Some considerations about the base levet, the fluvial pyracy, knickpoints and morphogenesis of the longitudinal profile of rivers.

Abstract

Facing considerations based on davisian and dynamic equilibrium theories, four themes are discussed in this papel. In general, the sea base level changes are considered as having effects on longitudinal profile of rivers, with erosion and agradation phases, and the cyclic interpretation of lands-capcs has bases on these concepts. However, considering the behavior of the hydraulic geometry and channels patterns, and the concepts related with the dynamie equilibrium and probabilistic theories, it is possible that the sea base leveI changes did not cause erosion and deposition phases. Therefore, the kinckpoint regression, as cyclíc headward erosion, is not a valid concept for the landscape evolution.

In relation with the fluvial pyracy, as result by headwater regression, considering the systemic approach, it is not possible Between two opposite headwaters always will have a separative zone where the input is zero. As it is necessary to have water and sediment input yield by a drainage area for promove erosion, it is possible that the zero zone changes its position but maintains its presence. It is not possible that a headwater captures the other, located in opposite slope.

The morphogenesis of the longitudinal profile of rivers is related with the hankfull discharges, considered as the more effective flow on the channel sculpture, and not with the highest floods.