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L’eau en partage

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Philippe Cecchi

Postface

Nick van de Giesen

Texte intégral

1This book presents a series of studies that share a geographical and thematic focus: small reservoirs in northern Cote d'Ivoire. For anyone interested in this topic, the book presents a comprehensive overview of the many facets that encase these complicated systems. Given the local socio-economic importance of these systems, this alone would make this an important scientific contribution to the field of regional development. However, this post-face does not attempt to briefly review the content but to reflect upon its wider relevance and upon some emerging issues. Specifically, three issues will be put forward:

  • international relevance,
  • multi-disciplinarity and scale,
  • importance of connectivity between small reservoirs.

International relevance

2Throughout Africa, many large reservoirs and associated irrigation schemes were constructed during the 1970's. In general, the performance of these large schemes was unsatisfactory, mainly because of the lack of proper governance structures at these higher organizational levels. Presently, international donors are hesitant to finance further large-scale irrigation development. At the same time we see that small reservoirs tend to be more successful in providing village populations with water for fishing, irrigation, households, and cattle. Although there are also small reservoirs that do not always perform well, they score, in general, much better than larger schemes. At the same time we see that some of the negative effects of large reservoirs are not relevant in the case of small reservoirs, specifically with regard to forced migration of people and loss of wetland habitats. This has made small reservoirs a popular intervention tool for governments and NGO's. This phenomenon is not limited to the Cote d'Ivoire. Small reservoirs can be found in all semi-arid parts of the world, be it in Africa, Latin America, or Asia.

3The first Millennium Development Goal is to overcome hunger in the world. Improvement of the water productivity will be a main instrument to reach that goal. Africa's dependence on rainfed agriculture limits technological innovations based on agro-chemicals and improved germplasm. The unreliability of the rainfall, particularly in the form of within-season dry spells, limits the returns on such investments. Given the difficulties that surround large scale irrigation development in Africa, diffuse development of water resources seems to be a good way forward. Small reservoirs are an especially interesting option as they extend water availability into the dry season and can be used to overcome dry spells during the rainy season.

4As becomes very clear from this book, irrigation is just one of many positive aspects of small reservoirs. These reservoirs also provide water for cattle, fishery, household, and less obvious economic activities such as basket weaving and brick making. As a result, small reservoirs are popular objects that development organizations like to build. Not surprisingly, we have seen a continuous construction of such reservoirs and we will undoubtedly continue to find more and more of these structures throughout the savanna areas of the world.

5Although one reservoir may mainly have positive effects locally, an important question that pushes itself forward is what happens if one hundred reservoirs are constructed, or one thousand? To understand the impacts of such ensembles is the central question of international research, such as can be found, for example, in the Small Reservoir Project, which is part of the large "Challenge Program Water for Food." As this book already suggests, for some issues, the impact will be more or less linear. For example, hydrological losses through evaporation will, more or less, simply add up. The same holds, to first order, for primary productivity of the reservoir ensemble. To develop tools to assess linear ensemble impacts is perhaps not trivial but definitely doable. Much more difficult are some negative impacts such as market saturation, ecology (eutrophication, algal blooms), and human health. Such impacts can not simply be summed over all reservoirs but are highly non-linear. To complicate matters further, the total effects are not just non-linear functions of the number of reservoirs but also of the way reservoirs are connected through physical and social networks.

6For the international development community, perhaps the main direct merit of this book is that it opens a window on all these different aspects. On the basis of this specific case of small reservoirs in northern Cote d'Ivoire, the reader is exposed to the complexity that small-scale, village-level socio-economic development entails.

Multi-disciplinarity

7Most people will readily agree that the analysis of natural resources and rural development require more than one discipline. The idea that one single technology such as aquaculture or improved plant water availability through irrigation will solve malnutrition, is no longer commonly shared in the expert community involved in development programs. In the framework of this research project, this is not a newly acquired insight but the starting point for the analysis. From the start, the research involved limnologists, ecologists, health scientists, hydrologists, etc. Their results form the bulk of this book.

8Ideally, the final analysis would bring together the insights from all disciplines and transcend traditional scientific method by presenting a complete picture. Such a type of inter- or transdisciplinary research does not yet exist. It is, therefore, not surprising that also this book does not accomplish this. In the end, the reader has acquired knowledge of all or, at least, most facets surrounding small reservoirs. That these facets are interdependent becomes clear but the exact nature of the myriad of links between these facets remains beyond our analytical capacity.

9Probably the most interesting new methodological insight where it comes to interdisciplinary research is the importance that spatial scale has. At a micro scale, a reservoir may be seen as an extra breeding ground for vectors such as mosquitoes. At a larger scale, this does not automatically translate into higher malaria morbidity. At the micro level, it may suffice to carry out a medical-entomological survey on vectors. To understand the larger scale impact on human health, however, a large number of surveys, both social, medical, nutritional, and entomological, is needed to understand the impact on human health of small reservoirs. The number of disciplines and the complexity of the interactions between different determinants of socio-economic development apparently grow exponentially when the scale of the analysis increases. Finally, a small reservoir is not a geographically isolated entity; it is not an inverted island. The functions and functioning of a small reservoir depend to a large extent on the watershed in which it is situated.

Connectivity and networks

10All good research leads to new scientific questions that need to be answered next. The statement that “more research is needed”, often seems an obligatory platitude. Still, looking at the presented studies as a reader who is not directly involved with the topic, perhaps the largest value is the emerging realization that networks are important. This aspect emerges when we zoom out and contemplate the ensemble effects of small reservoirs. The insights in this issue provided here are really new and do form the basis of extensive recent international research on this topic. This insight goes beyond the insight that the cumulative effects may be non-linear, such as in the case of market saturation and malaria morbidity. Such non-linear effects can probably to a large extent be captured by functions that combine densities of, and distances to, small reservoirs. What is new here is that the connectivity topology of the system matters.

11In its simplest form, the connectivity of the system follows the logic of the watershed: there is a hierarchical upstream-downstream network that connects reservoirs along a hydrological cascade. All things that are passively transported by flowing water, such as mollusks, certain pathogens, sediments, and nutrients, are subject to this logic. If an upstream reservoir is enriched with, say, phosphorus then downstream reservoirs clearly run a high risk of eutrophication. The matter becomes really complicated when the hydrological network is overlaid with a social network. A good example of the latter is when groups of fishermen, who are infected with schistosomiasis, have access to several reservoirs. How the invested mollusks then spread through the region depends on the hydrological network and the contacts that other social groups have with water downstream.

12With the new élan that pervades the present landscape of development aid, many new donors and agencies come to the scene who may not be aware of the immense complexity that surround issues like water productivity, nutrition, and human health. Small reservoirs are loci where environmental and social issues meet. The seeming simplicity of these structures is unraveled in this book and the full inter-woveness of the many factors that determine rural development is exposed. Especially when it comes to ensembles of reservoirs and their network-based interactions, does it become clear that there are no uncomplicated ways forward. As such, this book has a heuristic value for all people interested in science-based development that goes well beyond the topic of small reservoirs in northern Cote d'Ivoire.

Auteur

September 2006
Prof.sdr.ir. Nick van de Giesen
Water Management, Civil Engineering & Geosciences TU Delft
Stevinweg 1, 2628 CN Delft PO Box 5048, 2600 GA Delft Netherlands
E-mail:

© IRD Éditions, 2007

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