Web-Based GISfor

Hydrological Impact Analysis

Bernie Engel, Professor and Head

Larry Theller, GIS Specialist

Agricultural and Biological Engineering

Purdue University

This workshop gives an introduction to web-based GIS for Hydrological analysis.

At the end of the workshop you would be able to access available watersheds, delineate these watersheds and change the land use within these watersheds.

Several outputs are then available to assess the feasibility of the proposed changes.

Workshop Focus

https://engineering.purdue.edu/~lthia/MSDSS/index.html

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

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

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 slopewon’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 ) or STATSGO

• Elevation data 30m or 10m DEM (for contributing area)

L-THIA Example AnalysisFebruary 2010

Uses Wisconsin data. Discussion slides to follow the PDF:

WQ Tools Workshop2.PDFBernie Engel,

Agricultural and Biological EngineeringPurdue University

https://engineering.purdue.edu/~lthia/MSDSS/WQToolsWorkshop.pdf

Online Watershed Delineation• Launch the webpage at:

https://engineering.purdue.edu/~lthia/wi/

• Click on Wisconsin 10/30 meter

• You should be at the Watershed Delineation Map Interface

https://engineering.purdue.edu/~lthia/

Water layers are toggled on, watersheds are toggled off. Water is NHD High Resolution Streamlines

Enter: Monches, WI and click Search button

High Impact Target layers from Michigan State Institute for Water Resources, and HUC layers from EPA streaming data services.

Water features show up over “satellite” images and in urban areas.

This is the development area

This is a good delineation point. Click “delineate” button then click here.

Brief wait for calculations

Watershed (HUC8,10,12) info

Pour Point (point clicked on) coordinates in local coordinate system.

Landuse and soil breakdown for WatershedArea in acres of each unique landuse – hydrologic soil pair.

Online models with data populated form this delineated area

Option to view this watershed over Google Maps. Choose this.

Click pushpin to see toolbar.To edit landuse: Click tab: Digitize Then click link “Online Digitize”;

Pour Point

Foreground LayersBackground

Layers

Set the layers for edit session, then click here

Click “polygon” button and draw one with a final click on start point; then right-click inside to see pop-up menu for landuse selection. Last step is to click “Apply BMPs…”

Right-click inside new polygon to select landuse; and click toggle button to “Apply BMPs”

Online models with data populated from this delineated area.

Tabular breakdown of area of all unique pairs of soil and landuse types.

The L-THIA spreadsheet will be populated by these automatically.

LTHIA Online tools

• EPA Region 5 : L-THIA Hydrologic Impact Assessment Tool

– https://engineering.purdue.edu/~lthia/

• Burns Ditch - Trail Creek

– https://engineering.purdue.edu/mapserve/www/lthia_bdin/

– Swan Creek Management System

Main page: http://35.9.116.206/swancreek/home.asp

L-thia Page: https://engineering.purdue.edu/~lthia/swancreek/

Links below region 5 states go to Watershed Management Systems. These have BMPs added to the landuse tools.

https://engineering.purdue.edu/mapserve/www/lthia_bdin/

Online Watershed Delineation• We will be using some tools to navigate in the map

• At the top of the Map Interface locate the following four tools

• Ignore the tools within the map area for the moment

Online Watershed Delineation• Click on the center of Logan County then click on the zoom in

tool

• Repeat the zoom in tool until Highways appear in the map (this should take two zoom ins)

• Do two more zoom ins into the Logan County

• Click on the “elbow” in the following Highway then click on pan

• This centers the map at the “elbow”

LTHIA• Save drawing, then merge digitized land use with watershed

map (buttons are at the bottom of page)

• The land use before and after digitizing will be presented:

L-THIA Input Page After Changing Land Use

Multiple scenarios – offer multiple development options. User constructs scenario by online digitizing.

LTHIA

• Select the Run L-THIA button, this should take a few seconds

• The L-THIA Output presents two scenarios (before and after land use change)

NPS Pollutant Loading Chart

The End