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Many may not remember or even be aware but, in September 1995 while Dominica was being battered over three weekends by the "Storms of '95", a landslide in the Carholm area severed the Layou-Carholm Road. This was one of a series of major landslide events that would eventually lead to the long-term damming of the Matthieu River – a small tributary of the Layou River – on 24th November 1997, and the subsequent formation of the Matthieu Lake. The Matthieu dam was formed from the breaking off of a huge chunk of the Carholm Cliffs, and the week before the damming of the Matthieu River another major landslide had occurred in the same lower section of the Matthieu Valley.

Following the formation of the dam (the natural blockage that impounded the river) the water level in the Matthieu Lake began to rise, and water began seeping out of the lake in February 1998. In time, this "seepage" would become significant, and it is believed that the strength of the flow increased with the gradual rising of the water level in the lake.

During the life of "Matthieu", its water level fluctuated yearly with the rainy season/dry season cycle. For example, during the extended Careme of 2001, the water level dropped by 18ft from early January to the end of June. Then, with the onset of the rainy season the lake's water level rose by 31½ft over the lowest level recorded that year. But, even with the annual fluctuations, this body of water eventually became larger than Freshwater Lake, and attained a depth of over 142ft (i.e. over 7 lengths of 20ft pipe joined end-to-end), surpassing the depth of Boeri Lake when the latter is full.

We are fortunate to have had a lake form in our "backyard" in our lifetime, a "Miracle Lake" that persisted for 13 years, 8 months and 3 days before it emptied when the dam collapsed around 15 minutes before midnight on 27th July 2011.

Dams formed from landslide events typically last only a few days (as was the case with the two that formed across the Layou River in November 1997 from the Carholm landslides) or a few weeks. But Matthieu defied, and joined a small percentage of landslide dams worldwide that persisted for such a long time. And, for some, the dam and lake seemed to have become permanent features of our landscape and even attracted adventure seekers. But the Research & Monitoring Unit of the Forestry, Wildlife & Parks Division never "closed the book" on Matthieu during its existence, and actually conducted its last "regular" mid-month monitoring visit to the lake less than a fortnight before the dam failed. At the time, the Matthieu had a depth of about 142½ft, and that level was already 10ft higher than that of mid-April that year.

During the 4993 days of its life, the Matthieu dam and lake survived the intense shaking from the major earthquakes of November 2004 and November 2007 and their aftershocks. The lake also saw some significant increases in water levels from the rains brought by two "big" tropical weather systems that affected Dominica, i.e. approx. 8ft rise from Hurricane Lenny in November 1999, and over 8ft increase from Hurricane Dean in August 2007.

So, Matthieu Lake is now empty, and its negative impacts have been very well documented. These include - but are certainly not limited to - the washing away of a small wooden house at Hillsborough and the centre-span of the York Valley Bridge; heavy losses at the Hillsborough Agricultural Station; severe stream-bank erosion downstream of where the Matthieu and Layou Rivers meet; and the death of the line of large mango trees that protected the edge of a section of the Layou Valley Road east of the agriculture station.

However, on the positive side, apart from the large volumes of fresh pumice sand that were deposited into the Layou River estuary - much of which has since been "dredged" from the river, Layou Beach widened considerably and in October 2012 it measured 590ft in width, making this beach the widest sandy stretch on the island. It is strongly believed that Mero Beach and even Salisbury Beach were re-nourished as a result of the collapse of the Matthieu dam.

But what's with the Matthieu River itself and the Matthieu Valley now? For one, the Matthieu River is flowing "normally" once again, and fish life has begun to return as the "ti-ti-wi" and other species can once again migrate upstream into the Matthieu. A section of the river where the lake once existed now flows with very little gradient, as part of the valley floor was raised several feet on account of the large amounts of soil that slumped while the lake was emptying.

A lake no longer exists in the Matthieu Valley, although there is a pond of sorts. And with the moist, rich soils that now exist in the valley the re-vegetation of the area has been swift, with Bwa Flo or Balsa (a pioneer species) leading the way. In fact, by March 2014, i.e. 2 years 8 months after the lake emptied, some of the colonizing Bwa Flo had already reached a height of over 30ft and a diameter of over 8 inches, and were already flowering!

And the question that has been asked repeatedly is, whether we might see another "Miracle Lake". In my view, this is hardly likely, but for this to re-occur a landslide much larger than those which occurred in November 1997 would have to dam the Matthieu River again. But, only time will tell.

By Arlington James


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