Introducing the Gwent Levels Landscape / Geological Landscape
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Part One – The Scheme Plan / Summary of Engagement Living Levels 43 Image Credit: Nigel Pugh Living Levels 44 Living Levels 45 Part One – The Scheme Plan Introducing the Gwent Levels Landscape / Geological Landscape The Gwent Levels area lies just beyond the southern Before they were reclaimed and separated from extent of a number of ice-sheets that covered the Severn Estuary by a sea wall during the Roman northern Britain during the period of glacial maxima period, the Levels would have been a changing during the last 500,000 years. The valley of the River patchwork of saltmarsh, reed-swamp and peat bogs. Severn was recut by glacial meltwater each time the The coastal plain comprises three discrete areas: ice-sheets retreated. the Wentlooge Level, which extends from the River Rhymney to the mouth of the River Usk (c.27km2); the The Gwent Levels are a distinctive topographic zone Caldicot Level, which extends between the River Usk comprising of a low-lying, flat and expansive coastal and the bedrock promontory at Sudbrook (c.47km2),; plain up to 6km wide that extends up to the Severn and a third smaller area known as the Mathern Level Estuary. Its elevation is typically between 5 - 6m AOD between Sudbrook and the River Wye (c.5km2). and generally below 10m AOD. Living Levels 44 Living LevelsLiving Levels 45 45 Part One – The Scheme Plan / Introducing the Gwent Levels Landscape The northern edge of the Gwent The Severn Estuary is fed by The Severn Estuary is backed by Levels is marked by the boundary the major rivers of the Severn, a low, flat depositional coastline between the slightly higher Wye, Usk and Avon. The estuary of soft Triassic and Jurassic rocks ground in the north, underlain expands in width from the mouth exposed along the shore creating by sedimentary rocks mainly of of the River Severn as it flows a wide rocky inter-tidal area Lower Old Red Sandstone from westwards to meet the Bristol including expansive tidal flats, the Devonian Period, and the Channel, creating a classic comprising of sand, mud and shin- lower, flatter land on reclaimed expansive funnel shape. The gle with occasional rocky outcrops estuarine alluvium to the south. funnelling efect of the South Wales exposed at low tide. The rocks are The estuarine alluvium is mainly coastline and the North Somerset visible in the clifs and prominent a blue-grey, silty mud up to 13 coast of England has a profound coastal headlands with wave-cut metres thick that gives rise to efect on the physical nature of platforms at their base, such as at heavy textured, poorly drained the Estuary. The immense tidal Black Rock near Sudbrook. clayey soils. range of the Severn Estuary and its coastal geometry combine to build Mud, sand and gravel sediments Prehistorically found at locations up the largest tidal bore in the UK deposited in the Holocene period across the Levels, the only further up the estuary. It boasts the have produced a varied sea bed of surviving peat bog on the Levels second highest tidal range in the flats and bars, with associated shal- is on the Caldicot Level south world, between 12 and 14m, which low waters and numerous shoals. of Magor. There are also some is second only to the Bay of Fundy The strong tidal streams, combined localised areas of peaty soils found in Canada. with the gradient of the seabed across the back fen. These most and thick mud, sand and gravel commonly occur as a layer of peat The Severn Estuary has seen sediments, produce waters of high covered by a clayey topsoil, but major and minor fluctuations in turbidity with an opaque brown where the soft black peat extends the heights and range of tides coloration and constantly shifting to the surface these areas are since the last glaciation caused by sediments and water depths. particularly wet. variations in both the land and sea level. During the last 7000 years, there have been huge changes in sea level with fresh water habitats on the Gwent Levels inundated by the sea. Living Levels 46 Part One – The Scheme Plan / Introducing the Gwent Levels Landscape Image Credit: Stuart Wilding Historic Landscape The initial eforts to drain parts both on the Levels and on the well as a record of the changing of the Levels were made during dry land. Monks Ditch appears to environment covering many the Roman period (AD 43 - 410). represent a clear boundary within thousands of years. Recent years The full extent of this drainage the Levels, with land to the east has shown that entire prehistoric remains unknown and most of the potentially being held by English landscapes lie buried in the Levels. reclaimed land was subsequently lords whilst that to the west was flooded. However, some of the held by Welsh landlords (Rippon, The Levels are also rich in major drainage elements and axial 1997; 2014). earthworks preserving elements of alignments within the present the medieval and later landscape. landscape could have been first Over the last few decades the These include several moated established during this time (Allen field patterns on the Gwent farmsteads, sea and reen-side et al., 1992; Fulford et al., 1994; Levels have been studied in order banks and surface ridging in fields Rippon, 1996; Marvell, 2004). Any to understand the history and created to improve drainage. sea wall constructed at this time is sequence of this reclamation likely to have been seaward of the and the establishment of the The distribution of major archaeo- present one and no evidence has drainage network. The process logical discoveries shows a marked survived for a Roman sea wall. of reclamation and settlement bias towards the intertidal zone, was not constant and certainly since this is where the alluvium The current landscape of the there was a time at the end of the that overlies the prehistoric and Gwent Levels is predominantly a 14th century when population Roman landscapes has been result of the process of drainage decline and climate change led eroded away. Like the peat layer and recolonisation which to the (temporary) abandonment itself, this density of archaeological commenced during the Medieval of some areas of land (cf. Rippon, sites is likely to continue inland, but period (c. AD 1066 - 1500). This 1996; 1997). simply lie undiscovered. Another was linked to the post-Conquest concentration of sites lies along the settlement of south Wales and The Gwent Levels consist of up fen-edge, where there has been the influx of English settlers with to c.13m of alluvium and peat, considerable development expos- associated socio-economic stratified within which there ing the archaeological remains. elements that afected land are abundant traces of people’s ownership and land use. Some of exploitation of that wetland A variety of processes have led to the drainage may be associated environment during the prehistoric the creation of the “historic land- with monastic ownership and the period onwards. Particularly scape”, giving rise to diferent areas establishment of grange farms rich are the peat deposits, which possessing their own character. preserve wooden structures as A broad distinction can be drawn between landscapes created in a gradual way, and those that were Living Levels 47 Part One – The Scheme Plan / Introducing the Gwent Levels Landscape Image Credit: Ray Ok Figure 4 — Topography and Hydrology laid out in a single episode. fen. These areas tend to have Water Management and the landscapes of an “intermediate” Drainage System The former can be termed nature; rather more regular in lay- The distinctive pattern of the “irregular”, and are of great out than the “irregular landscapes”, drainage system in the Gwent complexity. They have small but not so rigidly planned as the Levels landscape is illustrated on irregularly shaped fields, often “regular” variety. Intermediate Figure 4. incorporating the meandering areas are characterised by a fairly lines of former tidal creeks. A rectilinear pattern of fields and The method of drainage was first piecemeal process of landscape roads, with just the occasional established in the Levels nearly formation occurred, in the farmstead or cottage. 1800 years ago. It takes the form eleventh to fourteenth centuries of a hierarchy of drainage (“high medieval” period). Roads The “regular” landscapes are very channels, which are now of are sinuous and broad, often with diferent. Their fields are rectan- considerable historic and nature an abundance of roadside waste; gular and occur in large blocks conservation importance. these “droveways” were vital for of similar sized fields. The roads moving livestock from summer to are straight and narrow, lacking The maintenance of this system winter pastures. Settlement was roadside waste. There is very little has always been a co-operative ef- dispersed, with hamlets, isolated settlement, mainly as these fort by farmers and the authorities farmsteads and cottages scattered landscapes occupy the lowest- in power. The former have tried to throughout the landscape. There lying land. A very diferent process protect their livelihoods and were a number of commons that of reclamation was responsible for prevent fertile lands being de- became the focus for settlements their creation; the large-scale and stroyed by flood. The latter, (e.g. Broadstreet in Nash; Whitson; rapid enclosure of extensive tracts beginning with the Roman legions and Peterstone). of land, in a single episode. and continuing with the medieval monasteries, marcher lords, the Colonisation started on the higher In addition to the distinctive Commissioners of Sewers, and ground towards the coast. The and characteristic field patterns a range of modern bodies, have lower-lying “back fen” was only belonging to diferent phases of been seeking to preserve their drained later, as population rose, enclosure described above, other interests in, and responsibilities for, increasing the demand for land.