Alan H. Rea

Predicting the probability and volume of postwildfire debris flows in the intermountain western United States

Empirical models to estimate the probability of occurrence and volume of postwildfire debris flows can be quickly implemented in a geographic information system (GIS) to generate debris-flow hazard maps either before or immediately following wildfires. Models that can be used to calculate the probability of debris-flow production from individual drainage basins in response to a given storm were developed using logistic regression analyses of a database from 388 basins located in 15 burned areas located throughout the U.S. Intermountain West. The models describe debris-flow probability as a function of readily obtained measures of areal burned extent, soil properties, basin morphology, and rainfall from short-duration and low-recurrence-interval convective rainstorms. A model for estimating the volume of material that may issue from a basin mouth in response to a given storm was developed using multiple linear regression analysis of a database from 56 basins burned by eight fires. This model describes debris-flow volume as a function of the basin gradient, aerial burned extent, and storm rainfall. Applications of a probability model and the volume model for hazard assessments are illustrated using information from the 2003 Hot Creek fire in central Idaho. The predictive strength of the approach in this setting is evaluated using information on the response of this fire to a localized thunderstorm in August 2003. The mapping approach presented here identifies those basins that are most prone to the largest debris-flow events and thus provides information necessary to prioritize areas for postfire erosion mitigation, warnings, and prefire management efforts throughout the Intermountain West.

NHDPlusHR: A National Geospatial Framework for Surface-Water Information†

The U.S. Geological Survey is developing a new geospatial hydrographic framework for the United States, called the National Hydrography Dataset Plus High Resolution (NHDPlusHR), that integrates a diversity of the best-available information, robustly supports ongoing dataset improvements, enables hydrographic generalization to derive alternate representations of the network while maintaining feature identity, and supports modern scientific computing and Internet accessibility needs. This framework is based on the High Resolution National Hydrography Dataset, the Watershed Boundaries Dataset, and elevation from the 3-D Elevation Program, and will provide an authoritative, high precision, and attribute-rich geospatial framework for surface-water information for the United States. Using this common geospatial framework will provide a consistent basis for indexing water information in the United States, eliminate redundancy, and harmonize access to, and exchange of water information.

Stream-Network Navigation in the U.S. Geological Survey StreamStats Web Application

StreamStats is a U.S. Geological Survey Web-based geographic information systems application developed as a tool for water-resources planning and management, engineering design, and other applications. The primary functionality of StreamStats allows users to obtain drainage-basin boundaries, basin characteristics, and streamflow statistics for gaged and ungaged sites. Recently, tools that allow stream-network navigation were added to StreamStats. These tools allow users to select any point along a stream and locate activities upstream and downstream from the selected point, such as streamgaging stations, dams, and point-source discharges, and obtain information about such activities. Users also can obtain stream-reach addresses and estimates of streamflow statistics for the selected points.

Use of the StreamStats Web Application for TMDL Analysis

StreamStats (http://streamstats.usgs.gov) is a U.S. Geological Survey (USGS) Web-based geographic information systems application developed as a tool for water-resources planning and management, engineering design, and numerous other applications, and is a useful tool for analyzing Total Maximum Daily Loads (TMDLs). StreamStats users can select data-collection station locations shown on an interactive map interface to obtain previously published streamflow statistics, basin characteristics, and descriptive information for the stations. Users also can select any location along a stream to obtain the drainage-basin boundary, basin and climatic characteristics, and streamflow statistics for the location, estimated based on either regional regression equations or on the flow per unit drainage area for the statistics at nearby streamgaging stations. These estimates of streamflow statistics can be useful for TMDL analysis. For example, StreamStats applications for several states provide estimates of 7-day, 10-year low flows, which are used by many states for permitting of effluent discharges.