This data release includes time-series, qualitative descriptions, and laboratory testing data from two monitoring stations installed in Puerto Rico following Hurricane Maria in 2017, which led to tens of thousands of landslides across the island (Bessette-Kirton et al., 2017). The stations were installed to investigate subsurface hydrologic response to rainfall and develop a quantitative link between rainfall and landsliding. The Toro Negro site is located within the state protected Toro Negro rainforest near 18°10’N, 66°34’W and the Utuado site is located outside the city of Utuado near 18°17’N, 66°39’W. The soil found at the Toro Negro site is low-permeability, fine-grained and cohesive, and underlain by saprolite. In contrast, the soil found at Utuado has higher hydraulic conductivity, relatively incohesive, and shallowly underlain by granodioritic bedrock.
Instrumentation was installed at each site to measure precipitation, air temperature, barometric pressure, volumetric water content, pore-water pressure, and soil matric potential, at 15-minute intervals. An electronics enclosure, rain gage, and an instrumented soil pit (SP1) comprised each site for continuous monitoring. Volumetric soil water content was measured at 5 depths below the ground surface in each pit, using ruggedized dielectric sensors (range of 0-0.64 volumetric water content in mineral soils). Soil matric potential was measured at each site with two tensiometers (-80 to 100 kilopascals [kPa]) and one dielectric ceramic disc sensor (-6 to -1000 kPa). Pore-water pressure was measured at two depths with vibrating-wire piezometers (0 to 70 kPa). Each pressure sensor has an integrated thermistor and the associated temperature readings are included. In October 2019 an additional soil-pit was established at Toro Negro (SP2) to clarify the signal of two existing volumetric water content sensors with questionable readings. The data released with this report have not undergone any significant alterations since being recorded by the datalogger and are subject to inaccuracies related to equipment failure or loss of calibration. Missing data is represented as “not a number” (NaN). Also, there are time periods where groundwater conditions are outside of the instruments’ measurement range and these clipped data have been left in the record. Additionally, the tensiometer data returns erroneous data once it cavitates, and a Boolean data quality flag (vector “tensiometerFlag”) has been added to show where the data are likely reliable (1) or not reliable (0). The vibrating-wire piezometers are equipped with low air-entry filter tips (50 micron) and allow limited suctional range and these values should be viewed with skepticism. All values recorded by the piezometer are dependent on filter-saturation and, consequently, readings will be invalid during and after long periods of drought, until the tip has become re-saturated.
Soil samples were taken from the documented soil pits at the time of installation and their index properties were measured in the Unsaturated Soil Mechanics Laboratory at Colorado School of Mines. The properties measured include particle size distributions (ASTM-152H), Atterberg limits (ASTM D-4318), soil classifications (USCS), specific gravity (ASTM D-854), unsaturated and saturated soil hydraulic properties including hysteretic saturated hydraulic conductivities and unsaturated soil-water retention curves using the TRIM method (Wayllace and Lu, 2012), strength properties including cohesion and the angle of internal friction determined using direct shear tests on saturated samples (ASTM D-3080) that included modifications for measurements at relatively low effective stresses (i.e., 0.2-20 kPa) (Likos et al., 2010).
An additional “monitoring.readme.pdf” file is included and contains these details along with naming conventions for the hydrologic monitoring data. Logs of the soil pits at Utuado and Toro Negro are documented in the “PR UTU-ELT Monitoring Site Soil Pit Logs.pdf” file. An additional “testing.report.pdf” file is included summarizing the soil samples, geotechnical testing methods, and results. Further details of this study can be found in the accompanying journal article (Thomas et al., 2020).
References:
Bessette-Kirton, E.K., Coe, J.A., Kelly, M.A., Cerovski-Darriau, C. and Schulz, W.H., 2019, Map data from landslides triggered by Hurricane Maria in four study areas of Puerto Rico: U.S. Geological Survey data release, https://doi.org/10.5066/P9OW4SLX.
Likos, W.J., Wayllace, A., Godt, J., and Lu, N. Modified direct shear apparatus for unsaturated sands at low suction and stress. Geotechnical Testing Journal, 33(4), 286-298, 2010.
Thomas, M.A., Mirus, B.B., Smith, J.B., 2020, Evidence that soil-hydraulic properties can modulate utility of hydro-meteorological thresholds for rainfall-induced landsliding. Hydrological Processes, https://doi.org/10.1002/hyp.13885.
Wayllace, A., and Lu, N. Transient water release and imbibitions method for rapidly measuring wetting and drying soil water retention and hydraulic conductivity functions. Geotechnical Testing Journal, 35, 1-15, 2012.
