ArcHydro – Two Components Hydrologic  Data Model  Toolset Credit – David R. Maidment University of Texas at Austin

ArcHydro – Data Model Hydrography Network Channel Drainage HydroFeatures  Based on inventory of all features for an area  Behavioral model – trace direction of water movement across landscape Credit – David R. Maidment University of Texas at Austin

 Developed with National Hydrogrophy Dataset (NHD) in mind Tools intended to be used with NHD  Integrated raster-vector database ArcHydro – Data Model Credit – David R. Maidment University of Texas at Austin

ArcHydro - Tools  Set of tools used to derive end-products Flow network Hydrologically conditioned DEM  Iterative, step-by-step approach with required inputs  Raster several formats, vector utilizes geodatabase only

ArcHydro - Tools  Set of tools used to achieve end-products Flow network Hydrologically conditioned DEM Catchment delineation  Iterative, step-by-step approach with required inputs  Raster several formats, vector utilizes geodatabase only Credit – David R. Maidment University of Texas at Austin

ArcHydro  Pros Semi-automated derivation of key products Semi-supported Free Integrates data from multiple sources and of different types  Cons  Semi-automated  Install can be difficult  User interpretation and editing introduces subjectivity  Need to know what default settings mean  Few training resources

Hydrologic Applications

Hydrologic Modeling  Process-based - try to represent the physical processes observed in the real world  Dozens available – TOPMODEL, SWAT, HSPF, etc.  Variables - Surface runoff, evapotranspiration, etc.  Increasing GIS integration Predict response of hydrologic systems to changing variables, i.e. precipitation Credit – Pajaro Valley Water Management Agency

Hydrologic Modeling - Hydraulics Model hydraulics of water flow over land and through channels  Assess peak discharge, volume estimates, runoff curve numbers, etc.  HEC-RAS  Increasingly GIS-based or integrated

Erosion Analyses Locate sites of likely gully and other streambank interface erosion  Terrain Analysis approach – Stream Power Index (SPI)  High SPI values indicate high potential overland flow  Quantitative, spatial, repeatable

Water Storage Utilize LiDAR to accurately identify size, depth, and location of depressions in the landscape  Reduce Peak Flows  Reduce sediment and nutrients transported downstream

Water Storage NRCS will have tools available in the future to better calculate  Rough calculation  Perform Pit-fill  Subtract original DEM from pit-filled DEM to locate larger depressions  Multiple methods for determining volume

Floodplain Mapping/Delineation National Flood Insurance Program  Local communities regulate development in floodplains  Requires accurate floodplain maps 100 Year Flood boundary Keep building out of 100 year inundation area

 Administered by FEMA  Utilizes Flood Insurance Rate Map (FIRM)  Update process to digital (DFIRM) Floodplain Mapping/Delineation Credit – FEMA

 Mimic flooding at various stages to determine land area and locations inundated Flood Inundation Area Mapping  Needs Highly accurate land elevation data – LiDAR DEM Modeling Capabilities- Hydraulic Engineering Center–River Analysis System (HEC–RAS) Stream-gauge heights/peak-flow readings

Flood Inundation Area Mapping LiDAR DEM Hydrologic Conditioning Calibration Stream gauge Data Model (HEC- RAS) Conditioned DEM Flood Surface Elevations Inundation Area Map Credit – USGS

Flood Inundation Area Mapping Hydrologic Conditioning - Key Credit – USGS