Conversion of elevation from Wusong Datum to Chinese 1985 National Datum to WGS84

Question

I want to combine/compare raster data from a digital elevation model (EarthEnv-DEM90) with surface water level data from China. Unfortunately the water level data is given in a vertical Datum with the name Wusong Datum (or Wu Song) while the DEM is given in WGS84.

I may be able to convert the Wusong Datum to the 1985 National Datum (Yellow Sea Datum or EPSG 5736) by subtracting 1.84m. Although I'm not entirely sure that value is correct (because Ive found different statements about this), it should be good enough for the purpose I've in mind.

So my actual Question is:

How do I convert the water level values from EPSG 5736 to water level values that fit into my WGS84 DEM?

Answer 1

I may have found a somewhat sufficient conversion, although the number of sources is to small to be sure that this is correct. Anyway here is what I have gathered:

"Wusong Datum" = "1985 National Datum" + 1.836m (Guiping Wu and Yuanbo Liu, 2015)

"1985 National Datum" = WGS84 + 0.357m (GUO Hai-rong et al, 2004-02)

-> WGS84 = "Wusong Datum" - 2.193m