The Darent Cray Catchment

Topography: The Darent – Cray catchment covers about 400 square kilometres to the south of the Thames estuary. It is bounded to the east and south by the Medway catchment, and to the west by the Ravensbourne catchment. The River Darent is fed by a number of short headwaters which originate in springs surfacing to the south of Otford on either side of Homesdale, the valley between the North Downs escarpment and the greensand hills to the south. These springs arise where underground water percolating the chalk Downs and the greensand ridge encounters the impermeable Gault. Clay underlying Homesdale. North of Otford rainwater is absorbed by the chalk, and drains northwards within the chalk aquifer, resurfacing only on encountering impermeable strata around the Cray valley, giving rise to the River Cray, and points further west, where the headwaters of the Ravensbourne catchment originate. The course of the Cray is deflected from the Ravensbourne catchment by the high ground around Chislehurst, and bears eastwards to be joined by the Shuttle near Hall Place. The small Stanham River joins the Cray in the tidal Crayford Creek just before the confluence with the now tidal River Darent between Dartford and the junction with the Thames estuary a little to the east of Crayford Ness.

History: The average flow of water has dwindled considerably, even within recent years. Considerable quantities of clay, sand and gravel have been extracted for the building industry, leaving large and deep flooded pits in Homesdale, the Darent valley and the Cray valley. Although water is not being taken directly from these rivers, appreciable quantities are abstracted through boreholes in their adjacent aquifers. In the summer of 1991 the Darent dried up completely, and as early in 2006 as February the ponds in Priory Gardens, Orpington were emptying following two consecutive winters of low rainfall. Conversely, following an abnormally wet winter Priory Gardens were waterlogged early in 2001. The greater volume of water in earlier centuries is evidenced by contemporary illustrations and the number of water mills along the Darent and Cray. None of these mills now function. Some of the mill buildings have been converted to housing and other uses; the remainder have gone, their sites identifiable by weirs and mill ponds. Associated industries, such as paper making, have declined and closed. The nature of the watercourses has been considerably affected by human intervention. Water flow is regulated by weirs. Long ago canals were cut to divert the natural courses of the tidal Darent and the lower Cray. Numerous ditches have been cut in agricultural areas to drain or irrigate the land. In urban areas, linked land drainage systems remove rain water through pipes instead of the natural watercourses. Flood alleviation schemes include raised banks and culverts.

From sources to the Thames:

*All map references in this pack are within the 100 kilometre square TQ of the National Grid The first three digits define ‘eastings’ to the nearest 100m, the last three digits the ‘northings

Westerham Westerly: The westernmost limit of the Darent catchment is formed by the saddle of relatively high ground at the head of Homesdale around Limpsfield Common, just Within Surrey. To the west of here, the River Eden and its tributaries flow southwards. To the east, Homesdale slopes gently eastwards from nearly l50m / 490’ above sea level for seven miles to 64m / 210’ at the head of the Darent ‘valley between Sevenoaks and Otford. The river follows the valley floor, as does the A25 road. It first surfaces at 416529* in a hedgerow adjacent to wetland just within the Darent catchment and the county of Surrey. One mile downstream it is joined by a stream flowing south from the Clacket Lane services area of the M25 motorway. Just before reaching Westerham it is augmented by a short channel flowing from the lake in the grounds of Squerryes Court, another source. After a further 300m it flows into a pond beside the foundations of a former water mill. This pond is also fed by the principal headwater of the Darent, which originates in springs around Crockham House, one mile to the south at 4485l9*, over 160m / 525’ above sea level, on the north slope of the greensand ridge, which forms the watershed with the Eden.

Sundridge Sundries: Between Westerham and Sundridge the Darent is joined by sundry short streams descending from the north and a longer stream originating at 462524, nearly l’/‘Om / 560’ up on the greensand ridge below Toy’s Hill, and passing through a string of ponds beside Valence Wood on its journey to Homesdale.

Chipstead Claypits: Below Sundridge the river fills large worked out clay, sand and gravel pits near Chipstead which are now used for fishing and sailing. It is joined by a stream originating from springs on the north slope of Ide Hill which passes through Dryhill on its way to Chipstead. This flows for over three miles from its highest source 170m / 560’ above the sea to a lake about 73m / 240’ high. Another stream surfacing two miles south of Chipstead at 508531, over 140m / 460’ up, descends through ponds towards Riverhead. Ponds in Bradbourne Park feed the Darent through the lakes of the Sevenoaks Wildfowl Reserve between Sevenoaks and Otford.

Eastern Extent: The valley floor between the North Downs and the greensand hills rises from about 60m / 200’ south of Otford going eastwards for several miles to a high point at about l07m/ 350’. From the lake at Lower St Clere, 578587, about 116m / 380’ up on the southern slope of the North Downs, the Honeypot Stream flows southwards to the valley floor before following the railway westwards to join the Darent south of Otford alter four miles. Other minor streams and ditches drain the valley, which is boggy in parts and contains many small ponds. There is a mill pond and former silk mill at Greatness with a stream flowing northwards to the Darent, and also a large working quarry.

Otford Orifice and Chalk Channel: Where the head of the Darent valley crosses Homesdale between Dunton Green and Greatness, the course of the river changes from east to north through the shallow sided valley leading to Otford. Here it is joined by the stream from Greatness, the Honeypot Stream and the Bubblestone, a short stream fed by St Thomas a Becket’s Well in Otford. There are other springs hereabouts, including one filling the duck pond within the roundabout at 528593, and another feeding a stream which crosses the Pilgrims Way at the corner of Rye Lane. Springs at 508592 source the Twitton Brook, which flows NE to join the Darent just to the north of the point where it enters the breach in the North Downs escarpment. This gap is out of all proportion to the size of the present day Darent. The ground rises gently from the valley floor about 60m above sea level for a kilometre on either side before topping 80m. The valley sides then steepen rapidly before beginning to level off at around 200m, where the Polhill and Otford Mount sides are some 4krns apart, and cease to rise on reaching about 210m, some 150m above river level. The cross sectional area of the valley where it penetrates the crest of the North Downs is between 400,000 and 500,000 square metres. This area diminishes steadily moving downstream, but the total volume of rock which is missing is some two billion cubic metres (ie two cubic kilometres), weighing some billions of tonnes.

How did such an immense channel come into being? The chalk was formed by the submarine deposition of the skeletons of marine creatures to form a horizontal sediment. At some time the chalk and other underlying sedimentary rock strata must have been pushed upwards to form the Wealden Dome, a hump back several times the height of the present day crests of the North and South Downs, midway between the troughs of the Thames valley and the English Channel. This high ground would have attracted heavy precipitation, which would have drained rapidly northwards to the Thames valley, forming straight north facing drainage channels. With no major nearby competitors, the Darent would have conducted immense volumes of fast flowing water, which would have rapidly cut a wide, deep and straight channel through the soil chalk to the Thames valley. Eventually the layer of chalk between the crests of the North and South Downs was completely worn away, then the underlying gault clay south of Homesdale, then the upper and lower greensand south of the present greensand hills. Finally some of the Weald sand and clay were washed away from the Central Weald, within which steep sided ghylls now run in all directions according to the local lie of the land. No water now reaches the Darent from the Weald due to the watershed formed by the greensand ridge, precipitation on the south side of which drains southwards into the Eden and other streams before being conveyed eastwards through the Medway, which finally flows northwards to join the Thames estuary at Sheerness. The effective catchment area of the Darent is now reduced to Homesdale and its adjacent aquifers, as the permeable chalk on either side of the Darent valley inhibits the formation of feeder streams downstream from the Twitton Brook.

Farningham Flatland: From Otford to Farningham the sides of the Darent valley rise steeply to the Downs above. Downstream from Farningharn the valley sides rise more gently to altitudes of less than 100m. The more horizontal landscape is accentuated by large sheets of water over worked out quarries which now serve as fishing lakes. From South Darenth to the M25 motorway the river forms two parallel streams with lakes and the moated NT property St John’s Jerusalem between them. After crossing Central Park the river is canalised through the centre of Dartford and an industrial estate before being joined by the Cray on Dartford Marshes.

River Shuttle and Wyncham Stream: The River Shuttle rises at 439744, over 551111 180’ above sea level near the top of Avery Hill Park and its watershed with the River Quaggy to the west. After flowing southwards through the park it turns east for a mile before being joined by the Wyncham Stream. This stream has its origins in ponds and streams draining NNE from Chislehurst towards the A20. It is continuously visible from 448725 to its confluence with the Shuttle at 45873 8, over a mile to the NNE. The Shuttle continues to flow eastwards, eventually alongside the A2 trunk road, and joins the Cray just before it passes under the A20 to enter the grounds of Hall Place.

River Cray and Stanham River: The Cray (named the ‘Stoneham River’ in the 1805 first edition of the Ordnance Survey map) rises in a lake in Priory Gardens, Orpington, at 467668, over 50m / 170’ above sea level, and also at the head of a short side valley at 458672, over 70m / 23 0’ above the sea. It flows northwards through St Mary Cray, beside a private fishing lake at St Paul’s Cray and into a further area of private fishing and wildlife lakes underneath the A20 and A223 roads. After passing through Foots Cray it enters Foots Cray Meadows, which are open to the public. It widens considerably before passing under the attractive Five Arch(es) Bridge and over a weir. It goes over several more weirs before reaching The Old Mill, now a licensed restaurant, in the middle of Old Bexley. It is joined from the west by the Shuttle before going under the A20 into the grounds of Hall Place, open to the public. From here the river bears east over a flood plain to Crayford, where it is crossed by the Roman Watling Street. It has been canalised on its way to the the former Iron Mills at Barnes Cray, beyond which it is tidal. The nowadays insignificant Stanham River (which nevertheless forms the administrative boundary between Greater London and Kent) meanders through the flood plain south of the Cray canal. for less than a mile before entering Crayford Creek at 532755. Its original length was about two miles.

Cray – Darent — Thames confluences: The Cray joins the Darent through the tidal Crayford Creek at 537760. The final tidal section of the River Darent, otherwise known as Dartford Creek, was straightened in 1840. The original meandering course is still delineated by the flood embankment to the east. There is a flood barrier with drop gates across the creek 300m before it enters the Thames estuary, 500m down stream from Crayford Ness, at 541780, opposite the mouth of Mar Dyke on the Essex bank. As the crow flies it is 17 .4 miles / 28.0 kms NNE of the Limpsfield source at the head of Homesdale. The distance by river is 24-25 miles / 39-40 kms. From the Crockham House source it is 17.2 miles / 27 .6 kms by crow, or 23-24 miles / 38-39 kms by river.