Just desilting the tanks is not enough!

Over the past several days we have had numerous opportunities to speak with villagers here in the Dry Zone of Sri Lanka. These hard-working cultivators are carrying on a tradition of rice growing that is thousands of years old. Yet they are firmly planted in the contemporary world of global communications and commerce. The traditional irrigation systems that were established by their ancestors, while still limping along, are severely impacted by a number of influences. 

For example, the agricultural chemicals, fertilizers, pesticides, and herbicides marketed by my country and other Western nations have resulted in severe health problems such as rampant kidney disease, which has introduced high rates of morbidity and mortality to the rural population. These same chemicals have perturbed the aquatic environment, leading to eutrophication, which has killed off native plants and fish species, favoring invasive introduced pest species.

 

A major problem that everyone has spoken about is the silting over of the agricultural waterways. In traditional times, silt was removed from the irrigation tanks periodically every six or seven years. When control of the tanks was taken over by the central government, villagers stopped taking responsibility for their maintenance. So in many cases here in the Dry Zone, silt has been collecting for 20, 30, 40 or even 50 years. It lies several feet deep in places and it has severely impacted the water retention capabilities and overall functioning of the tanks. 

Everyone wants to desilt their tank. No one we spoke to wants to do it by the traditional methods. So desilting means bringing in a backhoe and removing a foot or so of silt from the muddy area close to the dam. This practice provides more capacity for the tank but only temporarily. It also changes the contours of the tank bottom, which in the past provided the tank with complex functions of distributing and filtering water differentially. 

Tanks that are desilted today will start silting over tomorrow. What can be done about this? The tank systems have been severely perturbed, partly by road building, partly by the placement of culverts, partly by overgrazing, and partly by the destruction of native vegetation that complemented tank function in the past. 

It's easy to suggest that villagers plant more perahana and gasgommana plants (tall reeds, shrubs, and trees that filter and purify the water). Another great idea is to preserve the severely degraded  Kattakaduwa (shown above) in which villagers have started growing pet fish for international export. But all this takes social, political, and financial will. In our own society we lack the will to deal with seemingly intractable problems like poverty and racism. Our rampant consumption of resources has destroyed global ecology in an unprecedented manner. Can we in good conscience pretend to know what villagers should do to improve their degraded environment? Clearly, more questions have arisen since we began this research than we ever expected possible. We are very far from answers.

This reminds me of a colleague of mine, a sociologist. She spent two weeks interviewing rice growing villagers in southeast Asia through a translator and after that considered herself enough of an expert to publish a book. I don't need to rain on her parade but I do have to ask, with the complexity of problems we encounter, with the obvious language barriers, and with the seemingly insoluble issues we learn about when we spend the time, how can we claim expertise in a period of several days?

I leave it to you to decide. But from a standpoint of physical geography, topography, and soil science, simply desilting the tanks will not suffice. I look forward in these upcoming months of my Fulbright to lots of conversations that may shed more light on this issue.