Lecture 19

[Music] welcome back uh so uh after uh talking about the uh different landforms louia landforms now we will look at a few terminologies which have been used for uh the drainage which we see on the surface so mostly what we will come across because there's an very simple fundamental that if you're having a slope in any terrain and if you're having a precipitation then you will be bounced to see the the the formation of drainage so if you're having a slope in this direction as it has been shown in this figure also so you will see the development of the drainage now what are the terms which have been used for such uh drainage that we will quickly look at and that you will be using when you are identifying uh the different uh uh terrain and also the the different uh drainages okay so these are termed as uh uh also termed as the parallel drainage but in general it is they are termed as consequent streams okay so stream follows the slope developed on of development of slope maybe due to sudden tectonic uplift because the natural slopes are not usually seen because the slopes are seen because of the tectonic deformation mostly and then we have uh the so these are termed as consequent streams and and subsequent streams are not exactly following this slope they are developed so this is this is what has been uh shown here that they are almost right angle to the original slope of the land okay so the the slope we see here is this is the topography we are having so slope is in in this direction we are having because this is unfolded terrain and then we having the slope here this is a valley here okay but if there is an erosion which is taking place here so this is almost right angle to the the slope so those such streams are are ter as subsequent streams then if uh the stream is uh crossing the folded areas okay then they are termed as antecedent streams and then there is another one which is what we called the superposed uh streams which are in sizing the inclined surface and then which has been covered later on by the the the flat depositional stratum which has been made by because of the uh the deposition so if it is in sizing that then we term this as an superposed uh streams or drainage stream piracy again is an uh common process which one can come across in any area and this is basically because of the headward erosion of the drainage Evolution so time will come when this one of the the drainage basin will breach the uh the divide and you will see that it has been the the whole drainage has been taken up by one of the the drainage system okay and that is what we call stream piracy now coming to the drainage pattern the geometry of the stream network in a region that reflect aspects of underlying geology so as I told that there is a difference between the drainage pattern and the channel pattern so this you should keep in mind until now you will you must have uh uh understood the that uh the drain uh drainage pattern we will just see but the channel pattern mainly are the straight Meer and braided one now while I'll show couple of uh examples from the Himalayan region and then we'll move to the uh general part of that what are the different type of drainage pattern and what exactly talks about the subsurface one so if you look that this one this is in uh shaded relief map of and this exercise again you are going to do in your Labs so this is the area uh of northwest Himalaya and we so this you must be aware about this town rer and uhur so and this one is your K Valley here it goes to the the K Valley is here so and this is the town Kang and dhala so if you carefully look at the uh overall landscape then you will you'll be able to see that there is an divide here in the frontal part of the Himalayas and then you are having the drainages which are flowing in either direction so this is the drainage divide so you you will be able to pick up the drainage very easily from the uh digital elevation model this is again another uh example that you can use the uh data satellite data to generate a 3D prospective view of the terrain and you can rotate it or put it at different angle as you wish to view the terrain in best way now coming to this part uh again this will we will be uh talking about in the labs that how to extract the drainage but as what I was showing here is the same same area and this is the part where I was talking about the ren divide okay so you can clearly demarcate the drainage divide and this is based on what we have been talking about that one of the uh the drainage is flowing in One Direction on this direction and another one is in different direction this portion is again in flat area on the top where you are having the drainage which is flowing away from here and this is in this direction and the darker one is the major trunk stream okay so you can also talk about the order of streams here based on the extraction which we have done of the drainage so this you will be doing in one of your lab exercise okay so order what we see is the darker lines darker streams or thicker one are the higher order streams okay and that is the trunk streams and what you see here this one where I'm putting the cursor and this one is your Bas Reaver and this one is your satl so most common uh drainage pattern which one can come across in the areas are the dendritic which will be like uh if you are having a tree and then you're having the uh the tree stems which are growing it is typically like that okay so you will see in uh the dtic pattern then you have a radial pattern which again indicates about the the landform and then you are having a tras pattern tras pattern is mostly seen in a folded terrains so you are having the uh the harder rocks and softer Rock combination and mostly what has been seen here that the trunk stream is crossing this uh area and the uh the the tributaries will be almost at the right angle so you're having the the softer and harder rocks so you will have the resistance rocks are this one which are marked by darker uh color and then less resistance rocks will allow the formation of the the small lower order stream and that will be almost at right angle unless you see an folded terrain and then you are having in the if you are having a fractures in the terrain then you can come across this type of rectangular drainage that will be almost at the right angle to that so investigation along the sunun what we did was that uh uh this was the area which we were looking at and we uh we prepared a detail map and that what you are going to this is image and what right now I'm showing is in landet image and false color composite so what we uh we usually expect you to do is that you prepare such type of uh geomorphic map so what we have in this map is basically all the drainage has been marked here and then you are having The Terraces uh which have been marked in different color which have been named here as uh qt0 then qt1 T2 and T3 and so on so these are the the different teres which have been seen here and then along with that we have also marked the fults active fults here okay so this part uh we will try to cover if possible if you're having enough time left out with us then we'll try to teach how what are this uh uh this land forms and uh uh what are the import what are the important is the what is the importance of this in terms of the uh the earthquake hazard but uh right now what I would like to show you is that uh that there is there was an area uh which was we never expected that this type of uh feature will come across but based on the drainage we were able to judge that what exactly this area is showing and then we checked in the the field also okay so if I I would say that if you carefully look at uh this area particularly then what we we can you can make out is that there is a stream which is Flowing here in this direction and there is a stream in another stream which is Flowing or many streams which are flowing in like like that okay so you have a sort of an uh domal structure so this is a center here and then drainage is moving away from this okay so uh it is quite possible that this is an elevated portion and then you are having a slope on either side okay as what we were looking in the uh the radial drainage okay so this is typical of the radial drainage so when uh we looked at here in this area this is a closeup view of that so this you can see this one is the closeup view so so if you carefully see that what I was showing here that you have streams which are flowing like that okay over here and then some few streams are going like that okay and then over here like this like this here and then this stream is coming out here like this okay so this is the elevated portion what we can see here cuz this trage is going away from the center so this is typical of uh the domal area so Dome is something like if I put in cross-section then it will look something like this okay so it is having an slope on either side so now look at uh let us look at the what we see in the uh the U in field actually so this is the The Village known as Dan and this is CL not very far from nagad so what we we inferred that there is an sort of an F fault here and this area has been warpping because in the the folded terrains mostly what we see is that there's an the displacement which is taking place and this can result into a shown formation of of a doal structure or or folding here okay this I'm putting in section here so this is a top surface so this is exactly what we we inferred okay and there is another fault which goes here uh which has given rise to a different pattern of channels here so first look at this one here what we see is that because of this blocking of of resulted because of the theault not exactly blocking but there's because of the formation here in this area so if you if I put in cross-section this will be this will be seen something like this okay so you have uh a short of an uplift here so on this surface what has happened and one then further below what we see okay in terms of the drainage here and over here okay so this is the closeup here of this and if I carefully Mark the the streams stream here all the streams then you will come across that this area is showing it is coming like this you're are having Meander here and then going like this and then coming out like that okay again here you have the Meander and this is what we are talking about the tight Meander in this area Okay and then it becomes almost St straight so the the sinity decreases below this line okay and this is the uplifted area so if I say I was talking about that this is what we have so this portion is showing tight Meer and this is s like the sinity reduces so this an typical of a tectonic uh plantform I'm removing the line so that you can see it clearly what I was talking about okay so this is the line here which is responsible for the the change in the channel pattern so such change in the channel pattern are also been taken into consideration and uh sometime it could be related to the tectonic deformation then coming to another part here this is what we were talking about the based on the drainage pattern is the this is a closeup of that again I'm showing that this you can see now very clearly that what we're talking about the tight me so this is the portion in overall all the tages which are showing tight me now danh area when we looked at in the field it was very clear that the Topography is something like this okay so it was this is because of the doal effect so this is the area Dan and this one is here ban which is on the low Ling area but this is because of the the drainage which we show we saw s of an radial drainage it was because of the uh the typical uh doal topography in this region So based on the drainage pattern one can interpret what exactly uh the lithology is subsurface and second is the structure that is a geological structures okay so these are the uh the typical drainages which have been observed okay this what we were talking about when we talking about the consequent uh streams U that we can also term this as in parallel streams and this we have recently we see we have seen that this is radial drainage and uh so you will have uh like dender TI parallel trailes radial centrifugal then then and so on you will be looking at many such patterns okay so few of them are been listed here um that uh from the uh the type that is your dtic right up to the anular and the description is also given here then how it looks like okay so as I was talking about is a trailes it looks like a tree then what will be the geological significance okay so then there is an homogeneous material and crystalline rocks horizontal beds Gally Regional slope and then if you're having Subic then you are having minor structural control that is your tectonic or we can say the geological structures then pinet type is like you have fine grain material then rectangular streams you are having the area is jointed or fractured okay then you are having for example if you're taking parallel then you are having steep slopes that you will also see and then if you're looking at the radial one then you can say that it is flowing through uh uh the folded sedimentary terrain or meta sedimentary rocks and then you are having radial then you are having like domes or and and residual erosional features will be there then you are having for example aular then you a structural Dome okay so this are the the interpretations you can make out uh after identifying the different renage pattern so this exercise also you can do and as I told that we will uh teach you earlier we used to extract the drainage based on the satellite uh photographs or the satellite data used to draw with hand but now you are having the softwares which can extract the drainage easily okay so dtic pattern as we have t talked about that most commonly we will see this uh drainages and uh what are the uh the the information you can deduce from this okay so I have already discussed this part in the previous slide so I'll just skip this but you can go through and uh try to understand and recall when you are extracting the information from the satellite data so the dentritic parallel then you are having the radial one so as I we told that it is could be related to the higher topography and then you are having rectangular if you're are having jointed and fractured terrain then Tres mostly in the folded areas where you are having weak and resistive rocks anular again you are having an concentric path which will be seen and this could be because of the domal or Basin effect now quantifying the stream network basically the stream order in a basin can be ranked using one of the several screams so we are having two one is having shivery and another one is star so mostly we try to use the Stellar one so that uh the difference here uh is uh what we initially discuss is that in in this case in shv that what we have is you are having the first order to first order which will make the second order and even if the lower order stream is joining this will become third order but in case of so this will become third order here so two second uh like second order plus even first order is joining then it will make it higher orders and that will uh tremendously increase the number here okay like it can go up very high So to avoid that uh what is there in this tellar one that you having two first order streams okay so 1 + 1 will be two here second order and even if the first order is joining here this Remains the uh the second order only when 2 + 2 or 3 + 3 or any okay will will be there or even one as I as we talked about 1 + 1 then it will go into two in in this case 2 + 2 then joining then we will see third order and if three and three then we will see higher order and that what we we can can make out here okay so how this became fourth order this is based on this one here okay so you're having third order two two third order streams joining here so this becomes your fourth order and that's how one can classify and as I told that earlier we used to trace out all this demaret the first order second order and B based on that we used to come up with the the final order Basin and here it is you can see that in here in this four and this place it is coming to 18 so this is this this one is more advisable okay so this is mostly been used so having the fourth order Bas in here so now so earlier as I told that we used to uh Trace all the streams and then come up with the uh the Basin final Basin uh the main Basin what we we we are looking for and uh then we can also use this information for the uh bifurcation obtaining bifurcation ratios okay but now you can you can do this very quickly using the software you can extract this um drainages using uh DM and then you can also go for the uh stream mods okay so you can do that very quickly using the the software so this part we will be initially have discussed that this is what we see in the Stream order here and then we count the number of streams how many number of streams we see uh of the first order how many of the second order and so on okay so uh based on this will help in uh calculating the bifurcation ratio so when we are Lo looking at uh the suppose this uh is the part which is which are with us then the bation is been represented by a simple equation here that you have this is RB is bation ratio and you having Nu plus the divided by the next higher order streams okay and that will give you the ratio here so number of uh the segments here so for example you are having here so you can also use that this isn't what as for the heart and law but we can use that what we we have discussed in the previous slides now if you're looking at uh the first order then how many streams we are having this we say 10 okay so this is 1 here 2 3 4 5 6 7 8 9 and 10 so we are having 10 here and then two uh second order is three we we we see here 1 2 and this is three here and third order is your final stream so uh the first we will not get but the ratio we will get from the second one so this ratio is 3.3 and then ratio between the uh the second and third order is around three now what is the importance of this because usually this has been used by the the hydrologist or to have have the understanding of the flood intensity okay so the flood intensity is considered to be the dis to be a discharge along a channel over a time okay flood intensity will be influenced by rate of runoff that is how much amount of water is been uh just moving without infiltration the channel pattern shape and number of tributaries that will also will be important because these are the uh the the the collecting streams which are going to pour water into the mainstream and then distance Downstream also okay so from for example if you're having an streams coming here and so this is your merging point and then how much is at the downstream okay what is the distance from here so that will also uh play an important part okay from any drainage basin okay so from here this isn't like we have the collecting Point here so what will be the the discharge which we are expecting here at this point so these are the factors which will be affecting the flood intensity and all that so in stream orders the smallest tributaries are designated as we have discussed first order those with the first order tributaries joins are second order and so on this is what we have already discussed in the previous two slides okay so lower order streams have shorter lag time okay between the rainfall so the lag time is between the rainfall and the flood events okay and are more prone to flooding okay so lower order streams what we are talking about is you're if you're having many first order streams okay then that area is not at all good okay so that will have a l shorter lack time so this you should keep in mind when you are talking about high streams with many tributaries are less prone to flooding because that will have a higher lack time so this part you can keep in mind when you are talking about that okay so drainage network of a River Basin shape and channel pattern are the most vital morphometrical factors that play significant role in increasing rate of flow through the drainage system now even if even with the higher RB values that is a bifurcation ratio values in elongated Basin the hydrograph is very smooth suggesting less discharge okay so this is what you see is the less discharge even if you're having the higher bifurcation ratios higher bation ratios means you will have so uh like the the rounded Basin with same area this I I'll just show the figure here so that you can understand this one so we talking about we we we we are talking taking two uh different scenarios one is the elongated Basin another is the rounded Basin okay so the the the aim is that to know that what will be the the discharge here in this case and what will be the discharge here as we have been talking about the shape of the Basin will also play an important role and of course along with that the bifurcation ratio is also important okay but in higher the bifurcation ratios you are expecting that the the flooding will be very quick okay but in this case what we see here is that the shape should also been taken into consideration okay so so this is a discharge there's a time here so if you if you look at for this one the hydrograph is U gentle here but in case in this case okay you're having a rounded Basin in the hydrograph is uh quite quick okay so these are the cases which have been talked here that we we are talking here is like you have an elongated Basin so this one is your elongated Basin and this one is your rounded Basin okay so higher RB values in elongated Basin the hydrograph is very smooth suggesting less discharge okay so this is less discharge a rounded Basin with same Basin area so area is same okay the area is BAS and area is same usually if you if you will just look at the Basin area and you can judge that what will be the charge but you need to look at the shape also okay so rounded Basin with the same Basin area having low bifurcation ratios shows higher drain discharge so this is bit like something unusual what was the what is the reason for that that the smoother curve of the narrow Basin this is your narrow Basin here so if the smoother curve of the narrow Basin with higher bifurcation ratio can be explained by greater time lag so time which has been taken to travel so distance is also important okay so which is time taken to have an full amount of discharge here is comparatively more than compared to the rounded one okay so the it can be explained by the greater time la for the water to reach the outlet whereas the time taken from the upper edges middle and lower edges in the rounded Basin is less L causing higher discharge so even though the Basin area is same the discharge varies because of its shape so this the this important Point here is that you need to consider the shape of the Basin also okay the stream order and flood crust that is your hydrograph what we have seen here that uh there's a discharge and time here okay so whether it is like this or like this or it is like smooth and very okay so what is the importance of this hydrograph and the stream orders and all that that we have discussed briefly ahead the lower order stream tends to respond rapidly to any like even if it is stormy condition or it is a cloud burst and all that with steep hydrograph so it will be very quick okay and because water has has to travel a very short distance so this is a lower order streams will not have an larger distance to be covered so what has been shown here the the lower order streams okay hence such streams provide less time for flood warning in the of the downstream resident because they have smaller drainage basin and carrying coarser and larger sediments of the for the G for the given area Okay whereas the higher order steams with numerous tributaries have longer lack time between the storm and the downstream flat okay their hydrograph are less peaked okay so it will be like for in this case it will be like something like this okay but in this case you will expect that the hydrograph is quite peaked one okay so and and covers longer time period flood warning time for Downstream resistence is longer so this if you are having higher order basins then you are to some extent you have an time to give or issue an warning but in terms of the lower order uh stream or the Basin areas it will be have you will be having less time to issue the warnings okay so now you can use this uh information to talk about the uh that which area will have quicker flood and which areas will have the floods which will be uh slightly delayed okay and that you can issue the warnings and all that so this is what is the beauty of using the drainage pattern and all that and try to look at at the uh the stream orders and then extract the information okay so using the satellite data you can do this actually so I'll stop here and we'll continue in the next lecture with more information on this aspect and also we'll talk about as I have I told in the previous lecture also that we we are going to do one more exercise that is on the morphometric analysis okay so this is one of the part of the morphometric analysis be doing so with this I'll stop here thank you so [Music] [Music] [Music] much