howdy everyone and welcome to the video where we will start to explore some different types of floods by looking at a few case studies as examples now there are different types of floods and if you have a textbook on hazards or geology there's a lot more detail that we can spend talking about all the different types of floods but we're going to categorize floods in in this class into three main categories that we'll call regional flash floods and storm surge now regional floods occur seasonally under unique circum circumstances like when winter or spring rains fall on a snow pack releasing large quantities of water which streams cannot handle and they can also be influenced when the ground is frozen because remember there's less infiltration and more runoff in those situations persistent wet conditions that saturate soil can also increase runoff aiding a flood so if the soil is completely full of water and it can't hold anymore it's going to promote runoff at that point and subsequent storms producing more and more runoff can lead to extensive regional flooding like the Mississippi River flood in 1993 and in 2011 for example now flash floods occur with little to no warning they produce rapid rises in water levels and they can have devastating flow velocities several contributing factors such as high rainfall intensity and conditions will promote flow funneling into narrow channels so that means canyons and mountainous regions and urban areas such as cities with parking lots development and storm sewers and deserts with hard dry ground are all especially vulnerable to these types of events now storm surge flooding occurs when water is pushed up onto dry land by onshore winds and this can sometimes rise the sea level up to 20 to 30 feet and this rise in water is due to the onshore winds and also the low atmospheric pressure that is pressing down onto the water and pushing it up onto the land now usually storm surges are related to hurricane activity and cause nine out of the 10 hurricane related deaths in a storm it is clearly the most dangerous part of the storm a grave example of this happened in the year 1900 at Galveistston in Texas where the storm surge killed 8 to 12,000 people and we're not going to spend too much time talking about storm surge flooding in this module because we have an entire separate module on hurricanes later on this semester so let's just take a look at some case studies and some examples of some regional floods that we've seen in our country with the Mississippi River we've used the Mississippi River drainage basin in a lot of examples so far so this is a perfect place to study these regional flood events and this Mississippi River as we learned in the previous videos has this delta that's formed um at its mouth that's constantly changing and evolving but it's also constantly responding to the modifications that we're making to it and to the changes that we see in our weather and climate and the Mississippi River has had major floods in our country's history such as in 1927 37 47 73 79 83 93 2008 2011 so forth it's going to continue to do this into the future as well now here's a view of the flooding of the Missouri Mississippi River network in uh 2011 this view is from the International Space Station and you can see some levies on the banks of this river um notice that the inner leveies have been breached so here we have our meander this is our cut bank this is our point bar you can see that these leveies here these outer levies some of them remained strong and did not break this left all this land still dry but some of the leveies over here these inner leveies did break and that caused the flood waters to inundate the areas here but our levies sometimes work so these outer levies did work and save all of this land over here which is why flood mitigation is so important because it saved all those farms and development now here's a photo from that flooding um that just shows the incredible force of the flood waters i mean water is such a powerful tool and flood waters are truly incredible here's a photo from the 2008 flood on the Mississippi River and you can barely see the top of the flooded levey here so there were levies here that got overtopped that year the river's height greatly exceeded the levies that were put in place so sometimes our mitigation strategies are just not enough for mother nature here's another image from 2008 this one's from Iowa this is showing a railroad bridge that acted like a dam but the combined force of the rushing water and all of this debris that include entire homes likely destroyed this bridge okay so those were some examples of regional floods let's now take a look at some flash floods there are several contributing factors such as high rainfall intensity and conditions that promote the funneling of the flow into narrow channels and flash floods tend to occur in mountains canyons deserts and in urban areas because of the parking lots and storm sewers and just impervious surfaces that prevent infiltration now in flash floods 50% of the deaths actually occur in vehicles and that's why it is so important that you actually pay attention to your warnings and do not travel during a flash flood event and if you do come across a flooded roadway never try to drive through it now flash flooding is common in desert areas which often receives most of their annual precipitation in a few large storms now the hard dry ground makes infiltration really difficult so when they do get those few large storms it promotes a ton of runoff and here's a photo of a flash flood in a desert region of Israel which has washed over a highway forcing the evacuation of these truckers by helicopter in 2015 Death Valley National Park experienced a thousand-year storm over two weeks in October of that year the area around the park received a series of unusual storms with unusually high precipitation now some areas received more than the normal yearly rainfall in just a few hours and remember the ground in deserts is hard packed but it also has very little vegetation so it does not soak up water very quickly and the steep slopes that surround Death Valley also cause rapid surface runoff this resulted in major flash floods throughout the park causing significant damage and there was even a more recent event that happened that I should probably make a video about um very similar event happened again less than a thousand years later by the way but here's just some of the damage showing how powerful and eros of the roaring waters can be in just a short amount of time destroying roads so even after the event makes it very hard for people to come in and help recover and rescue if you're not able to drive through the flood damage was especially bad at Scotty's Castle which is a tourist attraction here in the park and it was closed indefinitely um and then had a bunch of funding problems and COVID and I actually don't know if it ever reopened i know it was supposed to reopen um I think it was supposed to reopen maybe in 2022 but I haven't checked to see if it reopened last I looked it was still closed now here are some photos showing Scotty's Castle and the flood damage in the gift shop which filled it with a foot of mud a foot of mud inside remember it's not just water we're also carrying a lot of sediments in these floods here's an area of Scotty's castle that was eroded to a depth of 8 ft and cut eight feet into the ground that area has been covered by interlocking cement blocks to prevent further erosion in a future event that could eventually undermine the foundations of nearby buildings now another notable flash flood occurred that same year in Utah in Zion National Park this one was deadly though this one killed 20 people and 13 of the people killed were from two families including nine children that ended up being swept away in their vehicle nearby seven experienced hikers were also killed in Keyhole Canyon off Zion Canyon in the national park here's a photo of the rescue team searching for survivors by boat because that's the only way you could travel in this area after this event and here are the remains of the vehicles in which 13 people were killed you can see here a rescue dog struggling in the mud searching for the victims and these flood waters do not just contain powerfully flowing water but also mud and even debris as well pieces of homes pieces of buildings and vehicles now this is Keyhole Canyon this is where seven hikers were at at the time of the flash flood and you can see here that there's very little chance of surviving a flash flood in a place like this flash floods have been proven to be deadly in Zion Cany Canyon many many times and these are the seven experienced hikers that were killed unfortunately the weather report was received just after they had checked in at the park so it was too late to warn them now has anyone been out to Rocky National Park if you've been to Rocky Mountain National Park chances are you have driven through here on US Route 34 this route goes through the Big Thompson Canyon in Colorado which is a gorgeous place near Estes Park right outside the National Park as gorgeous as this place was and how often it's traveled it was the site of the worst flash flood in US history big Thompson Canyon is a popular tourist attraction because it's about an hour northwest of Denver and it's really close to the the national park there were approximately 2500 to 3,500 people hiking fishing and biking at the time of this event and this flash flood killed 143 people five of whom were never found now this flood was triggered by a nearly stationary thunderstorm near the upper section of the canyon and that storm dumped 12 in of rain in less than 4 hours however most of the people killed were in the lower section of the canyon where they didn't receive much rain at all a wall of water more than 20 ft high raced down the canyon at about 14 mph destroying 400 cars 418 homes and 52 businesses as well as washing out most of US Route 34 now during the flood the stream changed from a twoft trickle to a torrent that was 19 ft deep carrying 10ft boulders with it the only chance you had to escape was climbing up the canyon walls which you can see are very steep in this region if you were in a vehicle or in a building those things became literal death traps so hopefully you now understand the difference between a regional flood and a flash flood and why it's so important that we understand how our land how our landscape responds to changes that we make and to changes that nature is going to make in our next and final video we'll finally start to look at how we can live along rivers and streams i'll see you there