Aggregate Industries' surface water management plan for Straitgate Farm has yet to be approved. In 2016, we posted: Pre-Commencement Condition 6 states:
Watercourses originating from Straitgate pass through four communities downstream; communities that are prone to flooding. Any quarrying at Straitgate Farm must not make the situation worse, either during work or afterwards. DCC has requested that any plans make the situation better. How this could be so, with the loss of millions of gallons of groundwater storage capacity in the unsaturated layer of sand and gravel on top of the hill above these communities, remains to be seen.
No development hereby permitted shall commence until a Construction and Environmental Management Plan... has been submitted to and approved in writing by the Mineral Planning Authority. The Plan shall include... (d) details of the management of surface water during the construction and soil stripping phases
The plan is still up in the air because the company has yet to produce any reliable infiltration rates. Condition 13 states:
(b) Updated infiltration tests shall be carried out using an infiltrometer and shall be undertaken in strict accordance with BRE Digest 365 Soakaway Design (2016) and must be undertaken within the Budleigh Salterton Pebble Beds. A representative number of tests shall be conducted in order to provide adequate coverage of the site, with particular focus placed on the locations and depths of potential infiltration devices;
The results of these tests will inform the size of attenuation ponds required to stop downslope flooding, remembering Condition 25 which states:
No water body shall be created within the site other than the approved weigh bridge lagoon.
Why is it important to get these infiltration tests right? Look at the problems at Venn Ottery, with fingers being pointed towards Aggregate Industries' worked-out sand and gravel quarry, uphill and nearby.
More than a million tonnes of material were removed between 2011 and 2016, material that would have previously acted as a 'sponge' for rainfall above a downstream community.
We’ve posted about surface water run-off problems from this site before.
Back in 2015, Devon County Council admitted in correspondence that flooding in Venn Ottery was "to do with the quarrying activities". Newton Poppleford and Harpford Parish Council minutes also reported:
Cllr Cole reported that the Quarry Manager was taking further remedial action to create a better settlement ponding system and other works to alleviate the problem of the Neighboring fields being washed out. A new pipe was to be placed under Green Lane where it had washed out.
In 2016, Devon County Council's monitoring report for the quarry reported:
Significant amount of run off was present in the waterbodies at the time of the visit.
In the same year, local people – in response to the company's planning application to restore the quarry to a higher level than was previously approved following "an error with the previous estimated amount" – reported "ongoing issues with surface water run-off from the quarry". The Council responded, saying:
6.22 It is accepted that there have been a few occasions when surface water has discharged from the site, but in these instances the operator has acted quickly to remedy the situation and it is considered that the final restoration of the site (which includes water storage features) will adequately deal with any surface water issues.
Clearly, it hasn't, and the problem has become worse.
Last year, Venn Ottery "experienced its worst flooding event", according to the Venn Ottery & Southerton Residents Association. A Devon County Council report says nine properties were flooded internally. VOSRA claims:
The increased run-off from the (now closed) Venn Ottery Quarry brought a river of water along the track from the Otterdene area to Venn Ottery green, where it crossed along 2 routes to join the stream that runs alongside the green and through the back gardens of 1-5 Barton Mews.
VOSRA compiled an extensive dossier of previous flooding events – including the map below – which was sent to East Devon District Council, Devon County Council, the Environment Agency, and the local MP. The dossier claims:
From about 2012 onwards residents in the houses on west side of Venn Ottery green have noticed an increase in the volume of water running along the unmetalled road and across the green. Within a couple of years of starting quarrying in 2010, water from the quarry site caused the track that runs westeast from the Otterdene (Happy Valley) area towards Venn Ottery to become impassable, and the field nearby to (behind Dartwood, Brookdell) to be waterlogged. Similarly, ’Puddle Lane’ became even more muddy. When requested by the local community, Aggregate Industries provided quantities of pebbles to improve the drainage and raise the level of the track to some extent.
The quarrying ceased and in 2017-18 the land was ‘restored’. An area on the northeast was formed into an attenuation lake to hold back excess water run-off. The lake is not very large so cannot always retain all the water, which then runs downhill and into VO.
VOSRA is calling for action:
The attenuation pond at the eastern corner of the closed quarry site is undersized and has no controls on overflow. Extension of the pond and the installation of a sluice to control the outflow could greatly reduce the speed at which water flows.
How did this attenuation pond come to be so undersized, when such important details should have been scrutinised by Aggregate Industries’ expert consultants, as well as the relevant statutory bodies?
Could it be that infiltration rates in this material – the Budleigh Salterton Pebble Beds, the same material as at Straitgate – were assumed to be higher than in reality? At Straitgate, Aggregate Industries assumed inflated infiltration rates of 1m/d to size attenuation features, ignoring results of soakaway tests, which showed "Insufficient drop in water level".
The problems at Venn Ottery, however, don’t stop at downslope flooding.
A bridleway was provided by Aggregate Industries on the eastern side of the site as a condition of the S106 agreement associated with processing the material at Blackhill, to "provide a safe alternative for part of the HGV route".
Last month, part of the bridleway was washed away. Water running off the site has left a deep, unsafe canyon, and the bridleway has been closed.
Once upon a time, in answer to critics of the Venn Ottery plans, Aggregate Industries claimed:
We shall be putting back a lot more than we're taking away.
Locals, bailing water out from their houses, having their PROW swept away, might not be so sure.
