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 whether a dam was constructed with a fishway.
Open and save the map
First, you'll open a map of the Mersey River Watershed.
- Go to the Mersey River Dams web map.
- Click the thumbnail.
The map opens. It shows the Canadian province of Nova Scotia.
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 haven'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 Classic. 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 tutorial uses Map Viewer.
- If necessary, in the pop-up window, click Open in Map Viewer or on the ribbon, click Open in Map Viewer.
Map Viewer opens.
- If necessary, on the ribbon, click Sign In. Sign in to your ArcGIS organizational account.
Note:
If you don't have an organizational account, see options for software access.
- On the Contents (dark) toolbar, click the Save and open button and choose Save as.
- In the Save map window, for Title, type Mersey River Watershed - Candidate Fishway Locations.
- For Summary, type This map was created to assess candidate dams for fishway construction in the Mersey River, Nova Scotia, Canada.
- Click Save.
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.
- In the Layers pane, point to the Mersey River Watershed layer. Click the 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 Settings toolbar, click Bookmarks and choose Add bookmark.
- Type Mersey River Watershed in the text box and click Add.
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 whether dams have been upgraded with fishways.
- On the Contents toolbar, click Layers. Click the Mersey River Dams layer to select it.
- On the Settings (light) toolbar, click the Labels button.
- In the Label features pane, click Add label class. For Label field, choose Dam ID.
- For Label style, click Edit label style.
- In the Label style window, change the font size to 18 and the color to yellow.
- Close the Label style window.
The dams are labeled. Next, you'll zoom to the first dam.
- Press the Shift key while you draw a box around Dam 1, the red dam at the southern extent of the watershed.
The map zooms in and you can see more detail in the imagery layer.
Note:
Satellite imagery is updated periodically, so your map may differ from the example images.
At this scale, you cannot easily decide whether the dam has a possible impact on fish passage, so you'll zoom in farther.
- 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 zoom in to Dam 2.
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.
- Return to the Mersey River Watershed bookmark and zoom in to Dam 3.
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.
- Return to the Mersey River Watershed bookmark and zoom in to Dam 4.
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.
- Return to the Mersey River Watershed bookmark and zoom in to Dam 3.
- 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.
- Return to the Mersey River Watershed bookmark.
- 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.
- Return 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
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.
- If necessary, open your Mersey River Watershed - Candidate Fishway Locations map from My Content.
- Hold Shift and draw a box around Dam 5 to zoom to it. Ensure that no other dam features are visible in your current map extent.
- On the Settings toolbar, click the Analysis button.
- In the Analysis pane, click Tools.
- In the Tools pane, expand 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, for Input point features, click Layer and choose Mersey River Dams.
Tip:
To learn more, click the information buttons next to the Create Watersheds tool and its parameters.
- For Result layer, 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.
- Click Environment settings. For Processing extent, choose Display extent.
- Click Estimate credits.
The Create Watersheds tool doesn't consume credits, but it's always best to check the credit estimate before running an analysis tool. Checking the estimated credits allows you to ensure that the analysis is within your credit budget. If the amount of credits the tool will consume appears higher or lower than expected, the check can also allow you to identify errors in your analysis parameters before you run the tool.
- Click Run.
- When the tool finishes running, zoom to the Mersey River Watershed bookmark.
Two new layers are added to the map as a group layer: 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.
- In the Layers pane, expand the Watershed Dam 5 layer. For the Adjusted Points layer, click the More Options button and choose Remove.
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.
- Zoom in to Dam 6 until no other dams are in the map extent.
- In the Create Watersheds pane, change the Result layer name to Watershed Dam 6 Your Name.
Note:
If you closed the Analysis pane after the Create Watersheds tool finished running, you can access the tool from the History tab. If necessary, reopen the Analysis pane and click the History tab. Next to the Create Watersheds item, click Options and choose Open tool.
- For Environment settings, confirm that Processing extent is set to Display extent and click Run.
The tool runs and the watershed for Dam 6 is added to the map.
- Expand the Watershed Dam 6 group and remove the Adjusted Points layer.
- Navigate to the Mersey River Watershed bookmark.
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.
- 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.
- In the Create Watersheds pane, click the back button and search for the Overlay Layers tool. Open Overlay Layers.
- In the Overlay Layers pane, for Input layer, click + Layer and choose Watershed Dam 5 WatershedFeatures. For Overlay features, choose Watershed Dam 6 WatershedFeatures.
- For Overlay settings, for Overlay type, click Intersect and choose Erase.
- Change Result layer name to Difference in Watershed Area and add your name or initials.
- Click Estimate credits.
The Overlay Layers tool costs credits to run. Credit cost is usually based on the number of input features. Because you have two watershed features, the tool will take 0.002 credits.
- Click Run.
When the tool finishes, the result layer is added to the map.
- For the Difference in Watershed Area layer, click the 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.
- In the Contents pane, remove the Watershed Dam 5 and Watershed Dam 6 layers.
You'll also turn off the dam labels.
- In the Layers pane, click the Mersey River Dams layer to select it. On the Contents toolbar, click the Layers button and turn Enable labels off.
- 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.
- In the Layers pane, click Add.
- In the Add layer pane, click My content and choose ArcGIS Online.
- In the search bar, type Mersey Hydrology. To limit the search results to layers, add owner:Learn_ArcGIS and press Enter.
- In the list of results, for the Mersey_Hydrology layer, click the Add button.
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.
The default symbology makes it difficult to distinguish between the Difference in Watershed Area layer and the Mersey_Hydrology layer.
- Click the Back button to return to the Layers pane.
- In the Layers pane, click the Difference in Watershed Area layer to select it. On the Settings toolbar, click the Styles button.
- In the Styles pane, under Pick a style, for Location (single symbol), click Style options.
- Click Symbol style.
The Symbol style window appears.
- In the Symbol style window, click Fill color. For Hex, type f0ce7d and press Enter.
- Click Done, then click Outline color. For Hex, type cf960e and press Enter.
- Close the Symbol style window. In the Style options pane, click Done two times.
The symbology for the Difference in Watershed Area layer is updated.
- 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.
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).
- In the Layers pane, click the Mersey_Hydrology layer to select it. On the Settings toolbar, click the Filter button.
To filter the layer, you'll create an expression. Expressions use the general form of <Field name> <condition> <Value or Field>.
- In the Filter window, click Add expression.
- For Expression, ensure that Feature Code is set in the list of field names and leave the condition set to is.
- In the value box, click the default value, WABD50 and choose WARV50 (a coded value for small streams).
The results of the filter are shown on the map. The only streams visible are those that meet the criteria of having a Feature Code equal to WARV50.
- Click Add expression.
Another query box is added to the window.
- Build another expression and set the Feature Code attribute value to WARV55 (another coded value for small streams).
Adding the second query makes all the streams disappear from the map. That's because the filter results are currently set to Match all expressions. Because you want to filter for any features that have the WARV50 or WARV55 value, you will update the match type to display features that match at least one of the expressions instead of all.
- Above the query boxes, for Filter results, click Match all expressions and choose Match at least one expression.
- In the Filter pane, click Save.
The map now displays fewer hydrology features: only small streams, which are most suitable for Atlantic salmon spawning.
- 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.
- On the Contents toolbar, click the Analysis button.
- In the Perform Analysis pane, click Feature Analysis. Search for and open the 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.
- In the Summarize Within pane, for Input features, click + Layer and choose Mersey_Hydrology.
- For Summary ares, click + Layerand choose Difference in Watershed Area.
- For Calculate statistics, ensure that the Summarized length units are Kilometers.
This parameter will calculate the total length of the line features in the area boundary.
- For Result layer, type Potentially Accessible Streams and add your name or initials to make it unique in the organization.
- Click Estimate credits. Once you've reviewed the credit consumption, click Run.
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.
- On the Contents toolbar, click the Legend button.
The legend appears.
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.
- On the Contents toolbar, click the Layers pane. Click the Difference in Watershed Area layer to select it.
- On the Settings toolbar, click the Labels button and choose Add Label Class.
- For Label field, click the Expression button.
An expression editor window appears with a script area and functions to build a custom label.
- In the Expression box, delete the text and type or copy and paste "Fishway opens 24.44 km salmon spawning habitat" (make sure to include the quotation marks).
- Click Done.
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.
- For Label style, click Edit label style. Change the font color to white. For Halo, change the color to black.
- Close the Label style window.
You no longer need the Potentially Accessible Streams layer now that you've labeled the map with the summary information.
- 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.
- In the Layers pane, drag the Mersey River Dams layer to the top of the layer list.
The Mersey River Dams layer is now visible on top of the Difference in Watershed Area layer.
- Save the map.
In this tutorial, 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 through 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 tutorials in the tutorial gallery.
