- [Voiceover] Okay. So we got our bankfull channel depth. What we've got now, is we have our channel thickness, which we're using as a proxy for our bankfull channel depth, and we have, from our story analysis. And we have some sediment from the bottom of that channel, Out of that bottom of that bar, that we're using as a proxy for the bedload that that channel would've moved. So we're ready to move onto the next depth. Taking that bit of information and calculating the bankfull flow that that river would represent. In other words, how much water and how much sediment would that channel have moved, given that depth and that grain size at the time of bankfull flow. So we have a series of calculations you walk through here. We have all kinds of things that we have to walk through and calculate. One there is the slope, using the grain size, and we estimate from the grain size and the critical shear stress it would take to move that grain, we can estimate how much slope that channel would've needed given that the water depth it had. And, from there, we can calculate bankfull discharge from the slope and the channel depth. And now we can turn around and make an estimate of the roughness of the channel, and then make a estimate of how much water that channel would've moved. What would've been its bankfull flow. Then what we can also do is take that information. We can can make an estimate of the amount of bedload that channel would've moved at bankfull flow. Then we go to what's called the Van Rijn Method, as it's called, which is a 13 step set of equations, which I've only put down the last one here, that is used to calculate how much suspended load the channel would've moved. Very often there's more than one way than the Van Rijn method, so there is a couple of the things I like to use. Wright and Parker particularly, as alternative way to calculate the concentration of suspended load. But I still fundamentally used the 13 steps of the Von Rijn. But there's some later things that have been proved on a step or so on it. So sometimes you go to those and say "Well, I'll plug that in and I like that better". Ultimately though, what this workflow will give you, in this set of calculations, is it will give you, for every channel story that I measured in my section, like, for instance, channel number five here, it will give you a set of numbers. What was the bankfull flow? Or over in here, what's the total amount of suspended load that the channel would've moved? What's the bedload it would've moved What's the water it would've moved? So that's what these numbers all represent. It's for each channel in my section. I've done these calculations based on this. So what that's giving me is a set of bankfull of just how much material that settlement would've moved under bankfull conditions. Okay. So the next thing is that, of course, with that, there's, all we have is the vertical thickness of the channels in all these calculations. I did leave out an important step is that channels are not just the thickness. They're a width as well. So, for each of these channels, if I only have a vertical section, I have to estimate how wide the channel would've been to try to get its full geometry. So, the actual bankfull geometry and all these widths. I've gone through the literature, and here's one example. This is some work by Blumenthal. This simply looks at channel fills and says, for a given channel fill thickness, what would be the potential width? And there's a range of width that you typically see in a typical channel for a typical depth. There's other equations that are used by Allen that you can run to that will give you numbers as well. But, again, if you only, you have to have the channel width because if you can, you may be able figure out the slope from just the channel depth alone. And you may be able to figure out how much bedload and suspended load it would've moved over one unit width. But to know just how much sediment the channel would've moved in total, you have to know how wide the channel was. So if you only have a vertical core, you're gonna have to estimate that. So just as an example. This is one works from Blumenthal that actually does that. There's other works out there that people used to do aspect ratios, given a thickness of the channel, how wide would it be. So we have to use one of those if we don't already know the width of the channels from our data. Alright. From their there's several different curves that have been used over the years to try to actually say, from story thickness, what's the bankfull discharge. So this an example from Davidson and North. It's always good to plug-in somebody else's data, somebody else's approach and see if it matches yours. But the one thing that the Davis and North approach does that's really handy is using this basic equation. And I won't belabor their method, I'll just simply point to their paper. You can calculate what would've been a likely drainage area for your channels. Given a certain depth of your channels, how much drainage area will it have likely had. That's pretty handy because once you calculate how much sediment that those rivers likely moved, you can make some broader estimate of just how much area that those channels were probably draining to do it. When you do these calculations, we make another assumption. We simply say, of all the channels, there a couple dozen channels are so that I measured. The reality of it is, is it's only the largest ones are probably representative of the system that was draining the source and feeding the sink. Because the smaller ones are probably tributaries or distributaries in the system. And the big trunk ones are the ones that we're interested in. So what I will do is, of all those channeled that I picked out, out of that, these particularly four biggest ones. And I ran the numbers for those. So there is the average bankfull depth for each of the channels. There's the suspended load, and the bedload it moves, and the water discharged. And then, using the approach from Davidson and North, I calculated an estimate of how much drainage area these things had. Then, using this equation here, converts drainage area to drainage link, I can actually figure out about how far back that drainage would've reached. So that gives me a sense of about how far ahead were these rivers would've cut. So, a broad estimate of that. Alright. So just as a note for these particular rivers, these are the proto-Nile. These channels here that would've fed the Bahariya Oasis in the Cretaceous would've headed somewhere up here, no more than about 1000 kilometers from the area where we were measuring the fulcrum. Lo and behold, the paleogeographic reconstructions over here of those same rivers, from other independent work just plotting the paleogeography for that time, That's about what they have. So, so far, so good. The method is Passel last test.