Post Wildfire Flood Modeling

Post Wildfire Flood Modeling

Description

Flood modeling is composed of several different models that are utilized by the United States Army Corps of Engineers (USACE). The flood models include the River Analysis System (RAS) and TUFLOW models. (2015, Retrieved the United States Army Corps of Engineers Publications).The RAS model gives access to perform one-dimensional steady flow, unsteady flow, sediment transport/mobile bed computations, and water temperature modeling. The TUFLOW model is modeled under a license offering a more complete model of the entire watershed with inputs of rainfall, net runoff & sheet flow, flow concentration, and conveyance along the various watercourses.

Duration: ~10 hours

Duration averages about ten hours for the TUFLOW depending on hardware, location, and size of the basin. While the RAS modeling takes about five hours.

Responsible Resources

U.S. Army Corps of Engineers are responsible for modeling of the RAS and TUFLOW at the Hydrologic Engineering Center. It is important to note that the TUFLOW modeling requires licensing for bandwidth. When RAS can be run by FEMA independently or by the USACE.

Triggers

Modeling for the RAS needs to be requested through the U.S. Army Corps of Engineers.?

Predecessor

Soil Burn Severity Maps are needed from the field to begin the flood modeling processes.

Inputs Requirements

Necessary inputs for flood modeling are:

1)?????Discharge and rainfall data from NOAA

2)?????Manning numbers

3)?????Vegetation data

4)?????BARC data

5)?????QC of the data sets by those running the data.

Products

Flood modeling produces:

·????????RAS and TUFLOW peak flow rates

·????????Flood vulnerability maps.

Issues/Other Considerations

1. Knowledge of emergency management data required for model output used in the creation of risk maps.
2. A need for an increase in communication bandwidth for running the TUFLOW models, as in the field computer systems are not powerful enough to run these numerically intensive models.??
3. It was found that the data grid outputs from RAS and TUFLOW are too complex for most stakeholders - there is a need for a better understanding of each model by the stakeholders.
4. HEC has identified similar issues and is working towards solutions, it is recommended that a partnership between FEMA and HEC be formalized.?

Flood Modeling Spatial Mapping Products

"The fires created conditions that greatly increased the threat of flooding, erosion, and debris flows.?Because the winter rainy season was about to begin, Federal, State, and local government officials were concerned about the potential effects of the fires on communities within and adjacent to the burned areas.?The wide range of efforts at all levels of government to address this threat also necessitated an effective means for developing and sharing information about the threat and measures being implemented to reduce it.?Consequently, the Federal Emergency Management Agency … and their Federal and State agency partners … coordination of efforts … successfully led to the development of science-based products that provide information about natural hazard risks that could occur after containment of the fires and to recommend a set of standard operating procedures to facilitate work in the future."?(Watershed Clearinghouse-FEMA 4240-DR-CA)?

The final activity in the PWRA activity chain (process) produces the Geospatial products.?These Geospatial products include maps and tabular data, which support preparedness efforts, through FEMA and other emergency management partners at the state and local level. Mapping products are also used to help support communities through FEMA programs: individual assistance, public assistance, and hazard mitigation.?The Flood Vulnerability Maps, cited in Table number 4, are used to communicate risk information to Federal, State, and local officials for preparedness, mitigation, and recovery activity. These maps are categorized as special advisory flood Vulnerability maps and are produced by the Army Corps of Engineers, H&H modeling using RAS.??FEMA NFIP specialists share these maps with local flood plain managers.

The following is an example of a GIS text box required for Flood Modeling Spatial Mapping Products:

Entire watershed modeled to simulate the complete process of (except for infiltration) rainfall, net runoff & sheet flow, flow concentration, and conveyance along the various watercourses.?Hydraulic data produced in TUFLOW (Classic) model application (50-ft computational grid).?Data is for the pre- and post-burned conditions using the 100-yr, 2-day rainfall event.?Model uses both: 1) an assumed rainfall pattern based on n-yr 48-hour rainfall depth value applied evenly through simulation period, and 2) the 1997 rainfall pattern applied to the n-yr rainfall depth.?Additionally, over the burn areas, flow is bulked by 150% and the model uses post-burn Manning’s roughness values.?For model geometry, IFSAR is used for the Valley Fire area and a combination of IFSAR and LiDAR is used for the Butte Fire area, and basin terrain data (IFSAR).

Table 4: Flood Modeling Spatial Mapping Products (Watershed Clearinghouse FEMA-4240-DR-CA)

Table 4 represents the products produced for Flood Modeling Spatial Mapping Products including name of the map, descriptions, naming conventions, and inputs. (Watershed Clearinghouse Data and Products_20151120.xlsx, Ethridge)

Flood Vulnerability 100-yr Model - Address Sites in Burned Area

Description

This map depicts specifically requested potential housing site locations in relation to burned areas and 100-year event flood model developed by the U.S. Army Corps of Engineers (USACE). Entire watershed modeled to simulate the complete process of (except for infiltration) rainfall, net runoff & sheet flow, flow concentration, and conveyance along the various watercourses.?Hydraulic data produced in TUFLOW (Classic) model application (50-ft computational grid).?Data is for the post-burned condition using the 100-yr, 3-hour rainfall event.?Model uses the 1997 rainfall pattern based on the Knoxville precip gage and adjusted for the n-yr volume, post-burn Manning’s roughness, and basin terrain data (IFSAR).

Naming Convention

FireName_FocusArea_Model_AddressSite_Date

Input (Key Data Layers) dep100post97p, USGS Debris Flow Model 100-yr, Address Sites

Flood Vulnerability 100-yr Model - Address Sites in Burned Area

Description

This map depicts specifically requested potential housing site locations in relation to both the burned area and 100-year event flood model developed by the U.S. Army Corps of Engineers (USACE). Entire watershed modeled to simulate the complete process of (except for infiltration) rainfall, net runoff & sheet flow, flow concentration, and conveyance along the various watercourses.?Hydraulic data produced in TUFLOW (Classic) model application (50-ft computational grid).?Data is for the post-burned condition using the 100-yr, 3-hour rainfall event.?Model uses the 1997 rainfall pattern based on the Knoxville precip gage and adjusted for the n-yr volume, post-burn Manning’s roughness, and basin terrain data (IFSAR).

Naming Convention

FireName_FocusArea_Model_AddressSite_Date

Input (Key Data Layers) TUFLOW post100d3h97p, Address Points, BARC

Flood Vulnerability 100-yr Model - Address Sites in Burned Area

Description

This map depicts specifically requested potential housing site locations in relation to both the burned area and 100-year event flood model developed by the U.S. Army Corps of Engineers (USACE). Entire watershed modeled to simulate the complete process of (except for infiltration) rainfall, net runoff & sheet flow, flow concentration, and conveyance along the various watercourses.?Hydraulic data produced in TUFLOW (Classic) model application (50-ft computational grid).?Data is for the post-burned condition using the 100-yr, 3-hour rainfall event.?Model uses the 1997 rainfall pattern based on the Knoxville precip gage and adjusted for the n-yr volume, post-burn Manning’s roughness, and basin terrain data (IFSAR).

Naming Convention

FireName_FocusArea_Model_AddressSite_Date

Input (Key Data Layers) TUFLOW dep100post97p, Address Points, BARC

VALLEY FIRE: FLOOD VULNERABILITY model -?focus areas

Description

This map depicts a requested address locations in relation to the 100-year event flood model developed by the U.S. Army Corps of Engineers (USACE). Entire watershed modeled to simulate the complete process of (except for infiltration) rainfall, net runoff & sheet flow, flow concentration, and conveyance along the various watercourses.?Hydraulic data produced in TUFLOW (Classic) model application (50-ft computational grid).?Data is for the post-burned condition using the 100-yr, 3-hour rainfall event.?Model uses the 1997 rainfall pattern based on the Knoxville precip gage and adjusted for the n-yr volume, post-burn Manning’s roughness, and basin terrain data (IFSAR).

Naming Convention

FireName_FocusArea_Model_AddressSite_Date

Input (Key Data Layers) TUFLOW post100d3h97p, Address Points, BARC

Flood Modeling RAS Mapper

HEC-RAS has the capability to perform inundation mapping of water surface profile results directly from HEC-RAS. Using the HEC-RAS geometry and computed water surface profiles, inundation depth and floodplain boundary datasets are created through the RAS Mapper. Additional geospatial data can be generated for analysis of velocity, shear stress, stream power, ice thickness, and floodway encroachment data. To use the RAS Mapper for analysis, you must have a terrain model in the binary raster floating-point format (.flt). The resultant depth grid is stored in the .flt format while the boundary dataset is store in ESRI's Shape file format for use with geospatial software.

HEC RAS software links are:

https://www.hec.usace.army.mil/software/hec-ras/features.aspx

https://www.hec.usace.army.mil/software/hec-ras/features.aspx#Mapper

Data Structure