Find a location for the proposed fishway

You'll examine each of the dams on the Mersey River to determine which is most suitable for a new fishway. You've been provided with data for dams in the Mersey River Watershed, but it's possible that the data has not been updated to reflect upgrades to old dams. You'll open a map that contains dam locations, and aerial imagery from ArcGIS Online. In many locations, the imagery will allow you to determine if a dam was constructed with a fishway.

Open and save the map

First, you'll open a map of the Mersey River Watershed.

  1. Go to the Mersey River Dams web map.
  2. Click the thumbnail.

    Mersey River Dams map thumbnail

    The map opens. It shows the Canadian province of Nova Scotia.

    Default map

    You've been assigned to search for a potential fishway location on the Mersey River Watershed layer, which is outlined in yellow (a watershed is the area of land within whose boundaries all water drains to the same final location). The dams on the main branch of the river are symbolized in blue and red. Blue indicates a fishway is present; red indicates that there is no fishway.

    You'll sign in (if you aren't already) and save your own copy of the map to make changes to it.

    Note:

    Depending on your organizational and user settings, you may have opened Map Viewer. ArcGIS Online offers two map viewers for viewing, using, and creating maps. For more information on the map viewers available and which to use, please see this FAQ.

    This lesson uses Map Viewer Classic.

  3. If necessary, on the ribbon, click Open in Map Viewer Classic.

    Map Viewer Classic opens.

  4. If necessary, on the ribbon, click Sign In. Sign in to your ArcGIS organizational account.
    Note:

    If you don't have an organizational account, you can sign up for an ArcGIS free trial.

  5. On the ribbon, click the Save button and choose Save As.

    Save As option

  6. In the Save Map window, for Title, type Mersey River Watershed - Candidate Fishway Locations.
  7. For Summary, type This map was created to assess candidate dams for fishway construction in the Mersey River, Nova Scotia, Canada.

    Save Map window

  8. Click Save Map.

    The map is saved to your Content page. The map's name change is reflected at the top of the page.

Inspect dams for fishway suitability

Next, you'll use the World Imagery Basemap to examine each dam on the Mersey River. You're particularly interested in dams that are symbolized as having no fishway (red points), but you'll examine the imagery surrounding all the dam sites for a clear assessment of fish passage upstream. You'll zoom to the study area to begin your analysis.

  1. In the Details pane, click the Content button.

    Content button

  2. In the Contents pane, point to the Mersey River Watershed layer. Click the More Options button and choose Zoom to.

    Zoom to option

    The map zooms to the Mersey River Watershed.

    Mersey River Watershed

    You'll want to return to this view, so you'll save it as a bookmark.

  3. On the ribbon, click Bookmarks and choose Add Bookmark.

    Add Bookmark option

  4. Type Mersey River Watershed in the text box and press Enter.

    Mersey River Watershed added to Bookmarks

    From the current extent, aquatic connectivity along the Mersey River is troubling. Dams located closer to the outlet of the watercourse have a greater impact on stream connectivity than those located farther upstream. Two dams without fishways are located near the outlet of the river where the Mersey River meets the Atlantic Ocean. These two dams could potentially restrict fish passage up the entire river. You'll inspect the imagery to see if dams have been upgraded with fishways.

  5. Point to the Mersey River Dams layer, click the More Options button, and choose Create Labels.

    Create Labels option for the Mersey River Dams layer

  6. In the Label Features pane, for Text, choose Dam ID. Change the font size to 18 and the color to yellow.

    Label Features pane with label text, size, and color changed

  7. Click OK

    The dams are labeled. Next, you'll zoom to the first dam.

  8. Press the Shift key while you draw a box around Dam 1, the red dam at the southern extent of the watershed.

    Dam 1 on the map

    The map zooms in and you can see more detail in the imagery layer.

    Dam 1 in detail

    Note:

    Satellite imagery is updated periodically, so your map may differ from the example images.

    At this scale, you cannot easily decide if the dam has a possible impact on fish passage, so you'll zoom in farther.

  9. Click the dam to open its pop-up.
  10. In the pop-up, click Zoom to.

    Zoom to option

  11. Close the pop-up and, if necessary, zoom out one or two levels so you can see the holding pond to the right of the dam.

    Dam 1 in more detail

    While this dam is on the Mersey River, it appears to create a holding pond rather than block the entire river. You're concerned with dams that block the main branch and tributaries (smaller streams that feed into the main branch of the river).

    Next, you'll examine the second dam to learn how to visually identify a fishway in the imagery.

  12. Zoom to the Mersey River Watershed bookmark and zoom in to Dam 2.

    Dam 2 in detail

    Dam 2 is symbolized as having a fishway. If you take a closer look at the imagery, it's possible to see a fishway northeast of the point feature.

  13. Return to the Mersey River Watershed bookmark and zoom in to Dam 3.

    Dam 3 in detail

    Dam 3 is symbolized as having no fishway. Upon taking a closer look at the imagery, you can confirm there is no visible fishway at this location. Without a fishway, it seems that Atlantic salmon would not be able to access areas upstream from this dam.

  14. Return to the Mersey River Watershed bookmark and zoom in to Dam 4.

    Dam 4 in detail

    Dam 4 is symbolized as having a fishway. If you take a closer look at the imagery, you can confirm there is a fishway north of the dam.

    Why would engineers spend time, money, and energy to construct a fishway that fish can't access from downstream locations? You'll return to Dam 3 to investigate.

  15. Return to the Mersey River Watershed bookmark and zoom in to Dam 3.
  16. Pan and zoom the map to explore the area south of the dam.

    Can you see anything that might explain why a dam with a fishway was built upstream from a dam that restricts fish passage?

    How else could a fish circumvent this barrier?

    A branch of the river deviates from the main channel. If you follow this branch upstream, it reconnects with the main branch west of Dam 3.

    Overflow detail

  17. Return to the Mersey River Watershed bookmark.
  18. One by one, zoom to and examine Dams 5, 6, and 7.

    For each of the three remaining dams, there have been no upgrades to infrastructure. Atlantic salmon migration stops at Dam 5. For this reason, Dam 5 is the most suitable dam on the watershed for fishway construction.

  19. Return to the Mersey River Watershed bookmark.
  20. Save the map.

You've performed a careful visual inspection of each dam in the Mersey River Watershed. You determined which dam is most likely to have the greatest impact on Atlantic salmon migration. You also learned, by comparing your dam data to satellite imagery, that it can take multiple data sources to understand a problem. Without the use of the imagery basemap, it would appear that fish could not navigate past dams 1 or 3. Next, you'll calculate the watershed area that could be made available by constructing a fishway on Dam 5. Then, you'll use the result to summarize a stream dataset to determine the potential amount of accessible salmon spawning habitat.


Quantify the accessible habitat

The construction of a fishway is an expensive process, both in terms of financial requirements and planning effort. Before the construction can be seriously considered, determining the amount of habitat made accessible is paramount. Previously, you identified which dam is the best candidate for constructing a fishway. Now, you'll estimate the amount of salmon spawning habitat that would be made accessible by the proposed fishway.

Create upstream watersheds

Before you can quantify the amount of spawning habitat that would be made accessible by a fishway on Dam 5, you must calculate the watershed area upstream. First, you'll zoom to the dam. You only want to analyze Dam 5, so you'll ensure no other dam features are in the map extent. This way, you can run analysis on only features that are visible on the map.

  1. If necessary, open your Mersey River Watershed - Candidate Fishway Locations map from My Content.
  2. Hold Shift and draw a box around Dam 5 to zoom to it. Ensure that no other dam features are visible in your current extent.

    Dam 5 with no other dam features in the map extent

  3. In the Contents pane, point to the Mersey River Dams layer and click the Perform Analysis button.

    Perform Analysis button

    Tip:

    You can also access the Perform Analysis pane by clicking the Analysis button on the ribbon.

  4. In the Perform Analysis pane, click Feature Analysis.

    Feature Analysis option on the Perform Analysis pane

  5. Expand Find Locations and click Create Watersheds.

    Create Watersheds tool

    The Create Watersheds tool calculates the drainage area of a point based on ArcGIS Online hydrologic data (curated, authoritative data maintained and hosted by Esri).

  6. In the Create Watersheds pane, enter the following parameters:
    • Ensure Point features to use for calculating watersheds is set to Mersey River Dams.
    • For Search distance to nearest drainage, type 0.

    Create Watersheds tool parameters

    The search distance parameter specifies the distance from the point that the tool will search to find the largest drainage line. The dam is located on the river, so a search distance of 0 is appropriate.

    Tip:

    To learn more, click the information buttons next to the Create Watersheds tool and its parameters.

  7. For Result layer name, type Watershed Dam 5 and add your name or initials.
    Note:

    New items created by analysis operations must have unique names within your ArcGIS Online organization; otherwise, their URLs will conflict. Once the layer has been created, you can rename it in your map.

    You'll also ensure that you run the analysis only on features in the current map extent. This way, you'll only analyze Dam 5.

  8. Verify that the Use current map extent box is checked.

    Use current map extent box

  9. Click Run Analysis.
  10. When the tool finishes running, zoom to the Mersey River Watershed bookmark.

    Watershed upstream of Dam 5

    Two new layers are added to the map: the watershed layer and an adjusted points layer. The adjusted points layer contains the actual location used to calculate the watershed. This layer is not necessary for future analysis, so you'll remove it.

  11. In the Contents pane, point to the Watershed Dam 5 - Adjusted Points layer. Click the More Options button and choose Remove.

    Remove option for the Watershed Dam 5 - Adjusted Points layer

  12. In the Remove window, click Yes, Remove Layer.
  13. Point to the Watershed Dam 5 layer, click the More Options button and choose Rename. In the Rename window, remove your name or initials and any underscores and click OK.

    Calculating the watershed area upstream from Dam 5 includes the area upstream from Dams 6 and 7. Fish that bypass Dam 5 will be restricted by Dam 6 and will not have access to that area. You'll also calculate the watershed area upstream from Dam 6, so you can identify the difference—only the watershed area that fish could access if a fishway is constructed on Dam 5.

  14. Zoom in to Dam 6 until no other dams are in the map extent. In the Contents pane, point to the Mersey River Dams layer and click the Perform Analysis button.
  15. In the Perform Analysis pane, click Feature Analysis. Expand Find Locations and click Create Watersheds.
  16. For Search distance to nearest drainage, type 0. For Result layer name, type Watershed Dam 6 and add your name or initials.
  17. Confirm that Use current map extent is checked and click Run Analysis.

    The tool runs and the watershed for Dam 6 is added to the map.

  18. Remove the Watershed Dam 6 - Adjusted Points layer and rename the Watershed Dam 6 layer to remove your name or initials and any underscores.
  19. Navigate to the Mersey River Watershed bookmark.

    Watershed layers for Dam 5 and Dam 6 on the map

    Your map contains two watershed layers symbolized in cyan blue. Both dams are on the same river, so they have similar upstream drainage areas. The area that would be made accessible by a fishway is in the southern extent of the watershed, where the two watershed layers do not overlap.

  20. Save the map.

Find the difference in watershed area

You've identified your area of interest as the difference between the watersheds of Dams 5 and 6. To determine how much salmon spawning habitat would be made available, you'll isolate this region using the Overlay Layers tool.

  1. In the Contents pane, point to the Watershed Dam 5 layer and click the Perform Analysis button.
  2. In the Perform Analysis pane, click Feature Analysis. Expand Manage Data and click Overlay Layers.

    Overlay Layers tool

  3. In the Overlay Layers pane, for Choose input layer, ensure Watershed Dam 5 is chosen. For Choose overlay layer, choose Watershed Dam 6.

    Overlay Layers tool input and overlay parameters

  4. For Choose overlay method, click Erase.

    Choose overlay method parameter

  5. Change Result layer name to Difference in Watershed Area and add your name or initials.
  6. Click Run Analysis.

    When the tool finishes, the result layer is added to the map.

  7. Rename the Difference in Watershed Area layer to remove your name or initials and any underscores.
  8. Point to the Difference in Watershed Area layer, click the More Options button, and click Zoom to.

    Now that you've determined the area where the watersheds for Dam 5 and 6 overlap, you no longer need the Watershed Dam 5 and Watershed Dam 6 layers.

  9. In the Contents pane, remove the Watershed Dam 5 and Watershed Dam 6 layers.

    Difference in watershed area on the map

    You'll also turn off the dam labels.

  10. Point to the Mersey River Dams layer, click the More Options button, and choose Manage Labels.
  11. In the Label Features pane, uncheck the Label Features box.

    Label Features box in the Label Features pane

  12. Click OK.
  13. Save the map.

Add the hydrology feature layer

You've isolated the watershed area upstream from Dam 5 that would be made accessible if a fishway was constructed. However, for Atlantic salmon conservation, the item of importance is not watershed area but the amount of freshwater streams available for spawning. You'll add hydrology data for all freshwater features found within the Mersey River Watershed to your map.

  1. On the ribbon, click Add and choose Search for Layers.

    Search for Layers options

  2. Click My Content and choose ArcGIS Online.

    ArcGIS Online option

  3. In the search bar, type Mersey Hydrology. To limit the search results to layers, add owner:Learn_ArcGIS and press Enter.

    Search bar

  4. In the list of results, for the Mersey_Hydrology layer, click the Add button.

    Add button for the Mersey_Hydrology layer

    The Mersey_Hydrology layer is added to your map. The layer contains hydrology features that are within the Mersey River Watershed boundary, such as rivers, streams, and lakes.

    Mersey hydrology layer

    The default symbology makes it difficult to distinguish between the Difference in Watershed Area layer and the Mersey_Hydrology layer.

  5. Click the Back button to return to the Contents pane.
  6. In the Contents pane, point to the Difference in Watershed Area layer and click the Change Style button.

    Change Style button

  7. In the Change Style pane, under Select a drawing style, for Location (Single symbol), click Options.

    Change Style pane

  8. Click Symbols.

    Symbols button

  9. On the color palette, click the light orange color in the second row, fifth column.

    Light orange fill color

  10. Click the Outline tab. On the color palette, click the darker orange color in the fourth row, fifth column.

    Dark orange outline

  11. Click OK.

    The symbology for the Difference in Watershed Area layer is updated.

    Overlay feature with updated symbology

  12. In the Change Style pane, click OK and click Done.
  13. Save the map.

Filter the hydrology data

In this scenario, you're interested in identifying features that could represent potential high-quality salmon spawning habitat. Atlantic salmon favor cool freshwater streams with silt-free substrate and fast-flowing, oxygen-rich water. To show features that best represent this habitat, you'll filter the Mersey Hydrology layer.

A filter uses logical expressions to find features in a layer based on attribute values in its table. The features of interest will appear on the map; all the others will be hidden (but not deleted).

  1. In the Contents pane, point to the Mersey Hydrology layer and click the Filter button.

    Filter button

    To filter the layer, you'll create an expression. Expressions use the general form of <Field name> <condition> <Value or Field>.

  2. In the Filter window, ensure that Feature Code is set in the list of field names and leave the condition set to is.
  3. Under the input box for attribute values, choose Unique.

    Unique option

    You can now choose from a list of valid attribute values for the selected field.

  4. From the list of attribute values, choose WARV50 (a coded value for small streams).
  5. Click Add another expression.

    Add another expression option

    Another query box is added to the window.

  6. Build another expression and set the Feature Code attribute value to WARV55 (another coded value for small streams).

    The filter query expression is currently set to Display features in the layer that match all of the following expressions. Because you want to filter for any features that have the WARV50 or the WARV55, you will update the match type to display features that match any of the expressions instead of all.

  7. Above the query boxes, change the query expression match type to Display features in the layer that match any of the following expressions.

    Display features in the layer that match any of the following expressions option

  8. Click Apply Filter.

    The map now displays fewer hydrology features: only small streams, which are most suitable for Atlantic salmon spawning.

    Filter applied on the map

  9. Rename the Mersey Hydrology layer to Mersey River Streams.
  10. Save the map.

Summarize the potential spawning habitat

Now that you've added the hydrology layer and filtered the data to extract the habitat that is most suitable for salmon spawning, you'll summarize the amount of habitat made available with the construction of a fishway.

  1. In the Contents pane, point to the Difference in Watershed Area layer and click the Perform Analysis button.
  2. In the Perform Analysis pane, click Feature Analysis. Expand Summarize Data and click Summarize Within.

    Summarize Within tool

    The Summarize Within tool generates statistics on features that fall within the boundary of a polygon layer. You'll calculate the total length of streams within the boundary of the Difference in Watershed Area layer.

  3. In the Summarize Within pane, for Choose an area layer to summarize other features within its boundaries, confirm that Difference in Watershed Area is selected.
  4. For Choose a layer to summarize, confirm that Mersey River Streams is selected.
  5. For Length of lines in, choose Kilometers.

    Summarize Within tool parameters

    This parameter will calculate the total length of the line features in the area boundary.

    You do not need to choose a field to group by because you've already filtered your data to only include streams, so you'll skip the Choose field to group by step.

  6. For Result layer name, type Potentially Accessible Streams and add your name or initials to make it unique in the organization.
  7. Click Run Analysis.

    The tool runs. When it finishes, a new layer is added to the Contents pane. The attribute table for the new layer stores the summary information that you want, which you can also see in the legend.

  8. Rename the Potentially Accessible Streams layer to remove your name or initials and any underscores.
  9. Point to the Potentially Accessible Streams layer and click the Show Legend button.

    Show Legend button

    The legend appears.

    Legend containing the summarized stream length

    More than 24 kilometers of freshwater streams would be made available by the construction of a fishway on Dam 5. Now that you've determined the total amount of habitat made available, you'll label this information in your map.

  10. In the Contents pane, point to the Difference in Watershed Area layer. Click the More Options button and choose Create Labels.
  11. In the Label Features pane, for Text, choose New Expression.

    New Expression option

    An expression editor window appears with a script area and functions to build a custom label.

  12. In the Expression box, type or copy and paste "Fishway opens 24.44 km salmon spawning habitat" (make sure to include the quotation marks).

    Custom label expression

  13. Click Test.

    The Results window appears to confirm that your custom label is valid.

    Results window confirmation

  14. Click OK.

    The label is added to the map, but it's difficult to read against the imagery.

    Unformatted label in map

    You'll change the label style so it's easier to see at all map extents.

  15. In the Label Features pane, change the font color to white. For Halo, change the color to black.

    Label Features window

  16. Click OK.

    You no longer need the Potentially Accessible Streams layer now that you've labeled the map with the summary information.

  17. Remove the Potentially Accessible Streams layer.

    The Mersey River Dams layer is currently not as visible because the watershed layers are above them. You'll reorder the layers.

  18. In the Contents pane, drag the Mersey River Dams layer to the top of the layer list.

    The Contents pane with highlights showing how to reorder the layers

    The Mersey River Dams layer is now visible on top of the Difference in Watershed Area layer.

    Formatted label in map

  19. Save the map.

In this lesson, you visually examined a series of dams on the Mersey River and learned to use aerial imagery to find a good candidate location for a new fishway. You used analysis tools to create upstream watershed areas from river barriers, determined the area that salmon could potentially access via a new fishway, and calculated the amount of habitat available within this area. Finally, you labeled your map to clearly display your findings.

Having completed this exercise, you've learned to derive a simple estimate of available aquatic habitat. Although detailed field surveys, habitat assessments, and local analysis would be required, this initial work you've completed today represents an important first step in the funding application process.

You can find more lessons in the Learn ArcGIS Lesson Gallery.