Thesis
Flood mitigation and nutrient reduction benefits of flood control wetlands
University of Iowa
Master of Science (MS), University of Iowa
Spring 2021
DOI: 10.17077/etd.005846
Abstract
In this study, we investigated the potential peak flow and nitrate reduction benefits of a recently constructed flood control wetland using a PCSWMM model. The predicted peak flow reductions for the NRCS type A and type D design storms, for the 2-, 5-, 10-, 25-, 50-, 100- and 500-year return periods, were 15-26% and 9.6-17%, respectively. The wetland storage volume (130.4 ac-ft) above the pool level provided ample peak flow mitigation benefit for all scenarios, including the 500-year type A storm with the maximum simulated inflow of 79.3 m3s-1 predicted to decrease to 60.6 m3s-1, a 23.6% reduction. In contrast, a smaller wetland in the same watershed predicted only a 0.9% reduction for the 500-year type A storm. This smaller wetland did not have sufficient storage to provide attenuation for all storms, while the wetland of interest did. Nitrate sensor data (R2 > 0.8 compared to grab samples) was inserted into the model and used to predict a concentration reduction between 9.7 and 68% for decay coefficients between 4x10-6 and 8x10-5 hr-1. Holding the decay coefficient constant at 5.5x10-5 h-1, a baseflow of zero m3s-1 showed a 60% predicted nitrate concentration reduction while the maximum simulated baseflow (0.5 m3s-1) produced a 27% predicted reduction. Our predicted nitrate reduction range was consistent with removals cited in the Iowa Nutrient Reduction Strategy (11 to 92%) for wetland to subcatchment area ratios between 0.5 and 2%. The Strategy states an average area ratio of 0.78% will provide an average nitrate concentration reduction of 52%. The area ratio for the wetland in this study was 0.95%, which suggests the predicted maximum nitrate concentration reduction of 68% is likely to be achieved after the wetland is fully mature.
Details
- Title: Subtitle
- Flood mitigation and nutrient reduction benefits of flood control wetlands
- Creators
- Ashley J Knudson
- Contributors
- Craig Just (Advisor)Bongchul Seo (Committee Member)Corey Markfort (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Civil and Environmental Engineering
- Date degree season
- Spring 2021
- DOI
- 10.17077/etd.005846
- Publisher
- University of Iowa
- Number of pages
- xii, 80 pages
- Copyright
- Copyright 2021 Ashley J. Knudson
- Comment
- This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/
- Language
- English
- Description illustrations
- color illustrations, color maps
- Description bibliographic
- Includes bibliographical references (pages 76-80)
- Public Abstract (ETD)
Iowa’s landscape was historically very diverse, including prairie, woodland, and wetlands. Now, with the advent of modern agriculture, over 90% of land in Iowa is agricultural. This change has worsened environmental and health issues, from extreme flooding to unsafe drinking water to algal blooms closing beaches. To help improve some of these problems, there is growing interest in constructing flood control wetlands in agricultural settings. Wetlands are well known for their ability to reduce nutrients, like nitrate, that runoff from fertilizer. These flood control wetlands are specifically designed to not only treat runoff but also have increased water storage capacity, so they slow the water and reduce flooding during storms. In this study, we built a model to investigate the nitrate reduction and flood mitigation of a flood control wetland being constructed in Eastern Iowa. The model showed the wetland was effective at reducing peak flow for design storms, including up to the 500-year return period storm, and for both high and low intensity storms events. The wetland also has high potential to reduce nitrate concentration, up to 68% reduction. Flood control wetlands can be a part solving many of Iowa’s water-related challenges.
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984097276402771
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