Project Title

Time-lapse monitoring of sidewall mass-wasting events in a Northeast Tennessee gully

Authors' Affiliations

Nicholas McConnell, Department of Geosciences, College of Arts and Sciences, East Tennessee State University, Johnson City, TN Ingrid Luffman, Department of Geosciences, College of Arts and Sciences, East Tennessee State University, Johnson City, TN Arpita Nandi, Department of Geosciences, College of Arts and Sciences, East Tennessee State University, Johnson City, TN

Location

Ballroom

Start Date

4-5-2018 8:00 AM

End Date

4-5-2018 12:00 PM

Poster Number

13

Name of Project's Faculty Sponsor

Ingrid Luffman

Faculty Sponsor's Department

Department of Geosciences

Type

Poster: Competitive

Classification of First Author

Undergraduate Student

Project's Category

Natural Sciences

Abstract Text

In the southern Appalachians, the dominant soil order, Ultisols, is highly susceptible to erosion. If left unmanaged these soils can develop into gully systems resulting in land degradation. This study examines gully development through sidewall mass-wasting events at a high temporal resolution using 30 minute time-lapse photography. Prior research at this site found significant mass wasting events occurring between weekly monitoring periods. By shortening the interval of observation to 30-minutes, a more accurate understanding of the frequency and intensity of these mass-wasting events, and their relation to meteorological factors, can be determined. Photographs of a gully (approximately 1.5 m deep by 3 m wide at the top) were captured every 30 minutes from 11/29/17 - 2/18/2018 with a WingScape outdoor time-lapse camera mounted on a plastic stake 3.16 m from the gully facing northwest and upstream into the gully channel. A total of n=1648 images were coded using presence/absence indices for six observed geomorphic processes: creep on NE facing sidewall, creep on SW facing sidewall, slump on NE facing sidewall, slump on SW facing sidewall, channel aggradation, and channel development. Precipitation and temperature data were collected every 5 minutes using a Davis Vantage Pro 2 weather station located 240 m from the gully, and were aggregated to various time intervals. Precipitation received in previous 0.5, 1, 1.5, 2, 3, 6, 12, 24, 36, 48, and 72 hours were calculated for each image. Two binary temperature variables were generated with values of “1” if temperature dropped below 0 °C (32 °F) during the prior 30 minutes or 24 hours, respectively, and “0” otherwise. Logistic regression models (forward conditional method) for the six geomorphic index variables were generated using the precipitation and temperature data. For creep on the NE facing sidewall, the significant independent variables are 3 hour and 72 hour prior rain, and freeze conditions in the previous 0.5 and 24 hours. On the SW facing sidewall, rain and temperature variables were also important for creep; rain in the previous 12 and 24 hours, and freeze conditions within the previous 24 hours were retained in the model. For slumping on both the NE and SW facing sidewall, recent and prolonged rain were important. Specifically, 1, 6, 12, and 24 hour rainfall were retained in both models, with the addition of 3 hour rainfall in the NE facing sidewall slump model. No temperature variables were retained. For channel aggradation (deposition of material in the channel), rain in the prior 12 and 72 hours, and freezing in the prior 24 hours were important, suggesting that freeze-thaw processes loosen the soil, and subsequent rain events carry material into the channel. When rain stops, the material is then deposited in the channel. Interestingly, no viable model could be developed for channel development (erosion) using these parameters. These results will be useful to quantify meteorological controls on gully erosion at short temporal scales.

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Apr 5th, 8:00 AM Apr 5th, 12:00 PM

Time-lapse monitoring of sidewall mass-wasting events in a Northeast Tennessee gully

Ballroom

In the southern Appalachians, the dominant soil order, Ultisols, is highly susceptible to erosion. If left unmanaged these soils can develop into gully systems resulting in land degradation. This study examines gully development through sidewall mass-wasting events at a high temporal resolution using 30 minute time-lapse photography. Prior research at this site found significant mass wasting events occurring between weekly monitoring periods. By shortening the interval of observation to 30-minutes, a more accurate understanding of the frequency and intensity of these mass-wasting events, and their relation to meteorological factors, can be determined. Photographs of a gully (approximately 1.5 m deep by 3 m wide at the top) were captured every 30 minutes from 11/29/17 - 2/18/2018 with a WingScape outdoor time-lapse camera mounted on a plastic stake 3.16 m from the gully facing northwest and upstream into the gully channel. A total of n=1648 images were coded using presence/absence indices for six observed geomorphic processes: creep on NE facing sidewall, creep on SW facing sidewall, slump on NE facing sidewall, slump on SW facing sidewall, channel aggradation, and channel development. Precipitation and temperature data were collected every 5 minutes using a Davis Vantage Pro 2 weather station located 240 m from the gully, and were aggregated to various time intervals. Precipitation received in previous 0.5, 1, 1.5, 2, 3, 6, 12, 24, 36, 48, and 72 hours were calculated for each image. Two binary temperature variables were generated with values of “1” if temperature dropped below 0 °C (32 °F) during the prior 30 minutes or 24 hours, respectively, and “0” otherwise. Logistic regression models (forward conditional method) for the six geomorphic index variables were generated using the precipitation and temperature data. For creep on the NE facing sidewall, the significant independent variables are 3 hour and 72 hour prior rain, and freeze conditions in the previous 0.5 and 24 hours. On the SW facing sidewall, rain and temperature variables were also important for creep; rain in the previous 12 and 24 hours, and freeze conditions within the previous 24 hours were retained in the model. For slumping on both the NE and SW facing sidewall, recent and prolonged rain were important. Specifically, 1, 6, 12, and 24 hour rainfall were retained in both models, with the addition of 3 hour rainfall in the NE facing sidewall slump model. No temperature variables were retained. For channel aggradation (deposition of material in the channel), rain in the prior 12 and 72 hours, and freezing in the prior 24 hours were important, suggesting that freeze-thaw processes loosen the soil, and subsequent rain events carry material into the channel. When rain stops, the material is then deposited in the channel. Interestingly, no viable model could be developed for channel development (erosion) using these parameters. These results will be useful to quantify meteorological controls on gully erosion at short temporal scales.