Basic Spatial Analyses for Lake and Stream
Many impairments to water quality are related to the surrounding landscape.
Some of these effects are related to immediate factors such as shoreline
characteristics, erosion, and riparian vegetation, while others are related
to watershed scale factors, such as land use patterns, the amount of impervious
surface, homeowner activities, and numerous other factors.
Geographic Information Systems provide a means to quantify various aspects
of lake, riparian, and watershed characteristics. By linking these spatial
characteristics with water quality, a water quality manager can identify
key sources of impairment, and consequently find appropriate remediation
strategies. In addition, the maps created through GIS analyses provide
an effective means of conveying information to decision makers and the
In this laboratory, you will use on-line GIS resources from WOW and
other sites to answer questions on lake, river and watershed attributes
- Explore the GIS tools and resources on WOW, DuluthStreams and Lake
Access to find and retrieve spatial data on lakes, rivers and watersheds
- For any given site, learn to identify a watershed and identify the
dominant stressors, particularily land use, that affect water quality.
Part I: Using GIS Tools and Resources on
WOW to Compare Urban and Rural Lakes
Use the WOW Internet Map Server (IMS) to retrieve lake and watershed
data for Medicine Lake in the western Minneapolis region and Shagawa Lake
near Ely, Minnesota, about 250 miles northeast of Medicine Lake. Before
you start using IMS, you should look at the Quick
Click one of the following links to launch an IMS session in a separate
Use the Identify and
in IMS to answer the following questions:
The fetch of a
lake determines in part its susceptibility to mixing by wind events.
the longest fetch of Medicine Lake? Shagawa? (note: the prevailing winds
in Minnesota are generally from west to east)
Given regional wind patterns, do you think the fetch has a significant
Use IMS to answer following questions, put your answers in the table
What is the area of each lake?
What is the maximum depth of Medicine Lake?
(Hint: make Bathymetry the active layer, then use the Identify
on the deep hole)
What is the maximum depth of Shagawa Lake?
(Hint: go to our cheat
Use the Query function to
determine the amount of forest, agricultural and urban lands in the watershed.
answer as a percent of
Land Use Calculations
- Use the IMS Query function to
extract the Land Use data from the watershed. You can select data individualy
by land use type, or select it at once. The quick way to select it
all is to use Area > 0 as your Query String
- Save the data and get it into EXCEL - Option 1
Copying the selected data from the Arc View IMS frame:
2.1 Select and highlight all all of the fields displayed in the bottom
ArcView IMS frame.
2.2 Right click the mouse key to copy the highlighted fields. Select Copy.
2.3 Load Excel, click on File> Open a blank worksheet.
2.4 Highlight the first cell, and right click the mouse to Paste the
- Save the data and get it into EXCEL - Option 2
Saving the data to a text file:
3.1 Click on "Save Attributes to Text File" -
help box pops up
3.2 Choose File>Save As
3.3 In the Save dialog box, Change the type
of file (Save as Type) to text file (txt)
3.4 Type in a sensible file name and choose a location to save
the file. Save it.
3.5 Load Excel, click on File> Open and
select your text file
3.6 Excel will complain that it doesn't recognize the file.
Too bad for it, click OK to
launch the Text Import Wizard
3.7 This is a comma delimited file, so make sure the Delimited file
type is checked and click on Next
3.8 Click in the Comma box to tell Excel this is
a comma-delimited file. The fields will magically align
3.9 Click on Finish to load the data into your worksheet.
- Calculate the percentages of each land use type in the watershed
4.1 You will notice that the column headings do not carry
over. They are (in order):
Area (in square meters - the native format for storing area
Landuse(the more aggregated class used to select the data)
Shape- the type of data (in this case - polygon)
ID- an index number for the individual polygons
4.2 There are a number of ways to calculate the percentages
the data and use @sum to calculate the subtotals by
more elegant way is to uUse
the Data>Pivot Table function - this is worth exploring
|Watershed Area (Aw)
|Lake Area (AL)
|AW : AL ratio
| Agriculture (%)
How might the differences in water quality between the lakes be related
to differences in land use?
How do you think lake water quality might be related to the Aw:AL ratio?
Use the IMS to look at the lake shorelines. How do you think lake water
quality differences be related to shoreline development?
What would you suggest is the major environmental stress factor to Medicine
Lake? Shagawa Lake?
Part II: Using GIS Tools and Resources on
WOW to Assess Stream and River Systems (optional exercise)
Creek (Duluth, MN) originates in a swamp drainage in a level to rolling
landscape with light agricultural and exurban (between suburbia and ruralia)
land use. It flows along the Duluth-Missabe and Iron Range (DMIR) railyard
in the City of Proctor, just outside Duluth, MN. At the DMIR, taconite
pellets from the Iron Range are transferred to a second set of rail cars
to make the short trip to the ore docks in the Duluth Harbor. The Creek
makes a steep drop to Lake Superior, and flows through the Lake Superior
Zoo, where the DuluthStreams Stream Monitoring Unit (SMU )is located.
From there it is <1 km to its discharge into the St. Louis Estuary/Duluth
Harbor in the western arm of Lake Superior.
Kingsbury Creek IMS Session contains a number of key spatial data
layers, including roads, hydrography, land use, and a recently developed
impervious surface layer. In addition, a set of high resolution air photos
becomes visible when you "zoom in" for a detailed view of the
Use the IMS tool to follow Kingsbury Creek from its origin in Mogie Lake,
through Proctor, and down to the Zoo. By turning different layers on and
off, you can get a good idea of what the dominant impairments to this
urban stream might be. List the dominant features you have observed.
Select "Real-time Data" as the Active Layer. Using the Hyperlink
click on the Stream Monitoring Site at the Lake Superior Zoo. This will
launch the Data Visualization Tool in a separate window. Scroll through
the Summer 2003 data and locate a storm event.
How do the various water quality parameters change in response to a rainfall?
What aspects of land use might be responsible for these changes?