Day 8: The return trip

The trip home went quite well.  It was fun to drive all the way across the island again, eat Jamaican Patties in the airport, and then see beautiful views of the Caribbean out the window. 

Now that we're back in Boston, our work turns to writing a report that incorporates the data we collected.  We will present our data in conjunction with the data from previous field trips and summarize our recommendations for future groundwater searches.  The report will also be sent to the Water Resources Management Agency (WMRA) in Saint Lucia as a reference for their future work.    

Yes, we were technically in Saint Lucia for a class project.  But the more important part of this experience is that we contributed to a much larger effort.  We became part of a team which will eventually find a solution for a real-world problem.  And our results, even though they don't point us to the absolute best place to drill in the Roseau Valley yet, will help with the long-term search for ground water in the area. 

Our whole team is shown below:

Group picture outside of the WRMA.  The people in the photo are from MIT, Harvard, and the Water Resources Management Agency of Saint Lucia. Photo credit: KMK.

Day 7: A chance to step back

On our last day of field work, we drove to a high point on the side of the Roseau Valley to look at the entire valley and get a larger perspective on the work we've been doing.  The north and south sides of the valley are flanked with rolling hills, while the valley floor is extremely wide and flat.  We are exploring the idea that the rolling hills, made of fractured volcanic rock, contain water within their fractures.  Furthermore, we are exploring the idea that the same structures that create the rolling hills might also exist below the valley floor, but covered by a thick floodplain of clay and silt.  Our resistivity measurements on the valley floor over the past week are helping us to find the volcanic structures below the valley and determine whether they have fractures or pores that contain water. 

Conducting a hilltop sounding, with the Roseau Valley in the background.

We took one short sounding on the top of the hill which produced some nice resistivity data.  We have inverted this data to get an estimate of the resistivity of hill material.  If similar resistivities exist below the valley floor, it may suggest the underground roots of the same hills that make up the valley walls. 

Resistivity data going down to 35m depth on the hilltop.

 

Sponsored Message: A Short Post About Coconuts

Brought to you by the friendly coconut farmers and water resource managers of Saint Lucia. 

While we were visiting the well this afternoon, one of our guides grabbed a bamboo stick and knocked down half a dozen coconuts from a coconut tree.  We collected the coconuts and brought them to the road, where the entire group took a break.  

If you cut a piece of the skin away with a cutlass, you can drink the coconut water from the center.  It is highly sought-after here in Saint Lucia-- in fact, you can find people selling bottles of coconut water on the street.  We drank it straight from the coconut.  

Mmmm coconut water.

Drinking more coconut water.  This kind of coconut actually has a smooth green skin when it's ripe. 

Then, our guides split the coconuts in half with a cutlass and showed us how to eat the coconut jelly.  This is the part that shaved coconut is made out of.  Actually, eating the miniscule layer of coconut jelly inside the fruit gave me a new appreciation for the shaved coconut that I usually see in supermarkets and take for granted at home.   And by the way, both the coconut water and the coconut jelly were delicious!

An open coconut filled with coconut jelly, which we ate with makeshift spoons made of slices of coconut skin.  

Day 6: Fixing bad data + making water quality measurements

Our data analysis from yesterday suggested that a few of the points we have measured in the past might have errors.  The resistivity values took an unusual turn at the deeper part of one particular sounding.  However, for resistivity measurements, an anomaly at depth may be representative of a surface feature somewhere along the line that just changes the possible paths for electrical current in the ground.  

So, in order to identify the errors, we went back to the field and surveyed that sounding for nearby disturbances, such as buried metal, culverts, or other obstructions that would change the conductivity of the ground.  We found that one of our electrodes was very close to a culvert during the final measurement, meaning that the measurement was suspect.  Tonight, we were able to remove that reading from the inversion and produce a new result.  

This afternoon, we  went on a trip to several local sources of water with our colleagues at the Water Resources Management Agency.  This included a well and a slowly-flowing stream which we tested for conductivity and pH.  Although this particular well was not in Roseau Valley, it is an example of a type of water resource that could be developed in Roseau Valley.  

Today's lunch spot: beside the largest river in the Roseau Valley. 

Sending a high-tech sampling device (a measuring tape and then a plastic cup on a string) down into the well to collect water.

Testing the pH of the small river at our site visit this afternoon.

Day 5: Data analysis begins, with some photos

Much of today and yesterday were spent on coding for data analysis.  If we can analyze the data correctly, we now have enough information to make some preliminary conclusions about the resistivity of the material below the Roseau Valley.  So we split up the work of performing inversions and analysis, and are now contributing pictures and text files and spreadsheets to a shared group folder at a frightening rate. We work in the morning before going to the field, at night after dinner, and at whatever other times we can manage in between.  Hopefully we'll have an interesting result.  

In the afternoon, we had enough time to run two more soundings in the field.  They're going faster now that we have established a team routine.  Guided by our preliminary results from last week, we chose two new locations to probe and conducted soundings there.  The activities in the field are much the same as in previous days, so today I decided to show a few more pictures of our group at work.  

Taking a break. We often have more people than we need during a sounding, so we rotate taking breaks to make sure each person gets enough rest from working in the sun. 

Pounding an electrode into the ground before a measurement. 

Recording a measurement back at the current source, our home base during soundings. 

Day 4: Data collection

Today we conducted three more lines of resistivity measurements, which took pretty much the entire day.  Each line had electrodes spaced at maximum 150 meters in each direction from the starting position.  Using the three lines, we were able to cover 900 meters of the valley.  The three vertical soundings that we measured will be combined to generate a 2-D image of the layers of rock below the valley.  

Diligently placing electrodes 150 meters away from the central point.

Day 4: Flora and Fauna of Saint Lucia

While doing fieldwork in and around the Roseau Valley, we have seen many interesting kinds of plants and animals.  These include:

• Mongooses (or mongeese?)
• Banana trees
• Soursop fruit trees
• Yellow/orange coconuts

And:

An African snail climbing a banana tree

A horse which usually has a cattle egret sitting on its back

A dwarf coconut tree that's only about 10 feet tall

And a bunch of MIT and Harvard students.