content@managingwater.co.uk Fish Passes & River Structures


Pumping Stations and Eel Management


Pumping stations are heavily relied upon in low lying areas for protecting land and property from flooding but clearly as with any water structure they will impact upon the natural life occurring with in the channels. There have been various investigations into the effects of pumping on fish and eel populations and what solutions are available.


A investigation carried out by INBO (The Flemmish Research Institute for Nature and Forest), in 2009, set out to determine the effect that pumping stations have on the fish and Eel population in the Flanders region. They monitored 153 pumping stations, of which 76 operated propeller pumps and 34 Archimedes screw pumps. They monitored the number and types of fish passing through the pumping stations and assessed the nature of injuries caused and the mortality rates.


With propeller pumps the mortality rate for Eels was 95 - 98% whereas with the archimedes screw pump the mortality rate was 16 – 19%. Pumping stations are one of the main causes of silver eel mortality in Flanders, next to ‘angling’ and ‘predation’. Whilst Archimedes screws are less harmful to fish and eel populations than propeller pumps they do still cause an unacceptable level of fish mortality.


Last month (October) the Environment Agency's Eel Management Plan


Implementation Group held a workshop on eel and fish passage in East Anglia to look at the effects of pumping stations on fish passage in the Anglian region.


At the workshop, a report 'Prioritisation of Pumping Stations in Anglian Region for Eel Passage' was presented. The report was written by Dr David Solomon and Ros Wright and presented by the former.


With just under 450 land-drainage pumping stations in the region it would be a huge task to monitor each and every one. The report provides a process for categorising and prioritising pumping stations for the passage of eels, elvers and coarse fish. A methodology was developed to assess the extent of obstruction represented by the structures and an approach to identifying the relevant importance of the areas of waterway that are


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affected. Structures affecting a large area of potentially productive fishery may be considered a higher priority for remedial action than one affecting a small area of less productive water. For freshwater fish the WFD status of the area being drained is relevant to the prioritisation process. Another key factor is the existing availability of alternative routes to or from the pumped catchment.


For the report proxy indexes for prioritising elver and adult eel passage facilities and a third index for prioritisation of coarse fish screening at pumping station intakes were developed. The application in the report of these indexes to pumping stations in East Anglia enables operators in the region to better understand the priority sites for screening and bypass facilities, and enable operators to target implementation within existing replacement and capital project programmes.


The solutions


To reduce the mortality rate of fish passing through pumping station pumps the obvious remedy is to prevent fish passage, there are three main approaches to achieving this:


Discourage fish from travelling through the pumps


There are three main methods. The first is to install grids at pump intakes to restrict access. However physical barriers require regular maintenance and pump effectiveness can be severely hampered by debris.


The second is the use of strobe lighting or acoustic noise producers to deter the fish. However, the effectiveness is questionable as Eels appear unaffected by acoustic effects and strobe lights have had mixed results in deterring fish. In Holland it is commonplace to use a combination of the two.


The third method is to deter the fish is by running the pumps backwards as part of the start up process. The reverse movement and propellor action and noise may suffice in driving the fish away from the intake before the pump is switched back to its usual direction.


Stobe lights installed at Welches Dam pumping station - courtesy of Aquatic Control Engineering


To provide alternative routes for fish and eel passage


Fish passes and Eel/Elver passes used to bypass the pumping station.


Fish-friendly pumps


As the name suggests, these are pumps designed to allow fish passage through the pump with causing any damage to the fish.


Fish-Friendly pumps courtesy of Bedford Pumps


Grids can be used to prevent fish entry


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