Résumé : This paper concentrates on the proper use of fountain codes for the transmission of sporadic data in a wireless sensor network (WSN). Fountain codes offer great perspectives for the self-organization of WSNs: they self adapt to the channel error rate without any control data. When deploying fountain codes on a WSN, two problems arise. First, the size of the data transmitted by a sensor is small in comparison to the size considered traditionally with fountain codes. The analysis of the decoding overhead for fountain codes is often done for large data. Second, the communications are done in an hop-by-hop fashion. It implies that the destination of the data can not acknowledge instantaneously its reception to the source. Therefore, the transmissions of useless packets for the destination can not be prevented. The impact of this flooding traffic is analyzed. It depends on the data size and on number of hops between the source and the destination. The context of our study is a line network, i.e. a cascade of erasure channels. The flooding traffic has been evaluated as well through realistic simulations for three different relaying strategies where packets are lost due to both small scale fading and collisions for an unslotted IEEE 802.15.4 medium access layer.