The Environment Agency Flood map is helpful in tracing the suface watercourses - certainly when flooding might occur!
http://maps.environment-agency.gov.uk/wiyby/wiybyController?x=357683.0&y=355134.0&scale=1&layerGroups=default&ep=map&textonly=off&lang=_e&topic=floodmap#x=550564&y=167015&lg=1,&scale=11
Being on high ground Swanley (in the Swanley Hills) is not devoid of watercourses but I want firstly to describe bigger picture.
About 200,000 million years' ago I understand that the Swanley Hills were beneath the seas. [Going by the number of pebbles on my allotment I can well believe that point!] However, about 200,000 BC to 10,000BC it is likely that the Swanley Hills were under ice or severely affected by icy conditions. Thus, the cave shelters may confirm the late Ice Age conditions at Oldbury (Ightham). It seems that the downs may have been formed by moving ice. [This may account for my pebbles.]
Rivers and other Watercourses: The Swanley Hills are bounded by the River Thames (north-ish) and the River Medway (south-ish). Swanley is bounded at some distance by the River Cray (eg Foots Cray on the A20) which eventually flows into the River Darent (eg Farningham on the A20). The Darent flows nothwards into the River Thames - joining it after going through Dartford.
Flows towards River Darent (Sutton-at-Hone): I believe that all watercourses passing through the Swanley are underground. A huge hole which appeared a few years' ago - in the lower part of the High Street - had dye put in it which re-appeared in the River Darent at Sutton-at-Hone.
Excavations in the valley near the Iron Age settlement (off Wested Lane) revealed water flowing in a natural pipe in the chalk. [This may be part of the mapped watercourse on an Environmental Agency plan of watercourses liable to flooding (in Swanley). The plan showed a stream (or dry bed) flowing northwwards from the hillside towards the pond (London Road) - down under the railway and then northwards towards Hextable - it twists and turns and may be the same as the "piped" water course.]
Flows towards River Cray: A watercourse is visible as a "ditch" beside the A20 westwards of Swanley. it flows generally north-westly and (I suppose) enters the river Cray.
Finally, in very wet weather water collects in the fields near the Bull Inn (Premier Inn). It seems to be a "collecting area" and may be part of the source of the watercourse mentioned immediately above.)
Wells and Ponds: In Swanley the two surface ponds that I know of are situated at:
- a fenced pond enclosure with may fine trees - beside the B2178 east of the town centre opposite the St Georges Estate;
- a field pond near Five Wents - beside the lane to Swanley Village.
