# Upstream to a river and tributary of a river - What is the underlying difference

What is the difference between a stream/ river upstream to a river A and a tributary of River A? I know that all tributaries are upstream to its river (A) and feeds into river A, but can there be a stream / river / lake upstream to river A but does not flow into it.

In other words, if a waterbody is not connected to river A , can you still call it upstream to River A.

Edit: I am interested in the semantics of these terms. This question is not related to any software, however modelling streams as either Tributaries of a river or just as upstream to a river is a GIS task (outside the scope of this question). If I say a particular stream "stream 1" is a tributary to a river A, then it automatically implies that "stream 1" is upstream to "river A". If so then modelling explicitly that "stream 1 is upstream to river A" is redundant, unless there is indeed a case where "stream 1 is upstream to river A, but its not a tributary of River A"

• Can you clarify the context of your question? Does this relate to a specific tool/script/software, logical model, or just general terminology? Can you give an example of what you might consider upstream that is not connected or expand on why you think there might be a difference between upstream and tributary? – Chris W Apr 11 '14 at 4:13
• I am interested in the semantics of these terms. This question is not related to any software, however modelling streams as either Tributaries of a river or just as upstream to a river is a GIS task (outside the scope of this question). If I say a particular stream "stream 1" is a tributary to a river A, then it automatically implies that "stream 1" is upstream to "river A". If so then modelling explicitly that "stream 1 is upstream to river A" is redundant, unless there is indeed a case where "stream 1 is upstream to river A, but its not a tributary of River A". – naga Apr 11 '14 at 12:08
• Your scenario can exist in a vector network. It depends upon how you define "connected". If connected is a polyline that connects at a node but you are not interested in its direction of flow then you can have the scenario where two streams are touching at the catchment boundary and are flowing in opposite directions. This is often referred to as a "saddle" and is usually a flat wet marshy area or a small lake. – Hornbydd Apr 11 '14 at 12:25
• If this question is purely about semantics, it might be better off at English SE than here. – Martin Apr 11 '14 at 12:28
• Thanks @Hornbydd! So two streams can be touching in a catchment boundary but flow into two seperate channels. If so then, both the streams will be upstream to the rivers they do NOT flow into? I mean, is it correct to say that a stream that does not contribute to a waterbody, is upstream to that waterbody (by water body I mean all rivers, lakes etc.) – naga Apr 11 '14 at 13:19

Any answer is going to be semantic in nature - your definitions of upstream, tributary, network, etc. are going to dictate the answer.

From a network (continuously connected features) point of view, I'm going to go with there is no difference and you cannot have a water body upstream of another without it being tributary. If you do have one that isn't connected, it's called a sink and it breaks things into separate networks. That situation certainly does happen in nature (all standing water to a degree), so from a physiographic point of view yes you can have a water body that is upstream (topographically higher in the same catchement) but not connected and therefore not tributary.

I typically only view 'tributary' as applied to flowing water and not still bodies. By definition, upstream implies within the same catchement, such that water eventually all flows to that point. Tributary essentially means flows into. I can think of no case where water would be upstream but not flow into and still be part of the network.

A stream could split via natural or manmade means, but everything above the split would then be upstream and tributary to everything downstream along both paths even if water would not naturally take that path. That also assumes that your definition of tributary allows for non-natural flows. Nearby we have diversion structures that bring water from one side of the continental divide to the other, however we do not consider those rivers on the source side to be tributary to those the water flows into on the other side.

In the case of a saddle, as Hornbydd mentioned above, that source node would be upstream to both channels, not just one. But the moment you leave that node you are no longer 'instream' with one of the channels, so you could not say one flowing in the opposite direction is upstream of the other. *Up*stream inherently implies flow and direction, so while that geometric situation can exist, you can't apply the terminology without considering direction of flow.

Unfortunately there is no monosemantic translation of the term "upstream" into my native language, so probably I just can't get you right. But if "upstream" is an adjective in your context and if you mean that it characterize the situation that tributary is lying "upper" then the main river, I think that there is no much sense in this expression. Firstly, it's due to the fact that the main river channel is the only "lengthwise coordinate" in the river. And the comparing between the different tributary locations is done relatively to the main river channel only (usually we measure the length of the path from the current point till the river mouth/estuary).

However, the river network schematization methods that are traditionally well-known in Soviet/Russian hydrology are fundamentally not preclude situations when the tributary is not connected directly to the main river but still ought to be classified as a tributary and belongs to the main river bassin (e.g. does not form the local endorheic basin). I can mention two differing cases:

1. Actually this situation is trivial in the conditions of large river floodplains that a characterized by a high terrain ruggedness and landscape complexity. The small tributaries has no "direct surface access" to the main river channel but often flow into the numerous shallow floodplain lakes that interact with a main river throughout the groundwater during the most part of the year (excluding the flood season, when the system of lakes and tributaries interacts directly with a main channel).

2. There is a specific type of a karst river (have no idea about the English equivalent) with a very specific hydrological regime. Their appearance corresponds with the occurrence of surface layers of limestone. These rivers always have a channel on the surface, but their riverbed is often dry: they кгт underground and and join the main river only during the short periods of full-flowing

Please feel free to ask me to clarify anything you're interested in.

• Thank you so much for your detailed answers @Vitaly and @Chris! I could mark both the comments as answers if possbile. – naga Apr 12 '14 at 3:16
• To help clarify for you, in this context upstream and downstream are typically used as relative direction adjectives considering the direction of flow at a given location. You can think of 'upstream' as 'before' or 'against the flow' and 'downstream' as 'after' or 'with the flow'. The terms upper and lower can also be used, but are usually applied to regions or sections rather than specific points. – Chris W Apr 12 '14 at 3:26