TINJAUAN RINGKAS BERBAGAI TEKNIK TERKINI UNTUK MENENTUKAN KUAT GESEK EROSIF TANAH
DOI:
https://doi.org/10.32722/pt.v18i1.1291Abstract
ABSTRACT
Stream bank erosion manifests in two main modes, namely mass failure and fluvial erosion. Fluvial erosion is a quasi-continuous entrainment of individual soil grains or grain flocs or chunks from the bank face due to the hydrodynamic shear flow action. It occurs under water with retreat lengths in millimeter or centimeter scale. The interaction between fluvial erosion and mass failure determines the shape and retreat rate of the stream bank (Rinaldi et al., 2008). It is not rare, fluvial erosion which occurs at the bank toe later triggers slumping of soil mass known as mass failure. Despite its importance, the mechanism of fluvial erosion is less understood. This is predominantly due to lack of technique for measuring two key bank soil parameters that determine fluvial erosion rate, e.g., erosion shear strength τcand the erodibility coefficient M (Papanicolaou et al., 2007, Grabowski et al., 2011, Sutarto et al., 2014a). The goal of this manuscript is to provide a short review on the various techniques for measuring τcand M proposed and applied in various studies. The advantages and the limitations of each technique are discussed to get a glimpse on where we stand and what challenge remains to overcome.
Key words : Fluvial erosion, erosion shear strength, erodibility coefficient
ABSTRAK
Erosi tebing sungai terjadi dalam dua model utama, yakni erosi gerusan dan longsor atau keruntuhan. Erosi gerusan ditandai dengan tergerusnya butiran atau bongkahan tanah, secara hampir kontinu, dari permukaan tebing akibat daya gerus air sungai. Erosi gerusan berlangsung di bawah muka air dan magnitudo erosi sangat kecil dalam skala millimeter hingga centimeter saja. Interaksi antara erosi gerusan dan longsor membentuk profil permukaan tebing sungai dan mendikte laju pergerakan mundur tebing sungai (Rinaldi dkk., 2008). Tidak jarang erosi gerusan, yang umumnya lebih dominan terjadi di tumit tebing, memicu longsor tebing. Meskipun demikian pentingnya peran erosi gerusan, pemahaman tentang mekanisme erosi gerusan tidak sebaik pemahaman tentang longsor tebing. Hal ini disebabkan belum adanya metode akurat yang disepakati bersama untuk mengukur dua parameter kunci tanah yang menentukan laju erosi gerusan, yakni kuat gesek erosif τcdan koefisien erodibilitas M (Papanicolaou dkk., 2007, Grabowski dkk., 2011, Sutarto dkk., 2014a). Artikel ini memaparkan hasil tinjauan ringkas tentang teknik pengukuran parameter τcdan M yang ditawarkan dan sudah diaplikasikan dalam berbagai studi. Kelebihan dan kekurangan dari masing-masing teknik juga akan dibahas untuk memahami sejauh mana kemajuan yang telah dicapai dan permasalahan yang masih harus diatasi.
Kata kunci : Erosi gerusan, kuat gesek erosif, koefisien erodibilitas
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References
Aberle, J., Nikora, V., McLean, S., Doscher C., McEwan, I., Green, M., Goring, D., & Walsh, J. 2003. Straight benthic flow-through flume for in situ measurement of cohesive sediment dynamics. Journal of Hydraulic Engineering 129(1),63-67.
Darby, S.E., Rinaldi, M., & Dapporto, S. 2007. Coupled simulations of fluvial erosion and mass wasting for cohesive river banks. Journal of Geophysical Research: Earth Surface ,112, F03022.
Gharabaghi, B., Inkratas, C., Krishnappan, B.G., and, Rudra, R.P. 2007. Flow characteristics in a rotating circular flume. The Open Civil Engineering Journal 1, 30-36.
Grabowski, R.C., Droppo, I.G., & Wharton, G. 2011. Erodibility of
cohesive sediment: The importance of sediment properties. Earth-Science Reviews 105, 101-120.
Hanson, G.J., & Cook, K.R. 2004. Apparatus, test procedures, and analytical methods to measure soil erodibility in situ.Applied Engineering in Agriculture 20(4),455-462.
Huang, J., Hilldale, R. C., & Greimann, B.P. 2006. Cohesive sediment transport. Erosion and sedimentation manual, C.T. Yang, ed., The United States Department of Interior, Bureau of Reclamation, Technical Service Center, Denver, CO. 4.1-4.54.
Kothyari, U.C., & Jain, R. K. 2008. Influence of cohesive on the incipient motion condition of sediment mixtures. Water Resources Research, 44(4), W04410.
Lawler, D.M. 1992. Design and installation of a novel automatic erosion monitoring system. Earth Surface Processes and Landforms 17, 455-463.
Lawler, D.M. 1995. The impact of scale on the process of channel-side sediment supply: A conceptual model “Effects of scale on interpretation and management of sediment and water quality”. International Association of Hydrological Sciences (IAHS), 226.175-184.
Lim S.S., & Khalili, N. 2009. An improved rotating cylinder test design for laboratory measurement of erosion in clayey soils. Geotechnical Testing Journal 32(3), 1-7.
Papanicolaou, A.N., Elhakeem, M., & Hilldale, R. 2007. Secondary current effects on cohesive river bank erosion. Water Resources Research 43(12), W12418.
Papanicolaou, A.N., Sutarto, T.E., Wilson, C.G., Langendoen, E.J. 2014. Bank Stability Analysis for Fluvial Erosion and Mass Failure. In: Proceeding of World Environmental and Water Resourcess Congress. Portland, Oregon, USA, 1-5 June 2014. Pp.1497-1508. doi:10.1061/9780784413548.150.
Papanicolaou, A.N., Wilson C.G., Tsakiris, A.G., Sutarto, T.E., Bertrand, F., Rinaldi, M., Dey, S., & Langendoen, E. 2017. Understanding mass fluvial erosion along a bank profile: Using PEEP technology for quantifying retreat lengths and identifying the event timing. Earth Surface Processes and Landform 42(11),1717-1732.
Pizzuto, J. 2009. An empirical model of event scale cohesive bank profile evolution. Earth Surface Processes Landforms, 34(9).1234-1244.
Rinaldi, M., & Darby, S.E. 2008. Modeling river-bank-erosion processes and mass failure mechanisms: Progress towards fully coupled simulations. Gravel-bed rivers VI: From process understanding to river restoration, H. Habersack, H. Piegay, and M. Rinaldi, eds., Elsevier, Amsterdam, the Netherlands. 213-239.
Sutarto, T.E., & Papanicolaou, A.N. 2012. Measuring Critical Erosion Strength of Cohesive Bank Soils in a Natural Channel Affected by Secondary Currents. In: Proceeding of the 3rd International Symposium on Shallow Flows. Iowa City, USA, June, 2012.
Sutarto, T.E., Papanicolaou, A.N., Wilson, C.G., & Langendoen, E.J.
a. A stability analysis of semi-cohesive streambanks with CONCEPTS: Coupling field and laboratory investigations to quantify the onset of fluvial erosion and mass failure. Journal of Hydraulic Engineering, 140(9).
Sutarto, T.E., Papanicolaou, A.N., Wilson, C.G., & Langendoen, E.J. 2014b. Misconceptions about Mechanical and Fluvial Erosionnal Strength: Implications to Streambank Stability. In: Proceeding of the 2nd International Seminar on Infrastructure Development. Balikpapan, Indonesia, 3-4 June, 2014.
Sutarto, T.E. 2015. A combined flume-imaging technique for measuring fluvial erosion of cohesive streambank soil. Procedia Engineering, 125, 368-375.
Sutarto, T.E. 2018. Teknik sensor cahaya untuk menentukan laju erosi tebing sungai. In: Proceeding of the 4th SENTRINOV. Bali, Indonesia, 23-24 August, 2018.
Vermeyen, T. 1995. Erosional and depositional characteristics of cohesive sediments found in Elephant Butte Reservoir, New Mexico. Technical report R-95-15, Water Resources Services, Technical Service Center, Bureau of Reclamation, Denver, USA.
