Document Type

Thesis

Date of Degree

2015

Degree Name

MS (Master of Science)

Degree In

Civil and Environmental Engineering

First Advisor

Larry J. Weber

Second Advisor

Nathan Young

Abstract

The primary objective of this thesis is to develop hydrologic and hydraulic models for the Soap Creek Watershed, IA for the evaluation of alternative flood mitigation strategies and the analysis of the differences between hydrologic and hydraulic routing methods.

In 2008, the state of Iowa suffered a disastrous flood that caused extensive damage to homes, agricultural lands, commercial property, and public infrastructures. To reduce the flood damage across Iowa, the U.S. Department of Housing and Urban Development (HUD) awarded funds to the Iowa Flood Center and IIHR-Hydroscience &Engineering at the University of Iowa to conduct the Iowa Watersheds Project. The Soap Creek Watershed was selected as one of the study areas because this region has suffered frequent severe floods over the past century and because local landowners have organized to construct over 130 flood detention ponds within it since 1985.

As part of the Iowa Watersheds Project, we developed a hydrologic model using the

U.S. Army Corps of Engineers’ (USACE) Hydrologic Center’s hydrologic Modeling System (HEC-HMS). We used the hydrologic model to evaluate the effectiveness of the existing flood mitigation structures with respect to discharge and to identify the high runoff potential areas. We also investigated the potential impact of two additional flood mitigation practices within the Soap Creek Watershed by utilizing the hydrologic model, which includes changing the land use and improving the soil quality. The HEC-HMS model simulated 24-hour design storms with different return periods, including 10, 25, 50, and 100 year. The results from modeling four design storms revealed that all three practices can reduce the peak discharge at different levels. The existing detention ponds were shown to reduce the peak discharge by 28% to 40% depending on the choice of observed locations and design storms. However, changing the land use can reduce the peak discharge by an average of only 1.0 %, whereas improving the soil quality can result in an average of 15 % reduction.

Additionally, we designed a hydraulic model using the United States Army Corps of Engineers’ (USACE) Hydrologic Engineering Center’s River Analysis System (HEC- RAS) to perform a comparative evaluation of hydrologic and hydraulic routing methods. The hydrologic routing method employed in this study is the Muskingum Routing method. We compare the historical and design storms between HEC-HMS, HEC-RAS, and observed stage hydrographs and take the hydrograph timing, shape, and magnitude into account. Our results indicate that the hydraulic routing method simulates the hydrograph shape more effectively in this case.

Public Abstract

In 2008, the state of Iowa suffered a disastrous flood that caused extensive damage to homes, agricultural lands, commercial property, and public infrastructures. To reduce flood damage across Iowa, the U.S. Department of Housing and Urban Development (HUD) awarded funds to the Iowa Flood Center and IIHR-Hydroscience & Engineering at the University of Iowa to conduct the Iowa Watersheds Project. The Soap Creek Watershed was selected as one of the study areas because this region has suffered frequent severe floods over the past century and because local landowners have organized to construct over 130 flood detention ponds within it since 1985.

Although the detention pond is a widely accepted flood control practice, its effectiveness as a system to reduce the peak flow rate has rarely been investigated. One primary objective of this thesis is to evaluate the benefits that these detention basins could bring to the downstream areas of the Soap Creek Watershed. The thesis also provides an overview of the physical characteristics of the watershed, which can help local residents gain a better understanding of their living environment with respect to streams, soil type, land use, and so on. In order to achieve this goal, we developed a numerical model that can mimic the process by which rainfall is converted into runoff. In addition, we developed a different numerical model that simulates how water flows through the channel. The second objective of the model is to compare these two models with respect to technology.

Keywords

publicabstract, antecedent moisture condition, distributed ponds, HEC-HMS, HEC-RAS, land use, routing method

Pages

xiv, 138 pages

Bibliography

Includes bibliographical references (pages 125-128).

Copyright

Copyright 2015 Jingyun Sun

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