Podcast: How river bank erosion affects livelihoods

River boat

Boat on the Brahmaputra River

7 January 2015 by Richard Hollingham

This week in the Planet Earth podcast, Greg Sambrook Smith of the University of Birmingham reports from Bangladesh on the effects of river bank erosion on the local people living alongside the Brahmaputra River.

To assist those who find text-based content more accessible than audio, a transcript of this recording is available below.

Richard Hollingham: This time in the Planet Earth podcast, the challenge of mapping one of the world's most dangerous waterways. I'm Richard Hollingham and I've come to the University of Birmingham to meet senior lecturer, Greg Sambrook-Smith who has recently returned from an international scientific expedition travelling the waterways of Bangladesh. Now we're going to hear, Greg, your audio diary in a few moments, but just set the scene for us first. What was the purpose of this trip?

Greg Sambrook-Smith: The Brahmaputra River in Bangladesh is one of the biggest in the world. It is also one of the most active. So bank erosion for the people living along the side of the Brahmaputra is a big problem, and one of the things that we were trying to do was understand those processes and one of the things is how big erosion areas within the river, these big scours that we would call them, how they move around and then influence that bank erosion. So we took out a multibeam echo sounder that mapped these features, and also a seismic system that looks at the deposits of these features, and really that is giving us information about how they have moved in the past to help us understand how they are moving around at the moment.

Richard Hollingham: Now, a multibeam echo sounder. Is this some sort of sonar-type device?

Greg Sambrook-Smith: Yeah. It is using sound. So it sends a ping of sound down to the bottom of the riverbed, that comes back up and then you can basically map out the entire surface in detail. And that gives us a lot of interesting information about the morphology of these features that we can use to help us understand about how the processes might be acting of scours moving around and interacting with the banks and when that erosion takes place.

Richard Hollingham: Now if anyone looks at a map of Bangladesh they will just how much water there is. Give us a sense of the geography, because essentially you were going south from the capital down.

Greg Sambrook-Smith: Yeah. So if we're looking at a map... you've got the Himalayas up in the north that is where the Brahmaputra is coming down. That is where all the water and sediment is being generated from that is in those big river systems. Then we've got Dakar, which is the capital of Bangladesh, that was where we fly into, and that is where we pick up the boat and then we are coming down one of the other rivers called the Meghna River that meets up with the Brahmaputra at a place called Chandpur and that is where some of our surveys started. Then we moved from there further down towards the Bay of Bengal, down some of the smaller channels at the southern part of the country.

Richard Hollingham: Now, I think we will get a sense of the boat when we listen to your audio diary, but what was it like? We're not talking James Bond-style yacht here, are we?

Greg Sambrook-Smith: No. It's quite slow moving and it has got quite a shallow draught so we could get into a whole range of places, not just the deep parts but also some of the shallow parts.

Richard Hollingham: So imagine it more like a ferry, an old ferry, something like that.

Greg Sambrook-Smith: Yeah. That's right. It does look like a lot of the ferries that are zipping around in the rivers, yeah.

Richard Hollingham: Right. Let's go aboard as you head down river.

Greg Sambrook-Smith: We have just got all the equipment set up and ready to go, so we're just hauling up the anchor now to get going on our first little test.

I don't think we want to head too much further in because otherwise we... okay... that's fine... is that long enough for the...

So where you collect this multi-beam data is quite difficult for the boatman because you have to basically imagine driving your boat up and down. We can see on the screen up on the bridge here where we've been and the data we've been collecting and we can see some lovely dune forms coming in on the screen. It's great when you can see the data coming straight in and you don't have to do loads of analysis beforehand, you can actually see exactly what you are getting. So there are some nice big dune forms going over at the minute and when we get to the end of where we are going to we will turn the boat round and the captain will orientate himself so that we will just have a little bit of overlap and then we go back down in the opposite direction collecting data again. It sounds like there is a boat coming up behind us, lots of noise going off as people try and indicate where they are and tell us to get out of the way sometimes.

I am stood here on the side of the boat with Professor Jim Best from the University of Illinois at Urbana-Champaign who is working with us on this project. Jim has a lot of experience with multibeam echo sounders all around the world, in other big junctions, in Argentina and on the Mekong River, for example. So, Jim, what is a multibeam echo sounder?

Professor Jim Best: Hello Greg. A multibeam is probably the best way of seeing what's there at the bottom on the river. So what is enables us to do is produce a map... essentially what we're doing is draining the river of all its water then looking at the bottom. So how it works is it projects sound actually into the water column, and what we're doing is project not just one beam but maybe 200 or maybe 500 beams of sound down into the water column. That sound is eventually hitting the bed and it is returning back to our sensor. So all we're doing really is measuring how long it takes for the sound to go from the multi-beam here near the surface down to the bed and back again and using that for these 500 beams we can actually detect what is happening to the riverbed.

Greg Sambrook-Smith: I've just come down from the bridge and I am just walking down the stairs and I'm going to go down to the bottom to see where the data has actually been collected, so we're just going to see what's going on down there.

Okay, so here I am. This is the dining room/data acquisition room. Just to paint the picture for you, we've got a few chairs and tables around the place as we eat our meals down the middle section. And if I come over to the side here, there are a couple of dubious looking characters, Mark Vardy and John Davis, also from the University of Southampton. They look like they are just sat watching satellite television, catching up with the football results, but let's find out what's actually going on here.

I can see three screens in front of me... so who wants to pitch in first? What's going on on these different screens? John, you talk us through it.

John Davis: It's far more interesting than football! So what we've got here and what we're looking at the moment is the three screens, we've got a fairly boring data display that is just really showing us our file structures on the computer. The middle screen is really the most interesting. That's giving us a very lovely coloured picture of the seabed. The colours represent the depths so we can see all the ripples and hollows and various other bits and pieces that are actually underneath us.

Greg Sambrook-Smith: Well it has been a day of problems today. We're getting an intermittent signal on the multi-beam, so the guys are just hanging off the scaffolding pole on the side of the boat, just unleashing some of the screws and we're just going to pull that up to have a look at a couple of connections on the top of the multibeam head. It is probably this water hyacinth that has been plaguing us all morning. It keeps getting attached round the boom head, the multibeam head and keeps having to stop all the time to clean these things up. It's very busy in the shipping lane as well, so a lot of the surveys have been a little bit disjointed.

A speed boat has just come round from the side, the captain is stool on the front of the speedboat hanging onto the main boat and then we've got John Davis perched precariously on the front of the speedboat, he's got his lifejacket on though it's good to see from the Health and Safety... so John is perched on the front of the speedboat with a couple of spanners and ratchets there and he is just having a look at the sound velocity that has been giving us trouble. So he is just checking the connection. It looks like that was probably all right. I am just giving it a bit of a once over and a little clean up trying to get rid of any of the extra weeds and things that looked like they might have been flapping around and causing us problems.

We have a new regular feature on the audio blog, it's a mango update. So today's mango report sounds something like this. "Umm... very good".

It was meant to be an early start this morning but we are marooned in the fog. So we are on the river here and we're meant to be heading off but we've just had a very leisurely breakfast because we can't actually see anything past a few metres off the boat. So the bell you can hear in the background that one of the crew is ringing is actually to make sure that no boats come and collide with us. It's got pretty thick. It's obviously very dangerous for us to move off so we're just sat here filling in a bit of time before we can head out. Hopefully it won't be too long but sometimes these fogs can sit around for a whole day, unfortunately.

There are not many places you end up in the world where it is completely pitch black, you can hardly see at all. Any natural light and the noises are all completely natural but we've just pitched up at one such place. We've been working down in the very southern part of Bangladesh today and we've just entered Sundarbans National Park which is a heavily protected area, so there is virtually no one around, no one is allowed to come and live in this part, they try to preserve this mangrove forest and all I can hear is the sound of the crickets. There's some lightening off in the distance which is the only real light we can see and it is almost completely quiet apart from that. But it is incredibly peaceful and incredibly quiet.

Richard Hollingham: Greg Sambrook-Smith's audio diary. Now, a few months on you are back in Birmingham. Have you recovered from that? No one seemed to get any sleep on that.

Greg Sambrook-Smith: It was so hot. There is no air conditioning on board. It's not like you just walk into a room and go... relax, it's nice and cool. You are constantly sweating, you can't sleep very well and so as the two weeks progresses you just get more and more tired. So it does take a little while to recover but I was straight into term and teaching the day after I got back so I'm not sure my first lecture went down very well!

Richard Hollingham: What about the data from this? You've got a wealth of this information from all this recording that you have been doing.

Greg Sambrook-Smith: Yes, the main thing that the post docs on the project are doing, they're crunching all that data at the moment. We had a project meeting only the other day, actually, a lot of the multibeam data that we talk about on the audio diary that's all been processed now and that's going to feed into the numerical modelling that we're developing. So, Andrew Nicholas at the University of Exeter, who wasn't on the boat with us, he's our numerical modeller, and that data allows us to validate his model and then try and predict and understand better where these areas of erosion will be moving and shifting to that we talk about.

Richard Hollingham: Ultimately what you are looking to benefit the people of Bangladesh with this information?

Greg Sambrook-Smith: Yes... in the initial instance it helps us understand just the science better, but then we also work with CEGIS the Centre for Environmental Geographic Information and
Systems in Dakar and one of their tasks is to try and help the local population in terms of predicting year on year where bank erosion might take place. So, ultimately, perhaps via the next project we can work with them a little closer in terms of trying to influence and update some of the techniques they are using so that we can help the population with that erosion issue.

Richard Hollingham: You said that the fundamental science here... I suppose the sorts of things you are learning about studying rivers in Bangladesh, where there are an awful lot of rivers, is relevant all over the world.

Greg Sambrook-Smith: These are generic processes, so really they are applicable to any river. So these scours that occur when two rivers meet and collide together and generate these big areas of erosion, those principles are just as valid in a small river system.

Richard Hollingham: Now you are going back again in April this year. Are you looking forward to it?

Greg Sambrook-Smith: Yeah, really looking forward to going back. We're going to take a slightly different set of equipment and do something slightly different. We will be working actually on the sandbars this time rather than looking at the channel to try and tie in what's going on on those big islands that side in the middle of the river - that will be good fun.

Richard Hollingham: Well thank you very much for recording your audio diary. We especially enjoyed the mango update! And we will put some pictures of Greg's trip on our Facebook page and Tweet some of them as well and for the latest news on the natural world do visit Planet Earth online. And that's the Planet Earth podcast featuring research funded by the Natural Environment Research Council. I'm Richard Hollingham from the University of Birmingham and Bangladesh. Thanks for listening.