Introduction to Stream Continuity and Fish Passage:
Stream ecosystems are dynamic environments. Many species inhabit streams, and many others in nearby forests rely on stream ecosystems. These ecosystems also play an important role in the global marine ecosystem, as many fish species make seasonal habitat, feed or spawn, in streamed environments.
Central to the health of stream ecosystems is the interconnectedness of the various streams in a watershed (MRP, 2005). Continuity in a stream environment allows for species the dwell within the stream medium to access all areas of the watershed. While barriers to continuity do affect riparian animals such as amphibians, reptiles, and small mammals, they generally have a greater effect on fish populations.
Fish rely on stream continuity for a number of essential life-cycle activities (MRP, 2005):
- Access to Coldwater Habitats:
In the summer months, some fish species will converge onto areas within stream ecosystems that provide a cooler environment. Some that cannot access these areas and relieve themselves from heat stress can be killed.
- Access to Feeding Areas:
Fish species often rely on specific areas within a watershed (wetlands for abundant levels of insects, for example) for food.
- Access to Breeding and Spawning Areas:
Many fish species travel far upstream to spawn. It is often the case that the further upstream the fish can migrate, the less chance for predators to reach them during spawning, or they’re offspring. It is, therefore, essential for fish species to have access to upstream habitat.
Culverts as Potential Barriers to Fish Passage:
Barriers to fish connectivity have been identified as a significant factor contributing to global fish population declines (Roni, et al., 2002). Barriers to fish passage often occur at road-stream intersections (Thompson & Rahel, 1998). Most often, the road crossing is built over the stream. This is done with either a bridge or a culvert (the rare exception being underground road tunnels).
Culverts are tunneling structures that allow a stream to pass underneath a road crossing. The general structure of most culverts is a pipe built into or underneath the road structure above (can also be made from concrete, brick, wood, etc.). It is intended that the stream continue through the culvert in the downstream direction. Culverts generally have a greater impact on stream connectivity than bridges. Unfortunately, road crossings are more often culverted because they are generally less expensive to construct (Gibson et al., 2005).
Culverts can be barriers to fish passage for a number of reasons. They can be “hung” such that they’re elevated too high above the natural stream level and fish cannot swim or jump into the structure. In some cases the stream velocity is too high for passage. Or there may not be the proper substrate to accommodate passage.
A single improperly installed or maintained culvert can impact a very large area of potential fish habitat. For example, it would only take one impassable structure near the mouth of the main river in a watershed for the entire watershed to be rendered inaccessible. The same situation can be applied to smaller scales (inaccessible habitat in upstream tributaries, etc.). The probability that a fish individual encounters an impassable culvert increases as the individual travels upstream. Unfortunately, as previously mentioned, these upstream habitat areas are often critical spawning habitat.
There are three broad issues with culvert designs that lead to the structure being a barrier to fish passage.
A detailed assessment of the culvert type, and of the criteria associated with the listed design issues, is required to conclude whether a specified culvert is a barrier to fish passage (MRP, 2005):
- Undersized Crossings:
Culverts that are not wide enough in diameter (as compared to the natural stream width) restrict the flow within the structure. This can cause many problems, including high flow velocity, erosion and outlet scouring, and upstream flooding or ponding.
- Shallow Crossings:
Culverts that are too shallow may not have a water medium deep enough for fish to pass through. Also, shallow crossings may not meet the required amount of bed material as natural substrate. Ideally, culverts should have an open bottom, or be submerged into the ground at the level of the stream bed.
- Perched Crossings:
Perched crossings are crossings that sit above the level of the stream at the downstream/outlet end of the culvert. Perching can inhibit fish crossing since they simply cannot swim through the crossing. The leaping ability of a fish is also taken into consideration when assessing the perch height of a culvert. Perching can occur from improper installation, or from gradual scouring at the outlet (potentially because of under-sizing).
Application to the Sackville River Watershed:
The Sackville Rivers Association is continuously working to protect and where necessary restore the environment of the SRW. Stream continuity is an essential aspect of the health of the ecosystem. The work of this culvert assessment will aid in assessing and restoring the health of the SRW ecosystem.
According to Mr. Walter N. Regan, President of the SRA, there are likely thousands of culverts in the SRW. This region is one of the fastest growing areas in the province. This project should provide a good indication of the types of culverts that are installed in the area, the quality of those culverts in terms of fish passage, and spatial range of fish in the watershed.
The main goal of this project is to gain a greater understanding of the spatial range of fish species in the SRW. This will be accomplished by developing a catalogue and quality assessment of fish passages (culverts) in the watershed. below are the culverts we have surveyed so far.
Following the initial cataloging and assessment, the SRA will: develop a final report discussing the findings, assess the health of the SRW from a spatial availability standpoint, and proceed with any potential remediation projects. A final map will also be developed (1:50,000?) that will identify all of the field sites visited, with some sort of scheming to
Installed Culverts Properly, and improperly
Culvert Bridge Drawing Plans
Take a look at the scaled drawing plans for the culvert bridge by KFC on Sackville Drive.