Wadis of Algeria are characterized by a very irregular hydrological regime. The question of estimating the maximum flow of wadis is relevant. We propose in this paper a method based on an interpretation of the transformation of surface runoff in streamflow. The technique of account the maximal runoff of flood for the rivers of northern part of Algeria based on the theory of channel isochrones is offered.The realization of this method is performed on the basis of hydrometeorological data standarts.

The catastrophic floods in semi-arid areas are often caused by floods storm that occur at any time during the year, including the hot season. The prevention of these floods could be done by the construction of small dam hills. This requires the control of theoretical concepts hydrological sizing, especially the hydrological structure to evacuate floods. We suggest a method to calculate the optimal regulation flow of the flood and also the development of a direct calculation formula of a laminated maximum flow. The analysis of the hydro graph's analogy at the input and the output of the dam, allow searching the dependencies between their characteristics. Knowing the characteristics of the hydrograph flood of the project and the reserved capacity for the amortization of the flood, we can directly determine the laminated maximum flow and project the hydrograph of the laminated flood.

Among the characteristics that determine the maximum throughput flood genesis, concentration time has an important place. The maximum phase shift of a flood rain is subjected to different types of river regulation. This is caused by the friction forces in the river bed, by the gradual change of the wetted area by the slope and also by the flow exchanges. The flood speed is proportional to the water level in the river bed or the corresponding flow.