| 00:00 | Great. What? We'll wait until income start? Well, let's get |
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| 00:27 | . We we covered a fair amount information yesterday, but most of it |
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| 00:36 | be background for you, uh which is new kind of mull |
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| 00:41 | You have any questions. Let me start. Do either of you have |
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| 00:45 | questions about what was covered last time you think would need a little |
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| 00:51 | No brother. Good. Okay, we're gonna talk about fluid flow and |
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| 00:56 | transport answers. We're gonna kind of into a little bit of hydraulics just |
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| 01:02 | this is the way we're gonna be to understand bed forms, which is |
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| 01:06 | way we're gonna understand sedimentary structures, is the way we're gonna build, |
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| 01:10 | and interpret deposition systems. So we about channel flow and again, focus |
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| 01:18 | this purpose. Rivers. Um we look at it as a function of |
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| 01:24 | . Um Is it uniform flow or it change with this non uniform? |
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| 01:31 | can also do time. So we talk about steady flow. Doesn't change |
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| 01:35 | time. Unsteady flow changes with time think about a flood. I did |
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| 01:39 | that um relative stability. That would laminar versus turbulent. Now, the |
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| 01:46 | is in rivers. Uh laminar pretty is, is just a word. |
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| 01:53 | don't really deal with non turbulent flow we get into the highly viscous turbidity |
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| 02:00 | , but we'll get back to that relative roughness, that is to say |
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| 02:06 | nature of the boundary. Is it hydrology rough for hydrology smooth? I'll |
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| 02:12 | defining all these as we go, velocity, tranquil or shooting again. |
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| 02:18 | be working on this later. So just start with um How about how |
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| 02:23 | is the flow? Clearly we want be able to measure the strength of |
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| 02:27 | flow and then predict what the nature sediment transport would be. Um And |
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| 02:33 | of the ways his velocity um problem the velocity changes with depth. And |
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| 02:40 | when we measure velocity to be average uh do we measure it at a |
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| 02:47 | depth? These are all things we to make decisions about. We can |
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| 02:52 | talk about shear stress, shear Uh That is the applied force um |
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| 02:59 | depending on not laminar or turbulent Uh So that's certainly hydraulically, something |
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| 03:09 | is potentially useful but we can think the basil ships risk um seems like |
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| 03:16 | you're interested with sediment flow and transport the bottom like bed load, uh |
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| 03:22 | whatever the shear stress is at the would be the most useful criteria. |
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| 03:27 | again it varies a little bit with nature of the channel. But you've |
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| 03:31 | this note, we could talk about velocity and actually again all of |
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| 03:37 | I will go into a little more but referred to as use star. |
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| 03:43 | . And um it's not a velocity rather it's a shear stress expressed in |
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| 03:49 | of velocity because frankly the units of stress stress are not intuitive. Whereas |
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| 03:57 | star or sheer velocity is at least in a term that is a little |
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| 04:03 | then the last thing we could do let's average let's look at um screen |
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| 04:08 | and so it's pretty power is particularly when it comes to try to predict |
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| 04:13 | the amount of deadlines for example. , so all these are terms that |
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| 04:18 | used in the literature uh and I take a subset of these uh to |
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| 04:24 | about Now. Let's start with downstream in slow. Okay. Um and |
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| 04:34 | we're looking at here is um a of pin a a series of flow |
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| 04:48 | . Yeah, is pointing out with fingers right now here here you can |
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| 05:03 | of these as streams of little packets water and at least for right now |
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| 05:09 | flowing parallel to each other. These time average. And if we look |
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| 05:17 | the top of the water surface, the measure of energy or it's like |
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| 05:26 | energy, not unlike water table, the water is moving, it's moving |
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| 05:31 | enough that there's a kinetic energy component the water motion. And that is |
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| 05:40 | through the energy line. So if put a little to hear the water |
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| 05:49 | expressing that extra portion of kinetic energy proportional to the support of the |
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| 05:57 | Now the problem is what happens is variation in let's say maybe a ripple |
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| 06:05 | yeah, well those flow lines begin converge uh they begin to converge and |
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| 06:15 | a result they take all that velocity squeeze it into a smaller area. |
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| 06:26 | means the velocity is increasing and because increasing, notice that the height. |
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| 06:35 | , that yeah, it's great. we're actually increasing the flow and as |
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| 06:41 | going up the back of the sun then those flow lines diverge as it |
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| 06:50 | in the back side down to And the velocity increases now in uniform |
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| 06:58 | None of this changes with time. just changing depth strength. And so |
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| 07:02 | we had a merging flow diverging Okay, now, with the converging |
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| 07:14 | , we're accelerating the velocity. So going to increase the load. So |
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| 07:19 | is going to be on the upstream of that uh with diverging flow where |
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| 07:27 | , we're gonna have increased deposition. , this idea of converging and diverging |
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| 07:34 | is simple enough to visualize river, we see it in all sorts of |
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| 07:39 | . Uh We can see it here called guys. Uh But this is |
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| 07:51 | deep sea sediments and suggesting that the is slow, might result in a |
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| 07:59 | in acceleration or deceleration. So we think about this in small term, |
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| 08:05 | little river or in big term, say, turbidity currents. Okay, |
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| 08:11 | , the second thing is, what changes with respect to time, |
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| 08:15 | time and again the velocity of discharge now, but notice the peak and |
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| 08:25 | , so this will be a storm . So this would be an event |
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| 08:31 | associated with that event, we're going see erosion and deposition. So it'd |
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| 08:37 | changing velocity. Uh when time is unsafe here and that means it's not |
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| 08:48 | to be. Now. When we at those slow lines, it goes |
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| 08:55 | basically zero at the bottom to some shear stress. That talks were applying |
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| 09:01 | stress. Gotta play here, play dressing. So that change in with |
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| 09:13 | is what this line represents. And shear stress you and we can talk |
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| 09:23 | molecular viscosity. That's basically the resistance two flow lines. We can talk |
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| 09:30 | the kinetic viscosity where in turbulent flow got a lot of exchange momentum between |
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| 09:37 | individual flow lines hitters are not perfectly , so its velocity is constant. |
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| 09:49 | as you apply a shear stress, us your strength, you get |
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| 09:54 | Okay, And with the Newtonian it has no shear strength. So |
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| 10:00 | soon as you put a little shear on that, it begins to |
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| 10:05 | And if it's a straight line, means that the viscosity is constant in |
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| 10:12 | particular case. Um we started relatively viscosity. So this would be a |
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| 10:19 | fluid fluid with the high viscosity, low viscosity. So it doesn't take |
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| 10:28 | lot of shift breath because I'm not . So the shape of this float |
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| 10:35 | , if you like, will vary on the viscosity and whether or not |
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| 10:39 | does or does not have sheer If it has a shear strain and |
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| 10:44 | have to apply a fair amount of for sure before it starts to. |
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| 10:51 | one of the big distinctions between, say most of what we're gonna look |
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| 10:56 | . Look at with sediment transport in or air. Is that all of |
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| 11:02 | fluids have no shear strength until you it's viscosity high enough in this concentration |
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| 11:11 | sediment high enough that we actually get sheer strength and that would be a |
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| 11:17 | flow or in some types of submarine flows and alluvial fan debris flows. |
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| 11:27 | , now, based on your it looks like it ought to be |
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| 11:31 | , just look at depth, looking . But as I may have mentioned |
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| 11:38 | time slope is really hard to figure . So conceptually this is real |
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| 11:44 | Uh in reality we're gonna have to something a little more indirect. Talk |
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| 11:53 | laminar versus turbulent laminar flow lines are , they don't the only interferences that |
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| 12:00 | viscosity, the skin viscosity, whereas turbulent, there's a lot of variation |
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| 12:06 | the elevation with full of progress. so the turbulence would look something like |
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| 12:13 | from time, instantaneous velocity fluctuations. tend to think about a uniform or |
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| 12:20 | velocity to define those flow lines and we do that, we let it |
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| 12:26 | from the base where which basically, , there's actually a parabolic shape to |
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| 12:34 | velocity profile. Whereas with turbulence it's people rhythmic profile, that transition from |
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| 12:47 | turbulent can be described on the basis the Reynolds and the Reynolds number is |
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| 12:56 | increases with increasing velocity. It goes a critical Reynolds number. And also |
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| 13:03 | have virtually all rivers on with a of minor exceptions. So what is |
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| 13:13 | ? Reynolds number? It's ratio of uh the viscous forces and essentially the |
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| 13:20 | directly proportional velocity. It's directly proportionate critical length. It is inversely |
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| 13:29 | disgusting. Okay, now the velocity you can use the logic but let's |
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| 13:37 | you the average positive country will use flow depth for critical um link and |
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| 13:48 | cinematic viscosity. This and then we've this. Reynolds lost Reynolds number for |
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| 13:56 | channel flow. Okay, so when we got critical number, go |
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| 14:01 | laminar to um turn That number is 500 and 2000. It turns out |
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| 14:10 | if you had A sheet of water cm High moving at a foot over |
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| 14:25 | seconds. It's gonna be tough. the only way to really go get |
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| 14:34 | flow. It make it really very slow or increased response increased |
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| 14:52 | So viscosity is really what plays a here. And it's the distinction between |
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| 14:58 | of sediment transport virtually all sediment transport rivers and the ocean except for turbidity |
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| 15:08 | Statham entry graphic close. Okay, , now it turns out that with |
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| 15:17 | rhythmic profiles and turbulence. Let's We're basically dealing with terminal close. |
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| 15:22 | can plot that on a long, clock. I can send me |
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| 15:29 | And it turns out that that slow you start. So this here you |
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| 15:42 | , you saw as I mentioned earlier the square root of G. Times |
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| 15:49 | So here velocity, I'm sure she . All we need to do is |
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| 15:56 | a measurement at two or three around or four places of different depths plotted |
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| 16:02 | oil paper and you get a slow when we go about trying to measure |
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| 16:13 | transport in the field or in the , in the ocean or in the |
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| 16:17 | , that's basically what we're doing. we're taking and certain depths you |
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| 16:27 | which is a form of basal ship . And so most of the work |
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| 16:33 | you see now uh is expressing set transport that is velocity, not even |
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| 16:40 | sheer stress, but you storm. that's the way to do it. |
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| 16:47 | there is one exception that and that when you get right down face um |
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| 16:57 | of the death that critical, you , today, elevation when you're just |
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| 17:06 | little bit above the block and that's pretty low depth. It actually |
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| 17:11 | Then you're going from number the So there's a basal laminar flows on |
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| 17:22 | it predominantly turbulent transitions in between have buffer zone. And this is where |
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| 17:32 | is generated. And we'll see this important in getting the setting up into |
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| 17:37 | center of the other thing is a , maybe the thickness of this |
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| 17:45 | So called viscous sub layer um can thicker than versatile the same. |
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| 17:54 | it's a sand braid is large enough it actually interrupts that base of |
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| 18:01 | So in hundreds you're getting at least . Of course you're going sam, |
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| 18:14 | just don't have that, the player all. And so that's the distinction |
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| 18:20 | and wrong with hydraulically smooth, It matter how big the grain is, |
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| 18:27 | not gonna be generating turbulence, whereas matter how I think uh sub layer |
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| 18:39 | , it can't maintain itself. Of , your grand setup turns out that |
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| 18:45 | important when we think about the inception sediment transport. And just real |
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| 18:55 | we don't get um rather we only ripped. Yeah, fine grained |
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| 19:06 | Let me read. Uh in order get this set in the movement, |
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| 19:15 | need to create something that interrupts the a ripple. So in order to |
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| 19:24 | this fine grain sand, it's smaller the laminar somewhere to move. I |
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| 19:31 | to create a ripple. Once the their language subject is gone, what |
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| 19:36 | it turns out, it doesn't matter little variation. A little bump in |
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| 19:41 | bottom is enough to initiate a report it's initiated, that's the form |
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| 19:46 | then you can transport down here. don't need a ripple to get this |
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| 19:53 | moving. So this will be the of same. So when you have |
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| 19:58 | grain beginning to move, it moves a triple bed form if you have |
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| 20:03 | grained sand beginning to move, It flows is plain bed. So the |
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| 20:10 | bed form and resulting sedimentary structures at inception of motion differ depending on what |
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| 20:18 | dealing with fine grained bottom to force hydraulically rough waters. Yeah. And |
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| 20:26 | is the same thing. Now this that mean profile that is into that |
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| 20:42 | . We have a lot of So we had periods of time. |
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| 20:50 | water first stuff and then sweep So what we see is the main |
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| 21:02 | varies a lot in terms of what called person sweeps. You look kind |
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| 21:08 | like this and what this is is way in which you've been get set |
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| 21:15 | higher up into the ward. So the way we begin to get our |
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| 21:20 | into the water column by these bursts sweeps. And this is this is |
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| 21:26 | injection started. So this is the really upset in the transport series of |
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| 21:36 | bursts. Now let's think about acceleration. Oh and let's look at |
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| 21:48 | happening this week gets steeper and steeper the flow gets deeper. The water |
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| 21:55 | accelerating and that wine between the energy energy in the water surfaces increasing. |
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| 22:04 | just visually tells us that we are . But now let's stop. So |
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| 22:13 | about we got except now instead of smooth transition we saw earlier, the |
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| 22:23 | ill aeration causes this really her Bulent jump. And so what's happening is |
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| 22:33 | going through a critical part. Don't around this and then we go back |
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| 22:42 | that critical height. This portion on left is streaming relatively uh slow for |
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| 22:56 | decision. We haven't changed the we just change the velocity slow. |
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| 23:01 | now going a lot faster elevation. the type of uh drop down. |
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| 23:11 | we slow it down even back but it can't go up slightly. |
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| 23:15 | has to go up to this hydraulic . And so what we do is |
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| 23:20 | define this as a sub critical scooper hydraulic jump is the way you |
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| 23:28 | Supercritical. Supercritical form a lot of . And that transition is defined by |
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| 23:37 | less than one Medical for one. Critical. So what does that look |
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| 23:44 | ? It flew? Well, here we go, coming down constant |
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| 23:51 | . It's increasing its philosophy. Come here, it's jumps all these |
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| 24:01 | So you can imagine that sediment, structures associated with this are gonna be |
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| 24:06 | different. And we used to assume this was mainly an issue with respect |
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| 24:14 | things like turbidity currents. But now realizing that this is actually a relatively |
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| 24:20 | feature, high velocity rivers, in storms. So what is that |
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| 24:26 | number? It's the second dimension. ratio. Talking about this one's inertial |
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| 24:32 | forces. Okay. Uh it is lossy ratio for the lost city of |
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| 24:42 | who have lost in gravity wave, wave is a wave. The way |
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| 24:47 | think of the gravity wave is if threw a rock and understanding water, |
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| 24:53 | speed at which that ripple propagates away the point of impact. That's the |
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| 24:59 | of the gravity wave from water. depth, it turns out the oh |
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| 25:07 | would. And today those directly proportional to a power square uh to water |
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| 25:22 | . And so if we think about average global la city relative to the |
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| 25:29 | , that's gonna determine whether or not sub critical or supercritical, whether or |
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| 25:37 | it's transport for grieving as well. we're finding uh really in the last |
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| 25:48 | years or so is that supercritical flow really pretty calm and more specifically, |
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| 25:56 | sedimentary structures born by sediment. Supercritical are much more common and this is |
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| 26:04 | classic example. You don't see what not looking now that we see the |
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| 26:13 | evidence of supercritical flow. We're seeing law. Okay, now there's one |
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| 26:21 | thing, uh the idea of very large depths, let's go back |
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| 26:37 | technician. How do you keep number local law states for high debt. |
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| 26:51 | when you're looking at something like uh canyon or submarine fan, water depths |
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| 27:00 | huge. And so we assume that supercritical flow wasn't possible, but what |
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| 27:06 | realized was we're looking at the wrong . What we needed to be looking |
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| 27:13 | is the depth of the flow of water that's concentrated as a sedimentary |
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| 27:21 | So now we're looking at the concentration the specific gravity of that water into |
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| 27:31 | the said compared to the top of gravity's. So we can have dents |
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| 27:38 | the metric Bruno. So we can sentimental gravity flows and supercritical 5000 water |
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| 27:47 | . So it's no longer just the of the ocean, but rather the |
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| 27:53 | or thickness of the sedimentary gravity So let's go back to that |
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| 27:59 | I gave uniform and verging Sloan's And we're looking at the energy line |
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| 28:17 | as it increases. You're accelerating, the height, decrease your decelerated. |
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| 28:28 | we can actually think of those terms terms of hydraulic head I don't like |
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| 28:35 | we can talk about elevation and it's just that the groundwater velocity. |
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| 28:45 | , that pretty much the water tape the head. While we're moving |
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| 28:53 | we have a component of energy that the Connecticut with velocity. Now, |
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| 29:05 | , what is different about these two conditions. Right. Describe the upper |
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| 29:21 | . Different florida. It's ST it's the relationship between the bottom purpose |
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| 29:39 | surface of the water and so here the upstream portion it's slowing down here |
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| 29:50 | the apologize to uh my own But here the water is slowing down |
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| 30:01 | . The water is uh the velocity increasing party, increased velocity, decreased |
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| 30:10 | and conversely this is decreased velocity, policy. What we would say in |
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| 30:21 | is that the water surface is out phase with the bottom for symmetry in |
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| 30:28 | upper upper diagram, the water surface in phase with the body on the |
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| 30:34 | side. So if you think about , ask yourself the question, where |
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| 30:44 | you experience erosion versus deposition for I've already told you to tell me |
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| 30:53 | . With the upper Yeah. What you expect? Erosion or deposition up |
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| 31:04 | . Yeah, it's accelerating in deposition . Uh What about down here, |
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| 31:17 | going in? You've got deposition upstream erosion down street. Now the fact |
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| 31:30 | this the upper zone is is the of the situation in tranquil flow. |
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| 31:37 | have food numbers less than one. lower it is an example of shooting |
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| 31:45 | through From a practical point, do think about how this lump will |
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| 31:55 | This lump in the upper zone will downstream erosion on the back deposition. |
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| 32:04 | look in is gonna actually migrate upstream . It's not that the sentiment moves |
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| 32:16 | but rather the deposition is Aisling up the upstream side because erosion here, |
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| 32:26 | gonna cause deposition here. The erosion the the out stream side will result |
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| 32:35 | deposition and bed for migration of It's a difference between a ripple in |
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| 32:41 | dune in the upper diagram in an day or other. Now we talked |
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| 32:55 | sediment being transported. We think about salutation, suspension. We're ignoring dissolves |
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| 33:02 | devolved by this. Uh we're either or dragging it, bouncing it or |
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| 33:10 | letting it be suspended either partially or by turbulence. And of course that |
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| 33:19 | , combined that think about bed load suspended load and we can subdivide suspended |
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| 33:25 | into this continuously submitted and wash load suspended again. Ignoring dissolve, assuming |
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| 33:40 | we're dealing with hydraulically rough boundary, say media endorsements. The flow lines |
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| 33:48 | converging over the other troops on top and according to the pressure, the |
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| 33:57 | changed the greatest pressures upon these pressures top. So we get it. |
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| 34:08 | we're also applying a shear stress. we're complying frictional drive and will give |
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| 34:19 | the fluid force that's gonna get that in motion either by rolling or |
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| 34:30 | Um There's no close separation, it uh follow is which uh and turbulence |
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| 34:52 | greater. And or article you also a uh a down flow Eddie that |
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| 35:04 | in separating and getting flow in So what we visualize is bed load |
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| 35:12 | and rolling and sliding some bounce either air or water. And eventually partially |
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| 35:25 | that any suspension, eating anything popping , go to the first six weeks |
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| 35:31 | are helping to maintain the sediment in . Otherwise it would just settle |
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| 35:40 | So we've got traction load or bed going down. Tenuous. Uninterrupted |
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| 35:49 | yep. Um I'll skip that. our interest at least to this point |
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| 36:01 | inception of motion. Have we applied force to share streets? They get |
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| 36:08 | sentiment mood whatever. So the shield is the one that's been used traditionally |
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| 36:18 | determine the transition from motion or no . The problem with this diagram is |
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| 36:28 | it expresses the very in terms of shear stress and sediment characteristics, for |
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| 36:42 | , horizontal, we've got you star great on the vertical axis you've |
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| 36:53 | So even though we can you've been frequent calculate these very it has no |
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| 37:03 | sense to it. So why don't take that and take the green |
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| 37:12 | owner or zone in the fluid strength on the vote. Now, clearly |
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| 37:21 | have to make some assumptions but let's assume that it's uh porch. |
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| 37:27 | we've got a constant density. Let's that it's water, fresh water and |
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| 37:33 | constant viscosity. Um And so we of narrowed it down to right |
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| 37:45 | And then here we're gonna use the and one m. We could use |
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| 37:52 | number of things. The key is difference in the shape. Now we |
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| 37:56 | see you have to apply increasing We get increasingly large diameters. |
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| 38:05 | so we've got no motion erosion but in something that makes more sense. |
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| 38:17 | . Now let's take a individual Um Okay and let's apply increasing press |
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| 38:31 | switched from stress velocity. I'll do all the time. But they're all |
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| 38:36 | . So more and more stress until hit this line and now the settlement |
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| 38:43 | , it's moving under higher and higher . Now it first moves as |
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| 38:52 | but at some point it's going to its doing suspension. Remember that diagram |
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| 38:58 | showed it showed the rolling sand eventually to suspension. So that's gonna happen |
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| 39:06 | here someplace. So how do we where did that transition is? Screen |
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| 39:16 | ? Well, we're gonna look at full philosophy. Um a sphere of |
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| 39:27 | . Okay. And uh the bigger is, the faster it bastard. |
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| 39:40 | so this would be the And it out that you can more or less |
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| 39:50 | this fall glossing by Houston. So you start is basically equal with the |
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| 40:02 | you like the shear stress, it's to the for philosophy. Then as |
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| 40:09 | shear stress increases, it goes into . If the shear stress is less |
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| 40:16 | the fall of loss, eat, moves extraction, recognizing this gradation that |
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| 40:22 | allows us, it's just to show happening to try to define this summer |
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| 40:38 | years. So now we've got a and now I've extended to other grain |
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| 40:45 | , still focusing on the no Bed load, rolling, bouncing |
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| 40:55 | And now I can forget it. And we'll come back to this shape |
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| 41:04 | this basically is the beginning of a phase diagram where we're going to look |
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| 41:10 | variables of you Star Aussie brain size predict bed forms and therefore sedimentary |
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| 41:20 | Now, a couple of other things keep in mind the courses range that |
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| 41:24 | be transported. The first was streamed confidence and that really goes back to |
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| 41:32 | shield because she was dr graham basically says folks should know and that's a |
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| 41:43 | fortune of the capacity that has to amount of sediment that can be |
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| 41:53 | but it's mainly a function of I'm sorry, Philosophy, ready for |
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| 42:00 | power. Three discharge proportional to So those are two terms, you'll |
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| 42:14 | confidence. How big can it move ? How much can be moved? |
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| 42:23 | we think about suspended sand. Just about that portion is not moving by |
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| 42:30 | we increase the philosophy increasing capacity. earth down here, we're just dealing |
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| 42:40 | very fine, but eventually we could the gravel being transported, suspension If |
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| 42:52 | had velocities of six or 7 Now that would only happen really catastrophic |
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| 43:00 | on uh but suddenly we can get certain amount of course of sand when |
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| 43:07 | have very bad into suspension. Now leads into uh the um Yeah, |
|
| 43:22 | . Did you, did you ever this in your uh, what, |
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| 43:34 | you for you? Uh This is pretty important diagram because what it says |
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| 43:44 | that same? What it, what says is that this line right |
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| 43:57 | It's more or less what we've been about for some time and it's the |
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| 44:01 | of deposition. You can also think it as the zone of no |
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| 44:06 | And so as we increase velocity of measure, nothing moves until here and |
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| 44:16 | it begins to erode. And of with erosion comes sediment transport. So |
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| 44:24 | zone of deposition is what I referred earlier. The motion. The zone |
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| 44:29 | erosion is what I referred to earlier sediment transport. Okay, conversely, |
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| 44:36 | the velocity slows down, sandman goes being moved her deposit. Okay |
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| 44:47 | though, you've got a funny situation it actually, when we get into |
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| 44:52 | pretty fine grain sand to silt and , we're getting a zone where it's |
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| 45:02 | hard to get it in motion, no motion motion. But then as |
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| 45:08 | dropping, it can stay in motion than it could be eroded. And |
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| 45:16 | common explanation for that is that it um cohesive. We're beginning to see |
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| 45:23 | inter granular uh cohesive forces, making hard to move. But once it's |
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| 45:31 | motion, the settling velocity is pretty . Now we're gonna take that and |
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| 45:39 | it just like and we're gonna this curve up in here. Yes, |
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| 45:52 | for more consolidated think about mud and down to the bottom. It's pretty |
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| 46:01 | to get that re suspend unconsolidated So uh it's not as hard, |
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| 46:10 | it's still harder than you would Now, here's that line for settling |
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| 46:19 | . There is notice that you can that settle in suspension at the loss |
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| 46:36 | much lower than would be required to an emotion. That's why it's so |
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| 46:47 | , so I'm just interested that's the diagram we get out of that |
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| 46:53 | I'm really interested in this zone right for sediments and dead load, suspended |
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| 47:04 | . Make it look like this. let's look at relatively emotional threats. |
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| 47:18 | can get five grand imperial transported in and there's some right here which is |
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| 47:30 | range of set that can be transported spent at the same time. So |
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| 47:38 | got this is better now let's imagine the increase the sheriff dress by two |
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| 47:49 | men now that sediment that was moving bed load, moving a suspended |
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| 47:58 | And now we've got a lot of with a wide range of range size |
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| 48:05 | his Bentley. Yeah. So that is we've got a tortured brain poorly |
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| 48:14 | . So whereas pretty well for So it began to need to think |
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| 48:25 | how does the variation or amount of stress affect a range of said. |
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| 48:36 | the flume studies as useful as they usually deal with the single grain size |
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| 48:45 | they call it the average princess. we know that in nature we get |
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| 48:49 | green size distribution. Yeah. So example, just imagine you've got your |
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| 48:58 | is going that's gonna cause variation in size that's been transported as forget about |
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| 49:11 | . So we could think about the , which is nothing to say about |
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| 49:22 | . You got me showing that is fact the case. And let's take |
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| 49:28 | our center, we've shown off. mean, as we know that there |
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| 49:35 | some mean statistical standard deviations given succession a great population. Now I've expressed |
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| 49:46 | distribution of grain size, not as , what is the rather than applied |
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| 49:56 | , But so as you increases your at some point, you begin to |
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| 50:04 | those the highest first scientist. So beginning to create a students of the |
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| 50:15 | material. And as we continue to the average shear stress, we are |
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| 50:23 | a larger, larger percentage of the ocean. And so that ratio average |
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| 50:39 | them average applied shares. For this critical carefulness of this population. It's |
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| 50:50 | the transport state. And as you that, your stress of fluid, |
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| 50:59 | increase the transport statement. That is measure of capacity. Uh We're gonna |
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| 51:07 | there. Um because what I want do at this point is to take |
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| 51:17 | flow and sediment in motion began to at the bed form that are |
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| 51:25 | that's on sediment transport and then the structures. So this is just the |
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| 51:33 | to it. So let's get the because I want to keep the recording |
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| 51:37 | this |
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