Influence of the envelope curve on the estimate of probable maximum precipitation (PMP) in the coastal region of Algeria

Probable maximum precipitation (PMP) is considered as a principal factor for estimating probable maximum floods (PMF) when designing various hydraulic structures. The estimation of PMP by the Hershfield statistical method was adopted in this paper for 112 rainfall stations in the three Algerian coastal basins (coastal region). This method is based on the adequate estimation of the frequency factor (K-m) using some envelope curves. Several researchers have used different types of envelope curves in their works such as the linear, exponential, and polynomial type. In this work, a new linear envelope curve was introduced and adopted. This paper will perform a comparison between linear, exponential, second degree polynomial, composite and proposed linear envelope curves. On the basis of the coefficient of determination (R-2) the proposed linear envelope curve was chosen to obtain reliable PMP values, thus avoiding underestimation and overestimation. The obtained PMP values vary from a minimum of 152.21 mm (station 109, BV04) to a maximum of 436.15 mm (station 47, BV02) with a mean value of 253. 32 mm. To comprehend the PMP spatial distribution in Algerian coastal region, the Inverse Distance Weighting (IDW) method was used with ArcGIS 10.5 software from the Environmental Systems Research Institute (ESRI).