The waterway

The waterway at Milford Haven and at Sandy Haven Pill is a drowned river valley - known as a 'Ria'. The geological history of the waterway is complex.

A major fault - a fracture in the Earth's crust - runs along the central axis of the deep channel. This is known as the Ritec Fault, which can be traced from Tenby to Pembroke Dock, and at the mouth of the Milford Haven it is picked out again by the steep-sided, straight valley in which the village of Dale is situated. The fracture has been in existence for over 400 million years.

The development of the scenery of Milford Haven is much more recent in geological terms. Around 50 million years ago, rocks and sediments that had previously been beneath the sea were uplifted to form land. Remnants of these former marine erosion surfaces can be seen throughout Pembrokeshire including the plateau of the Dale Peninsula, visible from the coastal path just past Sandy Haven.

On the newly created land surface a river valley gradually developed following the Ritec fault. During the Ice Age - which lasted from 2 million to 10 thousand years ago - huge volumes of melt water from local ice sheets gouged out a deeper section within the valley floor. At that the time sea level was much lower than it is at present, as much of the earth's water was stored in extensive polar ice caps and continental glaciers.

Much of Britain was covered by ice, including an ice sheet that occupied the present area of the Irish Sea, which at its greatest extended to cover all of Pembrokeshire and the Bristol Channel area.

The most recent glaciation reached its peak around 18,000 years ago, and 10,000 years ago, the global climate improved, polar and continental ice cover diminished and the sea level began to rise rapidly. Over time the sea rose reaching a height similar to its present level 3,000 years ago. It was during this time that the landscape of Milford Haven that we see today was formed.

Milford Haven Waterway is up to 20 m deep in places and is reputedly the second deepest natural harbour in the world, second only to Sydney Harbour, Australia. It is its underlying geology that has contributed to the development of Milford Haven as a port; currently the largest in Wales and the fifth largest in the UK.

Follow the lane for about a mile, past the campsite on the left, and cross the stile marked 'High Tide Diversion'. Follow the coastal path through the caravan park, keeping Sandy Haven Beach to your right.

As the path drops towards Sandy Haven beach notice how the pebbles match the rocks in the surrounding cliffs. These include red mudstones, siltstones and sandstones. There are also green sandstones and pebbly conglomerates as well as a scattering of rock types which were transported to the area by ice sheets. These include igneous rocks from north Pembrokeshire as well as flints from the north-eastern tip of Ireland.

At this point you can see how the coastline within the Milford Haven Waterway has developed by the effects of wave action on the former valley slopes of the flooded river, exposing the distinctive rocks known as Old Red Sandstone.

Although marine erosion has created wave-cut platforms and sea cliffs within the waterway, in many places the original valley slopes have not been completely obliterated. Above the slope of the cliff, remnants of the valley can be seen, and the deposits that surround them have been revealed. These red or orange stony clays with aligned slabs of rock were formed by the down-slope movement of waterlogged soils above frozen ground in the latter part of the Ice Age.

Sandy Haven is a tidal estuary and an important habitat for a variety of estuarine birds including curlew, redshank, teal, widgeon, selduck, and mallard. On the water there are herring, great black-backed and lesser black-backed gulls. Although this appears to be an ideal habitat for choughs they are infrequent visitors and do not nest here.

On the far side of the Sandy Haven is estuarine woodland where herons and egrets often roost. Up stream from here it is possible to find Atlantic salt marsh habitat. This varies from looking like a green grassland sward to being covered with sea lavender and sea wormwood. The salt marshes are scattered throughout the tributaries and are atypical of salt marshes in that the areas as they are small and isolated, but have a high species and community diversity.

The second beach that you come to is Kilroom Bay, continue along the coastal path to the right.

The cliffs here display the typical rock types of the Old Red Sandstone sequence. Not all the sandstones are red, some may also be purple, green or grey.

The layers of rock were laid down by rivers that flowed on an ancient continent south situated of the Equator, on a hot plain crossed by braided river systems, and represent sediments deposited in river channels and on flood plains.

The rocks were formed during the Devonian Period and are around 400 million years old. They reached their present position through continental drift - the movements of the plates which make up the Earth's crust.

In the Devonian Period, vegetation cover on the land was limited to very small plants (typically consisting of a fine rootlet with a spore case at the top and no bigger than a pin). These plants were confined to the margins of the land and grew in environments similar to the salt marshes which exist in Sandy Haven Pill today.

In the south-eastern corner of the bay the rocks have been folded downwards (this type of fold is known as a syncline). A collision of continents that occurred around 290 million years ago caused the folding and faulting that affects the rocks of south Pembrokeshire.

Kilroom Bay is surrounded by a narrow strip of marine grassland where there is red sescue grass, and in rock crevices clumps of thrift, kidney vetch and sea campion, buck and sea plantain.

The bands of colours that you can see on the Old Red Sandstone rocks are layers of differently coloured lichens: orange, yellow and black. The black layer is black tar lichen, which people often think looks like oil. Following this is the intertidal zone. This overall effect is known as 'vertical zonation'.

Carry on along the path - the embankment on your left marks the boundary of the disused Esso Oil refinery.

During the post war years, Milford Haven was affected by a gradual demise in the fishing industry. This period coincided with the development of the town as one of the world's major oil ports.

In the 1960's and 70's, four oil refineries were sited at Milford Haven, although presently only two remain. This walk follows the boundary of the decommissioned Esso refinery. However, there are now plans to reopen the site as a Liquid Nitrogen Gasification (LNG) plant in the future.

The area is now owned by Exxonmobil. Extensive partnership work with the Countryside Council for Wales (CCW) and the Pembrokeshire Coast National Park Authority has taken place. Part of the area has been designated as a Nature Reserve to ensure that the habitats and flora and fauna communities are safeguarded well in the future.

The site is a haven for mallard, widgeon, teal, gadwall, common snipe, little grebe, curlew, redshank, grey heron, lapwing, dunlin, herring gull, and the lesser black backed gull. Other bird species include stonechat, skylark, barn owl, chough, and peregrine.

Look out for badgers, horseshoe bat, pipistrelle and long-eared bat, field voles, stoats, rabbits and fox. Reptiles and amphibians including adder, grass snake, slow-worm, common lizard, frog, toad, palmate newt may sometimes be spotted. You may also see a great variety of butterflies and moths.

There are a fantastic variety of plants here - 302 species of vascular plants alone - three of which are recorded as being nationally scare; these are: dittander, greater broomrape and varigated horsetale.

As you continue along the path, Stack Rock Fort in the estuary, South Hook Fort on the headland and the chimneys of the refineries on the far side of the estuary at Pembroke come into view.

From this part of the path there are great views of the various forts and of the body of the Milford Haven Waterway. This is part of the Pembrokeshire Marine Special Area of Conservation (mSAC), a wetland of international importance.

It is home to one of the most diverse estuarine communities in the UK. In spring and summer the peaceful embankments and rivers provide breeding habitats and crèche sites for a multitude of birds.

Following the Sea Empress disaster in 1996 when 72,000 tonnes of crude oil was released into the mouth of the Milford Haven Waterway, there was great concern about the impact on the flora and fauna of the area.

Clean-up operations have been deemed to be largely successful with populations suffering from the initial impact of the oil but recovering in subsequent years.

Along the coastal path, the main habitat is coastal scrub which is characterised by the presence of gorse, bracken, blackthorn and hawthorn.

You can spot white throats which like to nest along here, as well as robins, dunnocks, stonechats, linnets, thrushes and blackbirds. Spring flowers include cowslips, primroses and bluebells, and in the summer, red campion.

Between the coast and Stack Rock Fort there is big bed of merle, a calcareous red seaweed that grows in a free nodule and lattice structure. Merle grows phenomenally slowly and is very long lived.

A number of merle beds have been dated, using radio carbon dating, indicating that often these reefs are at least 1000 years old. The Merle also provides an important habitat for specialist red algae.

Continue along the path past the site of South Hook Fort, and the pipeline jetties. Descend the steps onto the beach underneath the pipeline. Ascend the steps on the opposite side and follow the tarmac path.

More evidence of the effects of geological folding can be seen between South Hook Point and Gelliswick Bay. The Old Red Sandstone sequence here has been examined in great detail by geologists who are studying the ancient environments in which these rocks were formed.

Within the stones there are large, in-filled burrows of amphibious creatures, and fragments of primitive armoured fish have also been found.

Looking over to the opposite side of Sandy Haven, at Little Castle Head (near the navigation marker tower) the tightly folded rocks include layers of volcanic ash.

The forts were built in the 1860's as part of the 'Palmerston Defences'. They are Victorian Forts built on the recommendation of the Royal Commission in 1860 in response to the earlier Napoleonic Wars (1803 - 1815). They include Dale Fort, Stack Rock Fort, Chapel Bay Battery, South Hook Fort, Thorn Island Fort, and East and West Block House Batteries.

Although the pipelines may appear to be an unlikely habitat for wildlife, Cormorants and a variety of gulls love to sit here. Beneath and between the two jetties, there is an extensive community of eel grass that flourishes in this shallow sheltered environment, which is also home to a specialist red algae.

After the kissing gate, the path widens into South Hook Lane. Follow the road around to Gelliswick Bay. As the road bends to the left, look out for the Coastal Path marker on the right.

Take the steps leading up past the school and continue straight on to Wellington Road. Cross to St Annes Road and follow the road back downhill to the centre of Milford Haven.

Milford Haven

Milford Haven was founded in 1790 by Sir William Hamilton on an area that formed part of his Pembrokeshire estate. Prior to this the area was mainly agricultural with a small 12th century 'Beacon Chapel'. The inlet at Milford Haven was known as Hubberston Pill and a daily ferry sailed to Ireland from the hamlet of Hakin.

In the late 1700s Sir Hamilton sent his nephew Charles Francis Greville to plan and build a town and port on the east of the Pill which was hoped would attract the transatlantic trade that was flourishing at the time. In 1793, Greville recruited the help of a group of American Quaker whalers, and the French planner Jean Louis Barrallier. Greville hoped to establish a whaling industry in Milford, as at that time, whale oil was used for street lighting in the towns and cities across the UK.

Admiral Nelson, lover of Sir William Hamilton's wife, Emma, was a frequent visitor to Milford. Hamilton developed a major port with a ferry service to Ireland, a Royal Naval Dockyard and a fleet of whaling ships. It soon became one of the largest fishing ports in Britain. The fishing industry had declined by the 1950s.

At this time the oil industry moved to Milford Haven and a number of refineries were established, although now only two remain. The next industrial reincarnation of Milford Haven may include the processing of LNG, and as a harbour for cruise liners that visit the area due to its proximity to the Pembrokeshire National Park, the tiny city of St David's and a number of good golf courses.

Milford Town Museum is sited at the Town Docks in the old Custom House, and charts the history of the town so far. Herring gulls, lesser and greater black-backed gulls and comorants are often spotted around the Dock.

Thanks to Kirsty Morris, Pembrokeshire Greenways, Pembrokeshire County Council, Sid Howells and Blaise Bullimore - Countryside Council for Wales, Jane Hodges, Park Ecologist - Pembrokeshire Coast National Park, and ExxonMobile.