Debris Yield Modeling Application under Post-Wildfire Conditions with the Hydrologic Modeling System (HEC-HMS)

Abstract

<p>Predicting debris yield under post-wildfire conditions is important for hazard mitigation and flood risk planning. Current prediction efforts aim to reduce the amount and impacts of debris flows that minimizes environmental and economic impacts for communities. However, recovery efforts are difficult and costly. Debris flows and excess runoff block access roads and bridges, inhibiting emergency responses. It also effects the surrounding community's water supply and property. Therefore, having a debris flow sediment management plan is crucial. Predicting debris yield volume, estimating debris basin capabilities, and developing yield mitigation alternatives will mitigate future debris yield disasters. In previous versions of the Hydrologic Engineering Center, Hydrologic Modeling System (HEC-HMS) contains no capacity to simulate debris yield. However, the need for debris yield modeling exists throughout the Corps of Engineers, especially mountainous in arid and semi-arid regions. The HEC has added empirical models for prediction debris yield volumes under post-wildfire conditions. The goal is to develop tools within HEC-HMS that provide outputs necessary for developing debris yield mitigation strategies for managing debris yields within the burned watershed. This research discusses the addition of debris yield methods under post-wildfire situations within the watershed available in HEC-HMS 4.5. The new debris yield modeling capabilities will increase the application of HEC-HMS for debris yield modeling studies by directly computing yields from burn watersheds. Additionally, the model was coupled with the Hydrologic Engineering Center, River Analysis System (HEC-RAS) to ensure that debris yield output from HEC-HMS could be easily used as boundary conditions for predicting the hydraulic non-Newtonian debris flow runout and inundation.  The new debris yield methods use precipitation, topography, and soil burn severity information within the watershed to model debris yield. Reach and reservoir debris routing methods are being further developed, meanwhile existing sediment flow routing methods in reach and reservoir elements can be used with certain limitations.</p><p> </p><p>Keywords: Debris Yield Prediction; Post-Wildfire; Hazard Mitigation; Hydrology Modeling System</p>