Semidistributed Hydrologic Model for Flood Risk Assessment in the Pejibaye River Basin, Costa Rica: Fid-Bau Portal

Semidistributed Hydrologic Model for Flood Risk Assessment in the Pejibaye River Basin, Costa Rica

de Gonzalo, Carlos / Robredo, José C. / Mintegui, Juan Á.

A semidistributed hydrologic model addressed to flood risk assessment is presented. The model has been applied and calibrated by means of a multistep calibration scheme to the Pejibaye River Basin in a series of flash flood events that occurred between 2006 and 2009. The model consists of a rainfall-runoff module, a surface runoff routing module (unit hydrograph method), a base flow module (linear reservoir method), and a channel-routing module. Two different unit hydrographs were contrasted and two different approaches (continuous and discrete) were used for average rainfall estimation. Model parameters were initially estimated by using classical formulation and documentation, and afterward were compared with calibrated parameters. The combination of the different unit hydrographs and average rainfall estimation procedures presented significantly different prediction errors. Rainfall-runoff and base flow methods showed a stable and reasonable behavior. Rainfall input was highlighted as a major source of error. However, the continuous method for average rainfall estimation was noted to slightly reduce timing errors as compared with the discrete method. Overall, the model reproduced reasonably the flash floods analyzed in this paper, both in calibration and validation ( $R^{2}$ between 0.81 and 0.87; Nash-Sutcliffe between 0.70 and 0.80), and therefore could be also suitable for other watersheds with similar climatic and geomorphologic conditions.