Green-Ampt Parameterization for Rainfall Excess Determination

Harry DowningSWFWMDApril 18, 2008

Green-Ampt (GA) Parameter OutlineThe District has changed to GA?GA Process (General)Data Sources for Developing GA ParametersLook-Up Table Development (Soils and LU)ArcHydro Tools for GAParameter Generation

Questions

Rainfall Excess Process

Soil Parameter SourcesNRCS - Soil Survey and Soil Survey Geographical (SSURGO) Database - Depth to Water Table and Ksat

IFAS - Site Specific Soil Characterization Soil Moisture Retention Information

Table Information from Other Studies (Text Books)

Site Specific Characteristics from ERP Applications

Soil Survey Information

Soil Survey Information Continued

Soil Moisture for 200 cm Depth to WT

Soil Look-Up Table

Land Use Look-up Table

Creative Land Use Look-Up Table

ESRI ArcHydro Tools

ESRI Sub-Catchment Assignment of GA Parameters

Questions?

Infiltration and Percolation ParameterizationTake You Through Process that the District has Used

Parameters GenerationArea Of Unsaturated and Saturated InfiltrationPerimeter DevelopmentHydraulic Properties of the SoilExpected Depth to the Water Table (SHGWT or Higher)Development of Parameters for Input Into ICPR

Area of Infiltration

Area of Unsaturated InfiltrationFirst Make a Run with the GA Excess Option OnlyObtain the Maximum Inundation Area and Elevation from the Model ResultsDevelop a GIS feature class of the Inundation areas (area & perimeter) - unitsUse this Information for the Infiltration and Percolation Parameters for ICPR regarding initial area

Hydraulic Properties of SoilsSSURGO and IFAS DataERP InformationGeotechnical Information ReportsSoil Testing

Location of Soil Bores Within Hernando County

Vertical Hydraulic Conductivity Results

Results from ERP TestsSSURGO Results for Hydrologic A Soils Minimum Value 0.028 inches/hr Mean 21.25 Max 35 inches/hr

AssumptionsHorizontal Hydraulic Conductivity Greater Than VerticalUse of Vertical for Horizontal Should be Conservative

Depth to SHGWT Use SSURGO Potentiometric Surface Map Land Use Map Imagery

ICPR Parameterization

ICPR Parameterization Continued

Questions?

Floodplain ResultComparisons

Stage Plot Comparison at Node

Stage Plot Comparison at Node

Stage Plot Comparison at Node

Reasonableness of Floodplain

ITEMS TO CHECK !!Double Accounting - Between GA, and Infiltration and Percolation

Area of Influence Around Infiltration Areas

Questions?