Basics of Groundwater Hydrology by Dr. Garey Fox

so my role in all of this is I was going to give you guys kind of a brief overview of kind of groundwater hydrology so when you hear various terms and things like that you'll feel comfortable and answering questions or kind of kind of understanding exactly what maybe somebody's trying to say or trying to talk about and doc-doctor tagged me and Sally actually got us this little diet this little thing I think you put it together last night so we're going to use that just a little bit at a really great groundwater hydrology professor at Colorado State and the first day of class he told everybody all right everybody close your eyes but I'm not going to require you guys close your eyes because you might go to sleep on me so but he said what do you see and everybody was like oh I don't see anything and he was like exactly and that's groundwater okay so when you know one of the troubles that we have is with surface water it's easy to see right surface water is there you discharge it somebody can see it you can visually see it you can figure out what the lake levels are with groundwater who knows right if I tell you something's happening underneath the ground it's going to be really hard for you to prove me wrong okay and so that was another reason why he said it was a very good field to go into by the way because it was hard for people to prove you wrong so you know when we talk about groundwater we do have to talk about how it relates to the hydrologic cycle because we're a little bit limited on time this morning I'm not going to go into this much but I want you to think about this you know we've all heard about the hydrologic cycle we teach our kids about the hydrologic cycle now whether it's in class or in Boy Scouts or Girl Scouts or whatever program 4-h that we do but groundwater is a big component of that alright and so I want you to kind of keep that in mind that groundwater is a part of of that cycle that's going on within our hydrology and if we look at where the water is we you know in Larry covered this quite quite well for specifically for the state of Oklahoma this is on more of a global scale but groundwater is about 30 percent globally of our water supplies that we have available so it makes up it makes up a large percentage of the available water now groundwater is typically going to be managed on what's referred to as a basin you also hear you know with surface water you hear about watersheds and those type of things but groundwater is usually referred to as either a single aquifer or a group of aquifers that's called a basin and one of the probably most famous ones I always give my classes when is on a quiz right this large one right here is the Ogallala right and so the Ogallala or the High Plains aquifer it would be a groundwater basin all right and a lot of times and we'll talk about this more here in just a second but groundwater is a lot of times actually the source of the flow that's in rivers most of the time when we don't have precipitation events you have water that's in the river that's actually groundwater that's coming out and it's just like the lake Sally did not spit in this lake okay he actually put water through this groundwater and it will actually seep up into this lake so water that's in lakes and water that's in rivers and streams a lot of times is actually water that's actually being discharged from the groundwater system okay we're going to spend actually quite a bit of time on this one this is actually the definition of an aquifer okay and the easiest thing to think about I went to an in-service training we had for youth water education we had some guys from San Antonio come up and the guys from San Antonio we're talking about how this aquifer is this big underground hole well that might be right in San Antonio where they have limestone and karst aquifer systems but what we're really talking about is exactly what this little diagram this little thing is showing you it's really just water that's stored within the void space of those soil particles so when you have soil particles and you put them together you can't put them together where they're completely meshed together so there's a little space between them and the water will actually seep down into that space and that's for the most part in Oklahoma this is what we're dealing with okay so an aquifer is nothing more than basically think about it as soil and it has to contain water and it also has to transmit water that's the only those are the two require hermits were to be an aquifer it's got to hold the water in but it's also going to let the water out and waters got to be able to move through it otherwise it's by definition it's not an aquifer okay now you're going to hear about lots of different types of aquifers as we go through here so there's something that's referred to let's see where do we want to start the first one is something referred to as an unconfined aquifer alright and when a hydrologist make up definitions they make them as easy as they can possibly make them so that we can remember it okay so unconfined means it's not confined on both the top and the bottom okay so there's others a layer underneath here some kind of a clay layer or something like that and Clay's can hold water but clay doesn't transmit the water it doesn't allow the water to move through it and so an unconfined aquifer is just an aquifer that basically is not confined on the top it's only confined on the bottom alright and if I poke I should have brought my monitoring well I always bring my monitoring well when I teach groundwater if I poke a hole in this unconfined aquifer so this is our little monitoring well this would be of a pipe that's in the ground and it's got little slots cut in it so the water can flow into that pipe if I if I poke it into this guy it will write it well the water level will rise up to a level known as the water table okay so that's and that's an unconfined now the other type of aquifer that you'll see and these can be laid on top of each other there can be you know multiple sequences of confined aquifers underneath here the other type is this confined aquifer and unlike an unconfined it's got layers on both the top and the bottom okay typically what happens in a confined aquifer is you get a recharge area that's way over to the side over here okay so you get water that's coming in over here from the surface and it's flowing in and by the time we get over here you know it's like it's like being in a swimming pool right where this is you've got a cap on the top and the bottom of a swimming pool and you're swimming underneath here there's a lot of pressure on you okay and so the water that's in this confined aquifer is actually pressurized okay it's under pressure so if I poke a hole let's see we've got one over here so I poke a hole in here with a well and this is slotted the water will actually move into this well and it will actually rise up to a surface and I'll actually go beyond the water table and in some cases and this is what we refer to as this is called the pzo metric surface that's one of the only definitions hydrologists didn't make easy okay that's a pretty hard term so that's called the P geometric surface you guys ever heard of an artesian well artesian wells or wells that just continuously flow over time basically what you've done in artesian well is he either poked oh a well or there's a there's a spring that's come up it's the same thing with a spring but basically this water that's under pressure flows in here and then the PCO metric surface is actually above the ground surface so if this is the ground surface it will just continue to flow it will continue to flow until this pressure basically drops enough okay so if you're dealing with the none if you're dealing with a confined aquifer for example the Ogallala and parts of it are is confined the recharge zone for the Ogallala may not be right on top of the Ogallala it may be way away from the Ogallala okay so I've got family that live in Austin and in Austin you go through areas where they'll talk about critical recharge zone so sensitive recharge area okay those are the areas where you're they are seeing that it's it's actually recharging that confined aquifer let's see I think that I think that's about it you can't get areas where you get these little clay lenses that are underneath here and water will perch okay and so I think that's good for that slide all right so again what I want to make sure to emphasize here is that there are cases where like the guys in San Antonio we're talking about where there are caves that are underneath the ground right and they're big holes underneath the ground and we refer to that typically as a karst system okay that's typically a car system so we've got some kind of limestone deposits that have kind of you know you wrote it away and dissolved away and basically you get these kind of conduits that form and you'll see Springs that'll come out so you can have these over in the eastern part of the state kind of in the Ozarks okay you'll get these kind of car systems so that is one aquifer systems a lot of the aquifer systems you guys might be dealing with especially from an Ag standpoint are what we refer to as the aquifers that are the alluvial deposits okay so an alluvial deposit Lubell means what a Malin alluvial means yeah it means next to a river that the materials were laid down by flowing water it's basically what it is and so when you think about a river a river wants to meander and migrate it will actually move back and forth across the floodplain so those sediments have been laid down by a river system and those are for the most part going to be unconfined aquifers okay and those are going to be interacting with the with the river system quite a bit so we have in this in Oklahoma quite a few alluvial aquifer systems that are very important water supply sources for us okay okay so again aquifer properties two things about an aquifer it has to conduct the water in other words how fast can the water move through the porous media and we talked about that from as a groundwater hydrologist we talked about that as a parameter called the hydraulic conductivity so if you're ever looking through a groundwater report or something like that they're going to report hydraulic conductivity numbers all the time okay and that's just how easy does the water move through that soil which one do you guys think has a higher hydraulic conductivity in sand or clay sand okay typically the bigger the pore space the easier it is to move through okay so gravel would be even more than a sand okay so that's that's one of the properties the other properties is storage how much water can an aquifer hold so which one has a higher storage capacity sand or clay it's actually clay good okay yeah clay most of my undergrads get this wrong okay good okay so yeah it's typically a clay but a clay doesn't allow the water to move so a clay is not typically considered to be an aquifer material and there's a couple of different terms that are used that you'll see in reports things called the specific yield and storage coefficient if you're getting to reading groundwater reports those are basically just referring to how much storage capacity do we have within the aquifer okay so one of the things that we're really interested in with groundwater is well what happens when we start pumping water okay so if I put a well in here and this well actually pokes into this confined aquifer we can actually start to take water out of this well and it will actually cause something called drawdown okay so there will be a drawdown response and if I've got a well here and I'm a landowner here and I'm interested in pumping okay I could get interference between those two wells okay and that depends on a lot of different things we'll talk about that here in just a second but this pupping causes what's called drawdown and it's actually a cone if you think about it okay if I'm the groundwater well and the aquifers all around me when I start pumping it starts pulling water from all the way around me and it actually forms a cone as it as it draws down and this is either for confined or even if I'm in a nun confined it will cause a drawdown and drawdown is just how far is this lowered down so for example here's a 3d illustration of what that cone would look like okay and the shape of the cone and how far the cone goes out depends on the aquifer to be honest depends on how fast we're pumping it depends on a lot of different things we can even have situations to where we can pump a well and it can create a drawdown and start pushing water in and it Kievan pull water from streams if we're pumping out of an out of a nun confined aquifer so kind of keep these things in mind as we go through today with the rest of the presentations so I put a slide up here does my well influence my neighbors well you may get questions like that and this is called pumping influence okay this is called pumping influence and based on what I saw from the O WRB and Chris you guys can correct me if I'm wrong but pumping influence is only considered for those basins where you've got a maximum annual yield that's been determined okay so if you don't have a basin with a maximum annual yield they don't worry about a pumping influence okay but it but your your clientele your the landowners that you work with they made they may be concerned about this and what I would say is it depends and it depends on a lot of different things it depends on the distance between the wells the closer the wells right the more of an influence you're going to have it depends on the well characteristics so if we look over here there's a like an illustration here about pumping well that's in here so this is the one we could put a little syringe and pull some water out of this well don't know Solly's going to do that for you later but there may be somebody else that's got another well that goes down here and he's pulling out from way down here okay so think about it the idea that this is also you know depth related there are different depths that this things happening depends on the aquifer properties it depends on the pumping rate depends it depends on whether we have a stream or a lake in fact this pumping well could eventually dry out that lake if it pumped hard enough okay I talked about alluvial aquifers those are those aquifers that are right next to those stream systems so we've got an alluvial aquifer out here with a stream and one of the big things that we really have to think about as we I think in my opinion as we move forward with groundwater in the state of Oklahoma is how these and even in more detail I know the water board is starting to do this in greater detail but we need to consider how these things interact with each other so you can't get a situation where the stream is actually recharging the groundwater okay you can get a situation where the ground water is actually recharging the stream you can even disconnect it in some cases but those are kind of the scenarios that you get with respect to those aquifers and groundwater systems interacting and so when we pump next to a next to a river so here's my pumping well actually did a solve the math here actually did have my students do this they put up well in and the river is actually the right here and you can look at how this cone starts to develop and as you pop next to this river what you do is you actually can induce flow from the stream back into the aquifer to satisfy what's going on with this well and what you can also do is you can actually capture water that would have eventually recharged that stream you can capture it back in that well okay so very interesting things happen when you start pumping in alluvial aquifers I I did work at the University of Mississippi for a long time and the city of Memphis is one of the biggest cities that they've got the they got the Mississippi River flowing right by there but the water supply they uses actually deep groundwater and one of the things that they talked about was that they really like that deep groundwater because it's been down there for ten thousand years it's been filtered all the sediments out of it it's been interacting with all this soil it's very nice very good water and what they're concerned about is that they've been pumping it so hard that they're actually maybe pull in Mississippi River water in they're not so worried about from a sediment perspective but it may be some other water quality stuff that they're worried about there so if you get a little bit more details we could probably kind of help you answer that question about how likely that is but I would say that really depends on you know how far that spacing is and what kind of materials they have in terms of that that aquifer so this is actually a study that was done by Tyson Osler one thing I wanted to mention here as we go through here that I want you to keep in mind is the idea of Aquifer recharge there's been a lot of interest right now on how much water actually gets back down we've had all this precipitation right we had all this water that came in but what is actually the recharge rate that we get going down into those aquifers this was a study done by Tyson Austin err on a Water Center funded project so I really like to put this one up here being the water Center director but what these are these are numbers at each of the different Mesonet stations and these are annual recharge well they're not even recharge rates these are actually what we're called what I think he ended up referring to as drainage rates but these are in millimeters per year okay so if you take this number so if you have 30 millimeters right you divide that by 10 you get the centimeter so that's three centimeters out here and then you've got about 2.5 4 inches in it this is about an inch okay this is an inch per year that he estimated is getting back down into that aquifer now he doesn't have the data to go all the way down through all of this material to figure out how how much water is getting way down here he only was estimating this based on the very top okay so this is a probably a high number but at least gives us an estimate okay and you can look across the state and what you see across this state we don't get a lot of research it takes a long time okay it takes a long time to recharge these aquifers so as we continue to pull more and more more in warm water out we are not putting water back in at the rate that we're pulling out in a lot of these cases okay I don't know how much Chris is going to go into this but this gets to be kind of a you know a fairly complicated deal right and we've all been to what I showed you today was kind of hypothetical kind of simple aquifer systems one pumping well what happens when you trying to model an entire watershed or I'm not a watershed when you're entire an entire basin alright where you've got all these wells pumping or pumping at different rates or pumping at different depths you got aquifers that are in acting with the streams it gets to be a very complicated process okay and so a lot of times and what people will use and especially the water board will use and we as scientists will use our programs and the most famous program out there is probably mod flow and it's basically a groundwater flow model to model all of these basins so all the aquifers that we have a maximum annual yield study that's been on is pretty much got a mod flow model that's been developed for it across the state okay but I thought I would I thought I would point that out just kind of as an FYI so I'm going to wrap up there you guys have any questions beyond what we've talked about so far I'll be around all day but I wanted to give you kind of a brief overview right so if I quizzed you right now you could tell me what a confined aquifer was and if I poked a hole and a confined aquifer the water level is going to rise to where PC metrics earth is good yeah and if we have an unconfined aquifer I poke a well in it it's going to rise through the water table good you guys have the foundation that you need for me to set you up for these other guys okay so these other guys are you're going to rock it now because of that foundation you

Channel: OkstateWaterCenter

Views: 48,914

Keywords:

Id: 2Z6tJ9zdxVI

Length: 20min 3sec (1203 seconds)

Published: Fri Dec 18 2015