Event Navigation
Thesis Information
Title: Wildfire Impacts On Soil: Hydrophobicity Inducement And Water Drop Penetration Test
Program: Master of Science in Civil Engineering
Advisor: Dr. Arvin Farid, Civil Engineering
Committee Members: Dr. Bhaskar Chittoori, Civil Engineering and Dr. Ken Cornell, Chemistry and Biochemistry
Abstract
The increasing prevalence of wildfires in today’s day and age has amplified the need for post-fire remediation and environmental restoration, especially in the wildland-urban interface (WUI). One of these impacts is soil hydrophobicity, or soil water repellency, which is a well-documented phenomenon after wildfires, significantly impacting revegetation, slope stability, runoff, and erosion potential. To better understand the soil fire-induced hydrophobicity and its impact on other soil properties, variable levels of hydrophobicity need to be repeatably induced in different types of soils under different controlled testing conditions to measure other soil properties. To reach this goal, two ingredients are essential, (i) a method capable of inducing controlled levels of hydrophobicity and (ii) more robust and accurate hydrophobicity measurement procedures. Currently, there is no robust, repeatable method to create controlled hydrophobic soil samples. The most popular hydrophobicity measurement method, Water Droplet Penetration Test (WDPT), which consists of counting the seconds for a droplet to infiltrate into the soil under testing.
Attempts were made to induce various levels of hydrophobicity onto sands in a laboratory setting using two methods: (i) condensates of volatilized hydrophobic organic compounds and (ii) using hydrophobicity-inducing surrogates. This was done to achieve and measure various degrees of water repellency. The results were highly dependent on the establishment of the correct particle coating produced from volatilization of the fuel, and the measurement method. Low burn severity in the field does not necessarily correlate to low burn severity in the laboratory. Hence, the use of the hydrophobicity-inducing surrogate at various dilution levels was selected and a method was developed to induce various controlled levels of hydrophobicity.
On the other hand, despite its popularity, WDPT is very subjective and inaccurate. The subjectivity of WDPT stems from the determination of full penetration and lack of precision for accurate classification of the degree of hydrophobicity due to the lack of calibration or correction for significant properties of the soil, including grain size, moisture content, and particle lift. When hydrophobicity is induced, the WDPT was shown to be unsatisfactory when used solely to determine a consistent classification of soil water repellency. Infiltration data outlined both rapid and delayed infiltration rates when replicated, which can be attributed to the instability caused by particle lift, a function of degrees of repellency and grain size. This finding shows the inaccuracy of the test method as well as insight into the impact of particle lift on various grain sizes and degrees of water repellency. Understanding this phenomenon can pave the way for further calibration or finer measurement methods and scales.
