Design parameters

This report provides details of the design of the fish ladder that is planned to be installed at Torrumbarry weir along Murray River. This weir was first constructed in 1924 but it was extensively damaged in 1992 resulting to redesigning and reconstruction. Just like other weirs, Torrumbarry weir hinders natural fish migration in Murray River thus the fish ladder in this project is expected to help the fish move and migrate in the river (both upstream and downstream) more easily. Murray River flows approximately 2,530 km and it is one of the major rivers in Australia.

Fish ladders play a very key role in enhancing fish migration that contributes to fish production and diversity. These structures are designed to provide an alternative routes over weirs that obstruct free movement of fish in the river (Baumgartner, Zampatti, Jones, Stuart, & Mallen-Cooper, 2014); (Duguay & Lacey, 2015). Fish migrates from one place to another along the river to: search for food, breed, move to and from spawning areas, run away from predators and search for better environmental conditions (Edmonds, 2008).

Considering the important role that fish ladders play, there are several factors that must be taken into account when designing them. Some of the parameters that were considered in the design of fish ladder in this project include the following:

It is important to determine the characteristics of fish targeted before designing a fish ladder. The specific characteristics considered in the design of fish ladder in this project are: species of fish targeted, swimming abilities of the fish species, overall behavior of the fish, size of the fish species (minimum and maximum size), age of the targeted fish, run size and the fish species’ biological requirements such as spawning and rearing habitats. These parameters affect the ability of the fish to leap through the fish ladder effectively (Baigun, Nestler, Minotti, & Oldani, 2012). The main fish species in Murray River are: Murray cod, perch, catfish, European carp, Redfin, Callop, Macquarie and Bream (Murray River, (n.d.)).

The design of fish ladder is also influenced by the characteristics of the river including: river flows’ range, river velocities, river water surfaces, seasonal river flow rates, flow depth, etc. (Maeder, 2015). These factors affect the operability of the fish ladder. The fish ladder should be designed to operate efficiently under a broad range of hydrological conditions because these conditions usually vary from time to time.

The type of fish ladder model selected for this project is pool and weir. Pool and weir fish ladders are the oldest type of fish ladders. These fishways provide plunging flow to the fish and resting areas thus helping the fish with hydraulic assistance to move upstream. Pool and weir fish ladders have the ability to operate under two different types of hydraulic flow systems. First, these fish ladders can operate under the normal hydraulic flow system where the flow is plunging flow. Second, the fish ladders can also operate under the sporadic hydraulic flow system where the velocity of the plunging flow is higher. At this point, the plunging flow at the water surface gets converted to streaming flow. During streaming flow, the surface jet of the water passes over the fish ladder weir crests overpassing the pool surfaces. This means that the fish will not rest in the pool but will have a continuous flow or movement over the weir crests. It is difficult to manage streaming flows and that it shy it is recommended that the height of the spillway crest is big enough to accommodate the water depth even during heavy rainfall. It is also important to note that when the flow is transiting from plunging flow to streaming flow, the hydraulic instability created is likely to delay or affect the swimming of some fish species. This is because streaming flow is not able to provide the required hydraulic boost for the fish to jump and negotiate the fish ladder successfully.

Fish characteristics

In this design, the arrangement of the pools is in a stepped pattern and the pools with an overflow weir between the pools. The specific parameters that must be considered when designing a pool and weir fish ladder include: receiving volume of the pool, head differential from one pool to another, the pools’ water depth and slope of the fish ladder.

The team conducted a site visit to Torrumbarry weir in Echuca to collect some vital data to facilitate the design process of the fish ladder. One of the data collected was rock and soil data at the Torrumbarry weir site. This information was helpful in determining the most suitable type of material for the fish ladder’s foundation.

The fish ladder in this project was designed with a target of being fish-friendly, effective and efficient in enabling fish passage around the weir. The key parameters that the design team focused on determining are: flow depth, pool length and jump height. It is also important to consider the ease of constructing or installing the designed fish ladder at the site.

The width of the spillway crest of the pool weir fish ladder = 25.13 m. The height of the spillway crest of the pool weir fish ladder = 6 m. This height of 6 m is the maximum height of the spillway crest is usually active only during flooding.

The slope of the spillway chute is approximately 23 ° and its length is 13.9 m. The spillway chute ends at a flat apron of 1.1 m long.

The flat apron at the end of the spillway apron ends at 1.9 m deep and a dissipation or stilling pool of 15 m. The details of these parameters have been shown in the drawing of the pool and weir fish ladder.

Different water velocities of flow along the spillway chute were measured and the values obtained showed that velocities were below the projected flow supercritical meaning that the operability of the fish ladder would not be affected by the velocities of the water.

The water levels on the spillway were also measured and found to be below the maximum height of the spillway chute. This means that the height of the fish ladder was adequate to accommodate the typical water depth flowing at the weir.

The total width of the overflow weir is 11.25 m and the length of the upper pool, middle pool and lower poo is 7.50 m each. Each of the pools has a 3.75 m wide passageway/orifice located at the centre of the pool. Thus based on the arrangement of the orifices and the overall pattern of the fish ladder, it is of the category centre pool and weir fish ladder. This is simply because the orifices are located at the centre of the weir.

Depth of upper pool = 3.35 m, depth of middle pool = 2.81 m and depth of lower pool = 1.88 m

The summary of some of the design parameters of the pool and weir fish ladder in this project are as provided in Table 1 below

Table 1: Summary of design parameters of the pool and weir fish ladder

The view of the spillway, section of the pool and weir fish ladder and the plan of the pool and weir fish ladder

The overall timeline of the project is as shown in Table 2 below

Table 2: Project timeline

From the project timeline in Table 2 above, the project will be completed in approximately eight weeks.

Conclusion

The type of fish ladder selected for the Torrumbarry weir along Murray River in this project is pool and weir. This is the oldest type of fish ladder and hence there is adequate information to help the team design it effectively and efficiently. The spillway crest of the fish ladder has a length of 25.13m, height of 6m, a 13.9m-long chute at a slope of 23° ending at a flat apron of 1.1m long. The fish ladder has three pools – upper pool, middle pool and lower pool. Each of these three pools is 7.5 m long, 11.25 m wide and with a 3.75m-wide orifice. The depth and pool drop of the pools vary. This design of the pool and weir fish ladder is adequate to facilitate fish movement over the Torrumbarry weir at different flow rates and velocities.

References

Baigun, C., Nestler, J., Minotti, P., & Oldani, N. (2012). Fish passage system in an irrigation dam (Pilcomayo River basin): When engineering designs do not match ecohydraulic criteria. Neotropical Ichthyology, 10(4), 741-750.

Baumgartner, L., Zampatti, B., Jones, M., Stuart, I., & Mallen-Cooper, M. (2014). Fish Passage in the Murray-Darling Basin, Australia: Not Just an Upstream Battle. Ecological Management & Restoration, 15(10), 1-15.

Duguay, J., & Lacey, R. (2015). Numerical Study of an Innovative Fish Ladder Design for Perched Culverts. Canadian Journal of Civil Engineering, 1-35.

Edmonds, M. (2008, November 24). What Are Fish Ladders? Retrieved from How Stuffs Work: https://adventure.howstuffworks.com/outdoor-activities/fishing/fish-conservation/fish-populations/fish-ladder.htm

Maeder, C. (2015, February 11). Design of Fish Passages & Ladders with HEC-RAS. Retrieved from Civil GEO: https://www.civilgeo.com/design-fish-passages-ladders-hec-ras/

Murray River. ((n.d.)). Fishing in the Murray River offers a variety of fish species. Retrieved from Murray River: https://www.murrayriver.com.au/fishing/