ORCID Identifier(s)

0000-0003-1867-2203

Graduation Semester and Year

2017

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Sahadat Hossain

Abstract

A conventional landfill cover system is designed as a barrier layer system, with low hydraulic conductivity, to minimize the percolation of water from the cover to the waste. Evapotranspiration (ET) covers are currently becoming a popular alternative that are acceptable to landfill authorities, due to their cost effectiveness and nature-friendly performance. The principle function of the ET cover is to store the infiltrated water, using the water balance technique, until it is transpired by plants into the atmosphere, thus minimizing percolation. The performance of the final cover system is assessed by monitoring the soil moisture in the ET cover and the percolation of water into the waste. Current methods, which use small-scale field lysimeters equipped soil instrumentations to assess soil moisture, provide only discrete information and are unable to provide an accurate spatial or depthwise variation. Therefore, the development of a more efficient system for monitoring a full-scale ET cover system is vitally important. Electrical resistivity imaging (ERI) is an alternative method for evaluating soil moisture. A substantial number of studies have been carried out in laboratories and the field to correlate soil moisture and electrical resistivity; however, very few have correlated these parameters for the ET cover system, and there have been no significant studies on the relationship between soil moisture sensors and ERI. Therefore, the ERI method has the potential to be employed in the ET cover system to estimate the moisture storage and hence percolation of the ET covers system. To study the soil moisture in an ET cover system using ERI, it is necessary to acknowledge the differences in the soil conditions of the conventional cover system and the ET cover system. These differences can be attributed to the presence of planned vegetation and the resulting plant root systems. Therefore, the objective of this study is to perform detailed statistical analyses for the different soil conditions and develop field scale relationships between soil moisture and ERI. Model parameters will be developed to enable the estimation of soil moisture without the presence of other soil moisture instrumentation. Factors that might influence the ERI values are closely investigated to explain the differences in the soil conditions. Finally, a novel approach has been taken to evaluate the percolation rate in the lysimeters, using base layer moisture estimation and the field capacity of the cover soil. For this investigation six lysimeter sections, along with a control section of vegetated and non-vegetated sections, were constructed in the City of Denton Landfill, in Denton, TX. Monthly monitoring was performed; using soil moisture sensors and the ERI instrument, and the physical and chemical properties of the cover soil, along with vegetation’s and weather conditions, were monitored and recorded. Two years of investigations indicated a good correlation between soil resistivity and soil moisture, and two separate relationships were proposed: a compacted clay model with an R2 value of 0.92 and a vegetated clay model with an R2 of 0.87. Further model validation showed that the percentage of error remained within 5% for the developed models. Qualitative analysis of data showed the variations of different factors in the field, and the use of the ERI showed the comprehensive differences between vegetated and non-vegetated landfill covers. The changes in excess soil moisture at the base layer of the lysimeter showed a direct correlation with the rate of percolation of the lysimeters (r squared = 0.9324). The establishment of this trend made it possible to predict the rate of percolation, using the base layer moisture change, and constituted a novel approach to using ERI to predict the soil moisture of ET cover systems.

Keywords

Evapotranspiration cover, Soil moisture, Electrical resistivity

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

Download

Share

COinS