[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:02.38,0:00:05.38,Default,,0000,0000,0000,,Okay now that you know a little bit about\Nground water systems.
Dialogue: 0,0:00:05.38,0:00:07.43,Default,,0000,0000,0000,,Some of the vocabulary associated with\Nthem.
Dialogue: 0,0:00:07.43,0:00:10.15,Default,,0000,0000,0000,,Let's talk about groundwater flow.
Dialogue: 0,0:00:10.15,0:00:14.29,Default,,0000,0000,0000,,Groundwater is usually not stagnant,\Nokay, it's usually moving.
Dialogue: 0,0:00:14.29,0:00:17.40,Default,,0000,0000,0000,,It isn't moving fast like a stream but it \Nis usually moving,
Dialogue: 0,0:00:17.40,0:00:21.72,Default,,0000,0000,0000,,and typical flow rates would be on the \Norder of about a half a meter per day.
Dialogue: 0,0:00:21.72,0:00:26.39,Default,,0000,0000,0000,,It flows away from areas where it enters\Naquifers.
Dialogue: 0,0:00:26.39,0:00:31.74,Default,,0000,0000,0000,,Two places where water exits aquifers.
Dialogue: 0,0:00:31.74,0:00:37.88,Default,,0000,0000,0000,,We call places where water enters an aquifer\Nrecharge areas and places where water
Dialogue: 0,0:00:37.88,0:00:41.88,Default,,0000,0000,0000,,exits aquifers are referred to \Nas discharge areas.
Dialogue: 0,0:00:41.88,0:00:46.76,Default,,0000,0000,0000,,So you can say that water flows from\Nrecharge areas to discharge areas,
Dialogue: 0,0:00:46.99,0:00:49.10,Default,,0000,0000,0000,,and that's what's shown on the slide.
Dialogue: 0,0:00:49.39,0:00:55.53,Default,,0000,0000,0000,,The blue lines depict groundwater flow\Npaths and you can see that some of these
Dialogue: 0,0:00:55.53,0:00:57.40,Default,,0000,0000,0000,,flow paths are fairly short.
Dialogue: 0,0:00:57.40,0:01:02.81,Default,,0000,0000,0000,,The shortest ones, groundwater can flow\Nalong in a matter of days.
Dialogue: 0,0:01:02.81,0:01:09.25,Default,,0000,0000,0000,,Others, however, are quite long, uh, \Nwater can be isolated from the, um,
Dialogue: 0,0:01:09.25,0:01:13.40,Default,,0000,0000,0000,,from the surface and aquitards and\Naquifers for thousands of years,
Dialogue: 0,0:01:13.40,0:01:15.25,Default,,0000,0000,0000,,or even more.
Dialogue: 0,0:01:15.25,0:01:20.51,Default,,0000,0000,0000,,Some research, um, recently identified \Nsome groundwater that was at least as old
Dialogue: 0,0:01:20.51,0:01:28.48,Default,,0000,0000,0000,,as 1.5 billion years old, okay, and been\Nisolated in the subsurface for that long,
Dialogue: 0,0:01:28.48,0:01:31.04,Default,,0000,0000,0000,,which is incredible.
Dialogue: 0,0:01:31.04,0:01:34.14,Default,,0000,0000,0000,,Okay so that-that would definitely be\Nexceptional.
Dialogue: 0,0:01:34.14,0:01:40.55,Default,,0000,0000,0000,,So what controls the movement of rocks and\Nsediment, well the equation that we use to
Dialogue: 0,0:01:40.55,0:01:45.72,Default,,0000,0000,0000,,describe the flow of water through coarse\Nmaterials like sand was, uh, defined by this
Dialogue: 0,0:01:45.72,0:01:48.04,Default,,0000,0000,0000,,guy, Henry Darcy.
Dialogue: 0,0:01:48.04,0:01:53.21,Default,,0000,0000,0000,,And the equation that he used, or that he\Ndefined, is known as Darcy's Law.
Dialogue: 0,0:01:53.21,0:01:56.25,Default,,0000,0000,0000,,So at some point he must have asked a \Nquestion, what the heck controls the
Dialogue: 0,0:01:56.25,0:01:59.30,Default,,0000,0000,0000,,movement of water through sand?
Dialogue: 0,0:01:59.30,0:02:03.75,Default,,0000,0000,0000,,And I imagine that we've all asked that\Nquestion time or two.
Dialogue: 0,0:02:03.75,0:02:07.86,Default,,0000,0000,0000,,Although, he probably would've said it\Nin French, cause he was, um, he was
Dialogue: 0,0:02:07.86,0:02:13.32,Default,,0000,0000,0000,,actually a French engineer, uh, just to\Ngive you a little historical context on
Dialogue: 0,0:02:13.48,0:02:15.06,Default,,0000,0000,0000,,this topic.
Dialogue: 0,0:02:15.16,0:02:18.84,Default,,0000,0000,0000,,Uh, he was an engineer and he lived 'bout\Nthe same period of time as
Dialogue: 0,0:02:18.84,0:02:20.72,Default,,0000,0000,0000,,Abraham Lincoln.
Dialogue: 0,0:02:20.72,0:02:24.16,Default,,0000,0000,0000,,During his life he was very famous for\Nbringing a water distribution system to
Dialogue: 0,0:02:24.16,0:02:28.11,Default,,0000,0000,0000,,Dijon in 1840.
Dialogue: 0,0:02:28.11,0:02:31.80,Default,,0000,0000,0000,,Okay this was a big deal because very\Nfew places at the time had water
Dialogue: 0,0:02:31.80,0:02:33.32,Default,,0000,0000,0000,,distribution systems.
Dialogue: 0,0:02:33.32,0:02:38.39,Default,,0000,0000,0000,,Wasn't, it was also at this time that few\Nplaces had sewer systems, okay.
Dialogue: 0,0:02:38.39,0:02:42.54,Default,,0000,0000,0000,,So if you were living in a city, a good \Nreliable source of clean water was
Dialogue: 0,0:02:42.54,0:02:44.63,Default,,0000,0000,0000,,really important.
Dialogue: 0,0:02:44.63,0:02:49.53,Default,,0000,0000,0000,,Um, for reference, Paris didn't have,\Noops, Paris didn't have a water
Dialogue: 0,0:02:49.53,0:02:55.69,Default,,0000,0000,0000,,distribution system until 1865, a full\N20 years after the little city of Dijon
Dialogue: 0,0:02:55.69,0:03:00.18,Default,,0000,0000,0000,,um, got it's water distribution system.
Dialogue: 0,0:03:00.18,0:03:04.30,Default,,0000,0000,0000,,It wasn't until very late into his life, 2\Nyears before he died, that he carried
Dialogue: 0,0:03:04.30,0:03:08.67,Default,,0000,0000,0000,,out the experiments that perhaps he is\Nbest known for today.
Dialogue: 0,0:03:08.67,0:03:13.19,Default,,0000,0000,0000,,He performed the experiments in hospital,\Nthat might seem like, y'know a really
Dialogue: 0,0:03:13.19,0:03:17.34,Default,,0000,0000,0000,,odd choice, at the time there probably\Nweren't as many places where, uh, that
Dialogue: 0,0:03:17.34,0:03:21.08,Default,,0000,0000,0000,,were, y'know, convenient for setting\Nup experiments.
Dialogue: 0,0:03:21.08,0:03:27.56,Default,,0000,0000,0000,,The experiment that he performed, uh, he\Npublished results in his report in 1856,
Dialogue: 0,0:03:27.56,0:03:32.06,Default,,0000,0000,0000,,and uh, they were just described in a\Ncouple of pages in the very back of the
Dialogue: 0,0:03:32.06,0:03:38.20,Default,,0000,0000,0000,,report, I think one of the appendices \Nfor the, um, for the report.
Dialogue: 0,0:03:38.20,0:03:41.49,Default,,0000,0000,0000,,Uh, so it was very much just an \Nafterthought, but it turned out to be a
Dialogue: 0,0:03:41.49,0:03:45.11,Default,,0000,0000,0000,,very, uh, a really useful important piece \Nof work.
Dialogue: 0,0:03:45.11,0:03:49.76,Default,,0000,0000,0000,,So what we're gonna do now is walk through\Nsome aspects of Darcy's experiment.
Dialogue: 0,0:03:49.76,0:03:53.76,Default,,0000,0000,0000,,This will help illustrate some basic controls on\Nthe movement of water through porous
Dialogue: 0,0:03:53.76,0:03:57.59,Default,,0000,0000,0000,,medium, and also the process of science,\Nhow you can apply some basic reasoning,
Dialogue: 0,0:03:57.59,0:04:03.02,Default,,0000,0000,0000,,collect data, and then figure out\Nrelationships.
Dialogue: 0,0:04:03.02,0:04:08.82,Default,,0000,0000,0000,,So what Darcy did was, uh, set up a tube\Nthat contained some sand, and that
Dialogue: 0,0:04:08.82,0:04:13.83,Default,,0000,0000,0000,,tube had some smaller tubes in it called\Nmanometers poking into the, near the in
Dialogue: 0,0:04:13.83,0:04:16.15,Default,,0000,0000,0000,,flow and out flow end,
Dialogue: 0,0:04:16.15,0:04:22.16,Default,,0000,0000,0000,,and he'd float water through the sand tube\Nand, uh, observed how different variables
Dialogue: 0,0:04:22.16,0:04:24.89,Default,,0000,0000,0000,,affected flow.
Dialogue: 0,0:04:26.25,0:04:31.96,Default,,0000,0000,0000,,Hydraulic head is the name given to the\Nheight at water rises and the manometers
Dialogue: 0,0:04:31.96,0:04:35.73,Default,,0000,0000,0000,,relative to some arbitrary data.
Dialogue: 0,0:04:35.73,0:04:39.84,Default,,0000,0000,0000,,In natural environments we would typically\Npick sea level to be the datum.
Dialogue: 0,0:04:39.84,0:04:43.37,Default,,0000,0000,0000,,In a lab experiment you might just pick\Nthe bench top where you're carrying out
Dialogue: 0,0:04:43.37,0:04:46.75,Default,,0000,0000,0000,,the experiment, because it's more\Nconvenient.
Dialogue: 0,0:04:46.75,0:04:52.71,Default,,0000,0000,0000,,Hydraulic head is the sum of two\Ncomponents, the height that water rises in
Dialogue: 0,0:04:52.71,0:04:58.43,Default,,0000,0000,0000,,the tube as a result of water pressure, we\Ncall that pressure head, and then the
Dialogue: 0,0:04:58.43,0:05:04.37,Default,,0000,0000,0000,,height that the water has because of how\Nfar the tube is above the datum.
Dialogue: 0,0:05:04.37,0:05:08.23,Default,,0000,0000,0000,,Okay, so that would be elevation head.
Dialogue: 0,0:05:10.90,0:05:19.14,Default,,0000,0000,0000,,What Darcy observed is that water always\Nflows from high head to low head, okay,
Dialogue: 0,0:05:19.14,0:05:22.71,Default,,0000,0000,0000,,and that the rate of flow through that\Nsand tube is proportional to the
Dialogue: 0,0:05:22.71,0:05:26.46,Default,,0000,0000,0000,,difference in hydraulic head measured\Nbetween the manometers,
Dialogue: 0,0:05:26.46,0:05:31.62,Default,,0000,0000,0000,,in other words, Delta H, uh, the\Ndifference between this-this hydraulic
Dialogue: 0,0:05:31.62,0:05:35.97,Default,,0000,0000,0000,,head and this hydraulic head,\Nis Delta H right here.
Dialogue: 0,0:05:35.97,0:05:38.69,Default,,0000,0000,0000,,Okay, how about column area?
Dialogue: 0,0:05:38.69,0:05:40.72,Default,,0000,0000,0000,,How would this affect flow?
Dialogue: 0,0:05:40.72,0:05:43.63,Default,,0000,0000,0000,,Well this is really-really straight\Nforward, basically if you were to put a
Dialogue: 0,0:05:43.63,0:05:50.81,Default,,0000,0000,0000,,partition in the column such that the area\Navailable to flow, uh, was divided into
Dialogue: 0,0:05:50.81,0:05:56.90,Default,,0000,0000,0000,,the flow rate, uh, through each half of\Nthe sand tube, would be equal to one half
Dialogue: 0,0:05:56.90,0:06:03.82,Default,,0000,0000,0000,,of the total flow, okay, so from this, \NDarcy concluded that the rate of flow is
Dialogue: 0,0:06:03.82,0:06:08.98,Default,,0000,0000,0000,,proportional to the area of sand \Navailable.
Dialogue: 0,0:06:10.63,0:06:14.31,Default,,0000,0000,0000,,Lastly, what about the length of the\Ntube.
Dialogue: 0,0:06:14.31,0:06:19.77,Default,,0000,0000,0000,,Well Darcy figured out that if you keep\Nthe head difference between each end of
Dialogue: 0,0:06:19.77,0:06:25.96,Default,,0000,0000,0000,,the tubes the same but you lengthen the\Ntube, it effects the flow rate, okay.
Dialogue: 0,0:06:25.96,0:06:33.02,Default,,0000,0000,0000,,Uh, so imagine, in fact it causes flow\Nrate to decrease, imagine that this sand
Dialogue: 0,0:06:33.02,0:06:38.98,Default,,0000,0000,0000,,tube is one foot long, and that the\Ndifference in head is 6 inches.
Dialogue: 0,0:06:38.98,0:06:40.93,Default,,0000,0000,0000,,Okay, that's a pretty steep change in
Dialogue: 0,0:06:41.02,0:06:44.55,Default,,0000,0000,0000,,hydraulic head over the-over the length of\Nthat tube, right.
Dialogue: 0,0:06:44.82,0:06:48.24,Default,,0000,0000,0000,,And so water would want to flow through \Nthat fairly quickly.
Dialogue: 0,0:06:48.24,0:06:53.59,Default,,0000,0000,0000,,But if the tube were 10 feet long that 6\Ninch drop over 10 feet isn't nearly
Dialogue: 0,0:06:53.59,0:06:55.31,Default,,0000,0000,0000,,as steep.
Dialogue: 0,0:06:55.31,0:06:58.62,Default,,0000,0000,0000,,In that case the water wouldn't move\Nthrough as fast, okay.
Dialogue: 0,0:06:58.62,0:07:05.32,Default,,0000,0000,0000,,So from this we can conclude that, um, the\Nlength, the flow through the tube is
Dialogue: 0,0:07:05.32,0:07:08.09,Default,,0000,0000,0000,,inversely proportional to length.
Dialogue: 0,0:07:08.09,0:07:15.27,Default,,0000,0000,0000,,In other words, if all else is the same,\Nas length increases, flow decreases.
Dialogue: 0,0:07:18.90,0:07:24.02,Default,,0000,0000,0000,,Okay, so these 3 lines just summarized\Nwhat we just discussed flow is directly
Dialogue: 0,0:07:24.02,0:07:28.54,Default,,0000,0000,0000,,proportional to the, uh, difference in\Nhydraulic head between each end of the
Dialogue: 0,0:07:28.54,0:07:33.41,Default,,0000,0000,0000,,tube, it's proportional to the area of the\Ncolumn, and it's inversely proportional
Dialogue: 0,0:07:33.41,0:07:35.51,Default,,0000,0000,0000,,to the length of the column.
Dialogue: 0,0:07:35.51,0:07:40.00,Default,,0000,0000,0000,,Okay, this symbol right here is, uh,\Nmeans proportional, right.
Dialogue: 0,0:07:40.00,0:07:43.76,Default,,0000,0000,0000,,So this means inversely proportional,\Nbecause 1 over L.
Dialogue: 0,0:07:43.84,0:07:48.81,Default,,0000,0000,0000,,So if we put this together, okay, this is\Nwhat we get.
Dialogue: 0,0:07:48.81,0:07:55.56,Default,,0000,0000,0000,,Now we can replace this proportional sign,\Nwith a sign, with an equal sign, by adding
Dialogue: 0,0:07:55.56,0:08:02.75,Default,,0000,0000,0000,,a constant of proportionality, 'K',\Nand when we do that, this is what we
Dialogue: 0,0:08:02.75,0:08:05.04,Default,,0000,0000,0000,,get, okay.
Dialogue: 0,0:08:05.04,0:08:09.43,Default,,0000,0000,0000,,And if we just rearrange this a little\Nbit, we end up with this form of the
Dialogue: 0,0:08:09.43,0:08:13.65,Default,,0000,0000,0000,,equation, and that is Darcy's Law.
Dialogue: 0,0:08:13.65,0:08:16.38,Default,,0000,0000,0000,,So it really is not that complicated.
Dialogue: 0,0:08:16.38,0:08:19.94,Default,,0000,0000,0000,,If you understood each part, each of the\Nparts that we went through in the previous
Dialogue: 0,0:08:19.94,0:08:24.34,Default,,0000,0000,0000,,slides, this just combines them all into\None equation.
Dialogue: 0,0:08:24.34,0:08:28.16,Default,,0000,0000,0000,,Um, one of the things that might seem a \Nlittle mysterious is this 'K'.
Dialogue: 0,0:08:28.16,0:08:30.44,Default,,0000,0000,0000,,What the heck is 'K'?
Dialogue: 0,0:08:30.44,0:08:34.93,Default,,0000,0000,0000,,Well, 'K' is hydraulic conductivity.
Dialogue: 0,0:08:34.93,0:08:37.12,Default,,0000,0000,0000,,So let me explain this a little bit.
Dialogue: 0,0:08:37.12,0:08:42.39,Default,,0000,0000,0000,,Um, basically you can think of it as,\Ny'know, basically the same thing as
Dialogue: 0,0:08:42.39,0:08:47.61,Default,,0000,0000,0000,,permeability, it's a little bit different,\Nbut think about it as permeability.
Dialogue: 0,0:08:47.61,0:08:54.86,Default,,0000,0000,0000,,Aquifers have high hydraulic conductivity,\Num, because they can transmit water
Dialogue: 0,0:08:54.86,0:09:00.62,Default,,0000,0000,0000,,relatively easily, water can flow through\Nthem, they're fairly permeable, right.
Dialogue: 0,0:09:00.62,0:09:06.13,Default,,0000,0000,0000,,Aquitards have low hydraulic conductivity\Nthey're relatively impermeable.
Dialogue: 0,0:09:06.13,0:09:09.95,Default,,0000,0000,0000,,Water does not flow through them very\Neasily.
Dialogue: 0,0:09:09.95,0:09:14.84,Default,,0000,0000,0000,,In reality, hydraulic conductivity is a\Nlittle bit more then permeability.
Dialogue: 0,0:09:14.84,0:09:18.13,Default,,0000,0000,0000,,It combines permeability with properties\Nof the fluid.
Dialogue: 0,0:09:18.13,0:09:22.53,Default,,0000,0000,0000,,But in any case just think about it as a\Nmeasure of how easily water can flow
Dialogue: 0,0:09:22.53,0:09:26.22,Default,,0000,0000,0000,,through a porous meeting.
Dialogue: 0,0:09:26.22,0:09:30.26,Default,,0000,0000,0000,,Okay, so how do geoscientists use Darcy's\NLaw and this information that I just
Dialogue: 0,0:09:30.26,0:09:33.54,Default,,0000,0000,0000,,gave you?
Dialogue: 0,0:09:33.54,0:09:38.15,Default,,0000,0000,0000,,Essentially you can think of wells, uh, as\Nthe same thing as those manometers.
Dialogue: 0,0:09:38.15,0:09:42.67,Default,,0000,0000,0000,,They fill the same roll as the manometers\NI showed you in Darcy's experiment.
Dialogue: 0,0:09:42.67,0:09:47.79,Default,,0000,0000,0000,,So we can go out and measure the elevation\Nof water in a well, and that tells us the
Dialogue: 0,0:09:47.79,0:09:54.57,Default,,0000,0000,0000,,hydraulic head, where that water, where \Nthat well is open and an aquifer.
Dialogue: 0,0:09:54.57,0:10:01.19,Default,,0000,0000,0000,,Okay, so, so we can use these measurements\Nto help determine what direction ground
Dialogue: 0,0:10:01.19,0:10:06.98,Default,,0000,0000,0000,,water is flowing in an aquifer, okay, so\Nin the, uh, in the illustration shown here,
Dialogue: 0,0:10:06.98,0:10:11.09,Default,,0000,0000,0000,,this simple illustration, we would conclude\Nthat ground water is flowing from the
Dialogue: 0,0:10:11.09,0:10:12.64,Default,,0000,0000,0000,,left to the right.
Dialogue: 0,0:10:12.64,0:10:14.21,Default,,0000,0000,0000,,Towards well B.
Dialogue: 0,0:10:14.21,0:10:18.42,Default,,0000,0000,0000,,Because hydraulic head, uh, decreases\Nin that direction.
Dialogue: 0,0:10:18.42,0:10:27.01,Default,,0000,0000,0000,,Remember ground water always flows from\Nhigh head to low head, okay.
Dialogue: 0,0:10:27.01,0:10:31.95,Default,,0000,0000,0000,,And we can use this to help understand\Nflow rates, by assessing ground water
Dialogue: 0,0:10:31.95,0:10:36.32,Default,,0000,0000,0000,,flow and combining it with, uh, \Nknowledge of geological properties of
Dialogue: 0,0:10:36.32,0:10:40.64,Default,,0000,0000,0000,,aquifers we can evaluate how much water is\Navailable in aquifers and how that
Dialogue: 0,0:10:40.64,0:10:46.16,Default,,0000,0000,0000,,changes over time, okay.
Dialogue: 0,0:10:47.14,0:10:48.56,Default,,0000,0000,0000,,How do we use this?
Dialogue: 0,0:10:48.56,0:10:49.83,Default,,0000,0000,0000,,How is this useful?
Dialogue: 0,0:10:49.83,0:10:53.97,Default,,0000,0000,0000,,Well given the extent to which we rely\Non ground water as a source of drinking
Dialogue: 0,0:10:53.97,0:10:58.58,Default,,0000,0000,0000,,water and irrigation water, this \Ninformation is extremely important,
Dialogue: 0,0:10:58.79,0:11:03.24,Default,,0000,0000,0000,,because it helps us manage critical\Nwater sources more effectively.
Dialogue: 0,0:11:04.16,0:11:07.48,Default,,0000,0000,0000,,This is a huge, uh, this is a big deal.
Dialogue: 0,0:11:07.84,0:11:11.86,Default,,0000,0000,0000,,It's really important, these water sources\Nare extremely important so we need to be
Dialogue: 0,0:11:11.86,0:11:14.06,Default,,0000,0000,0000,,able to manage them effectively.
Dialogue: 0,0:11:14.06,0:11:17.84,Default,,0000,0000,0000,,One of the examples, um, that I'm\Ngoing to focus on in the le-in the next
Dialogue: 0,0:11:17.84,0:11:19.90,Default,,0000,0000,0000,,lecture, is shown here.
Dialogue: 0,0:11:19.90,0:11:22.52,Default,,0000,0000,0000,,It is the high planes aquifer.
Dialogue: 0,0:11:22.52,0:11:26.67,Default,,0000,0000,0000,,Okay, an aquifer that plays a vital role \Nin sustaining human populations in the
Dialogue: 0,0:11:26.67,0:11:30.44,Default,,0000,0000,0000,,Great Plains, and an aquifer that's up \Nagainst some serious challenges
Dialogue: 0,0:11:30.44,0:11:32.64,Default,,0000,0000,0000,,in the future.
Dialogue: 0,0:11:32.64,0:11:35.63,Default,,0000,0000,0000,,So I look forward to talking about that\Nwith you in more detail in the
Dialogue: 0,0:11:35.63,0:11:37.23,Default,,0000,0000,0000,,next lecture.
Dialogue: 0,0:11:37.23,0:11:39.79,Default,,0000,0000,0000,,Thank you for your attention.