Since I wondered how a river can have a negative depth:
> A river's stage at a point (a gauge reading) is not an absolute measure of the depth of the water in the channel, rather it is a depth with respect to an historical Datum level. In summary, when a river gauge reads zero or in the negative numbers - it does not mean that the river has gone totally dry or is running below ground. It means that the gauge is reading at or below the agreed-upon zero level.
> Silt may deposit in the river channel over time (filling the channel up), or the channel bottom may be scoured out to a deeper level by strong currents.
> Still, the gauge zero datum levels are not changed to keep continuity.
And depending on sediment transport dynamics for a particular reach of the river, the depth could be higher or lower at a given stage (i.e., height above datum) today than at the same stage in the past.
> A river's stage at a point (a gauge reading) is not an absolute measure of the depth of the water in the channel, rather it is a depth with respect to an historical Datum level. In summary, when a river gauge reads zero or in the negative numbers - it does not mean that the river has gone totally dry or is running below ground. It means that the gauge is reading at or below the agreed-upon zero level.
> Silt may deposit in the river channel over time (filling the channel up), or the channel bottom may be scoured out to a deeper level by strong currents.
> Still, the gauge zero datum levels are not changed to keep continuity.
https://www.weather.gov/ctp/NegativeRiverStages
So, these aren't depth, and apparently aren't even comparable.