Two-stage Agricultural Channels in Iowa's Drained Landsape to Improve Water Quality and Long-term Resilience

Issue

Iowa’s landscape consists of a dense network of constructed drainage ditches throughout farmlands and along roadways. The trapezoidal “one-stage” design lowers water tables and efficiently routes stormflow downstream, which supports food production and ensures public safety. Two-stage channels are a modification of this design where inset floodplains are constructed with a width that is three times the baseflow channel. This design increases conveyance capacity, reduces in-channel flow velocities during storms, and decreases erosion of channel banks. During storms, suspended organic-rich sediment and attached nutrients or pollutants accumulate in the vegetated floodplain. Phosphorus deposition and enhanced microbial removal of nitrogen via denitrification in these floodplains are important but not well constrained nutrient retention pathways that our project will evaluate.

Objective

In partnership with Polk County Conservation and JEO Consulting, we will collaboratively design and assess the effectiveness of a two-stage ditch constructed to improve water quality of agricultural drainage in Drainage District (DD) 4. Our long-term goal is to inform design, construction, and maintenance of the expansive network of ditches throughout Iowa and the Midwest. 

Approach

Our diverse team includes applied scientists and engineers at ISU and the University of Iowa, conservation professionals at Polk County Conservation and engineering designers at JEO Consulting. We will collaboratively design and assess the effectiveness of a two-stage channel constructed to improve water quality of agricultural drainage near Chichaqua Bottoms Wildlife area using a Before-After-Control-Impact (BACI) experimental design. In this research, we focus on the two-stage channel as a water quality practice and will measure geomorphic, water quality, vegetation and stability factors before and after construction of two-stage channel comparing them to conventional one-stage channels. Our integrated design, monitoring, and modeling approach will build on knowledge of similar practices throughout the Midwest and combine this with newly collected information to inform siting and decision-making approaches in Iowa.