Sedimentology and volumetric reconstitution of mud flow deposits in an alluvial plain: study in the Jacareí River basin, Paraná

Paz, Otacílio Lopes de Souza da; Paula, Eduardo Vedor de

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Papers • Soc. nat. 34 • 2022 • https://doi.org/10.14393/SN-v34-2022-64381 copy

Sedimentology and volumetric reconstitution of mud flow deposits in an alluvial plain: study in the Jacareí River basin, Paraná

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Extreme mud and debris flows can bury alluvial plains. In current literature, there exists a significant knowledge gap regarding this process, since information about the sedimentological characteristics and estimates of the volumes of these deposits, are still scarce. Such knowledge is important for understanding the role of these events in the morphogenesis of the alluvial plains of the highland mountain margins. The study area located in the Jacareí River basin (coast of the State of Paraná, Brazil) was recently buried by mud slides in March 2011, therefore, our objective is to analyze the sedimentology and estimate the volume of instantaneous deposits formed by the aforementioned gravitational processes. The deposits were mapped based on a geospatial database. Afterwards, samples were collected for laboratory analysis. To estimate the volume, field samples were collected, measuring the thickness of the deposits, which were then interpolated in a GIS environment. Pelitic (9%), psephytic (4%) and psammitic (87%) deposits were identified. The psammitic deposits showed two distinct behaviors as a function of the flow and burial dynamics of the alluvial plain. The total volume of the deposit was estimated at 1,7 million tons of sediment. The results demonstrate the magnitude of the 2011 event, since in a period of less than 24 hours the Jacareí river basin moved more than 8.5 times the annual production of sediments from the hydrographic units that drain into the Estuarine Complex of Paranaguá.

Keywords:
River geomorphology; Sediments; Landscape transformation

Class	Subclass/Description		Criteria
Pelitic deposits	Fine-grained material in portions of the floodplain not altered by the 2011 flood.		Absence of sedimentary material on the surface. Proximity to the slopes.
Psephytic deposits	Coarse-grained material (gravel). Consist of depositional fans and other points that debris flows reached.		Coarse material on the surface. Found in the upstream portions of the plain and in the mouths of the Prata and Tingidor rivers with a conical shape.
Psammitic deposits	Crevasse splay	Overflow deposition. Resulting from the rupture of banks due to the obstruction of the river channel.	Located on the edge of the canal. Conical shape.
	River bar	Central or marginal deposits to the anastomosing channel formed by the event	Areas with sandy material located on the margins or in the center of the anastomosed canal.
	Anastomosed riverbed	Anastomosed-type riverbed formed by the 2011 flood	Sandy material of darker tones, indicating moisture. Limited by debris deposits and flows.
	Buried plain	Deposit formed by the 2011 flood. It covers an extensive area of the plain.	Surfaces with sandy material and areas of wet looking vegetation.

Scars	Maps

Scars	Maps

Units/Subunits		Area (ha)	Area (%)	Sector of the alluvial plain
Pelitic deposits		25,06	8,76	Distal portions
Psephytic deposits		10,45	3,65	River mouths - Upstream portion
Psammitic deposits	Breakthrough deposit	4,48	1,56	Downstream portion
	River bar	5,28	1,85	Upstream portion
	Anastomosed river bed	23,04	8,06	Upstream portion
	Flood plain	217,68	76,12	Upstream and downstream portion

Unit	Sample	Mean	Median	Selection	Asymmetry	Kurtosis
Psammitic deposits - River bar	P-01	2,64	2,10	1,66	0,56	1,11
Psammitic deposits - River bar	P-02	2,48	1,96	1,60	0,59	1,30
Psammitic deposits - Anastomosed riverbed	P-03	2,28	1,58	2,29	0,48	1,22
	P-04	2,74	2,37	2,04	0,24	1,37
	P-05	2,54	2,39	1,30	0,33	1,55
Psammitic deposits - Breakthrough deposit	P-06	3,09	2,39	2,57	0,38	0,95
Psamitic deposits - Flood plain	P-07	3,61	2,91	2,56	0,38	0,77
	P-08	2,71	1,73	2,71	0,50	0,93
	P-09	2,69	1,76	2,59	0,49	1,05
	P-10	3,04	2,35	2,42	0,40	0,95
	P-11	3,63	3,04	2,27	0,41	0,90
	P-12	3,42	2,78	2,00	0,51	1,17
	P-13	4,19	3,74	1,91	0,40	0,93
	P-14	4,36	3,91	2,15	0,32	0,85
	P-15	4,70	4,46	2,28	0,16	0,83
	P-16	4,40	4,23	2,37	0,13	0,82
Pelitic deposits	P-17	5,00	5,07	1,90	0,00	0,90
	P-18	5,07	5,23	2,41	-0,08	0,80
	P-19	5,78	5,66	2,11	0,02	0,79

Class	Area (hectare)	Area (%)
Between 20 and 35 cm	60,3001	24,09
Between 35 and 45 cm	69,8435	27,89
Between 45 and 55 cm	83,4906	33,35
Between 55 and 75 cm	31,9649	12,76
Between 75 and 120 cm	4,7813	1,91

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[1] AUTHORS' CONTRIBUTION

Otacílio Lopes de Souza da Paz conceived the study, developed the proposed methodology, collected and analyzed the data and wrote the text. Eduardo Vedor de Paula conceived the study and contributed to the text. He conducted field campaigns and discussed the results obtained. Responsible for the acquisition of financing. Coordinator of the laboratory where this research was developed.