A process-based model for evaluating flood-reduction in the Clear Creek Watershed
Creators: name: Landsteiner, Samuel
Publisher: name: University of Iowa
Year: 2022
Subjects: Clear Creek
Flooding
Hydrologic Modeling
Iowa
Iowa Watershed Approach
public abstract
Hydrology
Hydraulic Engineering

description: Iowa’s agriculturally focused landscape, water resource management strategies, and changing climate attribute to a trend of increased flood risk across the state. Though the risk of severe flooding varies across different regions in Iowa, extreme flooding is likely to touch historically unaffected populations. The effects of extreme flooding are disastrous for impacted populations. Impacted Iowans and their loved ones are left to grapple with loss of property, major economic burden, and life-threatening scenarios. As a result of these trends in Iowa, several best management technologies (BMPs) have been introduced to the landscape. Unfortunately, landowners are frequently deterred by the costs of implementing these practices at a scale that yields significant benefits.
description: To create a replicable framework that resulted in meaningful reductions, the Iowa Watershed Approach (IWA) project was created under the Iowa Flood Center (IFC). In early 2016, IWA was awarded $97M in grant funding by the U.S. Department of Housing and Urban Development to employ a community-driven approach for watershed management over the next five years. Through the IWA – watershed stakeholders, engineering consultants, contractors, and the IFC cooperated under one banner to implement practices across several Iowa watersheds. Projects were designed and constructed to attenuate flooding and curb water quality degradation.
description: Though the individual impacts of these projects were determined by engineering consultants, their aggregate impacts were still a mystery. To determine the cumulative impacts of constructed flood mitigation practices, the IFC was tasked with employing a mathematical model to determine the benefits of BMPs installed across the IWA target watersheds. In collaboration with researchers at IFC, I was delegated the modeling efforts in the Clear Creek Watershed.
description: To evaluate the installed infrastructure projects, I utilized a complex mathematical model; the University of Iowa’s Generic Hydrologic Overland-Subsurface Toolkit (GHOST). GHOST accounts for a myriad of physical and chemical processes to simulate how water moves throughout the landscape on a watershed scale. GHOST is both sophisticated and inherently complex – considering both surface and groundwater flow in simulations. Using historical rainfall data collected via satellite between 2002 and 2020, each model is adjusted to replicate historical flow data collected by the United States Geologic Survey (USGS) at various stream gauges throughout the watershed. Once a model can reproduce observed conditions in the calibration process, the proposed infrastructure projects are included into the model to determine their benefits.
description: Alongside a team of IFC researchers, I helped develop a process to implement IWA BMPs in the Clear Creek Watershed. The process utilized relevant design parameters for BMPs provided by consulting partners to translate their behavior into a form usable by GHOST. Limited by model resolution requirements imposed by watershed area and the multiyear simulation period, modeled BMPs were constrained to only those practices that provided significant storage benefits – primarily ponds and wetlands.
description: I evaluated project efficiency by subjecting the model to a design storm and comparing streamflow between models with and without projects. Benefits of modeled BMPs were analyzed at both local and watershed resolution. I found constructed storage practices significantly reduced the likelihood of flooding locally, with peak flow reductions ranging from ~60-90% immediately downstream. At watershed and sub-watershed scales, the benefits of installed practices diminished significantly.
description: In the coming decades, climate models predict flooding in Iowa will continue to grow more frequent and strike with more intensity. Using a calibrated model to replicate historical conditions in Iowa’s Clear Creek watershed, we determined that installed BMPs can reduce peak floods experienced at the outlet by ~6%. Though this outlet reduction is seemingly negligible, the local impacts can protect both rural and urban project-adjacent population centers from a large range of potential storm scenarios. With additional investment, the replicable framework created through IWA can continue until watershed-scale benefits are eventually realized.