The fragmentation of river habitats through dams and poorly functioning culverts is one of the primary threats to aquatic species in the United States. The impact of fragmentation on aquatic species generally involves loss of access to quality habitat for one or more life stages of a species. For example, dams and impassable culverts limit the ability of diadromous fish species to reach preferred freshwater spawning habitats from the sea and prevent brook trout populations from reaching thermal refuges.

This app can be used to explore the barriers to aquatic connectivity -- dams and road stream crossings -- in the state of Maine.

Begin by selecting a prioritization scenario to display and region to zoom to. The five scenarios to choose from include alewife, American shad/blueback herring, salmon, coastal anadromous fish, and inland brook trout. The results can be displayed relative to the entire state, or only relative to that region using the "Statewide" or "Region" buttons. If the results are displayed relative to the region, only barriers within that region will be prioritized.

Interpreting the barrier data & results

When the "Explore" tab is open and a barrier is clicked, the name of the barrier, it's unique identifier, and other identifying information about the barrier are displayed on the left side of map. A Tier 1 barrier is a higher priority -- most potential gained from a passage restoration project -- while a Tier 3 barrier is a lower priority.

Below the barrier's identifying information, several of the barrier’s attributes are displayed using sliders. These sliders are designed to provide a quick and intuitive way to visualize the relative performance of a barrier versus the other barriers in the scenario. Each slider bar is arranged so that values that are desirable in a passage restoration project are on the right side of the bar. For example, a barrier that has the potential to open up 200 miles of habitat would have a value towards the right side of the slider bar since opening up a lot of upstream habitat is desirable in a passage restoration project for diadromous fish.

The slider bars are set up relative to the other barriers in the scenario. Thus, using the example from above, if the "best" barrier in the currently displayed prioritization would open up 200 miles of river habitat, its metric bar for Upstream Functional Network would be all the way to the right. The real-world value for each metric is displayed above each metric bar, along with a link to a description of the metric.

Several metrics are derived from the 'passability' score of a barrier. This score ranges from 0-1 where 0 is a complete barrier (e.g. a dam with no fish passage or a culvert with an outlet perch) and 1 is fully passable (e.g. a bridge with ample span). Details on the methods that were used to develop the passability score are details here.

Additional instructions on the use of the tool can be found in the tool user's guide or project report.

The custom analysis functionality allows users to run a prioritization using parameters of their choosing. The questions in the "Run a Custom Analysis" pane step through the available input parameters. Clicking on any of the questions will expand the input dialogs.

Filtering the Input Barriers

The input barriers for an analysis can be filtered based on geography (e.g. town, county, watershed) or other attributes (e.g. passability, barrier type). Filtering the barriers limits which barriers are included in the prioritization analysis. However, barriers that are excluded from the analysis through an input filter are still “present” through their effect on other barriers in the metric values. If, for example, a filter is applied to prioritize only barriers in Piscataquis County the results will include only those barriers in within the county. However, the “Count of Downstream Barriers,” for barriers in Piscataquis County will still include the mainstem dams in Penobscot County.

Weighting Metrics

The metrics which underlie the prioritization can be selected by assigning relative weights to them. The weights applied to each metric indicates the relative importance of the metric in a given prioritization scenario. The consensus diadromous fish scenario uses a set of weights selected by The Nature Conservancy and partners, but alternate scenarios could be developed using different metrics and weights, to reflect different objectives. For example, if the primary objective is simply to maximize the number of open upstream river miles, then 100% of the weight could be applied to “Upstream Functional Network Length.” The results of this prioritization would be analogous to sorting the barriers so that the one with the longest upstream functional network was on top.

Metrics are weighted by simply typing in a value between 0 and 100 in the input box next to the metric name. Clicking on a metric name opens a pop-up window with a simple description of the metric, its source data and units. A running tally of metric weights is provided and a warning message will appear if the weights do not sum to 100. Metrics are divided into five categories to provide a logical organization of metrics. However, the grouping has no bearing on the prioritization and the total metrics weights (which must = 100) can be spread across the metric categories in any manner desired.

Implicit in the prioritization is the idea that for each metric, either large values are desirable or small values are desirable. Generally speaking, “Upstream Functional Network Length” is a metric where large values are desirable in a potential passage project – the intent is to open up the most upstream miles of river habitat. In this case, the metrics are sorted in descending order where large values rank at the top. Conversely, the number of downstream barriers is a metric where small values are generally desirable – the intent is to open habitat that is in a more natural state to support healthy fish populations. In this case, the metric is sorted in ascending order where small values rank at the top. The sort order for each metric is described in the metric description slide which can be access by clicking on a metric name.

Model Barrier Removal

One or more barriers can be selected for “removal” when a prioritization is run. Doing so recalculates new metric values as if the selected barriers do not exist. This functionality can be useful for several reasons. First, it allows users to assess the impact of a proposed project on the priorities of the remaining barriers in the network. By removing a barrier, it becomes possible to see, for example, that the next upstream barrier becomes a priority.

Second, it can be used to address known data errors in an analysis. For example, if a user with first-hand knowledge of a particular barrier knows that it is actually not a barrier, then it can be removed and the priorities of the remaining barriers more accurately assessed. Removing a barrier in this fashion does not update the input database. The removal only persists for the duration of the user’s session. Future version of the tool may include functionality to directly incorporate user edits.

Third, and perhaps more importantly, removing barriers before running a custom prioritization can be used to assess potential projects that may include a series of barrier removals. This can be useful when a series of barriers are individually relatively low priorities, but when treated together may be a higher priority.

To select barrier for modeled removal, the "Show Selection Barriers" button can be clicked. This will load all barriers symbolized as black points. Clicking a point will add the ID of the selected barrier to the text input. Up to 10 barriers can be selected in this fashion. Alternately, if the barrier IDs are known, they can be pasted into the input box wrapped in single quotes and comma separated.

Summary Statistics

Optionally, summary statistics can be produced for the custom prioritization scenario results. These summary statistics can be used to evaluate and make relative comparisons between different geographies (e.g. town, county, watersheds). If summary statistics are desired, select the option to do so. This will reveal options to generate summary statistics for either the Result Tier or the Final Rank (the un-binned sequential results). The output table enables users to makes statements such as “Watershed X has a mean Tier value of 8 while Watershed Y has a mean Tier value of 5.” From this statement we can deduce that Watershed Y has more barriers with greater potential to benefit the target of interest, based on the metric weights chosen by the user, than Watershed X.