Swan Creek Workshop
November 10, 2009
Host: Toledo Metropolitan Area Council of Governments
Workshop by: Institute of Water Research – Michigan State University and Department of Agricultural and Biological
Engineering, Purdue University.
L-THIA and L-THIA LID Exercise
Presenters:
Bernie Engel, engelb@purdue.edu
and Larry Theller, theller@purdue.edu
Agricultural and Biological Engineering,
Purdue University
Introduction (slides) to LTHIA:
https://engineering.purdue.edu/~lthia/documents/lthia_intro_swan_crk.pptx
Introduction (slides) to LTHIA-LID:
https://engineering.purdue.edu/~lthia/documents/lthia_lid_swan_crk.ppt
This document:
https://engineering.purdue.edu/~lthia/documents/SwanCreek_LTHIALID_EX.docx
This document is a hands-on exercise and will address a series of questions related to one topic. The document
will explain how to use the two online tools, L-THIA and L-THIA LID to address the questions.
Topic: A developer has proposed a high-density (HD) residential development in one 12 digit HUC within the Swan
Creek watershed area. There are several aspects to consider:
A) What is overall impact (to entire subwatershed) of adding this development as HD Residential?
B) What is overall impact (to entire subwatershed) of same amount of growth as single-family mixed lot
development?
C) What is the projected benefit (in non-point source pollution terms) of using Low Impact Development
techniques rather than traditional high-density housing construction?
The online tools are linked from the Swan Creek main page here: www.iwr.msu.edu/swancreek/
or http://35.9.116.206/swancreek/home.asp
Swan Creek Workshop (L-THIA Portion) November 10, 2009
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Begin: Follow link to the LTHIA tool page here: https://engineering.purdue.edu/~lthia/swancreek/
We will use the first tool, [http://cobweb.ecn.purdue.edu/~eqip/swancreekoh-10/Index.html ] , to answer
Questions A and B and the second tool [http://cobweb.ecn.purdue.edu/~sprawl/LTHIA7/lthianew/lidIntro.htm ]
to answer questions C and D.
Open http://cobweb.ecn.purdue.edu/~eqip/swancreekoh-10/Index.html
The proposed development is about 320 acres just off South Berkley Southern Road at Neowash Road ( this is near
SR 295 and US 24.) The area is drained by a stream listed on the 303D list and the area is upstream from the Blue
Creek Conservation Area.
We provide step-by-step procedures below. To repeat the process, one could zoom in again, search for Whitehouse,
Ohio; or use the delineate by coordinate ability and enter : 41.489392, -83.807244
First visualize the area. Using the digital Watershed zoom tool or the LTHIA Google map search tool, locate
Whitehouse, Ohio and pan to the project area.
The Google engine is a national search engine. So, while you can search for street address or town
name, you should include state or zip code for best results.
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This map has the 303D streams turned on over Google Maps. To analyze this area in L-THIA we
need to determine a subwatershed which encloses the development.
One way to do this is to use the “Delineate by HUC 12” button and delineate the whole HUC 12.
Another way is to use the click to “Delineate by Point” button and delineate the small subwatershed
enclosing the planned development. (Another way on subsequent visits is to delineate by entering
the latitude- longitude coordinates of the point we click the first time through the process.)
Since the subwatershed developed by the click is a smaller area than the enclosing HUC 12
watershed, any increase or decrease in runoff or NPS compounds will be more noticeable in the
tables.
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Use the “Delineate by point” tool to click on the stream.
A good practice is to use road- stream intersections, which can later be located for subsequent
sampling programs. Click where the county road 151 crosses the stream.
This image has 303D streams and also HIT Sediment layer on.
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The resulting page has a table of landuse and soil distribution inside the subwatershed.
Leave the results page open and click the button “Review Google Maps lands” to see the outline of
the subwatershed. This will open a Google Map with the subwatershed over the display.
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This map displays the delineated subwatershed in green over the 12 digit HUC layer.
You may wish to browse the subwatershed, turning on and off the colored HUC12 layer, the HIT
layers, and toggle between ‘Map” and “Satellite” views.
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When you are ready to proceed click on the pushpin to open the toolbar.
Run LTHIA, shapefile download and the Per Cent Imperviousness tools are ready to use from the
toolbar unless you want to create a before –after scenario set ( which in this case you do.)
Download KML is available as a button which allows one to view the watershed in Google Earth.
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To continue creation of the scenario, click “digitize” tab to open the toolbar, then click the tool link.
The Digitize link will open a new window. You will see this map.
You will need to adjust the background layers, then click a button to start digitize then click the map
to send it to the next step. The left panel is the map background, here aerial photo; the right panel is
the subwatershed background, here hydrologic soil group from the SSURGO database soil.
When ready, slick the “online Digitizing” button and then click in the map to tell Internet Explorer to
move on to the next step.
This is the digitizing interface. The “help” button has example of the more complex (landsue and
BMP changes) tasks. The addition of a landuse change without a BMP change is easy.
You essentially draw a box where you want it and select the type of landuse it is and save it. After
that we will run L-THIA model on the before and after change scenario.
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The box is to be drawn near Bailey and Perry Roads. You want to change around ½ section or 320
acres to High Density Residential.
Visualize this with the scale bar and the 1 mile section line roads. Draw polygon then right-click
inside it to see landuse list.
Select High Density Residential – then you must hit “Step 1 Apply BMPs and/or Landuse changes”
button.
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Now we see the result page with the “before and after” scenarios. We subtracted Ag land and added
HD residential.
This example has about 300 acres changing to HD Residential. The bulk of this is on “D” soils. Follow
the link Run L-THIA Model to get an automatically populated spreadsheet.
LTHIA spreadsheet is populated, the county is set in order to pull 30 years from the rainfall
database to make average precipitation. The landuse changes are entered. Click the run button
below the spreadsheet.
The runoff appears as a table; the other results are available form the link on the left. Use the “back”
button of your browser to see different NPS predictions. Results are available as tables, graphs, or
pie charts. Tables may be copy-pasted into Excel.
The conclusion from this scenario is that high density housing does not change the runoff totals
much ( there is some increase over ag land) but does slightly lower the sediment in the runoff.
Our tables rate agricultural landuse to be a much higher risk of sediment loss than residential
landuse.
Part 2 Exercise Low Impact Development
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One question that can be addressed with the L-THIA Low Impact Development tool is “What would the impact be if
the proposed development of 320 acres of HD residential was instead built with LID practices?”
To proceed from the earlier example, open the results window and click the link “Low Impact
Development”.
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The results age is open on the left, the LID tool page is open on the right.
The Low Impact Development tool opens a spreadsheet which you fill out manually from the
previous results table or with data you are modeling.
For example if you want to model a buildout ( What if all the land zoned R1 in the watershed was
built on?) you can just enter the acres and soil groups into the spreadsheet, without using any map.
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You need to enter the “before” and “after” for what changed: residential and agriculture. Here the
user dropped the few acres of forest and rounded off the agricultural total to make it simple. If you
see a round off error (7.10000009 for example )in the 1/8 acre landuse, just manually round it off to
acres; the final totals must match, so user needs to do the same amount of round-off to both
scenarios.
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The LID spreadsheet has options to do a basic screening or a lot-level screening; and allows
impervious default to be adjusted to reflect local practice.
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The NPS results are available as tables or graphs. Remember any change that adds to the runoff
volume may dilute the predicted concentration of NPS chemicals, while their total load may
increase. With the addition of a lot of impervious surface the concentration in ppm or other units
will go down but total mass or load will go up because there are many more gallons of water (recall
one acre-foot is 3.26 x 105 gallons) in the runoff.
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