Influence of Precipitation Variability on Porewater Pressure and Surface Layer Failures in Naturally Undulating Slopes at Nau Kilo, Narayanghat–Mugling Road, Central Nepal

Samyog Khanal; Ranjan Kumar Dahal

Authors

Samyog Khanal Kajaria Ramesh Tiles Ltd., Team Venture Building, 3rd floor, Sinamangal, Kathmandu, Nepal Author
Ranjan Kumar Dahal Central Department of Geology, Tribhuvan University, Kathmandu, Nepal Author https://orcid.org/0000-0002-8780-900X

Keywords:

Hillslope Hydrology, Threshold, Porewater Pressure

Abstract

This study investigates the role of porewater pressure variations in slope failures within naturally undulated hill slopes characterized by topographic hollows. A representative slope with a distinct hollow and six rainfall-induced failures recorded between 2001 and 2023 was selected for detailed analysis. Seepage and slope stability modeling were conducted in GeoStudio using the July 31, 2003, precipitation event, with simulations incorporating 24-hour maximum rainfall data corresponding to 5, 10, 25, 50, and 100-year return periods. These events were normalized using 6-minute interval rainfall data, and potential seepage face boundary conditions were applied. The results demonstrated a threshold relationship between hollow area and maximum porewater pressure, indicating that larger hollows generate higher porewater pressures under extreme rainfall. Specifically, a hollow of 100 m² was found to develop a maximum porewater pressure of 6.94 kPa. The findings highlight that topographic hollows act as hydrological convergence zones, increasing subsurface saturation and instability during intense rainfall events. The developed threshold relationship offers a predictive framework for assessing slope failure susceptibility in similar geomorphic settings, contributing to more effective hazard assessment and early warning systems.

References

Acharya, K. P., Bhandary, N. P., Dahal, R. K., and Yatabe, R. (2016). Seepage and slope stability modelling of rainfall-induced slope failures in topographic hollows. Geomatics, Natural Hazards and Risk, 7(2), 721-746. https://doi.org/10.1080/19475705.2014.954150

Acharya, K. P., Yatabe, R., Bhandary, N. P., and Dahal, R. K. (2016). Deterministic slope failure hazard assessment in a model catchment and its replication in neighbourhood terrain. Geomatics, Natural Hazards and Risk, 7(1), 156-185. http://dx.doi.org/10.1080/19475705.2014.880856

Amatya, K., and Jnawali, B. (1994). Geological map of Nepal, scale: 1: 1,000,000. Department of mines and geology, International centre for integrated mountain development, Carl Duisberg Gesellschaft e. V., and United Nations environment programme.

Arita, K. (1973). Kathmandu region. Geology of the Nepal Himalayas, 99-145.

Auden, J. (1935). Traverses in the Himalaya. Records of Geological survey of India, 69, 123-167.

Beven, K. J., and Kirkby, M. J. (1979). A physically based, variable contributing area model of basin hydrology/Un modèle à base physique de zone d'appel variable de l'hydrologie du bassin versant. Hydrological sciences journal, 24(1), 43-69. https://doi.org/10.1080/02626667909491834

Bordet, P., Remy, M., Krummenacher, D., and R, M. (1964). Sur la stratigraphie des séries affleurant dans la vallée de la Kali Gandaki (Nepal central). Comptes Rendus Hebdomadaires Des Seances De L Academie Des Sciences, 259(2), 414-and.

Bronstert, A. (1994). Modellierung der Abflussbildung und der Bodenwasserdynamik von Hangen Dissertation, Karlsruhe, Karlsruher Institut für Technologie (KIT), 1994].

Campbell, R. H. (1975). Soil slips, debris flows, and rainstorms in the Santa Monica Mountains and vicinity, southern California (Vol. 851). US Government Printing Office. https://doi.org/10.3133/pp851

Cardinali, M., Galli, M., Guzzetti, F., Ardizzone, F., Reichenbach, P., and Bartoccini, P. (2006). Rainfall induced landslides in December 2004 in south-western Umbria, central Italy: types, extent, damage and risk assessment. Natural Hazards and Earth System Sciences, 6(2), 237-260. https://doi.org/10.5194/nhess-6-237-2006.

Carrivick, J. L. (2007). Hydrodynamics and geomorphic work of jökulhlaups (glacial outburst floods) from Kverkfjöll volcano, Iceland. Hydrological Processes: An International Journal, 21(6), 725-740. http://dx.doi.org/10.1002/hyp.6248

Crosta, G. (1998). Regionalization of rainfall thresholds: an aid to landslide hazard evaluation. Environmental Geology, 35(2-3), 131-145. https://doi.org/10.1007/s002540050300

Crozier, M. J. (1999). Prediction of rainfall‐triggered landslides: A test of the antecedent water status model. Earth Surface Processes and Landforms: The Journal of the British Geomorphological Research Group, 24(9), 825-833. https://doi.org/10.1002/(sici)1096-9837(199908)24

Dahal, R. K., and Hasegawa, S. (2008). Representative rainfall thresholds for landslides in the Nepal Himalaya. Geomorphology, 100(3-4), 429-443. https://doi.org/10.1016/j.geomorph.2008.01.014

Dahal, R. K., Hasegawa, S., Nonomura, A., Yamanaka, M., Masuda, T., and Nishino, K. (2008). GIS-based weights-of-evidence modelling of rainfall-induced landslides in small catchments for landslide susceptibility mapping. Environmental Geology, 54, 311-324. http://dx.doi.org/10.1007/s00254-007-0818-3

Dahal, R. K., Hasegawa, S., Yamanaka, M., and Bhandary, N. P. (2011). Rainfall-induced landslides in the residual soil of andesitic terrain, western Japan. Journal of Nepal Geological Society, 42, 137-152. https://doi.org/10.3126/jngs.v42i0.31461

Dahal, R. K., Hasegawa, S., Yamanaka, M., Dhakal, S., Bhandary, N. P., and Yatabe, R. (2009). Comparative analysis of contributing parameters for rainfall-triggered landslides in the Lesser Himalaya of Nepal. Environmental Geology, 58, 567-586. http://dx.doi.org/10.1007/s00254-008-1531-6

Dhital, M. R. (2015). Geology of the Nepal Himalaya: regional perspective of the classic collided orogen. Springer. http://dx.doi.org/10.1007/978-3-319-02496-7

Dietrich, W. (1987). Overview:" Zero-order basins" and problems of drainage density, sediment transport and hillslope morphology. International Association of Hydrological Sciences Publication, 165, 27-37.

Dietrich, W., and Dunne, T. (1978). Sediment budget for a small catchment in a mountainous terrain. http://dx.doi.org/10.1130/0091-7613(2001)029

Dietrich, W. E., de Asua, R. R., Coyle, J., Orr, B., and Trso, M. (1998). A validation study of the shallow slope stability model, SHALSTAB, in forested lands of Northern California. Stillwater Ecosystem, Watershed and Riverine Sciences. Berkeley, CA.

Dunne, T. (1978). Field studies of hillslope flow processes. Hillslope hydrology, 227-293.

ESCAP, U. (1993). Cambodia. United Nations.

Frattini, P., Crosta, G., and Sosio, R. (2009). Approaches for defining thresholds and return periods for rainfall‐triggered shallow landslides. Hydrological Processes: An International Journal, 23(10), 1444-1460. https://doi.org/10.1002/hyp.7269

Fredlund, D. G., and Xing, A. (1994). Equations for the soil-water characteristic curve. Canadian geotechnical journal, 31(4), 521-532. https://doi.org/10.1139/t94-061

Gansser, A. (1964). Geology of the Himalayas Interscience Publishers London. UK New York, NY, USA Sydney, Australia.

Guzzetti, F., Cardinali, M., Reichenbach, P., Cipolla, F., Sebastiani, C., Galli, M., and Salvati, P. (2004). Landslides triggered by the 23 November 2000 rainfall event in the Imperia Province, Western Liguria, Italy. Engineering Geology, 73(3-4), 229-245. https://doi.org/ 10.1016/j.enggeo.2004.01.006

Hagen, T. (1969). Geology of Nepal Himalaya. Report on the geological Survey of Nepal Preliminary Reconnaissance. Zurich. Memoires de la Soc. Helvetique des science Naturelles, 86, 185.

Hagen, T. (1969). Report on the geological survey of Nepal. Denkschr. Schweiz. Naturf. Ges., 81, 185.

Hilberts, A. G. J. (2006). Low-dimensional modeling of hillslope sub-surface flow processes: developing and testing the hillslope-storage Boussinesq model. Wageningen University and Research. https://doi.org/10.1029/2006WR004964

Jacob, A., Thomas, A. A., Nath, A. G., and MP, A. (2018). Slope stability analysis using Plaxis 2D. International Research Journal of Engineering and Technology (IRJET), 5(4), 3666-3668.

Janbu, N. (1973). Slope stability computations. Publication of: Wiley (John) and Sons, Incorporated.

Khan, M. I., and Wang, S. (2021). Slope stability analysis to correlate shear strength with slope angle and shear stress by considering saturated and unsaturated seismic conditions. Applied Sciences, 11(10), 4568. http://dx.doi.org/10.3390/app11104568

Kvalstad, T. J., Nadim, F., Kaynia, A. M., Mokkelbost, K. H., and Bryn, P. (2005). Soil conditions and slope stability in the Ormen Lange area. Marine and Petroleum Geology, 22(1-2), 299-310. http://dx.doi.org/10.1016/j.marpetgeo.2004.10.021

Lanni, C. (2012). Hydrological controls on the triggering of shallow landslides: from local to landscape scale University of Trento].

Le Fort, P. (1975). Himalayas: the collided range. Present knowledge of the continental arc. American Journal of Science, 275(1), 1-44.

Marquez, R. M. (2004). Three-dimensional slope stability analysis using finite elements. 2000-2009-Mines Theses and Dissertations.

Pack, R. T., Tarboton, D. G., and Goodwin, C. (1999). SINMAP 2.0-A stability index approach to terrain stability hazard mapping, user's manual.

Paniconi, C., Troch, P. A., van Loon, E. E., and Hilberts, A. G. (2003). Hillslope‐storage Boussinesq model for subsurface flow and variable source areas along complex hillslopes: 2. Intercomparison with a three‐dimensional Richards equation model. Water resources research, 39(11). http://dx.doi.org/10.1029/2002WR001728

Pasuto, A., and Silvano, S. (1998). Rainfall as a trigger of shallow mass movements. A case study in the Dolomites, Italy. Environmental Geology, 35(2-3), 184-189.

Paudyal, K. (2017). Geological and Petrological evolution of the Lesser Himalaya between Mugling and Damauli, central Nepal

Paudyal, K., Adhikari, L., Maharjan, N., and Paudel, L. (2012). Geological setting and lithostratigraphy of Bandipur-Gondrang area of Lesser Himalaya, central Nepal. Bulletin of the Department of Geology, 15, 49-62. https://doi.org/10.3126/bdg.v15i0.7417

Paudyal, K., and Paudel, L. (2011). Geological setting and lithostratigraphy of the Lesser Himalaya in the Mugling-Banspani area, central Nepal. Journal of Nepal Geological Society, 42, 51-63. https://doi.org/10.3126/jngs.v42i0.31449

Pradhan, S. (2014). Stability analysis of open PIT slope using FLAC

Rigon, R., Bertoldi, G., and Over, T. M. (2006). GEOtop: A distributed hydrological model with coupled water and energy budgets. Journal of Hydrometeorology, 7(3), 371-388. https://doi.org/10.1175/JHM497.1

Sassa, K. (1986). The mechanism of debris flows and the forest effect on their prevention. 18th IUFRO World Congress, Ljubljana, Yugoslavia, IUFRO.

Setyawan, A., Alina, A., Suprapto, D., Gernowo, R., Suseno, J. E., and Hadiyanto, H. (2021). Analysis slope stability based on physical properties in Cepoko Village, Indonesia. Cogent Engineering, 8(1), 1940637. https://doi.org/10.1080/23311916.2021.1940637

Shrestha, S., Shrestha, J., and Sharma, S. (1984). Geological Map of Eastern Nepal, 1: 250 000. Ministry of Industry, Department of Mines and Geology, Lainchour, Kathmandu.

Sidle, R. (1987). A dynamic model of slope stability in zero order basin. IAHS publ., 165, 101-110.

Stöcklin, J. (1980). Geology of Nepal and its regional frame: Thirty-third William Smith Lecture. Journal of the Geological Society, 137(1), 1-34. https://doi.org/10.1144/gsjgs.137.1.0001

Stöcklin, J., and Bhattarai, K. (1977). Geology of Kathmandu area and Central Mahabharat range: Nepal Himalaya.

Sun, Y., Yang, K., Hu, R., Wang, G., and Lv, J. (2022). Model Test and Numerical Simulation of Slope Instability Process Induced by Rainfall. Water, 14(24), 3997. https://doi.org/10.3390/w14243997

Tater, J., Shrestha, S., Shrestha, J., and Sharma, S. (1983). Geological map of western central Nepal, scale 1: 250,000. Department of Mines and Geology, Kathmandu.

Tsukamoto, Y., and Minematsu, H. (1987). Hydrogeomorphological characteristics of a zero-order basin. IAHS-AISH publication (165), 61-70.

Van Asch, T. W., Buma, J., and Van Beek, L. (1999). A view on some hydrological triggering systems in landslides. Geomorphology, 30(1-2), 25-32. https://doi.org/10.1016/S0169-555X(99)00042-2

VanderKwaak, J. E. (1999). Numerical simulation of flow and chemical transport in integrated surface-subsurface hydrologic systems.

Wagner, A., Leite, E., and Oliver, R. (1990). A landslide hazard mapping software (version 1.0), 2 volumes. ITECO CH and University of Lausanne, Switzerland, 4.