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.
- Sign in to your ArcGIS organizational account.
If you don't have an organizational account, you can sign up for an ArcGIS free trial.
- Go to the Connect Streams for Salmon Migration web map.
- Click the thumbnail to open the map.
Alternatively, you could click the Open in Map Viewer button.
The map opens to the Canadian province of Nova Scotia.
You've been assigned to search for a potential fishway location on the Mersey River Watershed, 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 save your own copy of the map to make changes to it.
- On the ribbon, click the Save button and choose Save As.
- In the Save Map window, in the Title box, type Mersey River Watershed - Candidate Fishway Locations. Leave the tags unchanged.
- For the summary, type This map was created to assess candidate dams for fishway construction in the Mersey River, Nova Scotia, Canada.
- Click Save Map.
The map's name change is reflected at the top of the page. The map is saved to My Content, which you can access from the content page.
Inspect dams for fishway suitability
You'll now use the ArcGIS 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 will zoom to the study area to begin your analysis.
- In the Legend pane, click the Content button.
- In the Content pane, point to the Mersey River Watershed layer. Click the More Options button and choose Zoom to.
The map zooms to the Mersey River Watershed.
You'll want to return to this view, so you'll save it as a bookmark.
- On the ribbon, click Bookmarks and choose Add Bookmark.
- Type Mersey River Watershed in the text box and press Enter.
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.
- Press the Shift key while you draw a box around the red dam at the southern extent of the watershed (dam 1).
To help you zoom to the appropriate dams, turn on numbered labels for the Dams layer: Point to the Dams layer, click the More Options button, and choose Create Labels. In the Label Features pane, for Text, choose Dam ID. Change the font size to 18 and the color to white or yellow, and then click OK.
The map zooms in, and now you can see more detail in the imagery layer.
At this scale, you cannot easily decide if the dam has a possible impact on fish passage, so you will zoom in farther.
Satellite imagery is updated periodically, so the images on your computer may differ.
- Click the dam to open its pop-up.
- In the pop-up, click Zoom to.
- 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.
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.
- Zoom to the Mersey River Watershed bookmark, and then zoom in to dam 2.
The second dam 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.
- Zoom to the Mersey River Watershed bookmark, and then zoom in to dam 3.
The third dam 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.
- Zoom to the Mersey River Watershed bookmark, and then zoom in to dam 4.
The fourth dam 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 the third dam to investigate.
- Zoom to the Mersey River Watershed bookmark, and then click dam 3 to open its pop-up. In the pop-up, click Zoom to, and then close the pop-up.
- 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?
- Pan south of the river island.
You'll notice a branch of the river that deviates from the main channel. If you follow this branch upstream, it reconnects with the main branch west of dam 3.
- Zoom to the Mersey River Watershed bookmark.
- Continue the process of navigating upstream to visually inspect the dams for fishways or natural channels that enable fish passage.
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.
- Zoom to the Mersey River Watershed bookmark.
- 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 from dams
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.
- If necessary, open your Mersey River Watershed - Candidate Fishway Locations map from My Content.
- Zoom in to dam 5, and ensure that no other dam features are visible in your current extent (you want to calculate the watershed using only the data that is visible in the map).
- In the Contents pane, point to the Mersey River Dams layer and click the Perform Analysis button.
You can also access the Perform Analysis pane by clicking the Analysis button on the ribbon.
- In the Perform Analysis pane, click Find Locations and click Create Watersheds.
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).
- In the Create Watersheds pane, verify that the point feature layer is set to Mersey River Dams.
- Set the search distance as 0.
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.
To learn more, click the information buttons next to the Create Watersheds tool and its parameters.
- Name the result layer Watershed Dam 5 and add your name or initials to make it unique in the organization.
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.
- Verify that the Use current map extent box is checked.
Running the analysis with this box checked ensures that the analysis is completed only on the desired dam (the one shown in the current map extent).
- Click Run Analysis.
- When the operation finishes, zoom to the Mersey River Watershed bookmark.
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 will remove it.
- In the Contents pane, point to the Watershed Dam 5 Adjusted Points layer. Click the More Options button and choose Remove.
- Point to the Watershed Dam 5 layer, click the More Options button, and choose Rename. In the Rename window, remove your name or initials from the layer name and click OK.
Notice that 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 will 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.
- Create another watershed using dam 6. (Repeat steps 2 through 12, substituting dam 6 in each instance where dam 5 is mentioned.)
- Zoom to the Mersey River Watershed bookmark if necessary.
Your map contains two watershed layers symbolized in cyan blue. Both dams are on the same river, so they will have similar upstream drainage areas.
- In the Contents pane, uncheck the box next to the Watershed Dam 5 layer, and then check it again to switch it off and on.
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.
- Save the map.
Overlay layers to find the difference in watershed area
In the previous section, you 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 will isolate this region using the Overlay Layers tool.
- In the Contents pane, point to the Watershed Dam 5 layer and click the Perform Analysis button.
- In the Perform Analysis pane, click Manage Data and click Overlay Layers.
- In the Overlay Layers pane, choose Watershed Dam 5 as the input layer.
- Choose Watershed Dam 6 as the overlay layer.
- Choose Erase as the overlay method.
- Change the result layer name to Difference in Watershed Area and add your name or initials to make it unique in the organization.
- Click Run Analysis.
When the operation finishes, a feature layer that represents the difference in watershed area is added to the map.
- Remove your name or initials from the name of the new layer.
- Zoom to the extent of the new feature.
- Remove the Watershed Dam 5 and Watershed Dam 6 layers.
- If you turned on numbered labels for the Dams layer earlier, turn them off:
- Point to the Dams layer, click the More Options button, and choose Manage Labels.
- In the Label Features pane, uncheck the Label Features box, and click OK.
- 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. In this section, you'll add hydrology data for all freshwater features found within the Mersey River Watershed to your map.
- On the ribbon, click Add and choose Search for Layers.
- In the Search for Layers pane, in the Find box, type Mersey Hydrology. To limit the search results to layers owned by Learn_ArcGIS, add owner:Learn_ArcGIS to the Find box.
- For the In setting, choose ArcGIS Online.
- In the list of results, locate the layer named Mersey Hydrology by Learn_ArcGIS and click Add.
After the layer draws, you can see that the layer contains hydrology features that are within the Mersey River Watershed boundary, such as rivers, streams, and lakes.
The default symbology makes it difficult to distinguish between the Difference in Watershed Area layer and the Mersey Hydrology layer.
- Click the back arrow to return to Content.
- In the Content pane, point to the Difference in Watershed Area layer and click the Change Style button.
- In the Change Style pane, for a drawing style, under Location (Single symbol), click Options.
- Click Symbols.
- At the top of the symbol window, confirm that the Fill property is selected. On the color palette, click a light orange color.
- At the top of the symbol window, click Outline.
- On the color palette, click a darker orange color, and click OK.
- In the Change Style pane, click OK and click Done.
- 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.
- In the Contents pane, point to the Mersey Hydrology layer and click the Filter button.
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).
Expressions use the general form of <Field name> <condition> <Value or Field>.
- In the Filter window, ensure that Feature Code is set in the list of field names.
- Leave the condition set to is.
- Under the input box for attribute values, choose Unique.
This provides a list of valid attribute values for the selected field.
- From the list of attribute values, choose WARV50 (a coded value for small streams).
- Click Add another expression.
Another query box is added to the Filter window.
- Build another expression and set the Feature Code attribute value to WARV55 (another coded value for small streams).
- Above the query boxes, change the query expression match type from All to Any.
Changing All to Any means that features that are either WARV50 or WARV55 will display in the map when you apply the filter.
- Click Apply Filter.
Notice that the map displays fewer hydrology features: only small streams, which are most suitable for Atlantic salmon spawning.
- Change the name of the Mersey Hydrology layer to Mersey River Streams.
- 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.
- In the Contents pane, point to the Difference in Watershed Area layer and click the Perform Analysis button.
- Click Summarize data and click Summarize Within.
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.
- In the Summarize Within pane, verify that the Difference in Watershed Area layer is set for the first parameter (the boundary).
- Choose Mersey River Streams as the layer to summarize.
- For Length of lines, choose Kilometers.
This check box 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 this optional setting.
- Change the result layer name to Potentially Accessible Streams and add your name or initials to make it unique in the organization.
- Click Run Analysis.
A new point layer appears in the map. Its table stores the summary information that you want, which you can also see in the legend.
- In the Contents pane, point to the Potentially Accessible Streams layer and click the Show Legend button.
The legend appears in the Contents pane.
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 in your map.
- In the Contents pane, point to the Difference in Watershed Area layer. Click the More Options button and choose Create Labels.
- In the Label Features pane, for Text, choose New Expression.
A Custom window appears with a script area and functions to build a custom label.
- In the Expression box, type "Fishway opens 24.44 km salmon spawning habitat" (make sure to include the quotations marks). Click Test.
A result box appears to confirm that your custom label is valid.
- Click OK.
The label is added to the map, but it's difficult to read against the imagery. You'll change the label style so it's easier to see at all map extents.
- Change the font color to white.
- Click OK.
- Remove the Potentially Accessible Streams layer (it's no longer needed now that you’ve labeled the map with the summary information).
- In the Contents pane, drag the Dams layer to the top of the layer list.
- 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.