Forecasted flood depth grids were generated for Hurricane Harvey using the National Weather Service’s (NWS) Advanced Hydrologic Prediction Service (AHPS) forecasted water levels.  These depth grids allowed for pre-event planning and early estimated hazard exposure counts.

Data Sources

Esri Hydrolines (detailed)

NWS AHPS River Forecasts

USGS National Elevation Dataset (30m DEM)


A Python-based script tool was developed to generate forecasted flood depth grids using Esri geoprocessing following the steps outlined below:

  1. Select hydrolines within basin of interest
  2. Generate hydropoints from hydrolines at 50m spacing
  3. Download NWS AHPS River Forecasts (Maximum Full Period)
  4. Interpolate surface from AHPS Forecasted Max Water Depths
  5. Extract USGS NED to hydropoints and add water depth
  6. Interpolate Water Surface Elevation Level (WSEL) from hydropoints
  7. Subtract terrain elevation from WSEL
  8. Manually QC forecast-based depth grids, removing areas of uncertainty

Access & Use Information

Public: This dataset is intended for public access and use.


Forecasted flood depth grids are based on forecast stream gauge water levels (valid on the day/time that they were generated) and are intended for situational awareness and preliminary exposure estimates in disaster response phase only, NOT damage estimates in disaster recovery or mitigation phases.

Downloads & Resources

Map Service



Madeline Jones


Uncertainties associated with this dataset may be attributed to the following:

X,Y location accuracy of the stream gauge (unknown)

Vertical accuracy of the stream gauge (unknown)

Vertical accuracy of the USGS NED is between 1-3m

Flood depth grids are generated from an interpolated water elevation surface, not H&H modeling

Levees, dams, roads, breaklines are not an input data source and should be used supplementally with this dataset


Jones, M. and Longenecker, H. Forecasted Flood Depth Grids Providing Early Situational Awareness during the 2017 Atlantic Hurricane Season, Abstract NH23E-2882 presented at 2017 Fall Meeting, AGU, New Orleans, LA, 11-15 Dec.

Longenecker, H., Graeden, E., Zuzak, C., Kluskiewicz, D., Eaneff, A., and Rozelle, J. A Rapid Flood Risk Assessment Method for Emergency Response Operations and Non-subject-matter-expert Community Planning (In Progress). FEMA.


Updated on March 30, 2021