Geomorphology-based unit hydrograph models for flood risk management: case study in Brazilian watersheds with contrasting physiographic characteristics.

Samuel Beskow,Alice A Steinmetz,Gabriela S Nunes,Lloyd D Norton,Léo F Ávila,Marcelle M Vargas,Carlos R De Mello,Tamara L Caldeira

doi:10.1590/0001-3765201820170430

Abstract

Heavy rainfall in conjunction with an increase in population and intensification of agricultural activities have resulted in countless problems related to flooding in watersheds. Among the techniques available for direct surface runoff (DSR) modeling and flood risk management are the Unit Hydrograph (UH) and Instantaneous Unit Hydrograph (IUH). This study focuses on the evaluation of predictive capability of two conceptual IUH models (Nash and Clark), considering their original (NIUH and CIUH) and geomorphological approaches (NIUHGEO and CIUHGEO), and their advantages over two traditional synthetics UH models - Triangular (TUH) and Dimensionless (DUH), to estimate DSR hydrographs taking as reference two Brazilian watersheds with contrasting geomorphological and climatic characteristics. The main results and conclusions were: i) there was an impact of the differences in physiographical characteristics between watersheds, especially those parameters associated with soil; the dominant rainfall patterns in each watershed had an influence on flood modeling; and ii) CIUH was the most satisfactory model for both watersheds, followed by NIUH, and both models had substantial superiority over synthetic models traditionally employed; iii) although geomorphological approaches for IUH had performances slightly better than TUH and DUH, they should not be considered as standard tools for flood modeling in these watersheds.

Highlights

Among the different observed natural hazards, Brunda and Shivakumar (2015) reported that flooding is the most frequent
It was found that Cadeia river watershed (CRW) (Figure 3) had rainfall events with duration considerably longer than Jaguara creek watershed (JCW) (Figure 4), which can be attributed to the predominant rainfall climatology of each watershed with respect to the events analyzed (CRW – frontal rainfall and JCW – convective rainfall)
On analyzing Curve Number (CN) values (Tables II and III), adjusted for the rainfall-runoff events, one can observe that they were clearly variable among the events, ranging from 11.4 to 87.8 and from 24.8 to 98.7 for CRW and JCW, respectively

Summary

Introduction

Among the different observed natural hazards, Brunda and Shivakumar (2015) reported that flooding is the most frequent. According to Ma et al (2014), several regions over the world have suffered from problems related to flooding. Its increasing trend is related to the population growth and occupation of higher risk areas, to the economic development and to the effects of climatic change on the hydrological cycle, especially on extreme events (Brunda and Shivakumar 2015, Perumal and Price 2013, Ryu et al 2016). Monitoring and early warning systems of floodings are not commonly used in developing countries, especially for small and medium-sized watersheds. Stream flow data sets are fundamental to determine the hydrological response of a watershed to a heavy rainfall event whenever flood risk management or hydrological and hydraulic designs are necessary. The lack of stream flow series has culminated in the development of models, primarily intended for peak stream flow estimation and hydrographs based on a rainfall event (Beskow et al 2015, Caldeira et al 2015)

Objectives

Methods

Results

Conclusion