Stormwater Forecast Script Tool (15 County Region)

This stormwater forecast script tool was developed by the Natural Resources Department at the Atlanta Regional Commission. WHAT IS THE STORMWATER FORECAST? In 2022, the District developed a novel water quantity-based indicator, the Stormwater Forecast, to support watershed managers with ongoing challenges related to water quality, streambank erosion, and nuisance flooding. The Stormwater Forecast is a planning-level estimate of the total potential storage volume required by Stormwater Control Measures to manage runoff from development at a basin scale under both current and future conditions. Based on current development patterns, the results of the Stormwater Forecast show the 15-county Metro Atlanta region should be managing up to 27 billion cubic feet of runoff volume with Stormwater Control Measures, and if regulations remain the same the total volumes are estimated to increase by up to 100 percent by 2040. STORMWATER FORECAST USER GUIDE The Stormwater Forecast User Guide outlines steps for calculating stormwater runoff volumes for an area of interest using the Stormwater Forecast and performing a Stormwater Forecast Gap Analysis using the custom stormwater runoff volume results. STORMWATER FORECAST GEOPROCESSING PACKAGE The Stormwater Forecast Geoprocessing Package contains the Stormwater Forecast Script Tool and a geodatabase with the following four parameters needed to execute the tool. AreaofInterest StormwaterForecast DevelopedArea NLCD_Imperviousness_2019.tif The Stormwater Forecast Script Tool provides users with an automated calculation method for calculating custom stormwater runoff volumes within an area of interest using the Stormwater Forecast. FIELD ABBREVIATIONS AND DESCRIPTIONS FOR STORMWATER FORECAST RESULTS Unique_ID = Unique Identification Characters for Stormwater Forecast Subcatchment NHD_Sub_ID = National Hydrography Dataset Subcatchment Identification Numbers HUC_12 = Hydrologic Unit Code-12 Identification Numbers County = County Name HUC_8 = Hydrologic Unit Code-8 Identification Numbers MRB = HUC-8 Major River Basin Name Area_Dev_a = 2019 Developed Area, in acres Impv_Area = 2019 Total Impervious Area within Developed Area, in acres AOI_19_WQ = 2019 Water Quality Volume for Area of Interest, in cubic feet AOI_19_CP = 2019 Channel Protection Volume for Area of Interest, in cubic feet AOI_19_OF = 2019 Overbank Flood Protection Volume for Area of Interest, in cubic feet AOI_30_WQ = 2030 Water Quality Volume for Area of Interest, in cubic feet AOI_30_CP = 2030 Channel Protection Volume for Area of Interest, in cubic feet AOI_30_OF = 2030 Overbank Flood Protection Volume for Area of Interest, in cubic feet AOI_40_WQ = 2040 Water Quality Volume for Area of Interest, in cubic feet AOI_40_CP = 2040 Channel Protection Volume for Area of Interest, in cubic feet AOI_40_OF = 2040 Overbank Flood Protection Volume for Area of Interest, in cubic feet Required Software: Esri’s ArcGIS Pro and Esri’s Spatial Analyst and Image Analyst Extensions