Save The Ribble

A blog dedicated to preserving the beauty and delicate ecosystem of the River Ribble, and opposing the Riverworks 'vision' to build a barrage on our River and develop on our riverbanks, floodplains and green spaces, causing damage to wildlife and the environment and increasing the risk of flooding to our homes. Save the Ribble Campaign is not responsible for the content of external blogs or websites which link here.

Wednesday, April 18, 2007

How the Ribble Works

As part of the various events at RSPB Marshside, Dr. Alan Bedford from Edge Hill University and Graham Clarkson of the RSPB gave a fascinating talk about how the Ribble Estuary works. You can find out more about walks, talks, and other wildlife events at RSPB Marshside.

The River Ribble: an intricate and dynamic Wetland Ecosystem.
We know that the Ribble’s inter-tidal ecosystem is a combination of fresh and salt waters, silts and nutrients, which give rise to the unique mudflats and saltmarshes in the Lower Ribble and particularly in the Estuary, and that the Ribble Estuary is such an incredibly rich habitat that the Ribble’s importance to wildlife is on an International scale.

Yet this ecosystem is a dynamic habitat, changing not just with the tides and the Seasons, but even in the space of a few hours.

The salinity of the Ribble’s Estuary is one of those elements which varies enormously, even in the course of a single day. Not only do the tides themselves vary - the height of the tides can vary hugely even over the course of a few days! - so does the flow of fresh water which washes down through the Ribble corridor to mix with the incoming tides. The amount and nature of this fresh water depends on the amount of rainfall higher up the Ribble valley, flowing down to the Estuary down the Ribble river, as well as down its many tributaries which all flow into the Ribble’s waters.

There are many tributary rivers which flow into the Ribble to swell her waters and provide numerous spawning grounds for migratory fish - including Atlantic Salmon and Sea Trout, these amazing fish make their arduous journey from the open seas back to their own birth places high upriver to spawn their own young.

These tributaries are not only the larger Rivers Darwen, Douglas (Asland), Calder, Hodder, and Crossens, but also the Rivers Lostock and Yarrow, Rivers Whitendale, Loud, and Brennand, the Rivers Brun and Tawd, and a huge number of smaller rivers and brooks, including Stock Beck, Pendle Water, Colne Water, Eaves Brook and Savick Brook, amongst many, many others - and ALL of these tributaries would be affected by a tidal barrage on the Ribble, not least because they would all be UPRIVER of the impounded waters.

The River Douglas and the Ribble.

This is yet another reason why the Ribble is so important: she is effectively nature’s water supply and the rainwater drain for a huge area of the North West, from Ribblehead in North Yorkshire to Lytham, St.Anne’s, Blackpool, and Southport; from Gisburne Forest and the Forest of Bowland to Settle, Clitheroe, and Ribchester; from Colne, Burnley, Accrington, Blackburn, Darwen, Wigan and Skelmersdale to Preston, Freckleton, Kirkham, Chorley, Leyland, Walton le Dale, Penwortham, Hutton, Longton, and Hesketh Bank… and many of these places also supply much of the Ribble’s essential silts and nutrients, washed downriver to the Lower Ribble and the Estuary by rainwaters.

The Ribble's silt-laden rainwaters washing under Penwortham Old Bridge to the Estuary

The Ribble’s intricate ecosystem, then, extends far beyond seeing the central river, or the estuary, in isolation: the Ribble is a living, breathing, ecosystem, a vital ecological organism.

Ribble Intertidal zone - an energy-rich and delicately-balanced ecosystem:
The Ribble is renowned for its high sedimentation – all that lovely mud! – which is carried downstream with the fresh water flows, and in from the Irish sea, and mixed up and distributed on those vital mudflats and saltmarshes by the swirling waters of the tides and the freshwater currents, every day, twice a day, as it has done for many thousands of years.

Mudflats in Penwortham

It is the Ribble’s mud which provides the strong mineral base of dead organic material which is the primary food source for the mind-blowing multitude of invertebrates which live in the Ribble’s mudflats, a multitude upon which the Ribble’s enormous bird population subsequently feeds. All that mud provides a food-rich habitat for over ¼ million birds every Winter alone – and approximately 1 million birds throughout the year, including those who stay for just a short time to refuel during their long global migrations - as this rich ooze supports so many millions of invertebrates it’s impossible to count them!

Ribble mudflats have more energy per square metre than Rainforest!

As the high levels of salt ensure the mudflats and saltmarsh don’t freeze in the winter months, this environment is a safe haven all year round for numerous migratory as well as native bird species who feed, breed, and roost here throughout the year.

Ribble Tidal Flats – neither “barren” nor useless!
The tidal flats form three basic areas: sand flats (at the geographical bottom of this intertidal ecosystem), the salt marsh at the top, and the mudflats in between, and are collectively known as tidal flats. The combined system is very rich indeed in terms of nutrients – and Dr. Bedford pointed out the nonsensical perception in the Riverworks documents that these vital wildlife habitats are “barren”, “unsightly”, and useless!

Rich Ribble mud - more energy per square metre than Rainforest.

Their vital importance to wildlife is why mudflats and saltmarsh are protected under UK, European, and International Law, and why they are currently a particularly high priority for both creation and restoration as part of the UK’s Biodiversity Action Plan Habitats, and as part of Defra and the Environment Agency’s biodiversity enhancement aims.
Defra and the EA also wish to invest in tidal flat maintenance and restoration as these also act as effective and sustainable flood defences to coastal and riverside communities.

Mud, Mud, Glorious Mud!
Whilst the Ribble’s harsh environment means that the mudflats are low in biodiversity in terms of the number of species per square metre, the enormous numbers of the relatively few species of invertebrates (worms and snails) that live there means the Ribble’s mudflats are so rich that they support more life per square metre than tropical Rainforest! The Ribble's mudflats also act as Nurseries to sea fish fry (babies) such as Plaice until they are mature enough to cope with the open seas.

It’s a Bug’s Life
Sand Hoppers, for instance, burrow in the mud and feed on the rich supply of micro-particles in there – and their digging is itself very important to stabilise the mud – and there are between 50,000 and 400,000 of these little diggers per square metre!!!
Those water snails we see at low tide leaving little trails wandering all over the mud and sand flats exist in the Ribble’s mud at the rate of 35,000 per square metre
Cockles siphon for food very close to the surface; lug worms leave their little tell-tale squirls of sand on the surface… and there are loads of other worms, snails and shellfish, all co-existing in the Ribble’s rich mud at the rate of many hundreds of thousands per square metre! No wonder that the Ribble is such a vital feeding ground for so many hundreds of thousands of birds all year round!!!
To read more about the importance of invertebrates to the inter-tidal ecosystem, see Buglife.

The Birds and the … Invertebrates:
The rate of heat loss in birds is huge, and high tides mean even less feeding time. Different wading birds have evolved different feeding styles and bills because, in such a tight feeding time-frame, they need to get feeding as quickly and efficiently as possible, each evolving unique methods to catch their favourite fast-food Bug-burger.

Each bird will look out for the tell-tale signs of their prey and catch them with their own unique method, some by touch and some by sight. Strong winds can create problems for visual feeders:

Shelduck for example, “scythe” the mud, squeezing muddy water out and leaving them with the creatures in their bills…
Knot feed by touch, feeling for the invertebrates in the mud – possibly even by the tiny vibrations of the creatures as they move. Their feeding is often referred to as “stitching”, the birds feeding in groups with quick movements of their heads…
Redshank are visual feeders, also using a “stitching” technique, and feed through the night too. They hunt alone, however, to avoid their prey being disturbed by other birds, and they consume 40,000 corophium (sand hoppers) per day – 2 per second of available feeding time…

Because of the high levels of energy these birds need to consume to stay alive, they have to use every opportunity to feed on the mudflats exposed by the receding tide.
Oystercatcher and Curlew, for example, have to feed for between 40% and 60% of the time during the summer months, 75% in the Winter, while Knot have to feed for 60% of the time in the summer months, and between 90% and 98% of the time between January and March – that’s pretty much constantly, just to stay alive.
In February 1991 for example, the cold killed 850 out of every 4,000 Redshank.
The Ribble’s incredibly rich mudflats are VITAL to a significant number of the Earth’s bird population.

Birds which feed on the saltmarsh plants (such as samphire) include Wigeon, Barnacle Geese, and Pink Footed Geese – and Skylarks - and need to feed prolifically to extract enough nutrients from plants, which are much lower in energy than invertebrates. Wigeon for example feed for 14 hours per day…
Skylarks feed on saltmarsh seeds and breed during the solstice tides as there is a much lower tidal range in mid-summer. Saltmarsh is an endangered habitat - it is rarer than Rainforest.

Ribble saltmarsh at Marshside - the best place in the North West to see and hear Skylarks.

Birds and the Ribble Estuary:
The Ribble Estuary supports more bird species in internationally significant numbers that any other wetland site in Britain – apart from Morecambe Bay sometimes! Despite the enormous difference in size of these two Lancashire wetlands, the Ribble and Morecambe Bay are almost indistinguishable from one another in terms of the bird species they support, and frequently change places between first and second position in the Wetlands Premier League. Only the Wash, on the East coast of Britain, comes close to these Lancashire giants in terms of the numbers of bird species supported.

The majority of wading birds tend to feed most intensively at incoming tide rather than outgoing tide as the incoming waters often encourage the invertebrates to the surface. The saltmarsh, a rare and protected habitat dominated by grasses, is often more useful for roosting and breeding than feeding for many bird species, providing a good site for spotting predators, safe for moulting and nesting and roosting at high tide. Yet, significant bird species also feed on the saltmarsh plants themselves, including Pink Footed Geese, Wigeon, and Skylarks.

Wind, Rain, and Tides…
The variable tides, moods and seasons of the Ribble are an intrinsic part of our love for this glorious River, and occasionally some of our local communities have close encounters with the Ribble when inclement weather conditions and tidal movements coincide!

Submerged bench in Penwortham, looking towards Broadgate.

This river flooding is due to high rainfall, and often occurs when in conjunction with high river levels, such as at high tide, and at certain phases of the moon - a situation which can be exacerbated when there are strong onshore winds, and is a particular risk during the Spring and Autumn Equinoxes.

Ribble in spate through Penwortham and Preston.

Defra and the Environment Agency keep a close eye on our flood defences and rainfall patterns as part of the Ribble Shoreline Management Plan, which is equally concerned with the long-term protection of the Ribble’s inter-tidal habitats, and plans for the next 50 to 100 years of Ribble coastal and the tidal sections of the river basin up to Penwortham Old Bridge.

The assessment of the flood risk and the Ribble’s ecosystem for wildlife and human communities further upriver is covered by the Integrated Ribble Catchment Management Plan - implemented as part of the EU Water Framework Directive as the Ribble is Britain's Pilot WFU River - which caters for the entire Ribble river system. This includes the whole catchment area and the numerous large and smaller rivers which feed into the Ribble itself, and covers everything from Fisheries issues to flooding to extraction and pollution issues to protecting and enhancing the Ribble's biodiversity and wetland ecosystem.

Both Plans aim to ensure the protection and enhancement of flood defences AND wetland wildlife habitat as part of their broader remit of river basin management, and it is the well-being and integrity of both which compliment each other in actively providing one of the richest wetland habitats in Europe at the same time as effectively providing Ribbleside communities with flood protection!

It is a fact that the intertidal wetland system of mudflats and saltmarsh acts as the most sustainable, effective, and cost-effective forms of flood defence provision from both sea level rises and higher rainfall. This is why the Ribble Shoreline Management Plan actively pursues the protection and (re)creation of more intertidal zones to protect both human and wildlife communities from the threat of climate change.
This is also why barrages and building on the river's floodplain will increase floodrisk to local communities.

The Ribble SMP has targeted Hesketh Out Marsh as the first major area of land to be returned to its original saltmarsh condition, and work has begun on this project, which will incidentally create one of the largest Wetland Nature Reserves in Europe whilst actively helping to protect Ribbleside communities from the sea, including Hundred End, Rufford, Much Hoole, and broader areas of South Ribble in particular, but the diffusion and absorption of the sea’s tidal energy it will effect also help to protect communities such as Preston, Penwortham, Freckleton, and Warton.
Hesketh New Marsh and Hesketh Old Marsh may be also be returned to the Ribble in future years, to add greater protection against flooding further upstream. This Plan also identifies other Ribble floodplain areas which could be returned to the intertidal zone in the long term – such as Banks, Hutton and Penwortham – to allow even greater scope for creating further wetland flood defences in decades to come, should the need arise as a consequence of climate change…
This is why the Environment Agency believe building on the floodplain is not a good idea!

The Tide is High but I’m Holding On!
But back to the tides… The highest tides mean less feeding time for the Ribble’s bird population who have less space and time in which to feed, and then only once the tide recedes again!

As the birds need to feed for between 60% and 98% of their time in order to mitigate the huge rate of heat-loss birds experience in the winter months, high tides can be a real problem for them. In February 1991 for instance, the cold killed approximately 850 out of every 4,000 Redshank.

When the mudflats are only exposed for a short time, due to high rainfall and high tides – such as we saw in Penwortham and Broadgate over this last Winter - whilst it has meant we have been able to see the Redshank, Oystercatchers, Dunlin, Sanderling, Teal, Shelduck, and other birds feeding higher up the mudflats much closer to us so we can get a good look at them (as long as we are careful they don’t see us and take flight!), it has also meant there is less exposed mud and for much shorter periods, putting real pressure on the ability of these beautiful birds to survive the Winter months. Luckily, the Winter has also been mild, so hopefully the high rainfall this Winter won’t have had a dramatic impact on the birds’ survival rates…

Even now, the wading birds such as Redshank, are still feeding on the mudflats as high upriver as Penwortham and Preston, their soulful cries echoing over the river, before they finally set off to their breeding grounds, many actually stay to breed on the Ribble’s saltmarshes, but the rest migrate back to Iceland, Southern Europe, and North Africa. The Redshank on the Penwortham and Preston mudflats are flocking together as they prepare to leave us until Autumn when the Ribble’s Winter bird population returns once again…

This flock of Redshank in Penwortham and Broadgate were chased off the Moorhens’ “patch” of mudflats every time they landed there!

The Ribble’s wetland ecosystem then, isn’t just a word, it’s a vibrant and vital interrelated ecological environment, each part dependent upon other parts, each micro-climate dependent on the whole.
This is why barrages, which interfere with the natural movements and behaviour of salt and fresh waters, silts and nutrients, cause so much damage to wetland ecosystems, and consequently, the Earth’s ecological and environmental sustainability.
This is why the Ribble's designation as a Regional Park recognises the vital importance of the Ribble Coast & Wetlands - to wildlife and human communities, now and in the long term.

Long Live the Ribble Wild!

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