Presentation Title

Physical Response of Post-fire Soil in Urban and Mediterranean Watersheds

Faculty Mentor

Alicia M. Kinoshita

Start Date

23-11-2019 8:00 AM

End Date

23-11-2019 8:45 AM

Location

169

Session

poster 1

Type of Presentation

Poster

Subject Area

engineering_computer_science

Abstract

Increasing wildfires impose environmental challenges in urban watersheds by altering their physical and chemical soil properties. In southwest California, invasive plant species in urban riparian systems have the potential to intensify geomorphic changes after fires due to their flammable characteristics. We used the Del Cerro brush fire in Alvarado Creek, a tributary to the San Diego River in California with dense vegetation cover of invasive Arundo Donax at stream beds, to analyze the post-fire sediment response after the 2018-2019 storm events in upland and riparian areas of the creek. 16 soil samples were collected in these areas which consisted of a top (0-6”) and bottom (6”-12”) layer. A Loss on Ignition (LOI) test was performed on soil specimens to measure the change in organic content after the post-fire storms. Particle size distributions for each sample were determined using a standard sieve analysis. Lastly, a Fall Cone Test was performed for top layer soil samples to determine the shear strength at which sediments less than 0.450mm are susceptible to commence transportation. The LOI analysis showed the upland top layer soil experienced a greater decrease in organic content. The particle size distribution charts showed sediments between 0.425mm-0.180mm were more susceptible to erosion in the upland area, these sediments decreased from 2.85%-13.4% by weighted mass and in the riparian zone from 13.4%-0.9%. The fall cone results showed that the upland soil increased 10% in water content at the liquid limit which translates to particles transporting because there was a decrease in shear strength from 2.8kPa to 1.9 kPa. Samples in riparian areas had poor particles size distributions and experienced lower rates of sediment movement after the storm events. This information will help to improve our understanding of the functions and interactions between upland and riparian soil processes in urban stream systems.

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Nov 23rd, 8:00 AM Nov 23rd, 8:45 AM

Physical Response of Post-fire Soil in Urban and Mediterranean Watersheds

169

Increasing wildfires impose environmental challenges in urban watersheds by altering their physical and chemical soil properties. In southwest California, invasive plant species in urban riparian systems have the potential to intensify geomorphic changes after fires due to their flammable characteristics. We used the Del Cerro brush fire in Alvarado Creek, a tributary to the San Diego River in California with dense vegetation cover of invasive Arundo Donax at stream beds, to analyze the post-fire sediment response after the 2018-2019 storm events in upland and riparian areas of the creek. 16 soil samples were collected in these areas which consisted of a top (0-6”) and bottom (6”-12”) layer. A Loss on Ignition (LOI) test was performed on soil specimens to measure the change in organic content after the post-fire storms. Particle size distributions for each sample were determined using a standard sieve analysis. Lastly, a Fall Cone Test was performed for top layer soil samples to determine the shear strength at which sediments less than 0.450mm are susceptible to commence transportation. The LOI analysis showed the upland top layer soil experienced a greater decrease in organic content. The particle size distribution charts showed sediments between 0.425mm-0.180mm were more susceptible to erosion in the upland area, these sediments decreased from 2.85%-13.4% by weighted mass and in the riparian zone from 13.4%-0.9%. The fall cone results showed that the upland soil increased 10% in water content at the liquid limit which translates to particles transporting because there was a decrease in shear strength from 2.8kPa to 1.9 kPa. Samples in riparian areas had poor particles size distributions and experienced lower rates of sediment movement after the storm events. This information will help to improve our understanding of the functions and interactions between upland and riparian soil processes in urban stream systems.