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