Southeast monsoon.

Flying to Denis on Thursday 16th July it was clear that the southeast monsoon was blowing strongly and had finally, properly established. Seychelles has two seasons determined by the direction of the prevailing wind either the northwest trade winds or the southeast monsoon. The southeast monsoon has been very late establishing this year and this affects the habits of many animals notably the breeding activity of seabirds that rely on the seasonal winds and related currents to bring the small fish they need to breed and successfully raise a chick.

I hadn’t been to Denis for a couple of weeks and last time I was there the southeast was blowing intermittently. On Thursday the white caps of waves were visible throughout the flight from Mahe to Denis. As the plane descended and approached the island, choppy water was evident on the surrounding shoals and then I saw something that I have never previously seen. A plume of sand was being carried offshore from “Pte Mme Guichard” on the northwest point of the island, off the shoal and into deeper water.

I have been monitoring the cycles of sand movement on the northwest coast since December 2005 and there is definite evidence of erosion. The difficulty in assessing such changes however is the fact that there may well be ongoing long-term cycles of erosion and accretion for which we have no information. It is therefore not possible to see short term changes in coastal profile in the proper context. Such thoughts are further complicated by ongoing changes in global weather patterns and the related issue of sea level rise. It is important however to monitor trends in coastal erosion in particular on the shoreline where key infrastructure is located in order to inform management decisions.

On seeing this sand plume going offshore and into deeper water it occurred to me that such sand loss may be permanent. Normally when I fly into the island I have camera ready for in case of a good photo-opportunities but on this trip because of the cloudy weather and poor light I hadn’t bothered. So I had to scramble to get the camera and snap some shots… so not great but good enough to show the occurrence… see photos in sidebar.

There was further evidence of the onset and stabilisation of the wind on the island. The sand promontory at Pte Mme Guichard has been largely eroded – a usual part of the island’s beach profile dynamics. I had reported previously (see post of 8th May amongst others) about the recovery of vegetation a Belle Etoile on the east coast following the cessation of grazing cattle there. This had greatly changed the view of the area with the former open meadows and casuarina-framed vistas obscured by the dense growth and foliage of papaya thickets. Well the salt spray driven by the “southeast” wind has changed this dramatically the leaves are gone leaving the barren stems to point accusingly at the sky.

Another key issue related to the southeast monsoon is that it will also mean that the Sooty tern season should get properly underway… but that is the subject of another post…