The present study is led on the Gourou watershed, in the autonomous district of Abidjan. Many quantities of sands and macroelements stream to this watershed's exutory in rainy season, blocking drainage canals and invading decantation basin. The objective of this work is to determine the origins of the sands in order to make map. To do it, we update the watershed's limits according to water separation lines. Then, we make a map of erosion zones susceptible to give up sands. The processing of all these data reveals a plurality of this sand blocking origins; the most producing zones being the ones situated near the road arteries. Sands come mainly from numerous bare zones of the watershed, from disorderly installed human activities and from the canals of the drainage network poor maintenance; some canals are being broken by place.