Comprehensive Guide to River Environments, Hydrological Cycle & Flood Management

[Applause] [Music] River environments and we're looking at

the hydrological cycle which as the name suggests is all to do with water let's start with the definition so the

hydrological cycle is the global circulation of water it is a closed system made up of both stores and

transfers and we'll be looking at what those stores and transfers are in a great amount of detail but what do we

mean by a closed system well it basically means that water can neither leave or enter the Earth's surface or

atmosphere what do we mean by transfer well that's the movement of water between stores and there's lots of

different transfers you need to know about the first one is evaporation evaporation is when heat energy causes

the temperature of the water to rise until it turns into steam and forms clouds next up is transpiration if you

do biology you'll know all about this it's where plants absorb water their roots and then they transpire that water

out of their leaves and I'm trying very hard not to mention Stato Etc because as geographers you just need to know that

that water evaporates from the surface of the plant's leaves a term which you may have heard is the combination of

those two terms and that is evapor transpiration condensation now which is the opposite of evaporation that's when

that water vapor cools and condenses turning back into a liquid and that's what you often find occurring at Clouds

now precipitation that's effective when water transfers itself from the atmosphere to the Earth's surface so it

includes things such as snow rain hail that sort of thing slightly more complicated now surface runoff that's

when water falls as rain and then it runs across the Earth's surface into surrounding streams and rivers through

flow is when water drains through the soil due to the force of gravity and again that water will collect in streams

and rivers groundw flow occurs in rocks of the aquifer remember an Acer is the porous rock that allows water to drain

through it and in this way water will reach Seas rivers and lakes so those are the different types of transfers you

need to know about but what sort of human factors can affect the amount of transfer that occurs well the first main

one is urbanization when we build cities and towns and we pave and we concrete and we tarmac the surface of the Earth

that basically increases the amount of runoff that occurs because obviously that water is not draining into the soil

it's not draining into the aquaus in the same way and you will find that urbanization does lead to an increase in

the speed at which these water transfers occurs deforestation that's another human activity it means cutting down

trees remember we cut down those trees for building materials to provide land for farming fuel Etc what happens when

we DeForest is we lose the top soil because it means we no longer have the tree roots holding down the soil and

again that will increase surface runoff we've looked at human factors but what about physical factors which affect

water transfers so the first one is rock type you'll find that non-porous rocks will allow water to run up far more

quickly because that water won't be soaking through the rock vegetation will also have a large effect if you have

more trees then that will increase the rates of rain interception as well as increasing the rates of transpiration

and as a consequence evapor transpiration we'll touch a little bit on storage here because the third

physical factor which will affect water transfers is global warming as temperatures increase you will find that

the stores of ice and snow reduce however there will be an increased trans to our seas and oceans due to increased

precipitation rates we will now deal with water stores and that's where water is stored within the hydrological cycle

and that falls into three broad categories that will be land sea and the atmosphere so we'll now go through those

in a lot more detail first of all lakes now water is stored in Lakes because it has a bottom made up of a non-porous

Rock which means the water can't drain away Rivers hopefully are quite self-explanatory as well as the sea you

find that soil is a good store of water because that water can't percolate through to the Bedrock other examples of

good water stores that you need to mention in your exam are ground water surface water clouds ice and then that

aquaa which remember is a porous rock that allows water to drain through it sometimes it's useful to see a pictorial

representation so you can understand how all the stores and transfers are linked so because it's a cycle it doesn't

really matter where you start but let's have a look down here so heat energy causes the water water's temperature to

rise it becomes steam it evaporates up to form clouds we said that any water coming from the clouds in the form of

hail rain snow is examples of precipitation so that's what we can see here we can see ice falling over there

through surface runoff where that water runs over the Earth's surface we know that water due to gravity will lead to

rivers lakes streams Etc so we can see how the water is returning to the Sea as a store vegetation interception we

already talked about which which is a physical Factor affecting water transfers those trees will be absorbing

that water at their Roots transpiration will be occurring as a result of that then down here we have examples showing

through flow and groundwater flow remember through flow is due to gravity where water drains through the soil

until it reaches either a stream or river groundwater flow occurs in rocks of the aquafer remember that's your

permeable Rock and involves the transfer of water to lakes rivers and the sea so you can't see absolutely everything on

this diagram but I'm hoping you understand how water's stored and how that water is transferred and remember

this is a closed system water is neither allowed to leave or enter the Earth's surface and

atmosphere now we're going to move on to the drainage basin what is a drainage basin well it is an area of land drained

by a river it's an open system and that means that the amount of water varies over time due to changes in external

inputs and outputs so what sort of inputs are there of a drainage base then the first one which is probably the

least obvious is energy from the Sun but then let's think about how would water be added to a drainage basin while

precipitation is a good method so remember that's anything that falls from the sky rain fall snow hail Etc as well

as water from tribut Tre basins remember a tribut Tre is a small river which joins the main river Channel what about

the outputs of a drainage basin now so how does water leave the drainage basin transpiration and evaporate

transpiration is going to be important here remember transpiration occurs from the leaves of plants as well as the

river's discharge which we will spend an awful lot of this video discussing just one thing to point out a drainage basin

is very different from a hydrological cycle in the ad drainage basin is an open system as I said previously the

amount of water that enters and leaves varies unlike the hydrological cycle where the total amount of water remains

constant now we're going to talk about characteristics and features of the drainage basin so remember again that's

the area of land drained by a river the first thing you need to be aware of is the source and that is the origin of the

river next up the Watershed that is the boundary of the drainage basin it's a raised piece of land which separates one

drainage basin from another the Channel network is if you think about a river it's covered by a network of tribut

trees so that Channel network is that area of land covered by both the river and its tributaries the mouth of the

river is the point where the river ends and that tends to be at a sea or an ocean and finally catchment that is the

area within the drainage basin now there are three different types of drainage basin first up those that collect water

and deliver it directly to the Sea so they'll be the ones you're most familiar with some drainage basins form parts of

much larger River drainage basins a good example of this is the river negro which is in South America now you'll find that

it's drainage basin forms part of the huge drainage basin of the river Amazon and then finally some drainage basins

don't drain to the sea or ocean instead they drain to Inland Seas or lakes and a good example of this is Lake Victoria in

Africa next up River discharge as we've already mentioned that as being an output of a drainage basin the river's

discharge is the volume of water carried by a river at any one place so what factors affect the river's discharge

well first of all the most obvious ones are things like precipitation and particularly rainfall will affect

River's discharge so remember that's the volume of water flowing at any one particular place obviously if it rains

more there will be a greater River discharge second up is vegetation now if vegetation is cut away it exposes bare

rock this reduces the time taken for the water to be soaked up leading to an increase in the river's discharge the

good thing about trees and other vegetation is their presence intercepts that rainfall usually and therefore

delays that rain reaching the ground and has the subsequent effect of reducing the river's discharge other fact factors

which affect the river's discharge include soil type length and width of river and the number of tributaries so

small rivers which join that main river channel in terms of human activity urbanization has a detrimental effect

and will increase River's discharge this is because urbanization so building of settlements increases the rate of

surface runoff and therefore decreases the lag time this will increase the peak in River discharge urbanization also

automatically means that vegetation will be cut down so as I was just saying that means that there'll be less interception

of rainfall meaning that there won't be that delay in that water reaching the ground so you'll end up with more

surface runoff and greater River discharge now we'll turn our attention to River regimes first of all let's

start with the definition of a river regime and this is the way in which the river's discharge changes over time

remember that the river's discharge is the volume of water carried by a river at any one place so we need to consider

why would that volume increase or decrease at any particular point in time we do also like to look at it over the

course of a year so we can make predictions and understand more about the behavior of river at any particular

season or point in time so if we consider the sort of things which will increase the river's discharge well

first of all heavy precipitation so heavy rainfall what that means is that the ground gets saturated very quickly

which increases surface runoff meaning that there's a shorter lag time so that water that falls from the sky will flow

directly into the the river so that will influence the river regime in that way increasing the river's discharge if we

increase the temperature so hotter days there'll be more of AO transpiration so that will remove water from the river

what about vegetation now some more biotic factors well vegetations such as trees will intercept that rainfall

meaning that there's a bit of a delay in that rain reaching the ground so you'll get slower infiltration of the ground

and that will increase the lifetime that means there'll be a delay in that water reaching the river in terms of land use

and humans activity this can actually alter the river regime in opposing ways so for example humans might put in

drainage channels more canals so obviously that will take water away from the river however urbanization generally

and I by that I mean building settlements what that means is there's less ground for that water to soak into

to infiltrate so in this situation you'll end up with more surface runoff and that water will wash into the rivers

meaning that there's a decreased lag time so look at it from two points of view either human behaviors which will

divert that water away into canals into drainage channels or the fact that we're building more concreting our surfaces

meaning that you get more surface run off and therefore greater River discharge and in that latter situation

you will find that that creates more of a flashy River regime other things humans do could include water

abstraction and that's where humans remove water from the river for particular uses that could be an

industry that could be to water crops so irrigation or that could even be for consumption purposes washing cleaning

Etc and then lastly dams again this is something that is human built dams are often built in order to trap water

within a reservoir and then through the process of HP so that's hydroelectric power these dams are used to generate

power for our homes again that will affect the river's regime so broadly speaking if you're asked to describe the

factors which affect River regim let's talk about precipitation let's talk about temperature let's talk about veget

ation land use water abstraction and dams and break your answer up into those various categories and provide the extra

details that I've already given you previously in this video a storm hydrograph graph which

shows how a River's discharge changes over time and that's typically before during or after a storm event why are

storm hydrographs so useful because they provide valuable insights into the relationship between rainfall and river

flow and that's important because lots of people build their homes within drainage basins and a huge amount of

time and money is spent building these homes so storm hydrographs provide valuable insights that enable you to

predict floods and understand how bad those floods will be so that people can make informed decisions about what to do

whether they can stay in their homes and put out sandbags or whether they need to leave but now we're going to go onto my

iPad and actually have a look more closely at a storm hydrograph so let's have a look at a typical storm

hydrograph so typically you'll find three things on these graphs to the right hand side we can see precipitation

so that tends to be rainfall and that's given in millimet on the left hand side we're looking at River discharge so

that's the volume of water flowing through the river at any one particular place and then at the bottom we have a

time scale now there are two types of flow which affect the discharge of a river in a storm hydrograph first of all

we have the base flow which is the normal discharge of the river which we can see bottom right in the baby blue

spotty section that is the river's usual discharge with the storm flow which we can see on the key on the left hand side

this is when you're going to see a huge increase in the river's discharge that tends to be in line with a huge amount

of precipitation and so we call the storm flow the extra discharge of a river which results from a storm so as

I've already said storm hydrographs show River discharge

precipitation and time they have a base flow which is the normal discharge of a

river as well as a storm flow which is the extra discharge of a

river which results from a storm now we're going to look at the features of different storm hyd graphs

so we'll start by looking at this portion where the bar chart is we can see that this is the peak rainfall or

Peak precipitation as you might imagine this is the maximum rainfall that occurs

moving over to the graph line as opposed to the bar chart always has this characteristic shape you can see this

push on the graph where it is steeply increasing that gradient we call that the rising Limb and this is the increase

of river discharge it doesn't necessarily have to occur straight after precipitation then you have the peak

discharge here which is the maximum discharge remember you will see that delay because it does take time for the

water to find its way to the river you may also see this described as Peak flow thing with geography is there's

lots of names for the same thing because there is that delay between the peak precipitation or Peak

rainfall and the peak discharge due to that time taken for the water to flow into the rivers we call that delay the

lag time so we've dealt with Peak rainfall Rising limb lag time Peak discharge but

what about this falling limb we can see that negative gradient of the graph Line This is known as the falling limb and

what it's trying to say is that as that storm precipitation levels decrease in turn River discharge will decrease

because less water will be entering the rivers and then last up base flow we can see

down here that's when the river discharge returns to normal so what factors affect the shape

of storm hydrographs well firstly the amount of precipitation or rainfall obviously the higher the

rainfall the greater the river discharge next up human activities

urbanization and deforestation both increase River discharge and that's

because of increased surface runoff the size of the drainage basin will also affect the storm hydrograph

and actually you find that large drainage basins are associated with less discharge small drainage basins are

associated with more disch charge which might seem a little counterintuitive rock type also has an

effect if you have an impermeable Rock like Granite you will see more discharge because that water's not going to soak

in if you have a permeable Rock like Limestone you'll get less discharge so do be prepared to compare

these various factors we can sometimes describe these hydrograph shapes in terms of whether they're flashy storm

hydrographs or if they're subdued storm hydrographs so the classic shape we have here is for a flashy storm hydrograph

we'll talk about the various characteristics shortly if this graph changed a little bit in shape so it was

more like this that would be what we would call a subdued storm hydrograph that's because we have a longer lag time

a lower Peak and a gently sloping Rising limb as we can see here so yeah longer lag time lower Peak discharge

Peak and a gently sloping Rising limb and we'll talk about the reasons as to why you get the flashy storm hydrograph

versus the subdued storm hydrograph right now so our flashy storm hydrograph we

know we're going to have a short lag time we'll have a high peak discharge and a steep Rising limb so

those are all descriptions of the graph we would see why do we get these various features

that we see on the graph well for a number of reasons you could have had an intense storm or rapid snow

melt steep slopes so if we consider the geology steep slopes mean that we'll get lots of runoff into those Rivers small

drainage basin will also give rise to flashy storm hydrographs in terms of human behaviors

deforestation and urbanization will increase surface runoff and therefore mean that you're more likely to get a

flashy storm hydrograph so there's lots of different factors you can talk about affecting the

shape if we look at the subdued storm hydrograph then what do we expect to see on the graph this time time as I've

already said you'll have a longer lag time lower Peak discharge shallower Rising

limb so the reasons for that subdued storm hydrograph will be opposite to the ones we talked about in the flashy one

so rather than an intense storm we would talk about steady rainfall gentle

slopes large drainage basins lots of vegetation because remember that

vegetation will intercept that rainfall And Delay that water reaching the rivers so let's look at some past paper

questions we're being asked to study Figure 1 B and identify the feature of the storm hydrograph labeled X so here's

Figure 1 B what is X I'm hoping you can see that that is the peak rainfall it's the top of the bar chart next question

study Figure 1 a suggest two reasons for the different storm hydrograph shapes for marks so here are our storm

hydrographs I'm hoping you can see this is a flashy storm hydrograph we've got that shorter lag time the higher Peak

discharge the Steep Rising limb this is a subdued storm hydrograph we've got a much lower Peak discharge a shallower

rising Limb and a longer lag time so we are going to State those differences and and then give a reason for it so in the

first storm hydrograph there is a shorter lag time and that could be due to urbanization and

deforestation increasing surface runoff and means less interception takes place make sure you write a nice full

answer here what else did we talk about we said about the rising limb we could say in

the first storm hydrograph there is a steeper Rising limb so we have that flashy storm hydrograph and we said that

that could be due to there being steep slopes which increase the rate at which water enters the rivers

now we're moving on to fluvial processes and really these are factors which affect the shape and the flow of rivers

and we'll be looking at things such as erosion weathering deposition and transportation and unfortunately these

words do sound quite similar and you do need to know them in lots of detail so first of all we'll start with erosion

and really this is the we in away of soil and rock in river banks and rivers now there are two types of erosion

vertical and lateral so vertical as the name suggests involves deepening the river and this is mainly due to

hydraulic action which we'll talk about Lots later in terms of where you find this sort of erosion is mostly in the

upper course of the river so near its source lateral erosion as the name suggests involves making the river wider

and it involves eroding away at those banks of the river this is actually more common in the middle and lower courses

of the river so vertical erosion we'll see towards the start of the river the upper course that involves making the

river deeper lateral erosion makes the river wider and it happens more in the middle and lower courses of the river

now there are lots of different ways in which erosion may take place some of these include hydraulic action which

we've just mentioned attrition solution otherwise known as corrosion and abrasion so we'll start with hydraulic

action and look at that in a bit more detail this is really due to the force of the river against the river banks and

what happens is there's air that is squashed within cracks and crevices found within those river banks which

weakens them and fundamentally leads to their erosion hydraulic action as we've already mentioned is the main source of

vertical erosion so we know that that River will get deeper as a result of hydraulic action next up abrasion now

abrasion can be responsible for both vertical and lateral erosion so that's making the river deeper and wider first

of all material carried by the river SC scrapes away at the River Bank hence how it makes the river wider this also

loosens material in the River Bank meaning that that is more easily Carried Away by the river sandpaper action

widens and deepens the river and you also may see that the river gets undercut by rocks rubbing away at the

bank so again just to mention abrasion is responsible for both vertical and lateral erosion attrition now another

similar sounding word this time it's rocks being carried by the river knock against each other and actually cause

these rocks to break apart and become smaller how about solution or corrosion in this case the river water itself

dissolves minerals in the river banks also if the water is weakly acidic it will dissolve soluble particles and so

this is a lot more gentle but again we can see that the river will become wider and deeper as a result of solution SLC

corrosion so we've dealt with erosion now but what about weathering as the name suggests it's how different types

of weather may affect the river shape and flow there are three types we are going to look at today mechanical

weathering biological weathering and chemical weathering and there is some overlap with the chemistry specification

for some exam boards so mechanical weathering the freeze th type of weathering so what happens here is that

water in very cold weather freezes within the cracks of rocks and when that water freezes it expands pushing that

crack wider so you can imagine how lumps of rock will break off those river banks chemical weathering is all to do with

slightly acidic rainwater dissolving soluble particles breaking down the rock in a more gentle way but again this is

still a type of Destruction to the river bank biological weathering biological always means to do with living organisms

here it's plant roots which grow in small cracks of the rocks and as those roots grow bigger they widen the cracks

causing it to potentially break off bits of rock weathering is tightly linked with mass movement because you can

imagine as those small chunks of rocks break off if this happens in a large quantity this is what we call mass

movement and particularly if you have a steep slope which we'll talk about Lots later you'll see a huge movement of

material down those river banks there are two types of mass movement one is soil creep and one is slumping so

slumping occurs when the bottom of a valley slope is worn Away by the river flowing the slope becomes unstable and

material slumps down towards the riverbed this is particularly applicable after heavy rainfall you can

actually imagine how that material will just fall off of the side of the slope after rain after it becomes unstable

what about soil creep unlike slumping which occurs quite rapidly soil creep as the name suggests is a much slower

process rather than occurring on steep slopes you'll see sore creep occur on gentle slopes where weathered material

gathers at the bottom of the slope and then it is eroded further by the river now we're going to look more closely at

the factors which affect weathering and remember Mass movement is tightly linked with weathering because once weathering

occurs and small bits of rock break off that means that they're more susceptible to move as a whole so what factors

affect weathering and mass movement and do you be prepared to explain them so first of all weather obviously heavy

precipitation heavy rainfall will increase the likelihood of mass movement taking place next up the slope gradient

so the steeper the slope the more likely mass movement will take place and you're looking for slopes above 5° in order for

mass movement to take place climate now hot wet climates will encourage biological weathering because

these sorts of climates the heat that extra water will encourage plants to grow their Roots get in the cracks

widening the cracks increasing the chance of biological weathering which therefore increases the chance of mass

movement because we'll have small chunks of rock breaking off now vegetation if you have more vegetation holding down

the top soil and this has the KnockOn effect of decreasing mass movement now we consider altitude so high altitudes

you'll find colder temperatures colder temperatures are linked with mechanical weathering so at very cold temperatures

you more likely to find that water and rocks will freeze causing that expansion of the cracks meaning the bits of rock

break off so remember that's the freeze th weathering and again that will increase mass movement last up the

geology so we're really looking at rock type here now very hard rocks such as Granite are less prone to weathering

meaning that mass movement is less lik to take place limone which is a lot more porous it's very easily affected by acid

rain because remember that calcium carbonate dissolves in the slightly acidic Grain water this is going to

break down far more easily you're going to get small chunks which break off increasing the chance of mass movement

Transportation now transport that means the movement of substances so really transportation in a river setting means

how material is moved down a river there were different ways of transportation one is saltation one is solution and the

last two are suspension and traction so always bear in mind what is the umbrella term well we're talking about

Transportation so how does saltation lead to material being moved Downstream well you have small sand sized particles

so very tiny particles which are moved Downstream by the river and that is saltation suspension this is when small

particles are held within the water itself and they're just carried naturally Downstream traction is when

the heaviest material that's sunk to the bottom of the river bed is R along the riverbed and then finally solution

materials are dissolved in the water and then carried along naturally in this way deposition this is the laying down of

material transported by a river let's try and think about where this is most likely to take place so where is that

material going to be laid down well hopefully it seems fairly straightforward that this would occur

most likely Where the River speeds are slower to give it time for the material to be

deposited where there's less discharge so less water flowing through the river any particular point and fundamentally

where there's less energy so a good place for this is where the river mouth meets the sea so what sort of things we'

kind of already mentioned them but what sort of things affect deposition so that will be sediment size it will be the

presence of any confluences it could be any natural barriers or blockages in the river if there's low rainfall meaning

less discharge the gradient of the river will affect it so obviously a shallow gradient will mean less deposition now

we're going to look at some past paper questions State one physical factor that

influences deposition in a river so remember deposition is the laying down of material transported by a river you

have so many options here you could talk about sediment size River speed gradient the presence of any confluences if

there's a blockage or any kind of barrier but they only want one factor so I'm going to go with sediment

size explain how a bra erodes the river Channel abrasion is a type of erosion so obviously that's

going to lead to the river being scraped away becoming wider and deeper but we need quite a specific answer here for

the two marks so first of all we're going to start by stating that material carried by the

river scrapes away the Riverside creating a wider

Channel you could be really specific and talk about sandpaper action widens and deepens the

river EX explain one weathering process in a river valley so do you prefer the freeze Thor weathering do you prefer

talking about biological weathering which is all to do with roots growing into small cracks or or maybe even

chemical weathering which is acidic rainwater which breaks down some of the Rocks so it's up to you but just pick

one and explain it properly I'm going to go with mechanical weathering so this occurs when water enters cracks in the

rocks the water freezes when it's really cold and when it freezes and turns into

a solid it expands which forces the cracks and The Rock wider and sometimes they break

off now we're going to move on to how the characteristics of River change in the upper middle and lower courses so

first of all let's understand the terms long and cross profile of a river so the long profile of a river is if you were

to take a river from its source to its mouth and effectively you were to look at how that River changes from the

source to its mouth in terms of the things we've just discussed so shape River speed sediment size discharge Etc

we'd be looking at how those things change from the source to the river mouth whereas the cross profile of a

river is if you were to basically cut slices into that River so you'd end it with just a cross-section so that could

be near the source it could be near the mouth it could be anywhere in between so we'd be looking at things like the width

of the river the depth of the river and a particular Point what that sediment size discharge and River speed is doing

so going into more detail let's look at the upper course of the river so near the source what would we expect to see

well we'd expect to see that the river is deep with steep sided v-shaped valleys you'd expect to see water tools

gorges and interlocking Spurs if you've been near the top of a mountain you'll notice that there's the presence of very

large Boulders very little sediment that means that River will be nice and clear and why is there very little sediment

well there hasn't really been enough time for erosion to take place we looked at that in a previous video all the ways

in which that river bank and bed is eroded away producing those small pieces of sediment which basically makes the

river less clear vertical erosion will be largely dominant here and that remember is the deepening of the river

in terms of human use you might find hydroelectric power so dams are built with a reservoir behind which provides a

source of energy from those turbines linking to the generator generating electricity there's often Hill sheet

farming forestry and it's often a good source of Tourism and that's because the upper course is often found in

mountainous areas and mountains make great places for ski slopes and other Alpine Sports as we enter the middle

course of the river we'll find that the gradient is shallower so those slopes will be less deep and the river is wider

we'll have increased River velocity partly due to increased water within that River the sediment shape will be

rounded smaller and smoother and because some erosion has taken place you'll find that there's sediment added to the water

so it'll be less clear Lal erosion is the dominant type of erosion found in the middle course of the river and that

will lead to things like meanders oxbow lakes in terms of land use you'll often find settlements farming and Industry in

the middle course of a river what about the lower course of river so as we approach the sea the mouth of the river

again you'll find that the river gets wider that slope will become gentler still you'll have increased River

velocity due to increased water volume and that could be due to tributaries adding extra water to the river you'll

have the smallest sediment found in this portion of the river and that's known as alium that often enters suspension

meaning that the river will be even less clear than it was before so in terms of how that River's Clarity and

transparency changes it will be the most clear at the upper course and then as you go to the the middle and lower

course it will become less clear again we'll see lots of lateral erosion evident which will lead to the formation

of Oxo lakes meanders and flood planes again so do be prepared to list these characteristics in the various parts of

the river in terms of land use you'll definitely see lots of settlements industry and farming in the lower course

of the river if we now summarize the long profile in both the upper and lower course of the river at the upper course

you'll find that the long profile is steep and the river is narrow whereas in the lower course of the river the long

profile is is shallow and the river is wide and deep now remember with this topic they could give you an Ordinance

survey map with a particular River and ask you to identify various characteristics in the upper lower and

middle course of the river so these are the sorts of things you want to be looking at remember if the contour lines

are close together that would indicate very steep valley sides so you'd often find that in the upper course of a river

make sure you can identify interlocking Spurs as well as flood planes when you see that snaking of the river remember

those would indicate meanders and you might even notice an oxbow lake in terms of land use be prepared to identify

towns which would indicate human settlement any industry taking place remember that will be more common on the

middle and lower course of a river now we're going to look at the formation of waterfalls Oxbow Lakes

levies River flood Plains Etc so let's start by stating what the physical land forms are of the upper course of the

river remember you'd expect to see v-shaped valleys interlocking Spurs Gorges River Rapids and waterfalls so

starting with v-shaped valleys how do they form well they form due to vertical erosion which acts to deepen the river

the River cuts downwards due to hydraulic action and abrasion the river erodes downwards you get freeze Thor

weathering which breaks off pieces of the river bank and causes soil creep but what about interlocking Spurs well very

similar to v-shaped valys we're going to have vertical erosion where hydraulic action and abrasion that River to deepen

what happens next is the River Winds and bends in order to avoid harder Rock and then repeated vertical erosion means

that parts of the land stick out in order to form the interlocking Spurs moving on to waterfalls so in order for

waterfall to form you need Hard Rock above soft rock which means that that soft rock below will be eroded first the

erosion undercuts the Hard Rock meaning that you eventually you'll get an overhang and then through vertical

erosion and hydraulic action you'll find that a plunge pool is created which acts to deepen the waterfall so we've dealt

with the upper course of the river what about the middle course of the river here you're likely to find flood Plains

oxbow lakes and meanders so remember meanders are those characteristic s-shaped bends in the river and they can

actually be very distinctive in places like the Amazon but how do they form well the river flows fastest on the

outside of the bend and flows slower on the inside of the bend so what you find is that on the inner Bend deposition

occurs because the river has less energy so more sediment can be deposited on the out to bend more erosion takes place due

to hydraulic action the river erodes and deposits laterally remember that meanders and oxbow lakes are very

tightly linked because eventually what happens if erosion is such that effectively the S on the Meander gets

cut off then you end up with an Oxo lake so again how is an oxbow lake formed well we're going to start by saying that

the river flows fastest on the outside of the bend and slowest on the inside of the bend again on the inside of the bend

deposition occurs because the river has less energy and therefore sediment can be deposited the outer Bend we see

erosion due to hydraulic action eventually the bank at the start and the end of the Meander will meet and full

flow breakthrough will provide a shorter pathway for the river and then the ox Lake forms due to deposition on the new

river banks now a flood plane is the area of land directly adjacent to a river and it's found in both the middle

and lower courses of a river a flood plane forms when River discharge is high and the river overflows its banks now

that river water May infiltrate the soil leaving behind find a layer of material which builds up to form the flood plane

moving on to the lower course of the river so what physical features do we find here well first will we find that

flood plane so again be prepared to describe how that flood plane is formed due to the High River discharge meaning

that the river overflows its banks alivium is deposited you'll also find levies the rivermouth delas and

potentially Islands well what is a levy well it's natural embankments that form by the banks of the river how are levies

formed they're created by by deposition so when the river flows over its flood plane the velocity of the river slows

this means that the river is unable to hold all of the sediment contained within it meaning that the sediment is

deposited what actually happens is the largest sediment is deposited first and then the smallest sediment is deposited

furthest away from the river and this is a process known as sorting and as you might expect this process repeats over

time meaning that eventually you get these natural embankments known as levies now let's look at some past paper

questions explain the formation of a river Meander so we'll start by talking about

how fast the river is Flowing on both the outside and inside Bend remember that the river flows fastest on the

outside Bend and then make the full comparison and

slowest on the inside Bend because of this on the inner band deposition occurs due to there being

more friction here on the outer Bend erosion occurs due to hydraulic

action now we're being asked to explain the formation of a waterfall remember a waterfall can only occur where there's a

band of hard rock sitting above sof a rock remember that softer Rock will erode

first and over time this creates an overhang which collapses as it's

unsupported moving on to uses of water and why there shortages and surpluses around the

world she looks so long hi everyone um if you've been following my science videos for a while

you know about Lyra but here she is in geography because she's going to help me with my

water quality video so broadly speaking what factors will affect water quality we can divide them into agricultural

ones industrial ones General human activity deforestation which means cutting down trees and then we'll be

looking more at Water Treatment both how it can improve water quality but also reduce it if not carefully managed now

to do well in your exam you'll need to provide lots of very detailed answers so we're going to take each of those

categories in turn so first of all how can Agricultural and farming practices reduced water quality well first of all

liquid slurry that's effectively animal fees animal poo can wash into rivers and they'll cause a phenomenon known as UT

tropication meaning that the rivers become very lacking in oxygen and all the aquatic organisms die but in this

way water quality is hugely affected next up with agriculture remember fertilizers added to soil to improve the

fertility of the soil these can also be washed into the rivers and the groundwater making it hugely

contaminated these are not things as humans we want to be consuming in our drinking water and last step

deforestation is a common agricultural practice sorry there's a dog barking now the reason why farmers DeForest why they

cut down trees is to provide more space to grow crops and more space to rear their livestock now what happens when

you cut down trees is that you have fewer tree roots to hold down the top soil so you get get surface runoff

meaning that more soil and silt flows into the river reducing the water quality now we're looking specifically

at how human activity can alter water quality now obviously homes are full of toilets which if the raw sewage from

those toilets is allowed to flow directly into the river you'll really reduce the water quality because of the

huge increase in bacteria in that water the same is true if you have leakages from sewage treatment plants so places

where that water is treated to make it safe for human consumption if those sewage treatment plants aren't carefully

managed then you can get massive leakage which will adversely affect the water quality of surrounding Rivers another

way in which water quality is reduced which you might not initially think of is the emptying of chlorinated swimming

pools remember that swimming pools have chlorine added to them in order to kill any bacteria present and to make them

safe for our use emptying this chlorinated water into Rivers obviously has a really detrimental impact on the

water quality and will affect all the aquatic organisms that live there the only good thing really that humans do to

improve the quality is through those seage treatment works if carefully managed and properly cared for they will

obviously remove all that Solid Waste remove all the bacteria and really the affluent from that sewage treatment

center should be really clean water so therefore in that way the water quality is improved next up how can industry

affect water quality well lots of factories use cooling systems and they use water in order to cool down their

Machinery now the output of those coing systems is much high temperature water which gets emptied into rivers killing

many organisms found there and generally upsetting the river ecosystems I'm sure you've seen lots of pictures in the news

when oil refinery spillages take place this is an awful episode because what happens is all the oil floods into the

rivers into the Seas causing all those poor seabirds to get stuck and widespread death to these

organisms and then the last industrial process I want to talk about is the iron refineries so this is places where iron

or gets processed in order to make pure iron that can be used in Building Bridges settlements Etc now you get some

really toxic chemicals getting washed out of these processing plants into rivers and you'll see the whole river

turn red just as a quick aside remember the term potable water is just water which is fit for human consumption so

what are the three main stages in managing the supply of Clean Water Well number one collection number two

treatment and number three delivery to the end user where is this fresh water collected from we've talked about this

in a previous video reservoirs lakes and rivers aquifers and Wells once we've got that water from these various sources

how is it treated well we briefly mentioned ATA surage treatment plant or at a water treatment plants so the first

step is filtration that removes any solid bits that have entered the water that could be as basic as stones or

Twigs then you have sedimentation which removes suspended particles so little pieces of sediment that make the water

cloudy and then the final step is chlorination the adding of chlorine in order to kill any bacteria present to

make that water safe for drinking that water is delivered to end users quite often along pipelines although in less

developed countries you'll often find a stand pipe where people collect the water in bottles and buckets so how is

the water supply managed well if we look at reservoirs and dams remember a reservoir is an artificial storage place

of water and it often has a dam to hold that water back now that water will be allowed to flow onto the pipelines which

Supply the houses as and when it is needed so that can be very carefully managed dirty or used water from homes

is taken to sewage treatment plants where it goes through those treatments we've just discussed and then it's piped

back to people's homes desalination as the name suggests involves the removal of salt so sometimes in some countries

such as in the Middle East they'll need to get their drinking water from sea waterer that sea water contains an awful

lot of salt which needs to be removed and that is the role of the desalination plant now we're going to be talking a

lot more in detail about the use of dams in managing the demand and supply of water as I've already said dams are used

to hold back Waters in Reser reservoirs and through careful management that water is allowed to run along pipelines

to people's homes the other great thing about dams is it can be used for hydroelectric power which remember is a

renewable source of energy when that water is let out of the dams it turns the turbine which is like a giant

windmill which turns the generator that can be used to power people's homes through the electricity it produces so

hydroelectric power is a fantastic byproduct of the building of a dam and for this reason you find lots of dams so

in Africa for example there's over 600 dams and in Europe as many as 1200 the fact that that water is held behind the

dam in the reservoir helps to prevent flooding further Downstream and it also enables water to be held back for

periods of time when water levels are naturally lower and there is a drought and this can therefore reduce water

insecurity now the great Renaissance Dam has huge had a huge amount of controversy attached to it so the people

in Egypt are concerned because they have a reduced control of that water and that water is so important for so many of

their livelihoods so they may end up suffering from water drought and then the people in Sudan are concerned

because when that water is released from the great Renaissance Dam it might overwhelm smaller dams and rivers which

have smaller capacity and it's really that ability of dams to control water where Rivers cross international

boundaries means that there are potential issues created as to who controls the water supply now let's look

at some past paper questions study Figure 1 a in the resource booklet explain two ways human

activity can affect water quality so here's Figure 1 a and let's try and zoom in on some things which will affect the

water quality so this sewage treatment plant down here is a good thing remember because it processes the sewage and

ensures that that water gets purified gets all those horrible microorganisms removed so it's suitable for household

use the same with the water treatment up here that will be improving the quality of the water in the dam in terms of

reducing the water quality this house obviously is going to be producing lots of raw sewage from that toilet right

there it even says ra seage out so if that gets untreated that will cause utri fication as it enters the river and

again we've obviously talked about the sewage treatment plant as being a good thing but again if there are leaks we're

going to see urif foration taking place down here as well we're going to start by talking about the discharge of

untreated sewage from houses then we'll talk about it from a positive perspective so water treatment

facilities can process the water to ensure that is a higher amount water suitable for household

use explain One Way agriculture can affect water quality I've already touched on it

before we could talk about ocation we could talk about anything to do with deforestation remember that's cutting

down trees to provide more space to grow crops or for livestock if we were to talk about livestock we could

potentially talk about cattle waste and that leeching into the rivers again contaminating the water as that will

increase the bacterial load lots and lots of options here I'm going to talk about the ufic answer so liquid

slurry that's really the feces from cattle can leech into the river so wash into

the river and because of all those extra nitrates that it contains it causes the

algal blo which is ocation and that KnockOn result remember is that you end up with the river being

starved of oxygen so all the aquatic organisms die first of all why is flooding such a

problem well flooding causes damages to people's home General infrastructure people's businesses their factories as

well as Communications you coming come on she's look she loves me really so

what physical factors affect flooding a level of precipitation or rainfall the density of the river Network as well as

its gradient if there's any existing saturation of the soil from previous flood events that will increase the

likelihood of flooding the time of year and any seasonal changes so when there's been a lot of snowfall and then the

temperature increases you'll get a snow melt which will increase the chance of flooding due to an increase in the

river's discharge and steepness of slopes so the relief of the land the steeper the slope The increased chance

of runoff and increased chance of flooding what human factors affect the risk of flooding well firstly the

population distribution and density various land use flood management strategies so if you've got hard

engineering structures in place such as flood walls that will decrease the chance of flooding embankments allowing

salt marsh regeneration again this will reduce the chance flooding and we'll look at this in great detail in another

video when you've got increased urbanization so people building houses you're going to have increased surface

runoff because firstly you'll have less interception by vegetation quite simply because that vegetation has been removed

in order to create more land to build settlements because building settlements involves an awful lot of concreting

Paving pulling down roads again you'll see increased surface runoff here and this increases the chance of flash

floods if you asked for quite a long answer an exam question with like eight marks asking you to analyze the reasons

why different areas are differently susceptible to flood risk we're going to look at both a combination of physical

and human factors so we want to be looking at you know whether urbanization has taken place if deforestation has

occurred increased concreting and Paving which leads to increased surface runoff leading to more flashy River regimes

meaning increased flood risk we want to look at the presence of any fledge management strategies so that seaw walls

salt marshes managed Retreats Etc any changes to weather or time of year so as we said increased snow melt or increased

precipitation what about the relief of the land so these are all factors you want to be looking at in that vsource

booklet because obviously the case study will vary from year to year they could ask you in slightly different ways but

these are the sorts of things you want to be looking at now we're going to be looking at

flood prevention strategies so broadly speaking that will be divided into hard engineering and soft engineering

strategies hard engineering strategies involves building artificial structures which try to control the rivers and help

prevent flooding in this way such as the building of seaw walls the hard engineering strategies tend to be more

more expensive and they need an awful lot of Maintenance soft engineering strategies do not involve the building

of artificial structures they take a more sustainable and natural approach to preventing River flooding that could

involve encouraging Wetland development I'm now going to describe the various hard and soft engineering strategies in

much more detail so starting with hard engineering strategies we'll be looking at the relative advantages and

disadvantages so starting with dams and reservoirs now the good thing about these is that water can be controlled

and also it provides a good source of renewable energy in the form of HP hydroelectric power the problem with

dams and reservoirs is they are very expensive and I have touched on this previously where Rivers cross

international boundaries you're going to have a lot of conflict in terms of who's controlling that water supply and it

could lead to a great deal of water insecurity for countries which are Downstream of those dams the building of

such dams and reservoirs also leads to a huge amount of damage to eco systems and loss of biodiversity as deforestation

occurs flood embankments in seaw walls hold back the flood water and prevent damage to farmland and settlements they

are very expensive and again they will adversely affect ecosystems and need to deforestation there is the potential to

increase the height of the seaw walls as sea levels change and clearly these will save lives help prevent damage to

settlements and they are a very effective way of preventing flooding although at the beginning there's just a

one-off cost they will need mainten M because in 100 years for example these sea walls will probably have been

breached and therefore they'll need to be rebuilt the next hard engineering strategy I want to talk about is River

straightening and River dredging so straightening the river increases the speed of the river meaning that it can

effectively hold more water which is good when you see increased River discharge which may lead to flash floods

and dredging means removing lots of sediment any waste that's enter the river again meaning that the river can

hold more water so through straightening and drudging we'll see the river can hold more water therefore helping to

prevent floods meaning that less damage occurs to people's homes and it means that people's lives less at risk in

terms of disadvantages that River dredging does need to be done fairly frequently so there's a cost in Cur with

that and River straightening because that increases the speed of the river it may actually increase flood risk further

Downstream turning our attention to flood relief channels this is when river water flows into smaller channels where

it can re-enter the river further Downstream by removing this excess water it reduces the chance of flooding and

all the disadvantages that come with that however this approach is quite expensive to build and if water levels

continue to rise then these River channels may also flood moving on to soft engineering approaches this

includes flood warnings and preparation flood control schemes and flood plain zoning so flood warnings and preparation

in this case the environmental agency monitors rainfall looks at the chance of floods and issues warnings either across

the TV or radio telling people when floods are most likely to occur so people can be warned and leave if needs

be or put any necessary precautions in place this could simply mean using sandbags to protect their properties

meaning that their possessions are saved and fewer insurance claims are made there are quite a few disadvantages with

this approach however firstly those flood warnings may not occur quickly enough people may not hear them secondly

it doesn't actually stop any of the flooding so although people's lives will definitely be saved if the flooding is

such that people's homes still get damaged then obviously this isn't a sufficient method flood plane zoning

involves using flood planes for very particular land uses and therefore restricting the building of houses and

factories in these areas which are more susceptible to flooding so more expensive buildings are built further

away from the river in areas less likely to flood and this obviously reduces damages to these types of buildings but

remember it's not always possible to change existing land uses and people will still will be inclined to build

there and buy their homes there so it's very important that you check whether your house that you're planning on

buying is built on a place that's likely to flood because in that case it should be avoided at all costs flood control

schemes encourages the development of wetlands and marshes because these act as great temporary stores of water

they're very natural and sustainable approach and encourage wide biod diversity increased speciation it's nice

and cheap but as with all things it's not always possible I think it's because it's cold ah please don't you're going

to tear a hole in my leggings she's growling because she hates it when she's moved but I can't

just sit in front of the camera all day you can find you a warm place to sit you know study Figure 1 a in the resource

booklet explain one advantage and one disadvantage of the flood prevention measures shown so we have details about

flood prevention measure in York in the UK so have a look at what we have here definitely use the key look we have

flood walls and Gates and we have a flood embankment so what's good about the flood walls well obviously they're

going to reduce the level of damage caused by the floods which could save people's lives particularly in the

people living around SB Terrace real disadvantages with flood WS though remember these are hard engineering

strategies they're very expensive because of the huge amount of work that goes into removing those trees which

they've already mentioned here to build new flood defenses 14 trees must be removed so from an environment Al point

of view that's terrible because that destroys habitats for wildlife and it's something that we'll need maintaining so

for an example in 100 years it's unlikely those flood walls will still be here so we're going to start with the

advantage which is that flood walls reduce the level of damage caused by floods

potentially saving lives disadvantage trees need

removing to allow flood walls to be built this destroys ecos

systems and animal habitats Now we move on to wave action so starting with the term fetch this is

the length of water the wind blows over if we consider the factors which influence the size of the Waves first of

all the strength of the wind the stronger the wind the bigger the wave the time frame that that wind is blowing

over the longer the wind blows for the bigger the wave and then lastly the fetch size because obviously the longer

the length of water that wind blows over the bigger the waves formed the prevailing wind is the dominant

Direction the wind is blowing across so in England the Southwest coast prevailing wind comes from a Southwest

Direction which means it blows over the length of the Atlantic Ocean so how do those waves form out at Sea the wind