hi everyone welcome back to my channel this video series is all about coasts and coastal landscapes as well as coastal management and today we're going to start off looking at the importance of waves concerning our coastline environments now as always there's a link in the description box below for the worksheets that you can complete while watching these videos and these will help you create nice revision notes or support you if you are learning from home so let's start by thinking about coastlines and what a coastline actually is so when i use this word coastline i am referring to where the land meets the sea and within our coastline environments and our coastal locations waves constantly influence the shape of our coastlines and yes we as people we do attempt to manage such changes that the waves create they cause erosion transportation and deposition and we can manage coastlines in different ways but we're not quite onto that yet so today we're just going to be thinking about how those waves influence our coastline so let me explain to you how waves form so if we were for example to hold a cup of water in front of us and blow over the surface of that cup of water that gust of air coming out of your mouth will travel over the surface of the cup and create friction this is the same thing that happens in the ocean or the sea waves are formed by the wind blowing across the surface of the sea and that transfer of energy creates friction across the water's surface this friction across the surface of the water creates these small ripples which eventually will develop into waves now wave energy can depend on something known as fetch and fetch means the strength of the wind and the length of time over which the wind has blown so the longer the fetch the greater the possibility of larger waves being created and potentially this may result in storm-like conditions so what happens then when waves reach and approach our coastline well out in the deep ocean or in your deep sea before they reach the coastline waves will travel in a circular orbit in the open water but as they approach the coastline friction with the seabed of the shoreline actually begins to distort the circular orbit and make that wave become a more elliptical shape the crest or the top of the wave then moves at a faster speed compared to the trough the base of the wave and that then increases the elliptical orbit when the wave eventually approaches the shoreline that wave will break and wash onto the shoreline the water then that rushes up the beach is known as swash and the water that retreats and flows back towards the sea is known as backwash now despite the relatively wavy surface of the open sea there is little horizontal movement this side to side movement in the open water this side to side movement only occurs when the waves break and surge up the beach through swash as they approach the coastline so out in your open ocean or open water you have very little horizontal movement that side to side movement in the water now when it comes to coastlines there are two different types of waves a constructive wave and a destructive wave and both of these waves can influence the shape of the cosine in very different ways so we're going to start off looking at a constructive wave and a constructive wave if we break this word down constructs the beach so these waves are what are responsible for building up those lovely sandy or silt shingle beaches now constructive waves have a relatively low wave height typically they are under one meter in height and constructive waves are known for having really strong swash all their energy goes into the approach and then washing up onto the coastline and because of that it can carry a lot and transport a lot of material onto the coastline but constructive waves have a very weak backwash and they use all their energy in the swash so when it comes to them retreating back into the sea through backwash they have no energy left and this causes deposition to take place so that sediment that sand that silt that gets dropped off on your coastline and that constructs and builds up your beaches now constructive waves are also known for having very long wavelengths and they also occur at a very low frequency and what that means is is that the amount of waves approaching the beach that wash up onto the shore is a smaller amount compared to a destructive wave so on average we will have eight to ten constructive waves approaching the beach per minute now if we then look at our second type of wave this wave is known as a destructive wave and again if you break this word down destructive we're thinking about the word destroy here so these are the types of waves responsible for erosion destroying the beach washing away part of your coastline and destructive waves in comparison to constructive waves have really tall wave heights on average they are over one meter in height and a destructive wave in comparison to a constructive wave has a weak swash so when a destructive wave approaches the beach it has very little energy because it takes so much energy to create that really tall wave height this means that when the wave breaks onto the coastline all of the energy is then released and that destructive wave has a very strong back wash then as it retreats back into the body of water what this means is is we will get increased amounts of erosion on our coastline here because of that strong backwash being able to use all its energy to pull all that sediment off the beach and destructive waves have shorter wavelengths they're higher in frequency as well so when destructive waves approach our coastline we can have 10 to 14 occurring per minute now if we were to quickly summarize the difference between each type of wave we've got constructive waves again and a destructive wave and if we're thinking about wave height our constructive wave has a low wave height typically under one meter whereas your destructive wave has a tall wave height typically over one meter in relation to the length of the wave your constructive wave has a long wavelength compared to your destructive wave which has a short wavelength and when it comes to wave frequency we will get 8 to 10 constructive waves approaching the coastline per minute in comparison our destructive waves we will have about 10 to 14 per minute now when we're thinking about the strength of the swash we're thinking about when the waves approach our constructive waves are the one that has the strongest swash and your destructive wave has the weaker swash because it needs more energy to generate that wave height the strength of the backwash when the wave retreats from the coastline your weak backwash is your constructive wave and your strongest backwash is associated with your destructive wave because they cause erosion and finally your net beach sediment refers to the amount of sediment that is present on the coastline and that net beach sediment can either increase on the coastline or decrease so when it comes to constructive waves because they construct beaches and they build up beaches because of deposition occurring due to that strong swash and that weak backwash our net beach sediment will increase in comparison a destructive wave because of its really strong backwash will have a net beach sediment which decreases because of erosion taking place so as always everyone thank you so much for watching please like and subscribe if you're finding these videos useful and i'll see you next time