the conceptual design for a new grass waterway practice that could be installed and tested at Kirkwood starting in 2021.  
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