FIRE HYDRO: A Simplified Method for Predicting Peak Discharges to Assist in the Design of Flood Protection Measures for Western Wildfires

Abstract

An EXCEL spreadsheet was developed to evaluate estimated peak discharges resulting from rainfall events in wildfire burn areas of Montana. This method, called FIRE HYDRO, is based largely on the USDA Natural Resources Conservation Service (NRCS) Engineering Field Handbook-Chapter 2 technology. The purpose of developing this procedure was to assist USDA NRCS and Forest Service personnel who were involved with post-wildfire reclamation work to estimate design peak discharges for the recently burned areas during the 2000 and 2001 wildfire seasons. It uses the NRCS Runoff Curve Number procedure. A supplemental portion of this method offers suggested Runoff Curve Numbers based on land cover prior to the fire, degree of severity of the fire, and slope aspect of the land. Issues involving hydrophobic properties of the soil resulting from wildfire are also addressed. The method yields four varying perspectives for the Runoff Curve Number of the subject area including the pre-fire value, post-fire I (with potential hydrophobic soils influence), post-fire II (without hydrophobic influence but little re-emergent vegetal growth), and post-fire III (after one growing season post fire until fully recovered landscape). This method was employed as a means to analyze the hydrology of the burn areas in an accelerated fashion to facilitate a timely federal response to wildfire disaster areas in Montana and other western states.