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A STELAR start to Cambodian fieldwork

It takes a couple of days, but once your body has acclimatised to the 25°C rise in temperature, the jet lag and the continuous presence of the sun, Cambodia is a great place to do fieldwork. It’s only been a few days since the STELAR-S2S advanced party arrived in Phnom Penh for the inaugural fieldwork camp and you can tell we’re all still struggling with the change from the British winter. Waking up and going down for breakfast in the hotel to be greeted by the zombie-like forms of Steve, Jules and Dan huddling around the table tells you we’ve not quite adjusted yet. Hopefully by the end of the 20 days we’ll be fully acclimatised.

 

Just experiencing the sheer scale of the Mekong river and understanding its importance to the Cambodian people  is again something that takes a while to adjust t;  not only is it the main source of food and water, but also the main transport network and a lot of peoples back gardens. It’s a beast (not a technical term, but aptly descriptive none the less). Just as an example, we visited an island in the middle of the river 10 km long and 2.5 km wide (a size big enough to hold a mid-size town). So coming from a background of gullies a few hundred meters long has required quite a recalibration of the senses.

 

The teams transport, RV Stelar

The teams transport, RV Stelar. Photo: Chris Hackney

The first few days of the fieldwork have mainly been focused on getting everything sorted for the crux of the fieldwork to come later on. Having found a boat to get us up and down the river, RV STELAR (left) and a willing driver, we set off out of Phonm Pehn looking for sites at which we can sampleriver bed, and bank material, whilst also keeping an eye out for unforeseen factors we may have to deal with over the next couple of years.

 

We’ve been making quite a few measurements since we’ve been here, stopping approximately every 5 km along the river. We’ve been sampling the river bed sediment using a grab sampler which is dropped off the side off the boat in and allowed to sink to the bed. A grabbing mechanism is then activated which clasps shut the container on the sampler, (hopefully) trapping a sample of the bed sediment inside. This has proved a bit hit and miss: with the strong current meaning the sampler drifts downstream without hitting the bed and the occasional failure of the grabbing mechanism.

 

Chris, Jules and Dan getting to know each other better coring the floodplain

Chris, Jules and Dan getting to know each other better coring the floodplain. Photo courtesy of Steve Darby.

On top of this, we’ve been taking bank material samples and floodplain cores to look at quantifying the grain size of the river banks and rates of flood inundation (and sediment deposition) on the floodplains, respectively. After sitting on the boat (which gets a nice breeze blowing in off of the river), taking a 5ft sediment core during the dry season is extremely exhausting: not only is the ground almost concrete, it’s pushing 30°C. After various trials, we’ve perfected the optimal technique (right); it has definitely brought the team closer together! The final part of the work we’re doing out here is trying to quantify the resisting properties of the river bank. This is needed to inform the river bank erosion model if we are to get an accurate representation of rates of erosion later on. To do this we use a Cohesive Strength Meter (CSM) which quantifies the threshold stress at which bank material is detached (below).

 

The STELAR team CSM the banks of the Tonle Sap River, Cambodia

The STELAR team CSM the banks of the Tonle Sap River, Cambodia. Photo: Chris Hackney

The next couple of days are taken up by meetings in Phnom Penh, set up to smooth the progress of the project over the coming years. They’ll make a nice change from being out in the mid-day sun (typical Englishmen!). After that it’s up to Kratie, 300 km north of Phomn Pehn, where we start the fieldwork proper. We’ll be making our way back down river to Phnom Pehn, covering the 300 km reach in detail and so will be doiing a lot more sampling in the mid day sun. It’s exhausting, but it’s great fun and I’m looking forward to the rest of our time out here. I expect it will look completely different when we come back out during the monsoon in August!

 


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