Caul Bourne

  • The River Caul Bourne and its tributaries rise from a series of springs emerging on the northern flanks of the Isle of Wight’s central chalk ridge, and flow for less than four miles across Tertiary sands and clays before entering The Solent, at the entrance to the Newtown Estuary.
  • View our film about how this river behaves around a meander bend and the channel features that can be produced.
  • The spring-fed pond in Westover Manor on the edge of Calbourne village is the source of the main river. The discharge can increase dramatically when the water-table is high following a period of prolonged rain. This video clip shows the river in spate in front of the beautiful chalk cottages in Winkle Street in Calbourne Village
  • When the water-table rises as the chalk aquifer fills, new springs emerge, pouring out onto the road and into channels which remain dry for most of the year (see video clip)

Report of The National Rivers Authority, Southern Region, July 1994

FLOODING AT SHALFLEET, ISLE OF WIGHT
Executive Summary

1.1 The purpose of this investigation is to determine the causes of flooding at Shalfleet, Isle of Wight. The investigation was initiated following the flooding which occurred on the 30th December 1993, when 4 properties suffered.

1.2 The Caul Bourne drains a catchment of approximately 16 km2 in the NW corner of the island and discharges into Shalfleet Lake, part of the Newtown River estuary. The watercourse is classified as main river for a length of approximately 8km from Calbourne to its outfall.

1.3 At Shalfleet the river divides upstream of the road bridge. The main watercourse falls some 2m and passes beneath the road bridge. A mill race continues at a higher level for approximately 400 m before falling 3.5 m at Shalfleet Mill at a downstream limit of the river.

1.4 The event of 30th December 1993 followed a period of 8-hour duration rainfall with a return period of approximately 7 years. Flood water rose to 0.5m above road level and inundated 4 properties to depths of up to 1.5 m.

1.5 This event has been assigned a return period of around 10 years. Whilst the low moisture deficit of the soil following prolonged rain in December could point to an underestimated return period, historical flooding records indicate a return period of 1 in 10 or less.

1.6 The combined capacity of the road and mill race culverts have been estimated as 10.8 cumec before the threshold of property flooding is reached. Blockage of the main culvert during the flooding substantially reduced this capacity.

1.7 Drainage for a 1 in 50 year event have been assessed as £21,765 and the net present value of benefits as £12,000.

1.8 With a comparatively small amount of benefit, the scope for carrying out flood alleviation measures is very limited and no proposals are considered.

3 Flood Damage

Properties flooded and damage cost estimate:

Yew Tree Cottage £17,878  (flood level 1.47m above floor level)
Brookside £7,289                       ”             1.33m        ”
Creek Cottage £7,289                ”            1.33m       ”
Brook Cottage £3,181                ”             0.22m       ”

 

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