Contribution à la modélisation de la relation "pluie débit" en absence de données hydrométriques (cas d'une zone urbaine , ville de Tipaza)

Abstract

This work is part of the rainfall-runoff transformation modeling problem in urban areas. Indeed, the phenomenon of inundation due to urban stormwater flooding, being increased, it became necessary to define and develop tools in order to predict such events, or rather to predict their consequences on the urban areas. Towards this, the city of Tipasa has been selected as the scope of application of this survey. The hydrological modeling of urban stormwater flooding taken, has two components: (i) the rainfall and (ii) its transformation into a flow through the urban area, this study is developed according two major axis, the first one inducing the second. The storm hazard is characterized through the modeling of the rainfall intensity-duration-frequency (IDF) curves. The methodology taken to establish the IDF curves is quite elaborated, in the sense that (a) it allows an application using a restricted data set (short series) via an approach based on partial duration series PDS (values above a threshold): exhaustive use of the available data. (b) The relationship of the IDF curves is established using a semi-parametric model, which means that the dynamic parameters (characterizing the region and the aggregation’s duration) are obtained by an empirical formulation, and the parameters characterizing the intensity value result explicitly from the underlying probability distribution function (global estimate over all aggregation’s durations), where typically the formulation of the IDF relationship is totally empirical (Montana, Talbot, etc..). Also, the modeled rainfall has a relatively realistic temporal distribution, in the sense that the position (in time) of the Storm peak is identified. The transformation of the rainfall into runoff at the outlet of the watershed has two levels of modeling. The first is the runoff production and the second the transfer of this runoff through the watershed. Considering the unavailability of hydrometrical measurements allowing the model’s calibration, it was used in this study a production and transfer functions whose reliability has been tested in different configurations and found to comply. And it doesn’t require any calibration for the use in the same context. Thus, the production function derived from the SCS-CN model, allows to take in account initial losses and continuing losses over the time and proportional to the intensity of rainfall in runoff producing. When it is difficult to describe a system through the laws of physics, the alternative is a simplified representation of the process, in rainfall-runoff modeling this conceptual representation is often a reservoir. Thus, the transfer of runoff hydrographs has been done through the use of a linear reservoir. Although, it does not differentiate between the two components (street and buried pipe: dual drainage) of the urban flow, it enables to determine the location and extent of the spill. The behavior of the urban drainage network in the city of Tipasa, is simulated for different solicitations, which allowed to judge it, as having a design defect (oversized outlets, and undersized upstream of these latter). Also, it is established that the modification of the lands’ occupation (urbanization) accelerates the hydrologic response of watersheds and increases the runoff. Similarly, the antecedent moisture condition soil involves the production of runoff.