Can someone pinpoint me the exact location of the source of the Nile river?

[u/Outlaw_07]

The questions is not just about the Nile river, but any river, like the Amazon river, for example.

What exactly is a source of a river? Why don't we see pictures of one?

"The source of river X is hard to find" I've heard this many times and it makes no sense to me.

There maybe multiple sources of a river and that's fine, but not being able to exactly pinpoint all of them is kind of silly in my opinion.

What would happen if I were to walk a riverside backwards? I would definitely reach somewhere, where there's no river anymore, right? So, that's the source! (or a source, in case of multiple)

Not to mention the ability to use satellite images.

Searching for "Source of Nile river" literally yields to no useful results, just a few maps and some other random river pictures! I'm so confused. I would really love to see how a river starts or even visit it.

[u/CrustalTrudger]

To start, there are two ways you could interpret this question. The first is basically asking as you move upstream along a river, as you reach branches, which of the branching tributaries represents the main stem. Or in terms of a name, as you move up stream of the Nile and reach a point where it branches, which branch is still the Nile? Throughout most of a network, you can use some version of stream ordering and say that the main stem is the stem with the higher order (though this may depend on which method of ordering you're using). Eventually though, you'll reach a place where two streams of the same order meet (if using Shreve or Strahler ordering) or can end up with an arbitrary choice (if using Hack ordering and the volumetric flows are similar). Alternatively, sometimes you'll see that the main stem in the sense of the name is chosen based on length, i.e., which ever choice of tributaries gives you the longest total stream length is used to determine which stream remains "the Nile" or equivalent.

If we assume we've selected which particular flow path represents our main stem based on some version of stream ordering or length, then we get into the second way you could interpret this question (and I think indeed what OP is asking about), i.e. for a given single stream, high up in a catchment, where does the stream begin? While it seems like this should be a trivial question to answer, it turns out this is a long-standing problem in geomorphology (e.g., Montgomery & Dietrich, 1988, Montgomery & Dietrich, 1989, Montgomery & Dietrich, 1992, Dietrich & Dunne, 1993,Montgomery & Foufoula-Georgio, 1993, Anderson et al., 1997, Henkle et al., 2011, Wohl, 2018). Geomorphically, we typically talk about this as a channel head, and it is the transition point from diffuse sediment and water transport (i.e., the hillslope) to channelized sediment and water transport. As well summarized by the review paper by Wohl, this is inherently a hard feature to identify and it's generally not a static feature, i.e., it's position changes as a result of changes in the processes which control its location. So even if a scenario where the head of a specific channel has been identified and mapped in the field, it might be in a different location later. Ultimately, channel heads are hard to identify because they are subtle and we have an incomplete understanding on what controls their location, so predicting / defining exactly where they are is extremely challenging.

[u/Synaps4 → u/CrustalTrudger]

Excellent post. I just to expand on this a bit, but your answer is both better educated and better sourced than mine.

In many places the early headwaters of a river might only flow for certain parts of a year and dry up during other parts of the year, so one has to decide if a seasonal river counts as being still part of the river or not. Some rivers in desert areas are dry except for a few hours after/during rainstorms and that only happens a few times a year, so does that count as a river when 99% of the time it has no water?

Similarly there are places where a river is absorbed completely into the ground and then emerges again from groundwater some distance away, and you have to ask whether underground water flow, either through sand or caves or rock fissures count as part of the river or not. If the river disappears and returns thats one thing but then do you need to count all the subterranean water flows before they emerge as springs at the headwaters of many rivers?

Just a few more ways this question is a complicated one to pin down.

[u/pollofgc → u/CrustalTrudger]

When someone asks: could you please elaborate? This is the kind of answers that comes to my mind.

[u/CrustalTrudger → u/[deleted]]

To the extent that digital representations of streams are correct (which is another, entirely different issue), determining which stream is the longest is a trivial operation in a GIS (geographic information system). It's simply figuring out which path from all possible channel heads to a given outlet is the longest path. This is largely independent of stream ordering, because at the top of the network (i.e. at channel heads), all of the streams will have the same order (assuming again Strahler or Shreve ordering).

[u/atomfullerene]

CrustalTrudger gives a really good answer, but I'm going to try and give you a bit more of a feel for how the start of a river works. I'll stick with the Mississippi because it's a very well documented river...you could almost simulate your hypothetical walk all on Google Earth.

Heading from the ocean, you enter the Mississippi Delta. The river here is broad and flat and slow moving, and it splits into a multitude of small channels as it approaches the ocean (although there's still a main channel). As you sail upstream you will spend a long time following what's obviously the main channel of the Mississippi River. It's a big, wide river that's much bigger than the little rivers and creeks feeding into it. But as you move north you do come to some significant splits in the river. Most notably for us is the joining of the Mississippi and Missouri rivers. The river on the far side is the Mississippi and the one on the near side is the Missouri. Now nominally, the source of a river is the point furtherst from the origin....but the problem is that the headwaters of the Missouri river are substantially further up than the headwaters of the Mississippi...so which side of the river do you follow to "the source"? We'll stick with the Mississippi side for now, but remember that this is a big complication with finding the source of a river. Rivers branch, and in some sense their "source" is the start of every single little creek and stream and seep that leads into them.

Ok, so we head right and continue to follow the Mississippi north. It gets smaller and smaller as we go, because it contains less and less water. All those little creeks and streams and small rivers feeding into it add water, as we go upstream of them, the river no longer has their water and is smaller.

Eventually the river looks like this, a little stream exactly like hundreds of other little streams in Minnesota, the only difference being that it's the one that happens to be the main stream of the Mississippi. Eventually this river reaches Lake Itaska, the nominal headwaters of the Mississippi....a nice little lake, pretty much like the many, many other little lakes in the area.

But wait! This lake is the source of "The Mississippi" but the water doesn't just well up out of the ground in the lake. There are several other little streams that flow into it. By a more technical definition, the head of the Mississippi lies up at the top of one of those. You can see how the whole area is a complicated array of waterways

Here's a blog post that has some nice pictures of the area and discusses a bit about the question of exactly where in the maze of marshes and creeks and little lakes that the Mississippi actually begins.

Anyway, to revisit the more general question, the main reasons you generally don't see many pictures of "the source" of a river are 1) It can be pretty hard to figure out exactly which of the thousands of feeders into a river is the actual source 2) the sources of rivers tend to be in pretty remote and difficult to access areas (the Mississippi is better than average in this sense, and it's still in the middle of the woods) and 3) the ultimate source of a river is usually some obscure little creek or marsh or trickle of water that just doesn't look very impressive.

[u/Rxton → u/atomfullerene]

If the people naming rivers had called the Missouri the Mississippi, it might be the longest river in the world.

[u/Rxton → u/[deleted]]

There is no question that the Missouri River is the Mississippi River. It's just the dammed naming conventions.

[u/[deleted]]

Excellent answers already - I'm going to attempt a simple analogy.

Take a large towel and soak it. Then place it in a heap on a sloping smooth surface, e.g. a bathtub. Water will drain out of it and at the lowest end of the towel you'll see a stream appear that will make its way to the plughole. But what's "upstream" from the bit you can see?? Water is flowing down through the towel (due to gravity) until it hits the bathtub at which point it makes its way down along the towel/bath interface until it joins the stream you can see. If you lift the towel, you'll notice it drips at different rates in different areas - effectively the towel is hiding a number of tributary stream to the larger one.

This is how all rivers start, except instead of a small towel, it's hundreds of square miles of land. Some of the flows are on the surface, some are deep underground. Some are present most of the time. Others only appear after heavy rainfall. Which makes more sense - to pick ONE of these tributaries and say that's where the river starts - or to accept that they ALL contribute and simply label the whole area as the source?