Table 2.

Elevation comparison of geomorphological units in the Mekong delta

Category and age	Geomorphological unit	Expected relative elevation	Mean elevation (m)
			Topo DEM	SRTM DEM	MERIT DEM
Pleistocene (and older) deposits	Weathered land	Very high	3.27	6.4	6.9
	Undifferentiated deposits	Higher	1.84	3.1	4.7
	Alluvial apron	Higher	1.38	2.8	4.2
Upper delta plain Holocene alluvial deposits	Flood basin	Benchmark	0.85	2.8	3.5
	Bank: natural levees and crevasse splay	Highest (++)	1.38	4.1	4.7
	Channel bar	Higher (+)	1.41	3.2	5.1
	Abandoned channel	Higher (+)	0.91	2.7	3.5
	Swamp	Lower (−)	0.85	2.6	3.7
	Back swamp	Lower (−)	0.66	2.4	3.5
Lower delta plain Holocene coastal deposits	Tidal flat	Benchmark	0.99	2.2	1.5
	Sand spit	Higher (+)	1.14	2.7	2.8
	Relict beach ridge or sand dune	Higher (+)	0.84	2.2	1.6
	Mangrove marsh	Equal (±)	0.97	2.4	2.3
	Salt marsh	Equal (±)	0.83	2.1	3.1
	Coastal plain	Lower (−)	0.53	2.1	2.9
	Marsh (inland)	Lowest (− −)	0.34	2.7	2.7

The expected relative elevation of the Pleistocene and Holocene deposits are compared to the elevation according to the Topo, SRTM, and MERIT DEMs; within the Holocene deposits relative elevation is given compared to the elevation of the benchmark (italic underlined) geomorphological unit, respectively, flood basin for the upper delta plain and tidal flat for the lower delta plain. Expected relative elevation was based on typical elevation characteristics of the depositional environment corresponding to the geomorphological unit (see Supplementary Fig. 6). Highest (bold underlined) and lowest (bold italic) mean elevations in each category are highlighted. The mean values are given with one additional decimal than present in the input data to distinguish mean elevation differences. See Supplementary Fig. 7 for the geomorphological map of the Mekong delta³⁹ and Supplementary Tables 3–5 for additional statistics