Document Type

Thesis

Date of Degree

Fall 2014

Degree Name

MS (Master of Science)

Degree In

Civil and Environmental Engineering

First Advisor

Athanasios N. Papanicolaou

Second Advisor

Christopher G. Wilson

Abstract

The overarching objective of this study is to assess the effectiveness and performance of ATIs. In doing so, this research provides a fundamental understanding of the flow and sediment propagation through a different combination of porous media (pea gravel and woodchips). The research hypothesizes that the theory of advection and diffusion describes the migration of flow and identifies a myriad of depositional networks of sediment. A key hypothesis of the study is that global and local pressure differentiation affects the flow pathways and distribution with intimate effects of sediment trapping efficiency and distribution within the permeameter. A significant goal of this study is to decompose the key mechanisms that affect this migration of sediment under a fixed value for the head and incoming concentration. The nature of the study is experimental and is supported by limited numerical and field analysis. Although the experimental setup is site specific to the conditions encountered in the study location, it offers a generic way of examining flow and sediment intrusion within a permeable bed. The study in that sense hypothesizes that the intrusion by Einstein is valid and it shows the change in the hydraulic gradient that occurs during an event and during a sequence of events. A secondary goal of this research is to understand the cyclicity in the migration of sediment in a sequence of different events, where the initial conditions of each run constitutes the outcome of the final result of the previous runs. The nature of those experiments is to mimic the occurrence of sequential events in nature, although the continuous examined in the laboratory as reflective of conditions representing extreme runs. This research also treats the hydraulic conductivity as a dynamic entity to reflect the effect of localized clogging on the propagation of flow. The experimental design of this research considers a series of experimental runs to address the aforementioned objectives of this research and test the posed hypothesis.

Public Abstract

The overall goal of this study is to demonstrate the effectiveness of an alternative tile intake (ATI) at reducing runoff, and sediment loads produced by heavy rainfall in intensively managed agricultural fields within the Clear Creek watershed in Iowa. An ATI is a best management practice (BMP) consisting of a 3-foot pea gravel layer atop a 1-foot layer of wood chips.

Gravel intakes have been shown to be highly efficient at trapping sediment and sediment-bound particulates, like phosphorus, by enhancing settling through ponding and filtration, while the addition of the wood chips is to facilitate denitrification, similar to a bioreactor. Additionally, these intakes can help reduce the flow rate of runoff into the subsurface tile drain network relative to conventional intakes. The primary method focus of this study was to model the intake design with a physical model in a laboratory to quantify the saturated hydraulic conductivity and filter efficiency of different combinations of pea gravel and wood chips. However, this study also conducted a study of prototype ATIs installed at a field site in the Clear Creek watershed. Due to drought conditions, only limited observations and data were obtained from the field site.

Replacing much of the field study, the Water Erosion Prediction Project (WEPP), a watershed modeling software, was used to simulate the field conditions at the site for calculating runoff volumes and sediment loads to the intake for rainfall events of different magnitude. A three-part control volume was conceptualized, consisting of the contributing hillslope, the ATI, and the subsurface pipe below the ATI.

Keywords

publicabstract, Agriculture, Gravel, Intake, Runoff, Sediment, Woodchips

Pages

xiv, 131 pages

Bibliography

Includes bibliographical references (pages 130-131).

Copyright

Copyright 2014 William D. Ettema

Share

COinS