The 26 December 2004 Indian Ocean tsunami triggered a number of international and national initiatives aimed at establishing modern, reliable and robust tsunami warning systems. In addition to the seismic network for initial warning, the main component of the monitoring system is the sea level network. Networks of coastal tide gages and tsunameters are implemented to detect the tsunami after the occurrence of a large earthquake, to confirm or refute the tsunami occurrence. Large oceans tsunami monitoring currently in place in the Pacific and in implementation in the Indian Ocean will be able to detect tsunamis in 1 h. But due to the very short time of waves propagation, in general less than 1 h, a tsunami monitoring system in a smaller basin requires a denser network located close to the seismic zones. A methodology is proposed based on the modeling of tsunami travel time and waveform, and on the estimation of the delay of transmission to design the location and the spacing of the stations. In the case of Western Mediterranean, we demonstrate that a network of around 17 coastal tide gages and 13 tsunameters located at 50 km along the shore is required to detect and measure nearly all tsunamis generated on the Northern coasts of Africa.