G102 Watershed Flood NOS Week PDF

1. Readings Must do: Videos in modules and some sort of interaction (with AI or take notes) This reading on the Concord Labs we will be doing, uncertainty and risk Should do: Sections 5.1-5.3 (Erosion/weathering), 11.5 Surface water from An Introduction to Geology Nice to do: Sections 1.1, 1.2,...

1. Readings Must do: Videos in modules and some sort of interaction (with AI or take notes) This reading on the Concord Labs we will be doing, uncertainty and risk Should do: Sections 5.1-5.3 (Erosion/weathering), 11.5 Surface water from An Introduction to Geology Nice to do: Sections 1.1, 1.2, 1.5, and 1.6 in An Introduction to Geology Flooding and Recurrence Intervals Stream Gauges Activities: Lab: Flood Risks & Impacts Module from Concord Consortium Website: https://learn.concord.org/geo-flood This week, you’ll dive into an online lab on the Concord Consortium website: Flood Risks & Impacts. With Earth’s climate changing, extreme weather events are becoming more frequent around the globe. In some areas, this means more intense rain and a higher risk of flooding—one of the most dangerous natural hazards humans face. In this module, you’ll work with the Flood Explorer model and study real-world cases to examine the factors that affect flood risk and impact. You’ll explore scientific factors like precipitation, topography, permeability, and the water table, as well as social factors, including population density and infrastructure. Through these investigations, you’ll gain insight into how flooding varies on both local and regional scales. Finally, you’ll look at the effect of rising global temperatures on future flood risks. By the end of this module, you’ll be able to answer the guiding question: How will flood risks and impacts change over the next 100 years? Discussion: Your own Illusion of Explanatory Depth Experiment In our weekly discussion, you’ll do your own Illusion of Explanatory Depth Experiment. How will your friends and family do? In Live Zoom Class In our live Zoom class, I will introduce myself and you’ll have a few activities to get to know your classmates. We will work on a mapping activity that invites you to explore and identify the watershed you live in, as well as which native tribes traditionally lived and used the land you now live on. Our individual task will be to screenshot a map showing the tribes that traditionally used the land as well as identifying your watershed (and producing a screenshot). Videos Transcript: Weathering, Erosion, and Deposition [Part 1] - YouTube https://www.youtube.com/watch?v=ewj629B4Oe8 https://docs.google.com/document/d/1WcOZtQrmGHk21tu5AyUTIRAKgbA4O8CiHBeCyTOSt1 A/edit?usp=sharing Transcript: (00:00) in this video we're going to talk about weathering erosion and deposition let's begin with some simple definitions of these three terms so weathering in this sense is the breaking down and changing of rocks as a result of exposure to the environment so if I have a large slab of granite in nature and over hundreds and thousands of years the waves of the ocean are crashing onto that rock inevitably the rock is going to break down into smaller pieces it might get rounded out it's essentially going to change as a result of exposure to its (00:33) environment and that's just one example of what weathering can be there are lots of different types and we're gonna look at those in this video after rocks are weathered they are often eroded and that process erosion is the transportation of the sediments that have been broken down by weathering so if you imagine little bits of granite being pounded off of that slab because it's being hit by wave after wave and then being carried away in the ocean current to a different location well the act of carrying those little chunks of (01:08) granite those weathered sediments from point A to point B that is erosion erosion is all about movement and transportation the final part of the process is called deposition so deposition is the dropping off of the sediments that have been weathered and eroded so to continue my example if those little tiny bits of granite broken off and weathered by the waves and then eroded or transported by the ocean currents eventually get deposited on a coastline many hundreds of miles away that is deposition the dropping off and (01:43) so to kind of summarize this and some of the other key ideas we're going to use this surface process flow chart which is available on the website and we'll begin by filling in the three boxes on the top to kind of summarize these three main processes starting with weathering which we know is breaking a part of rock and then erosion which is the transportation of the sediments and finally deposition or the dropping off of those sediments so another way to think about this this is just kind of a quick analogy that (02:14) and it helps me remember the differences between them is that weathering is like kind of like nature's hammer right its mother nature's way of taking big bits of rock and smashing them into smaller bits or changing them into something new and then erosion in this example would be something like a dump truck or a pickup truck carrying all the little bits and pieces broken apart by weathering from one location to another and then deposition is that dump truck kind of opening its tailgate and dumping everything out into a big pile on the (02:45) ground - that's deposition so that's just kind of a helpful little way to remember the difference is between these three parts of this larger weathering erosion deposition process now for the rest of this video we're really going to focus on weathering specifically and we're going to start by looking at the two main types of weathering and the first example we're gonna look at is called physical weathering now I just want to point out that physical weathering is also often known as mechanical weathering okay so physical (03:17) and mechanical are the same thing and this would be the breakdown of rocks into sediments and the key is that it's without changing their composition so this is literally changing size and shape of Iraq so the waves crashing against a boulder and breaking it into small pebbles that might be rounded out that's physical or mechanical weathering but it's still granted it's not changing the rock or what it's made of but that does also happen in nature and we have a different name for that that's called chemical weathering and so this is when (03:48) the rocks are changed chemically because of some reaction with usually something like when air or water in nature so the altering of rocks as a result of exposure to different substances so let's add this information to our flow chart so we're breaking down weathering into two smaller types the first is physical or mechanical weathering which is breaking cracking and grinding things like that and we'll see examples of those shortly and then chemical weathering which involve some sort of reaction that changes composition so (04:24) that's a really key difference between the two types of what so let's dive a little deeper into our physical or mechanical weathering and look at some different examples for our purposes we're gonna break this into four specific types frost action exfoliation abrasion and root wedging so we will start with frost action which by the way is also known as ice wedging there are a lot of different names for it and as you might imagine this involves ice and so what happens is take an area that maybe it's a little bit (05:00) above freezing temperature during the day and you get some rain or maybe some melting snow and you have some water that seeps into the cracks within a rock right and then the Sun sets and inevitably the temperature drops and that water freezes into solid ice now you may know already when water freezes it expands slightly and it gets a little bit bigger and so as it expands it's going to be pushing outwards on the rock that it has seeped into and that force believe it or not is actually strong enough to very slowly and gradually (05:36) break apart rocks and this process is known as frost action or ice sweating and so we see examples of this in all sorts of areas where the temperature is a little bit above freezing during the day and then below freezing at night and in fact a good example of this is what we call a pothole which you see all over the streets particularly in the northeastern United States in the springtime when you have these big fluctuations in temperature the water actually gets into cracks in the road and then freezes and expands (06:08) and then you drive over it the next day and it just breaks apart and you end up with these big nasty holes in the ground that's a good example of frost action or ice sweating second would be exfoliation and this is in a way kind of similar this involves temperature changes as well so this occurs in areas where you have really dramatic temperature changes where it gets very hot during the day and then very cold at night the the rock itself will actually expand slightly in the heat and then contract in the cold (06:39) and if this happens day after day night after night it weakens the outer layers of the rock until they eventually begin to crack and peel apart like this or like this right here it's almost like the rock is shedding its outer layers and physically or mechanically breaking apart largely as a result of these temperature changes a third example which is the most common and we see it all over the world is called abrasion so abrasion is basically whenever Rock grinds against other rock and it comes in many forms like here in the desert we (07:13) see a lot of wind abrasion where gusts of wind will blow grains of sand that crash into other rock and very very slowly over thousands and thousands of years will actually eat away at the rock and so wind wind abrasion is actually responsible for a lot of the interesting kind of rock formations that we see in the American Southwest we also can have water or stream abrasion as little pebbles and sediments are bounced along the bottom of a stream as the water flows and that's going to eat away at the rock that they're bouncing over we (07:44) also see this on coastlines as I mentioned before with waves crashing into rock and grinding it down by carrying little bits of sand and sediment and eating away at the rock and then finally with glaciers glacial abrasion is very common glaciers glide downhill pulled by gravity and they scrape along the rock and carve it away over many hundreds of years finally the last type of physical or mechanical weathering we're gonna look at is called root wedging and it's pretty self-explanatory this is when plant roots actually grow within the (08:18) cracks of rock and as the plants grow larger and larger they break apart the rock as they grow into it so we see examples of this all over the world and it's amazing how powerful tree roots and plant roots can actually be so much so that they will physically break apart rocks as the plants grow so those are four main examples of physical weathering and we want to add them to our flowchart here so under our physical weathering area we're gonna add frost action which is freezing and thawing of ice is going to crack apart rocks (08:51) we have exfoliation which is the alternating hot and cold old is going to crack rocks we have abrasion which is grinding of one rock against another or sand against rock and then finally root wedging which would be our plant roots growing into the rocks and so those are four main types of physical weathering now let's shift gears and look at the second type of weathering chemical weathering so remember this is the altering or the changing of rock as a result of exposure to different substances and we're going (09:22) to look at two main examples of this oxidation and carbonation we'll begin with oxidation which is a term you may have heard before it's the formation of rust and this is going to occur whenever the element iron is exposed to oxygen and that can happen in the air or in the water and so what we find are that there are a lot of rocks around the world that contain large amounts of iron and as that iron reacts with the oxygen in air or water it's going to physically rust and the result is that we see rocks that (09:54) look like they've been rusted they have this orange e color to them and that is actually a form of chemical weathering this rock is breaking down the rust is very crumbly this iron oxide that forms and it breaks apart the rock over time it's an actual chemical reaction with oxygen in the air or the water and then finally we have carbonation carbonation is really interesting this is responsible for the formation of these fascinating beautiful limestone caves that we see around the world and it's basically when water flows through the (10:28) ground it reacts with the different materials in the soil to create a very mild acid this carbonic acid and carbonic acid is strong enough that if it encounters certain minerals or rocks like calcite or limestone it will eat away or dissolve that limestone and so what we end up getting are these underground caverns where there once was a whole large expanse of limestone but that has all been kind of eaten away slowly by the dissolving of this carbonic acid so we see some of these amazing amazing landscapes around the (11:03) world formed as a result of this type of chemical weathering another thing that happens with this carbonation is that sometimes the ground will actually give way because all the rock beneath it has been eaten away and that's when we get something like this which is called a sinkhole which is when the rock is gone beneath and the ground collapses above and so those are two types of chemical weathering and again we'll summarize them on our flowchart so the first type was oxidation iron and oxygen gives you iron oxide or rust and (11:35) then carbonation which is when we have this acidic rain and acidic water dissolving limestone and giving us caves okay now there are two main types of weathering with some examples of each we have them nicely summarized on our flow chart and the last question we want to ask here is so what's going to affect weathering like what dictates the type of weathering we have in a region how fast it will happen etc and so we have three main things that we're gonna look at and the first is climate the second would be hardness how hard is the rock (12:10) or how resistant is it being weathered and then the third would be the surface area of the rock how much of the rock is exposed to the elements all right so let's start with climate and to understand this we look at this chart this is a very commonly used chart in geology and so what this shows is the effect of the temperature and moisture on what type of weathering will take place so for example in an area that is more hot so this part of our graph right here which is a higher temperature okay but not a lot of moisture because (12:47) remember if we go up on the chart that's a wetter area so this is an area right here that's hot and dry hot and dry we don't really see a lot of weathering we might get some wind abrasion like in the desert but nothing too severe if we then switch up to an area that is higher on the chart that is hotter and wetter that's where we're gonna start to see more of this chemical weathering this carbonation occurs a lot and a lot faster in areas that are hot and wet we see a lot of limestone caves and sinkholes in a place like Florida for (13:19) example where it's very warm and on the other hand if we go to the left side where it's colder lower temperatures this is where we're gonna start to see frost action happening because this is where we have a lot of change in temperature it's colder cold enough to get ice and enough water to have the ice forming and melting and forming and melting day after day anything up in this top area up here these are climate conditions that we don't really see on earth so they're not really relevant to what we're talking (13:51) about anyway this this graphic gives you a really good sense of the impact that climate has on the type and the severity of weathering that happens in a particular area in addition to climate we also have to look at hardness so of course we know that all rocks are different all minerals are different some are very hard some are very soft and that's going to have an impact on how quickly they're going to weather so if we look at a diagram like this which shows a cross-section of a waterfall what we'll notice is that some of the (14:22) rock layers like right in here right in here right here have been worn away more than other rock layers like this one is not worn away as much these ones down here this a little bit right here is not really worn away and that tells me that these are different types of rock and so I can conclude that this layer of rock right here which believe is like a shale is a softer Rock so when all of this water splashes up on it it's gonna start to wear away faster then a harder Rock like say a sandstone so the hardness of (14:57) the Rock has a big impact on how quickly it's going to be weathered and so finally the last thing we want to look at is surface area so surface area refers to how much of the rock is actually exposed so if I have two rocks like you see here they're going to be exposed to the elements at a different clip right so the only part of this rock for example that's going to be exposed is the outside of the rock so the surface is that I'm highlighting right here that's the only part that can get hit by rain and ice and snow and oxygen (15:29) etc that's the only part that can be weathered the center of this rock is not exposed its protected and therefore it's not going to be weathered whereas in the right hand side I have the outsides of these rocks but I also have these inside areas right because the rock is broken down we have exposed additional surfaces that can be hit by rain snow and ice and oxygen and other chemical reactions and so because this has more surface area the purple it's going to break down at a faster rate okay so we can summarize (16:06) these three things in our large box at the bottom of the flowchart we can summarize the factors that are going to affect weathering okay so weathering is most affected by these things the climate the hardness of the rock and the amount of exposed surface area that's what's really going to dictate how quickly a rock is going to break apart so in this video we took a look at the different types of weathering along with some basic definitions of weathering erosion and deposition and then finally at what effects weathering shortly I'm (16:38) going to release another video that's going to go into details about the processes of erosion transportation and deposition are dropping off of sediments so keep your eye out for those thanks for watching River Erosion and Deposition - YouTube https://www.youtube.com/watch?v=3YdEkegvJCQ https://docs.google.com/document/d/15vr_CDDROgPc-l5s9NhTHQgZbOfHth5ux6ctnMRtgxE/ed it?usp=sharing Transcript: (00:00) in this video we're gonna continue our look at weathering in this video we're gonna continue our look at weathering erosion and deposition paying particular attention to rivers and how they erode and deposit sediment across the earth as always we have a quick handout to go along with this video which you can go and grab at the website so let's begin by reviewing these key terms so weathering is the breaking down and changing of rocks as a result of exposure to the environment so when rock and nature is exposed to the air and (00:37) wind in water and ice those forces will eventually break rocks down from larger pieces into smaller pieces known as sediments in some cases those rocks might actually change composition as a result of these weathering interactions then we have erosion erosion is transportation so once my sediments have been broken down by weathering erosion is gonna move them from point A to point B so think about to give you an example from today's lesson sediments being transported by the movement of water within a river that's erosion finally at (01:14) some point deposition is gonna occur and this is the dropping off of sediments that have already been weathered and eroded so once they've been broken down once they've been moved then they get dumped somewhere and that process is known as deposition so again today we're gonna focus on one particular agent of erosion and that's rivers or flowing water on the surface of the earth these have a huge impact on shaping our planet and so we're gonna look at all the details about what they do to the surface and how they affect the rock (01:44) that they flow over so we'll begin with a simple question which is what is a river so if we had to actually define this term it's pretty simple it's simply water flowing downhill through a channel or some sort of defined pathway by the way you'll see I used the word stream in creeks and Brook we can use these essentially interchangeably oftentimes creeks and brook and stream' are used for smaller rivers whereas the term rivers used for a larger volume of water but for all purposes those can be synonyms so let's (02:20) look at the anatomy of a river or or what some of the parts of rivers are and we'll begin with this little diagram right here of little section of a stream or a river and the first thing and this is going to become very important is is when we see these curves or bends in rivers and we have a name for that those are called meanders and that's very important because at a meander we see a lot of erosion and deposition happening in specific ways which we will look at along the edges of their stream or the river we call those the banks so the (02:53) stream banks are the river banks and then along the bottom we call that the bed so the stream bed or the river bed so when we have a smaller stream that flows into and merges with a larger stream we call that a tributary and all together with all the tributaries and a main river we have a river system oftentimes a river system is part of what's called a watershed and so a watershed is an entire region of land it may be hundreds and hundreds of miles but it's an entire region of land where all of the tributaries the streams and (03:28) the rivers and all the groundwater in that region merged together and flow into one central water body whether it's a river lake or the ocean so that whole area of land is called a watershed or a drainage basin so let's talk about the speed at which a river flows or velocity of a river so the velocity of a river tends to depend on three main things the first being the amount of water within the stream and that's called discharge so typically speaking the more discharge the more volume of water within a stream (04:06) or river the faster that stream or river is going to flow next is slope so is this a steep stream bed or a fairly flat one so logic tells us that a steeper slope is going to make the river flow and a faster velocity and that's because gravity is going to pull that water hell faster finally the shape of the stream channel actually plays a pretty major impact so if you think about two streams so to think about a narrow kind of v-shaped stream channel which is you know pretty steep maybe a lot of water but but the channel itself is pretty (04:46) narrow and v-shaped or almost even like a u-shape well that water's going to be able to flow faster then a stream that's gonna have a very wide and flat bottom to bed and the reason that is is because the more area where the water is flowing over the rocky stream bed the slower it's going to go because of all of that surface area so that water has to flow over all of those rocks and in and all out of all those nooks and crannies as opposed to if we have a V shape that water is going to have less friction with the ground then it's going to be (05:20) able to go faster so typically a rounder deeper a more curved or v-shaped channel the faster the stream will flow versus a wide flat channel so if we look at a river channel which often does have this kind of V shape within the river itself the fastest velocity is going to be where we see this X right here so not along the beds where the water is kind of grinding against the ground but up away from the beds generally in the middle of the stream this does change if we're going around a meander in a stream a straight flowing stream will tend to (05:56) see it where this X is so fastest in the center up away from the stream bed so now let's talk about the age of a river and yes rivers do have ages you can tell by looking at a river whether it's a young newly formed river or a more ancient river and so we'll start with looking at the characteristics of a young river system and so these are going to be generally speaking kind of more intense so they're going to be steeper they're gonna have deeper more narrow channels with a faster flow of water they're gonna have fewer curves or (06:28) meanders and as a result of all that they're going to go faster and that means more sediment is going to be eroded and less will be deposited so all the rocks and the sand and the silt and clay are going to be right away not being dropped off and that's due to all of these characteristics together so if you see a river like the one in this picture right here you can conclude that this is a fairly newly formed River this has not been around for thousands and thousands of years on the other hand an older River is going to be exactly the (06:59) opposite it's gonna have a gradual slope so more flat as far as the bed goes shallow wide channels which all result in a slower flow velocity will often see these big wide curving meanders and the result is that we had a lot of deposition so sediment is constantly being dropped off and you can actually see that in this example right here with all of these sandbars within the the river flow that's all deposited sediment because the water is constantly slowing down and dropping off whatever it's carrying so now we've talked a little (07:36) bit about velocity it's important to point something out though it is pretty logical and that is the faster river is flowing the bigger the sediments that it can erode or transport which makes sense if I have a very fast flowing river it's going to be capable of transporting long larger sized sediments so sand and silt and clay but also in some cases it can even bounce along pebbles and in the fastest rivers possibly even cobble sized rocks this is very logical it's all summarized in this chart right here so if we look at this what we see along (08:10) the bottom here is the velocity of the stream so as I go from left to right the stream is going faster and then on the vertical axis I see size of sediment being transported so what I'll notice here is that let's say I have a velocity of a stream that is about one centimeter per second so if I come up and I hit the curve here and I go over the sediment that stream is going to be able to transport is going to be classified as sand right so it's going to be somewhere between point zero zero six and point two centimeters in (08:45) size so that's fairly small sediment that's what a river going that fast is able to transport but if I speed up to let's say 50 centimeter per second river so a much faster flowing river that's going to be able to carry pebbles and that is logical right because the faster the river is flowing the bigger the sediments it can carry only the fastest rivers on earth are able to carry big sediments so if I look you know maybe at a hundred or a little more than a hundred centimeters per second that kind of river is able to actually transport (09:24) rocks that are six seven eight centimeters in diameter so those would be classified as cobbles so this chart shows us that the faster the stream velocity the larger the sediments it can carry so if we look at those sediments this is what they would look like as they're being eroded within a river so obviously the smaller sediments are going to be suspended so the silt and the clay that's going to be carried along up in the body of the water itself and that's going to be subject to the currents and the velocity of the flow (09:57) sand might be hopping or bouncing along the bottom and then the bigger sediments that gravel the pebbles and possibly cobbles are gonna slide and roll and bounce along the stream bed so this is what it looks like and you can see massive amounts of sediment are eroded by rivers especially fast flowing younger rivers so when streams flow fast they're going to tend to erode sediments to pick it up and carry it away and when they flow slowly they're gonna deposit it they're going to drop it off so the logical question becomes okay well why (10:35) do streams speed up why does stream slow down because if you can identify that then you can predict where more erosion will happen and we're more deposition will happen so if we look at our meander again what we're gonna know is that on the inside part of curves water is going to be forced to slow down and the reason that is is because when water is traveling around a sharp curve like this on the inside part it can't go as fast it's a sharper turn and physics tells us that that water gonna be forced to slow down as opposed (11:10) on the outside of a curve it's got this big sweeping area to go and it's less sharp and therefore it can go faster I often think of this the same way I think of a racecar going around a curve on a racetrack you have a choice when you approach the curve do you slow down and hug the inside of the curve you have to slow down or else you'll flip or do you keep your speed and go on the outside of the curve where you can keep your speed up a little bit higher well it's the same in the river on the inside of a curve the water slows and on the outside (11:41) of the curve the water speeds up and so of course there's a consequence of that and that is that on the inside where it slows down the deposit sediment that they're carrying and you can actually see this in the picture by looking at this whole area right here all of this sand and sediment that was deposited there because the river slowed down and when the river slows down it drops off whatever it's carrying whereas on the outside where it speeds up its going to erode additional sediment and you can tell because all the sediment has been (12:11) worn away and you can see that with this steep riverbank so you can tell just by looking at a meander where the erosion and where the deposition has taken place similarly we have another diagram here showing meanders on this example one of the things to point out is that depending on the direction of the meander the shape of the channel is actually going to vary so if I look at this let's look at Point a here and point B here so a is the outside of a curve so that's erosion and B is the inside of the curve so that's deposition (12:45) so where there zero j'en the rock and the sediments being worn away so we're gonna have a steep more jagged kind of slope so that means that that would look something like this so this would be point a here and then where B is that's where the stuff is being dropped off so we would have a more wide flat deposition driven area of the river so a and B match up like that and we should be able to do that if I look down here at C and D so C is on the inside of this meander so C is going to have the flat slope and D is on the outside where it's (13:20) going fastest where we see erosion so that's going to be the steeper slope so let's look at some real-world examples here so here's a meander and a river and just by looking this right off the bat we can tell where there's deposition and where there's erosion so we should be able to label it with these terms right so inside of a curve is slow outside of a curve is fast so those words go there inside of a curve where it slows down we're going to get deposition and you can actually see the sediment deposited and the outside is going to be erosion (13:54) so you can see pretty clearly what's going on let's look at another example this is another great example so I'm going to bring my terms in so inside is slow outside is fast okay inside is deposition outside is erosion and again you can actually see it if you look at the diagram here this steep slope right here it's all steep slope that's because all of that sediment is being carried away as opposed to this whole region right here where all this sand and sediment is that's your deposition because the water has slowed down so we (14:31) see this all over the place and it becomes very very clear when we see stuff like this sediment right here this is the inside of a curve and that's there because the water has slowed and deposited what it was carrying and you can see this most rivers on earth it becomes very obvious what's happening here this is a great example because you can actually see within the water that all of this sediment you see how this water is cloudy the sediment is on the inside of the curve because that's where the deposition is taking place so if (15:04) that erosion and deposition continues long enough then those meanders might get so wide that it actually alters the shape of the river and it may even cut off a portion of the river to form something called an oxbow lake so over here this is our oxbow lake okay so that used to be part of the river but due to extensive erosion and deposition that part of the river actually got cut off and that shape of the channel has changed leaving that lake behind with this telltale kind of horse to shape so if you look at this this is (15:37) how that happens the erosion and deposition continue the meanders get wider and wider until the river actually meets itself in a location and then deposition takes over and cuts off that meander creating an oxbow lake so here's an example of an oxbow lake there are actually several in this picture and here's some more you can see them over here's an oxbow lake here's an oxbow lake here is an oxbow lake so those were all actually part of the meanders at some point in over time they've been cut off so let's finally shift our attention to (16:12) focus specifically on the deposition that occurs within a river so streams slow down not only when they're on the inside of a curve but also when they enter a larger body of water like for example if a river or stream flows into a lake a larger River or or even in some cases the ocean that water's gonna slow down and we know from our previous conversation here that when water slows down it can't carry as much so it deposits it so whenever water slows down deposition occurs so here we have a cross-section of a river flowing down (16:45) the side of a hill slope right fast fast fast fast fast but then it hits the lake and it slows down and because it slows down right there can't carry the sediment anymore so right in here we're gonna see lots of deposition I like to think about this the same way as I think about a water slide so if you've ever been on a water slide you know that as you're going down the slide you're going faster faster faster and then all of a sudden you hit the pool at the end and your body stops essentially and that's because you've entered this larger body (17:16) of water and the velocity slows down and the same thing happens in a river and when that occurs the sediment that the river is carrying is dropped off and so the sediment that is deposited creates this kind of weird accumulation of sand and silt and clay and that accumulation is called the Delta in some cases that Delta can become a new landmass so here's an example of a delta so all of this kind of grayish muddy sediment has been deposited as this little stream enters this larger body of water all of these Delta's (17:49) can actually they're massive you can see them from space on the Amazon River Delta it's huge amounts of sediment that have been deposited over time so the sediments that are deposited within a Delta are generally sorted out by size with the largest ones dropped off first and then smaller and smaller sediments as you get further and further out into the lake or the ocean so here's a diagram that kind of shows that because when the stream enters the body of water it slows off it slows down it's gonna drop the bigger stuff first and then as (18:28) it slows more smaller stuff and then as it slows more smaller stuff and then eventually smaller and smaller until it has deposited everything that it's carrying so that sediment that sorting is called horizontal sorting because the size of the sediments is sorted out from big to small from side to side okay sometimes though we'll have sediments that deposited very quickly and that might result not in horizontal sorting but in vertical sorting so rapid deposition you know for example if I have a rock slide on a cliff where a (19:06) bunch of sediment is dumped into a lake all at once then my biggest sediment is going to accumulate on the bottom and the smaller stuff is gonna settle a little bit slower and end up being on top and so we end up with this vertical sorting and we have a name for vertical sorting it's called graded bedding so that's when we have top to bottom small to large and this isn't what that actually looks like you can see on the bottom our larger size sediments and as you go up they're smaller and that would give us greeted bedding so horizontal (19:38) sorting occurs when the sediment happens gradually whereas vertical sorting happens when it occurs quickly that's key now final thing is because of this abrasion so this is a word we've used in other videos abrasion is a type of weathering when Rock kind of grinds against rocks now in rivers sand is constantly bouncing against pebble and rock and it's wearing it down and so the rocks that have been weathered and eroded and deposited by streams and rivers tend to be generally rounded and smoothed out something like we see in (20:15) this picture right here so if I were to just hand you one of these rocks even though you don't necessarily know where it came from you could interpret you could conclude that it's spent time in running water and that's how it got the smooth rounded shape that you see and so that's our look at rivers for today just to kind of sum up some of the key ideas meanders curves and rivers tell us about the age of the river and we can identify where erosion and deposition occurs we see sorting whether it's horizontal or (20:47) vertical and we see rounding in these sediments and so those are some of our key ideas for River erosion and deposition rivers are an incredibly powerful force that has been shaping the earth for billions of years and rivers all have a story to tell by looking at them and examining their characteristics and the characteristics of the sediments within them we can actually learn a lot about their age and how they have impacted the earth in the past and how they're changing the surface in the future they're an amazing force that (21:20) really leaves its imprint on our planet thanks for watching Rivers - YouTube https://www.youtube.com/watch?v=6wEN683XXiM Transcript: (00:00) [music] 97% of all the water on Earth’s surface is in the ocean. The remaining roughly 3% is fresh and found on land. Of that freshwater, 69% is trapped in glaciers and ice caps, and 30% can be found in pores and cracks, soaked into the ground (known as groundwater). (00:26) The remaining 1% of freshwater supplies includes water in the atmosphere or in plants or the biosphere, and water pooling or running across the surface. The water in lakes makes up 0.26% of all freshwater supplies; and rivers, streams, and creeks make up only 0.006% of freshwater on the planet. How does water move around between all the different reservoirs in which it’s found? Heat from the sun evaporates water (turns it into water vapor), moving it up into the atmosphere. (00:58) This atmospheric water will get moved around the planet by winds. When that air later cools, water vapor will condense back into liquid water and drop downward as rain, otherwise known as precipitation. Some of that rain lands directly in the oceans. Some lands in glacial or ice sheet areas. Some drops directly into the ground and soaks into it. (01:24) Where grounds are saturated with water and can hold no more, any rain that falls there will run along the surface into rivers, streams, and lakes. Eventually most of this running water will make its way back to the ocean. What about ocean water that soaks into the sediment and cracks on the seafloor? When this crust eventually sinks into the mantle at subduction zones, that water is squeezed out and because it’s less dense, rises upwards. (01:52) Since the addition of water to the asthenosphere drops its melting point, magmas form. The magmas produced are rich in water and rise upwards to produce volcanoes that release the water back into the atmosphere as a gas. Through continued evaporation and precipitation, running water, subduction, and volcanism, Earth’s water continually cycles in and out of the various reservoirs, processes collectively known as the hydrologic or water cycle. Now let’s focus on the 0. (02:24) 006% of freshwater found in rivers. Despite being such a minor component of water storage, running water is the most powerful erosional agent at work on Planet Earth. Running water weathers, erodes, and deposits material across Earth’s surface and produces a multitude of unique and varied landforms. (02:49) Even in deserts, where water runs on the surface for only a few weeks a year, that running water is still the most powerful of the forces at work sculpting that landscape. How does water get into a river? A river’s drainage basin or watershed is the area of land in which all the rain that falls will ultimately makes its way into that river. The line between two drainage basins or watersheds is called a divide. (03:12) The continental divide in the United States, for example, is a divide that runs along the top of the Rocky Mountains. Water that falls on one side of this divide will travel east and south into the Mississippi River Basin; and water that runs on the other side will travel west into different basins, such as the basin of the Colorado River. (03:38) We call the waters at the highest elevation of a drainage basin the headwaters. As water moves downhill it will be joined by more water from the ground or from other streams. Each of the small streams and rivulets that join together are called tributaries. The lowest point of a river, where it enters a lake or the ocean, is called the mouth. (03:59) Tectonics and isostatic uplift push the land up – erosional agents such as running water carve it down. As water moves downhill, it will carve out rock from the high country and carry it to the low country. Its work is done when the river has carved the land flat. Base level is the lowest level to which a river will erode – Ultimate base level for most rivers in the world is the ocean, unless a river is draining into an interior basin lower than sea level and with no outlet to the ocean. An example of this can be found in Death Valley, California, where the lowest point is (04:37) 282 feet below sea level. A lake might be a local or intermediary base level. In that local area, the rivers that feed into that lake will erode down only to the level of lake. Then their work is done until the lake drains downward and the rivers are back at work again. Why is running water such a powerful eroder or sculptor of the land? First let’s review a few terms. Weathering is the process of physical or chemical breakdown of rock. (05:08) Erosion is the transport of weathered debris or sediment from one location to another. Deposition is the dropping of the sediment into piles. Rivers physically weather or break down rock through two primary methods: hydraulic pressure and abrasion. As water moves downhill, the weight and velocity of the water puts pressure on the rocks over which it flows. (05:34) When cracks exist in those rocks, this pressure can gradually expand the crack. Also, the sediment carried along the base of a river, pushed downhill by the force of the weight of the running water (also known as bed load) will move across rock surfaces and scrape and abrade those surfaces. Chemical weathering as discussed in the Weathering video tutorial is aided by water, so when rivers put water in continual contact with solid rock, they increase the rate at which that rock will chemically break down, primary methods being that minerals will dissolve, oxidize, or turn into clays. (06:07) Once rocks have broken down through any activity, the river itself, gravity, glaciers, wind, humans, waves, etc., the river will pick up those weathered pieces and transport them to a new location. Discharge is the term we use to describe the volume of water a river transports past a given point every second. It’s measured in cubic meters per second (cm3/s). (06:33) The higher the discharge, the more sediment load a river can carry. The maximum sediment load a river can carry is called its capacity. As discharge increases, so too does capacity. New sediment can be carried by a river only if it hasn’t yet reached its capacity. Rivers that are at capacity will run across sediment but not have room to pick it up. (06:57) Similarly, when a river’s discharge decreases, like in the days after a storm, its capacity will shrink, and it has to drop sediment it can no longer carry. Additionally, the ability to pick up and carry a sediment grain of a particular weight or size depends on the river’s velocity. The greater the velocity, the greater the power and hence the larger the grain size it can carry. (07:20) We call the maximum grain size that a river can carry, its competence. Competence goes up as velocity goes up. Similarly, as velocity goes down, competence goes down. Result? When velocity drops, all the largest grains are dropped at the same place in a pile, creating a pile of well-sorted grains which means similarly sized. (07:46) Piles of sediment dropped by rivers are called alluvium, and they are easily recognizable by their excellent sorting and also by the rounding produced by the continual knocking about with other grains as they were transported by the river and as the river continues to move over them once they were deposited. Now that we know under what conditions rivers pick up sediment and under what conditions they drop it, where are we most likely to see both happening in a river? Let’s start by looking closer at velocity. Where along a river does velocity increase? Or decrease? The slope or gradient (08:23) of a river is the ratio of vertical to horizontal distance that a river moves down a hill. How does gradient impact the velocity? We would expect rivers to move faster down steeper slopes and slower on gentler ones. Where rivers move from the steep mountains onto the flat plains, gradient flattens out considerably, slowing the river. (08:49) The slower-moving river has a lower competence and has to drop sediment grains too big to carry. The alluvial deposits that form in these circumstances are referred to as an alluvial fan. Why flatter slopes at the base of the mountains? That’s where all the sediment from erosion of those mountains piles up. (09:10) The remaining water that runs down must now make its way across this pile of sediment and thus can split into many different rivulets or braids as it weaves it way through the pile. We call the pattern of such a river a braided river. In contrast, rivers high in the mountains typically have straight channels with a V-shape cross-section, as rivers erode downward as directly as possible, and gravity carries the slope material on either side downhill. (09:40) Where rivers go from flatter slopes to steeper slopes, like when they spill over waterfalls, the velocity speeds up and the river can pick up larger particles. How do waterfalls form? When you have a resistant layer of rock that is difficult for rivers to erode, they will find cracks and erode downward through those cracks to less resistant rocks below. (10:04) As the river erodes the less resistant rock underneath, it will undercut the top layer. Over time the continued undercutting will make the top layer unstable, and the overlying cliff will crack and fall. Another factor that impacts velocity is friction – the stickiness of the river bed that drags on the water within. Friction and drag are affected by the shape of the channel as well as the material over which the river runs. (10:28) Shallow channels or deep narrow channels have increased surface area so increased drag. A deep and broad channel, like a perfect semicircle, has the least amount of surface area to volume of water and the least drag. Large boulders like what’s found in the mountains in shallow streams produce high drag. Smooth rock surface or fine muds cause very little drag. Less friction or drag, faster river. (10:56) What about the width of the river? Just like with your finger on the end of a hose, when the channel of the river flow is constricted or narrows, velocity speeds up. Erosion increases, and the narrows can be eroded quite deep. Where channels widen, velocity drops, and depositions occurs. The discharge of a river also affects speed – the higher the discharge, the higher the velocity. (11:31) So what makes discharge increase or decrease? As already mentioned, discharge in a river is a function of how much water rains down in the drainage basin. Eventually all the tiny streams in the basin will join to the main river. So discharge should be highest the closer we get to the mouth of the river. Discharge will also change throughout the seasons as the amount of rain and snow melt varies. (11:53) If we can erode through a drainage divide and increase the area of a drainage basin, that should also lead to greater discharge. What happens at dams? Dams across a river will stop the flow of the river. That stop in velocity means sediment is dropped at the mouth of the river as it enters the lake. (12:13) We call sediment dropped at the mouth of a river where it enters another body of water, a delta. That delta sediment over time will cause the lake level to rise, so in summer the lake might need to be drained, and the sediment removed. Meanwhile, downriver, the water that spills over the dam has no sediment within and is dropping from great height with great velocity. It will pick up and erode sediment from the areas immediately below the dam. (12:37) How is material transported by a river? In addition to the bed load already discussed (the sediment pushed along the bottom of the river due to the pressure of the water moving downhill), rivers also carry particles in suspension, buoyed up by the energy of the water. This suspended load make the river look cloudy or opaque. (13:00) We can remove suspended load by letting a jar or bucket of river water sit for a few days still. The lack of energy gives the particles time to settle out and deposit in a layer on the bottom of the bucket. The finest muds might take more than a day to fully settle out. Also carried by a river are the dissolved ions produced through chemical weathering of the rocks up river. (13:24) This dissolved load can be removed only if the water is evaporated, allowing the ions to find each other again and crystallize. Let’s look more closely at what happens when rivers flood. Meandering rivers no longer have any downward-eroding work to do, as they move across flat plains close to sea level. However, they are now eroding horizontally, as they meander across the landscape, bending around obstructions, avoiding resistant rocks, and carving out new channels during floods. (13:54) Most of the year, the river sits in its channel. But when the discharge increases and the river’s level rises during heavy rains, they can overtop their banks and spill out into the surrounding land. That means a fast-moving river chuck-full of sediment will overtop its banks and immediately slow down as it spreads across the flat plain on either side of the channel. (14:16) These plains are known as the flood plains. The drop in velocity means deposition – the largest gravels depositing along the banks of the river creating structures called levees. The finer sands and muds deposit behind the levees across the flood plain. Rivers use their flood plains every time they flood, which is an annual process. (14:41) Some floods are heavier or more intense than others, and the heavier the flood, the more sediment is deposited in the flood plains. Also, the heavier the flood, the more water in the river, and the faster the river runs. That makes it more erosive and more likely to carve out a new channel or path. For example, in meandering rivers, the outside of the meanders or bends experience the fastest most erosive water, the inside the calmest. (15:04) Therefore, sediment piles up on the inside of these bends, and erosion increases on the outside. Over time, the bends get more and more extreme until during a flood, the pressure of the water can cut a new path right across a bend. The cut-off bend now becomes a lake, known as an oxbow lake, while the river has straightened itself out a bit. (15:29) After the flood, the water that remains in the channel also slows down and deposits any sediment that it can no longer carry on the bottom of its bed. That causes the river bed to rise, which also makes the river level rise, so the natural levees will also rise during the next flood, as will the flood plains. Over time, the entire region gets a thicker and thicker pile of sediment as the mountains continue to erode, and the sediment continues to pile up at the coast. (16:00) What happens when we build homes on the flood plains and build levees to keep the water out of those flood plains during floods? When the river tries to overtop its levees, it can’t. This puts extra pressure on other areas of the river, and if it can’t find anywhere to overtop, then after the flood, the sediment that it carried will be deposited on the bottom of the river bed only. (16:23) So the river itself will continue to rise, and the levees have to continually be built up to keep the river back, and that makes the flood plain level considerably lower than the river bed so when the river does eventually break through over top the levees or break through the leveess, the water that makes it into the flood plains will have to be pumped out, as the area is now lower than the river level. (16:45) This is true in the New Orleans area on the Mississippi River. The area of homes built on the flood plain are now sitting under the level of the river, and pumps are working 24-7 in some locations to ensure that water doesn’t migrate underground and turn these areas into lakes. After a flood breaks through the levees, it can take weeks or months before all the water is pumped back out. (17:08) Rivers flood when there’s more water entering the river than the channel can contain. This happens during heavy rains over long periods of time once the ground has been saturated and can hold no more water. What happens when we cover natural forested land with agriculture? The runoff is faster because there are no tree limbs and roots to soak up the water. (17:32) What about when we cover agricultural land with urban land, especially concrete? The rain runoff will go directly into the river with none soaking into the ground, so the rivers can reach flood stage much faster. The river channel and floodplain are part of the same system, together representing the path that the river will take at various stages in its seasons and journey. (17:58) Detailed mapping of the flood plain around meandering rivers shows that throughout the history of the river, its path has migrated back and forth across the plains as sediments continue to deposit and build over time. Building communities on the flood plains of rivers is a challenging feat that requires artificial levees to keep the river in its path and constant maintenance to ensure the river stays in its channel. (18:24) It requires dredging the bottom of the river to keep the bed from rising and it requires significant flood plains to be accessible elsewhere to release the pressure of the rising river. All natural rivers systems flood every year or two on average. The intensity of flooding varies, and often floods are described as 100-year events, 50-year events, 10-year events, and so on. (18:51) The goal of these terms is to consider the building requirements and risks for various levels of flooding. The higher the year provided, the more intense the flood will be. For example, 100-year floods are so intense they happen on average only once every 100 years. What that means for those who choose to live in the flood plains of a river is that we need to be prepared to handle the consequences of any of these events. (19:14) Pause now. [music] [music] Floods are increasing WAY faster than we expected - YouTube https://www.youtube.com/watch?v=pDIpbXjCtyg https://docs.google.com/document/d/1DOxyU5HPp8rTKsoKhpFNa6zbWo7ivP5AuBlX-02fn4w/e dit?usp=sharing Transcript: (00:00) - Extreme rain events are increasing at an alarming rate in the US and all over the world, but the problem isn't the amount of rain that falls in any one place, it's how long it takes the rain to fall. And fascinating new research sheds light on exactly how that's changing. Over the last century, global precipitation has only increased by 0.04 inches per decade. (00:24) But looking at individual regions in the US, we can see that some places have experienced 30% more rain over the same period. However, more rain isn't the whole story. That's why the organization First Street created a groundbreaking risk map that shows a big change in what NOAA calls 100 year floods. These are events so extreme that the odds of them happening in any given year are about one in 100. (00:51) - 100 year precipitation event is occurring more often about once every seven to eight years in the most extreme cases. - And that matters because infrastructure like sewer systems are built with this metric in mind. But why the change? It's because a warmer atmosphere is a thirstier atmosphere, meaning it can hold more moisture - For each additional increase in temperature. (01:14) By one degree Celsius. The air can hold 7% more water - Vapor. And that's fundamentally changing the hydrologic cycle. Dry times get drier and wet times get wetter at an exponential rate, and not only just on a yearly scale, but down to the hour and the minute. So First Street reanalyzed rainfall data across the US down to the minute their analysis uncovered an important trend and led to a new flood risk map of the United States. (01:42) It turns out that some places currently seeing less annual precipitation and more drought should also expect more flooding. In this episode we're gonna look at this map to see what regions are most at risk and how we can adapt with all this additional water. - This is not something that anyone should go through when it comes to a disaster, especially a hurricane. (02:06) - We can learn a lot from New York City when it comes to extreme rain because they're getting so much of it. Just last September, the city saw nearly eight inches of rain in a single day. - A place like New York City used to be very, very green, and it was covered in lakes and streams. And over time it's been filled in. (02:23) The - Same is true in nearly every city. We've replaced natural permeable surfaces with concrete and asphalt. Nearly 72% of New York City is now covered in impermeable surfaces. So instead of a natural water system, runoff has to be managed by a sewer system designed for a climate that no longer exists. - The original designers that built our sewer system did not know that we were gonna have 3, 4, 5, 8 inches of rain. (02:49) - One in a hundred year event in New York City actually occurs about once every 35 years. - This is a new problem, so they can only manage about one to two inches of rain per hour. - Our infrastructure just can't keep up with all the rain that we're getting. And the NOAA maps, which are referred to as Atlas 14 and Atlas 2 that we use to project flood risk and figure out where to upgrade our infrastructure for flooding, events aren't keeping up with the rain either. (03:16) - They use traditional historic methods for measuring precipitation risk. And for a long time, that was perfectly fine. The problem is if you have an increasing precipitation trend, then all of a sudden now the average doesn't actually capture what the current events are. It actually pegs them back to a climate that could be as far as 20 or 30 years ago. (03:35) - In other words, the NOAA maps look backwards and not forwards. So First Street decided to take a different approach to NOAA's data. - Our report was really focused on the extreme precipitation events as opposed to the average precipitation levels across the country. And it's not necessarily that we're seeing more of these events, but when we seen them, they're more severe, we're seeing more severity in the intensity of the rainfall events over shorter durations, which is causing more - Flooding. (04:01) Amit Shivprasad lives in Hollis, Queens. His neighborhood has been impacted by flooding events for a long time, but recently it's gotten worse. Looking around the area has very few green spaces to absorb Rainwater and Amit learned that this area used to be an actual lake. - So this is actually our house where you guys are right now. (04:21) So if if you look, it's actually sitting in the middle of a pond right now, and this is what the pond looked like back in 1928. If you - Look at an old map of New York City and see where all the creeks and the lakes used to be, and then you look at today's flood map, you can actually see that it's pretty much identical. (04:37) - FEMA's 100 year floodplain map derived from NOAA's Atlas 14 directly impacts the cost of and access to flood insurance. But since the map doesn't include flooding from rainstorms, many communities are left out. And as a result, overexposed - Flood insurance was never sold to anyone in this community because we don't live in a flood zone or a FEMA hundred year map. (05:00) But - Flooding has devastated this community. In 2021, after Hurricane Ida made landfall as a category four, it traveled up the Eastern US dumping record breaking rainfall in its path in New York City alone. It dropped over seven inches, peaking at three inches of rain per hour. Amit's neighborhood was not prepared. (05:19) - It started off as a normal day, had dinner with my folks and all the warnings start to go off. Ran downstairs, grabbed my poncho, with me and my dad took our shovels and rake went out to clean the basins like we do every single time it rains. But - The sewer basins on Amit's street weren't functioning that day. (05:35) - City was doing construction and they pretty much had all the basin covers covered. Notice as the rain was coming in higher. So I ran up and grabbed my keys, moved the truck up the block before I got back down the end of the block, the entire street was flooded. - The flooding killed 13 people in New York. (05:57) - 11 of those people died in flooded basement apartments, most of them here in Queens, 43-year-old Phamatee Ramskriet and her 22-year-old son, Krishah, also known as Tara, and Nicholas could not survive last night's rushing flood waters crashing through the wall and pouring into their basement apartment. - Tara and Nicholas were tenants in Amit's family's basement. (06:20) Before Ida he lifted the doors to his home, three to four feet to prepare for flooding, but the storm brought too much water. He no longer rents out his basement and now uses the space for community events. - Unfortunately, the wall collapsed and that's the reason why all the destruction happened. So I've done my part where it comes to repair. (06:41) I just pray and ask God that it never floods again. That's all. - Ida resulted in $75 billion in damages across the U.S. Over 33,500 buildings in New York City were destroyed, and Amit's remodel alone cost over $344,000. But not all areas were equally affected across the Hudson Hoboken, New Jersey didn't suffer the same flooding, and this is partly because of their efforts to adapt to this new climate reality. (07:10) - Flooding has always been a problem in the city of Hoboken. We were originally a tidal marsh, actually. The area where we were standing, it was marshland. All of these low-lying areas that were marsh that were filled in for industrialization in the early 19 hundreds are very subject to flooding today. We also have a combined sewer system where our storm water and our sewage flow into the same pipes. (07:32) Now with climate change, we're seeing more frequent storms, more severe storms. - To address the flooding issues, Hoboken has been building resiliencity parks around the city. We went on a tour of the largest park to understand how these green spaces operate. - This is one of the 19 rain gardens that is in resiliencity park. (07:49) And these rain gardens will manage water during a rain event. You'll see that it almost looks like a pond. Water is slowly being delayed from entering our storm water system. It's filtered through the rain garden through all the plants and the soil. Then that water slowly drains into the underground tank that's below the park and then goes out to our sewer system. (08:09) And that's all water that then is not on our streets. During a rain event, our million gallon detention tank that is under this lawn can detain storm water that comes from the park site itself, as well as from all of Northern Hoboken - And it's working. Hoboken has seen an 88% decrease in flooding events since installing these mitigation measures. (08:29) And only time will tell if these measures hold up against future climate changes. But it's strong proof of concept. The comparison of Hoboken and Hollis also follows another trend. Recent studies find that race and wealth play a big role in where natural disaster recovery efforts happen, and this impacts safety and economic outcomes for residents. (08:52) A study from 2018 found that in areas with at least $10 billion in damages from a natural disaster, white families actually saw a wealth increase of about $126,000 post recovery while black families saw a wealth decrease of $27,000. This map shows the extent of this wealth gap in some major cities across the U.S. (09:18) Hoboken is 64% white while Amit's neighborhood in Queens is just 1.4% white, - 1.3 million. New Yorkers live either in or directly adjacent to a flood plain, and that's gonna go up to be over 2 million. By the turn of the century. Half of those people are considered low income by HUD, our federal government, and half of those people are communities of color. (09:41) - Hollis, which is Amit's neighborhood in Queens and the adjacent Queens village, underwent a $24 million sewer expansion from 2019 to 2021 to try to address the flooding problem. However, the Hollis community still experiences frequent flooding. - My neighbor across the street, every time it rains, she comes over to our house 'cause she's afraid that her wall is gonna collapse again. (10:04) And you know, it's, it's, it's a sad thing. That everyone in the community is feeling the same way - As the climate changes and the wet times get wetter. Intervention efforts become increasingly more complicated and challenging. - And this is gonna be one of probably the biggest issues that we're gonna face over the next 20 years is gonna be where are we gonna stay and where are we gonna leave? There's no one solution for every neighborhood or for every place. (10:27) - But there's hope for flood mitigation efforts. Every dollar spent on flood mitigation sees up to an $8 return. - So we can manage that water with green infrastructure and turn New York City into a sponge in every neighborhood in every place that we can possibly do it. We'd like to absorb water, so that could be on our streets, it could be on our green roofs, or it could be in our parks. (10:48) - Now that we understand the challenges and opportunities to deal with urban flooding, let's get back to First Street's new risk map, which focuses mostly on flooding from heavy rainfall events. - There's about 8 million properties currently in FEMA's special flood hazard area compared to our about 17.7 million properties. (11:07) Most of that, about 65% of that gap that we see is actually driven by precipitation - risk. In fact, by FEMA's own estimate from 2015 to 2019, 40% of flood insurance claims came from outside of the high risk zones on the FEMA map. But maybe the most surprising is the update to NOAA's flood maps. This shows the difference between NOAA's maps and what First Street found where 100 year floods are now more like 35 year floods, like in the case of New York City. (11:37) Their study even found that in some areas, 100 year floods have now become just eight year floods, making them more than 12 times as likely. - The Midwest in particular sees a lot of underrepresentation of those one in a hundred year events, places like Southern Indiana and Northern Kentucky around the Louisville, Kentucky metro area. (11:56) They're seeing the one in a hundred year depth from the NOAA Atlas 14 records as much as one in seven or one in eight years. - According to First Street, not only the Midwest, but the entire Northeastern part of the United States has a hidden risk of extreme precipitation. And even in Northern California, which is seeing a decrease in precipitation overall, the likelihood of a 100 year flood is now one in 35. (12:21) With climate change, we're seeing strange patterns and complex impacts to our weather systems. We may not know exactly what a warmer world will look like, but it's clear that change is happening. So it seems like it will be wise for us to adapt. In this episode. We've learned the stakes of flooding from these extreme rainfall events and looked at places like the City of Hoboken, a place that's doing a great job at navigating these changes to our hydrologic cycle. (12:48) But I'm curious, how is your community adapting to these changes? Let us know in the comments below. Read/Watch Intro The Earth's Ever-Changing Landscape: A Tale of Weathering, Erosion, and Deposition Our planet Earth is a dynamic place, constantly undergoing changes that shape its surface. These changes, primarily driven by the forces of weathering, erosion, and deposition, are responsible for the diverse landscapes we see around us. Let's delve into these processes and explore how they interact to mold our world. Weathering: The Breakdown of Rock It all starts with weathering, the process that breaks down rocks into smaller pieces called sediments. This can happen in two main ways: physical weathering and chemical weathering. Physical weathering involves the mechanical breakdown of rocks, such as through the freezing and thawing of water or the grinding action of glaciers. Chemical weathering, on the other hand, alters the chemical composition of rocks, often through reactions with water or air. Place a comment where you see information that would address a common misconception before each video. Weathering, Erosion, and Deposition [Part 1] - YouTube Erosion: The Transportation of Sediments Once rocks are weathered into sediments, erosion takes over. Erosion is the movement of these sediments from one place to another, typically by natural agents like wind, water, or ice. Rivers, for instance, play a significant role in erosion, carving out valleys and transporting vast amounts of sediment downstream. Place a comment where you see information that would address a common misconception before each video. River Erosion and Deposition - YouTube Deposition: The Dropping Off of Sediments The journey of sediments doesn't end with erosion. Eventually, the transporting agents lose energy, and the sediments settle down in a process called deposition. This accumulation of sediments can lead to the formation of various landforms, such as deltas, beaches, and sand dunes. Place a comment where you see information that would address a common misconception before each video. Rivers - YouTube Flooding: A Double-Edged Sword While rivers are essential for shaping the Earth's surface, they can also pose significant challenges to human populations. Floods, often caused by excessive rainfall or overflowing rivers, can cause widespread damage and devastation. Understanding the dynamics of floods and implementing effective mitigation measures are crucial for protecting communities and infrastructure. Place a comment where you see information that would address a common misconception before each video. Floods are increasing WAY faster than we expected - YouTube Conclusion The processes of weathering, erosion, and deposition are fundamental to the Earth's dynamic nature. They shape our landscapes, create diverse ecosystems, and influence human activities. By understanding these processes, we can better appreciate the forces that have molded our planet and make informed decisions about how we interact with our environment.