Assessment of flood frequency after forest fires in small ungauged basins based on uncertain measurements

Abstract

A methodology is proposed for constructing flood frequency curves before and after forest fires in small ungauged basins. It follows the rainfall-based derived distribution approach using Monte Carlo simulation and allowing for uncertainty in some of the variables involved. The generalized extreme value distribution for annual maximum rainfall is used, combined with the SCS-CN method for estimating rainfall excess, and the rational method for peak flow estimation. For pre-fire conditions, uncertainty in the spatially-averaged curve number is assumed. For post-fire conditions, measurements of peak flood water level at the basin outlet are exploited, while uncertainty is considered both in these measurements and in the hydraulic roughness. Multi-variate Latin Hypercube sampling for correlated variables is used to assess flood quantiles. The methodology is applied to a small basin in Attica, Greece, which was burnt in 2007. Sensitivity tests are carried out regarding the effect of sample size and of the amount of uncertainty involved. © 2012 Copyright 2011 IAHS Press.