Consider the following statements regarding channel routing :

1. In channel routing, the flood hydrograph at various sections of the reach is predicted by considering a channel reach and an input hydrograph at the upstream end.

2. As the flood wave moves down the river, the shape of the wave does not change.

3. Flood waves passing down a river have their peaks attenuated due to friction.

4. The addition of lateral inflows can cause an increase of attenuation.

Which of the above statements are not correct?