YB299A Petitcodiac River Causeway Modifications
EIA Study
Report on Visit to Cardiff Wales
Purpose of Visit: To collect information about the Cardiff Bay Barrage and Fishpass
Dates of Visit: December 10-12, 2003
Visitor: Greg Gillis – AMEC Project Manager

Introduction

The AMEC Petitcodiac River EIA team learned of a fish passage facility (fishpass) in Cardiff Wales that is physically located in an area that has similarities to the location of the Petitcodiac River Causeway. The construction of the Cardiff Bay Barrage commenced in 1994 and was completed in 1999. The Barrage was constructed downstream of the confluence of the River Taff and the River Ely within the tidal range of the Severn Estuary.

Preliminary information on the Cardiff Bay facilities was presented in Maritime and Water Engineering, Special Issue, Cardiff Bay Barrage, Proceedings of the Institution of Civil Engineers, June 2002, Vol. 154. Following review of the information in this journal, contact was made with managers of the facility in Cardiff. Information exchange lasted about one month following which it was decided that a visit by a member of the AMEC team to the Cardiff facility would be beneficial. The goal of the visit was to understand the approach to fish passage that is used in Cardiff in order to determine if any of the information could assist fish passage at the causeway on the Petitcodiac River.

Greg Gillis from AMEC visited Cardiff on December 9, 2003. During the visit he met with several individuals from the Cardiff Harbour Authority including:

• Mr. Roger Thorney, Operational Manager for the Barrage,
• David Lowe, Operational Manager, Environment and
• Stuart Jones, Barrage Team Leader.

The personnel from the Authority were very helpful in providing information on the facility. In addition to information provided during the visit, other information was provided subsequently in letters or e-mail. The information presented in this report was taken from the documents provided, as well as from information gained during discussions with the Cardiff personnel.

The major similarities between the Cardiff and the Petitcodiac situations include:

1. The Cardiff Bay Barrage and Fish Passage Facility is located along the Severn Estuary, which has a large tidal range that is slightly lower than that of the Bay of Fundy.
2. The common mouth of the Taff and Ely rivers is located in the lower middle of the Severn Estuary, and the Cardiff Barrage is in the lower portion of the tidal range of the rivers.
3. The Barrage has created an upstream impoundment similar to that on the Petitcodiac River.
4. The elevation of the peak of the highest tides is higher than that of the upstream impoundment.

Differences between the two situations include:

1. The Cardiff Fish Passage Facility is designed to pass only Atlantic salmon and sea run brown trout. Other species rarely, if ever, pass through the facility, while a requirement of the Petitcodiac River Causeway Modification EIA Study is to ensure that all options meet fish passage requirements (upstream and downstream) for a wide variety of species and sizes of fish.
2. The normal suspended solids level in the Severn (and in the vicinity of the barrage) -approximately 1200 milligrams per litre (mg/l) is much lower than in the Petitcodiac River Estuary – approximately 30,000 mg/l.
3. The combined freshwater discharge from the Taff and Ely Rivers is about 10 times that of the Petitcodiac River, and the flows are more evenly distributed throughout the year. (Please refer to Table 1, attached.)

History of the Cardiff Bay Barrage

Cardiff was once a thriving seaport with a regular schedule of international shipping. Since the Second World War, and associated with the decline of the Welsh Coal fields, the port has been in a state of decline with major portions of the docks having been abandoned. This resulted in urban decay in the centre of the city. Several attempts at urban re-development, including construction of office towers and housing developments, did little to reverse this trend. The Secretary of State for Wales established the Cardiff Bay Development Corporation in 1987 to address this issue. The task was to spearhead the regeneration of 1,100 hectares of South Cardiff and adjoining Penarth – the old docklands area of the city. The resulting plan became the second largest regeneration scheme in Europe. The mission statement for the program was: “to put Cardiff on the international map as a superlative maritime city which will stand comparison with any such city in the world, thereby enhancing the image and economic well-being of Cardiff and Wales as whole.”

The plan involved the attainment of a series of targets including:

• Creating a superlative maritime environment by building a barrage across the mouth of Cardiff Bay and thus providing a 200 hectare freshwater impoundment and 12 km of continuous waterfront;
• Re-uniting the city and its waterfront by means of an new boulevard and rapid transit system;
• Providing 373,000 sq m of office accommodations;
• Providing 465,000 sq m of Industrial space;
• Providing 6000 new homes (25% being social housing); and
• The establishment of a link road to South Cardiff.

The plan to turn Cardiff Harbour into a freshwater impoundment was designed to facilitate its use by recreational boats, while maintaining commercial shipping at the docks that were still functioning. The plan involved the erection of a Barrage, at a cost of £125 Million (approximately $250 Million Canadian) across a portion of the harbour to separate the freshwater and seawater. Associated site remediation, installation of transportation infrastructure, and landscaping and environmental improvements brought the total estimated public investment to approximately £513 million ($1 billion Canadian). Private investment associated with the renewal project was £1.14 billion as of 2000.

The primary revenue source for the Cardiff Bay Development Corporation was Public Sector Funding (est. £444 Million) followed by £56 Million in proceeds from sale of lands. Government grants and Interest and Rebates totalled £9 and £4 Million respectively. The project has resulted in industrial development in the area as well as new housing, both social housing and exclusive housing.

The elevation chosen for the surface of the impounded freshwater bay (the Bay) was set below that of the highest tides to take the greatest advantage of the existing docks. A system of locks was constructed to allow the passage of recreational vessel traffic between the Severn Estuary and the Bay. A staff of 15 people work on a 24-hour rotation to operate the boat locks and sluices, as well as to provide for security. Every day, a staff member inspects the fish pass to conduct routine maintenance such as debris removal. The downstream channel is dredged every six months. The volume of dredged material in each dredging event is approximately 70,000 to 80,000 cubic metres. This material is dumped in the Severn Estuary approximately 4 km seaward from the Barrage.

Photo 1. Cardiff Bay Barrage Viewed from the Estuary (foreground)

The construction of the Barrage encountered a number of environmental challenges. The Barrage impounded the estuary of the Taff and the Ely Rivers, which have important runs of anadromous fish including Atlantic salmon and brown trout. The construction of the barrage prevented the free movement of these fish and also resulted in a loss of 200 hectares of marine fish habitat. Because of this, an Act of Parliament was required to approve the project subject to a number of provisions such as the maintenance of dissolved oxygen levels in the Bay at 5 milligrams per litre or greater through the entire water column, and the provision of upstream fish passage for Atlantic salmon and trout. The dissolved oxygen level is maintained by means of artificial aeration. A unique fishpass was incorporated in the development to attempt to achieve acceptable levels of fish passage. Included in the initial capital cost of the development was £6 million for the construction of the fishpass. The cost of running the fish passage facilities, locks and routine barrage maintenance is approximately £5 Million ($10 Million Canadian) per year.

Following are descriptions of the major water control components of the Cardiff redevelopment project including the barrage, the locks and the fish passage facility.

The Barrage

Cardiff Bay is the estuary for the Taff and Ely Rivers, the two main rivers in South Wales. The tidal range in the area is up to 14 m, which in the past at low water resulted in the exposure of extensive mud flats that limited development of the waterfront. The barrage that was constructed to separate the freshwater impoundment from the Severn Estuary is an 800 m long embankment constructed from sand and rock along with a 300 m long concrete section containing the locks, sluices, bridges, fish passage facilities and control building. The embankment on the Bay side is landscaped to provide a linear park, while rock stone armour protects the seaward side of the barrage.

Sluice Gates

Cardiff has a history of flooding, the result of combined high river flows and spring tides. Following the urban renewal project, the consequences of flooding in the Bay would be more severe due to the value of the newly installed infrastructure, including industrial, commercial and recreational development. Sluice gates were installed in the barrage and are operated to limit the risk of flooding.

There are five sluice gates, designed to close during high tides to prevent seawater from entering the freshwater Bay, and to maintain a preferred water level in the Bay. Each sluice gate can discharge up to 250 cubic meters per second. An on-site staff of 5 engineers maintains the gates. The gates can be operated as overflow or underflow structures, depending on the wishes of the operator. The normal mode of operation is overflow that minimizes turbulence in the approaches to the fish passage facility.

Photo 2. Sluice Gates, Stilling Basin and Fishway Entrances

Electricity for operating the facilities can be supplied from either end of the Barrage. Three on-site generators can supply complete back-up power. To help manage water flows, discharges and levels, telemetry links supply information from gauging stations on the Taff and Ely Rivers. The Barrage has level sensors, which record both Bay and tide levels in the estuary. In case of malfunction here are two back-up sensors for each side of the Barrage.

Locks and Bridges

There are 3 locks, each 40 m long, in the Barrage. Two locks are 8 m wide, and one is 10.5 m wide. The lock gates are 16 m high. There is 24-hour access for vessels to the lock gates, which are operated from the Barrage Control room, that is staffed 24-hours per day / 365 days per year. There are three Bascule Bridges that can be raised to allow ship passage through the Barrage. Each bridge weighs 88 tonnes and works by means of a cantilever system that is powered by an electrically driven hydraulic pump.

Fish Passage

Under the agreement with the regulatory authorities, 1000 fish must move upstream annually through the fish passage facility. If fewer than 100 fish annually move through the fishpass, a financial penalty is paid. The migrating fish are counted at a weir located at Blackwell in the River Taff (upstream of the impoundment). In addition, a video monitoring system that incorporates a series of cameras is situated in the bottom of a section of the fish pass. The system is being used to accurately count the migrating fish, as well as to identify the species of fish that are using the fishpass.

The initial fishpass facility failed to work properly, and as a result it was renovated. A detailed description of the fishpass follows. Plan and profile views of the facility are provided in Figure 1 (attached).

1. The Cardiff Bay fishpass allows adult Atlantic salmon, sea run brown trout and occasionally juvenile eels to move from the ocean into Cardiff Bay, which is a freshwater impoundment created by a dam (barrage) across the mouth of the confluence of two major rivers. (A comparison of the mean monthly flow of the rivers is compared with that of the Petitcodiac River in Table 1.) A species called the sand smelt, which is analogous to our rainbow smelt, cannot use the fishpass. Its numbers are undoubtedly diminished by a lack of access to spawning grounds, although a limited number of smelt gain access to the bay through the boat locks.
2. The lower portion of the fishpass is a pool-and-weir fishway. Flows in the pool-and-weir portion of the fishpass are maintained at 2.5 m3/s whenever the sea level is below Bay level. Three 0.5 m wide vertical slots provide access for fish into the fishpass. A cable pulls leaf gates upward from the bottom into the entrance1 slots to maintain optimal water levels (and water column cross sectional area) over the top of the leaf gates resulting in an exit velocity of 1.5 to 2 m/second.


Photo 3. Lower Pool-and-Weir Portion of the Fishpass at Low Tide

3. The elevation difference between the floors (as well as the tops of the weirs) of adjacent pools in the main fishway is 45 cm. The pools are 8 m wide and 3 m long. The pools drown out in succession as the leaf gates at the entrance rise to block the rising tide. This creates an ever-lengthening concrete walled canal.
4. At the top end of the pool-and-weir fishway, there are two steep-pass (Denil) fishways. One is used to pass fish when the Bay level is higher than that of the estuary. The other is used when the tide is higher than the level of the Bay.


Photo 4. Denil Portion of the Fishpass

5. When the Bay is higher than the estuary, a separate pipe provides water by gravity flow to the lower pools of the pool-and-weir fishway. This augments the discharge from the entrance slots, without increasing flow down the pool and weir system, and attracts fish into the fishpass.
6. When the tide rises high enough that the pool-and-weir fishway and the first steep-pass become “tide-locked” (sea level higher than that of the Bay), a gate at the exit (top end) of the steep-pass closes to prevent back-flow from the fishway into the Bay. At this state of the tide, water is pumped to the second pool from the exit end of the pool-and-weir fishway to maintain flow in the lower end of the fishpass. Water is also pumped to the second steep-pass fishway that becomes accessible to fish when a gate opens. This gives access for fish from the pool-and-weir channel to an upper pool. At the exit end, there is a blind weir that fish swim over and are sluiced into the impoundment. (A blind weir is a horizontal header pipe that acts as a weir. Water is discharged from the top of the pipe with 80% of the water flowing down the steep-pass, and 20% back into the Bay. The 20% back-flow transports the fish into the impoundment.)
7. The entire system is under the control of a computerized Process Logic Controller (PLC). The PLC can be over-ridden to allow manual control.


Photo 5. Display Monitor for the Fishpass PLC

8. After water is discharged from the fishpass entrance slots and the adjacent sluice gate #5, the flow enters a stilling basin (See Photo 2), which is essentially a concrete box with sidewalls of differing heights (steps). When the velocity of the flow over the lowest wall becomes too great, a second wall is over-topped, and when the velocity of the flow over this wall becomes too great, the third wall is over-topped. In this way, fish gain entrance to the chamber from which they can access the fishpass at a large range of flows and flow velocities.

During low river flows, the operators have difficulty operating the fishpass. There were significant mechanical failures with inlet leaf gate operation in the first year (2000), and therefore difficulties in maintaining the desired discharge velocity of 1.5 to 2.0 m/s at the fishway entrance.

Fisheries Management and Its Effectiveness in the Taff/Ely Basin

The Cardiff Bay Development Corporation (CBDC) stocks hatchery smolts annually in order to compensate for the impact of the Barrage on fish migration. As a worst case, it was anticipated that the Barrage would result in reduction of returns by about 35%. To compensate for anticipated reduced returns, two-year old salmon smolts were stocked - 10,000 fish were stocked prior to Barrage construction and 50,000 fish (since raised to 60,000) after construction.

The mean return of tagged adult salmon resulting from smolt stocking before construction was 0.66%. Returns of salmon from smolts tagged in 1998 that returned in 1999, the last pre-impoundment year, were 0.29%. An additional 0.02% multi-sea-winter fish from the 1998 release returned in 2000 for a total return from the 1998 year-class of 0.31%. In the year 2000, the year following the completion of the Cardiff Bay Barrage and impoundment (impounded on November 4, 1999), the return rate of adult salmon from tagged smolts was 0.25%. (A good return would be in the order of 3%)

Angler catch per unit effort for salmon in 2000 was 0.19 fish per angler-day compared with 0.15 fish per angler-day in the pre-construction and construction period (1992 to 1999). Sea trout catch per unit effort in 2000 was also 0.19 fish per angler-day compared with 0.45 fish per angler-day in the pre-construction and construction period (1992 to 1999).

Fish trapping at Blackweir index trap on the River Taff captured 0.097 salmon per hour in the pre-construction and construction period from 1991 to 1999 (2,159 fish in 22,342 hours of trapping). This can be compared with 0.035 fish per trap-hour (574 fish in 16474 hours) for the post-impoundment period of 2000 to 2003 (See Table 2, below). Trapping took 0.108 sea trout per trap-hour (2,410 fish in 22,342 hours) in the pre-impoundment period, and 0.067 per trap-hour (1,104 trout in 16474 hours) in the post-impoundment period (See Table 2, below).

Adult salmon and sea trout were tracked in the estuary using a combined hydroacoustic / radio tag system. The fish were obtained from the Taff and Ely rivers feeding the Bay (i.e. they had already managed to pass the barrage and enter the river once). The tracking demonstrated that the fish were easily confused, and few successfully re-entered the system from the estuary.

There is also concern about the effect of the system on the downstream migration and survival of post-spawned Atlantic salmon and sea trout (kelts). Seven kelt were tracked using the tagging system after the fish spawned in 2000. In addition, three previously tagged salmon were known to have entered the Bay. Only one was detected in the marine environment after the period of downstream kelt migration. If downstream post-spawning migration is in-fact a problem, it would have serious consequences in the case of trout in which repeat spawners provides a significant portion of the egg deposition.

Questions or comments regarding this site should be directed to:
Judy Cole
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