lthia – 2007 -2008 upgrades and training bernard a. engel tong zhai larry theller agricultural and...
TRANSCRIPT
LTHIA – 2007 -2008
Upgrades andTraining
Bernard A. EngelTong Zhai
Larry Theller
Agricultural and Biological DepartmentPurdue University
In conjunction with POLIS Center, IUPUI and
Indiana Dept. Environmental Management
Contents
Basic conceptsNew data layersHow web model worksIntegration with IWQATraining in 2008
Basic Model Concepts
Model is easy to run Always gives an output… Important to understand assumptions and limitations
Assumptions
Water flows across the surface to form flowshed • no storm drains
Water equally spread across landscape• No routing
Average antecedent moisture • soil is not saturated or frozen
Rainfall is evenly spread in local area
Limitations
Accuracy of landuse and soil data• Big limitation
Accuracy of runoff curve number • Hydrological impacts are understated
• LID not reflected
Accuracy of published NPS relationship• Lead in runoff based on 1990’s models
Long Term Hydrologic Impact Assessment (LTHIA) Calculates the chemistry and volume of
runoff water, based only on landuse and soil type.
Changing the landuse in an area will change the typical runoff chemistry.
This uses assumption called “curve-number.”
LTHIA in use for > 5 years.
Process FlowchartOutlet Point Selection
Using Aerials, roads, or streams Run Watershed
Delineation
To get contributing area
Watershed Delineation Result
Examine maps Reflect Land Use Change Using Online
Digitizing
Run L-THIA
Runoff and NPS Output/Impact
Evaluation
https://engineering.purdue.edu/~lthia
The screens used in the model
We break soils into 4 hydrologic conditions, which are used to estimate runoff volume.
We break landuse into 8 basic types, which are used to estimate chemistry.
Soil A Soil B
Landuse 1Landuse 3
Landuse 3
LTHIA isolates the flowshed to estimate the runoff, so it calculates runoff for the -shed.
Raster input
-Edit raster landuse layer-and change scenarios
The software uses raster files of landuse and soil
Curve Number Basics:
http://www.ecn.purdue.edu/runoff/documentation/scs.htm
Direct Runoff
rainfall to runoff ratio for different surfaces
Rainfall
Averaged mass of NPS contaminant from each landuse
EMC Table
Data Issues: Working with 10 meter DEMS means we can not use watersheds larger than 10 digit.So, if the user clicks on the mouth of the Wabash or the Tippecanoe River, they get the first upstream 10 Digit watershed.All contiguous 10 Digit watersheds are supported.
Take-Home points
DEM is only used to calculate flowshed
DEM is not used for erosion – or runoff
Runoff is based on surface type – not slope
won’t account for frozen ground30 year average rainfall
Chemistry is based on landuse averages
Databases provide input
Weather data (30 years of real rainfall)
Soil data (SSURGO )
Elevation data 10m DEM (for contributing area)
Process for Web-GIS ToolsOutlet Point Selection
Using Aerials, roads, or streams Run Watershed
Delineation
To get contributing area
Watershed Delineation Result
Examine mapsReflect Land Use
Change Using Online Digitizing
Run L-THIA
Runoff and NPS Output/Impact
Evaluation
https://engineering.purdue.edu/~lthia
LTHIA Web site
Choose to click a point, input X and Y, or select a 14 – digit watershed
Watershed Delineation and Result Page
Watershed Delineation and Result Page
Results Display
For Example,Add Low Density Residential, Commercial, and High Density Residential Areas
Change Land Use in the Watershed Using Online Digitizing Tool
Scenario Results Page
Present Land Use Data
After Change Land Use Data
Application Buttons forHydrological Model Operation
L-THIA Input Page After Changing Land Use
Multiple scenarios – offer multiple development options. User constructs scenario by online digitizing.
L-THIA Result Runoff Tables
Can display pre-and post calibration and also land-use change scenarios.
Comparison Chart for Runoff and Land Use to Evaluate the Land Use Change Impact on Hydrology
NPS Pollutant Loading Chart
Print and Download Page
Long Term Hydrologic Impact Assessment (LTHIA)
Added connection to the Indiana Water Quality Atlas
2001 NLCD landuse statewide Landuse based on parcels, selected cty SSURGO soil better DEM (10 meter) NHD High –resolution stream layer
Near Future:Calibration module in development:
15 counties landuse from parcel data
Hands-on Training
The End
Thank You
https://engineering.purdue.edu/~lthia