Flood and Storm Tracker (FaST) Maps

The initial USGS NAS FaST maps are created within 2-3 days of an event to quickly identify flooded 10-digit hydrologic units (HUC-10s) based on USGS Water Science Centers stream gages or storm tide sensors with water heights at or above flood stage. This map integrates flooded hydrologic units with known locations of established, or possibly established, introduced aquatic species. All hydrologic units surrounding known locations of introduced species are included as possible areas of infestation, until actual hydrologic connections have been determined (step 2, revised maps). The NAS FaST map identifies both the established species within a hydrologic unit and the potential species for new introductions (defined as established species in adjacent watersheds) due to flooding impacts.

The refined NAS FaST map enhancement provides information only on the locations with flooding conditions that could breach drainage divides. We utilize information on the relative flood height using the best available data from the USGS Water Science Centers including stream gages, storm surge gages, inundation maps (when available), and identified high water marks along with National Oceanic and Atmospheric Administration modeled storm surge. This information is combined with information on the elevation of the hydrologic units at the 10-digit level (HUC-10s) boundaries (drainage divides) identified from digital elevation models. The flood elevation data was mapped with the hydrologic units' drainage divide elevations to determine if the flooding conditions were of sufficient height to breach the boundary. These "connection points" are identified along the hydrologic units' boundaries. Drainage divide connections determined by upstream stream gages at flood stages were assumed connected along streams and not given connection points on the map.

Hydrologic units identified as being flooded and potentially connected as part of the refined NAS FaST map are established based on the best available data. This map may not include all flooded areas. The refined NAS FaST map focuses on the potential spread of nonindigenous aquatic species between hydrologic units and is not a map of flood inundation.

The final NAS FaST map enhancement includes information on flood connections at drainage divides and pre-storm species observations from the revised map with the addition of post-storm species observations approximately one year after the storm event. We map NAS specimens collected within a year after the storm event inside 10-digit hydrologic units (HUC-10s) where species were previously designated as potentially spread due to flooding in the revised map. We assume a potential pathway due to flooding based on best available data for each observation.

Historic USGS NAS FaST maps represent the potential spread of established, non-native aquatic species by flood waters at drainage divides one year after a major storm that occurred prior to 2017. Areas impacted by flooding are defined by 10-digit Hydrologic Unit Codes (HUC10) that contain flood elevation data, including high water marks and storm tide sensors, from the USGS Flood Event Viewer (stn.wim.usgs.gov/fev/). These data are compared to USGS Digital Elevation Model (DEM) data (www.usgs.gov/core-science-systems/ngp/3dep) at HUC10 boundaries to assess the potential inundation at drainage divides. Areas where flood heights are greater than DEM heights at drainage divides are labeled “connection points” where aquatic species may have a potential corridor for temporary movement. Observations of established populations from the USGS NAS database (nas.er.usgs.gov) are mapped in areas determined as impacted by flood waters. Each HUC10 within the flood-impacted area is labeled either as “present in the watershed” if the population was established prior to the flood being mapped or as “potential spread due to flooding” if that HUC10 shares a connection point on a drainage divide with a HUC10 that contains an established population of the same species. For validation of a species’ potential flood dispersal, established populations that were observed up to one year after a flood event are mapped as post-storm observations. These observations potentially arrived to that HUC10 by way of flood waters if they are new to that HUC10 and have a reasonable corridor by way of the mapped connection points.

Hydrologic units identified as being flooded and potentially connected as part of the historic USGS NAS FaST maps are determined based on the best available data. These maps may not include all flooded areas. The historic USGS NAS FaST maps focus on the potential spread of nonindigenous aquatic species between hydrologic units and are not maps of flood inundation.