Wednesday, 4 July 2012

Why did Straitgate Lake increase in size?

With water being such an important issue at Straitgate we were not surprised to see a water feature of some sort on the 1967 restoration plans. What did surprise us was its size - "Straitgate Lake" was to cover 32 acres. However, between February 1967 when the plans were submitted, and 9 July 1968 when the Public Inquiry started, Straitgate Lake had "grown" to an even larger 49 acres. From the report by the Inspector to the Minister of Housing and Local Government, then the Right Honourable Anthony Greenwood MP, 8 October 1968, on the applications to quarry at Blackhill on Woodbury Common, Colaton Raleigh Common, and Straitgate Farm, it seems apparent why this happened. 

In the submission by the Devon River Authority (now the Environment Agency) the report talked about the likely effect on flooding: "342) Villages affected by flooding from those areas generally including the proposed sites are as follows:- ..... Cadhay [from] Straitgate". (Thorne Farm estate had not yet been built.) "343) Although the pattern of development of these villages renders the present flooding conditions tolerable to some extent, any increase in the frequency and extent of such flooding as a result of the company's proposals would be intolerable. 344) Control of such flooding could be effected by means of either:- (a) Additional flood relief channels and culverts within the villages, or (b) Use of the proposed lakes for "balancing" flood flows with appropriate settings of the proposed overflow weirs. 345) Agreement in principle on the second solution has been reached between the river authority's officers and the company's representatives, and only matters of detail e.g. the precise settings of the overflow weirs, remain to be finalised."

It would appear therefore that Straitgate Lake had grown from 32 to 49 acres by negotiation in order to satisfy the requirements of Devon River Authority in mitigating the flooding effects on Cadhay. This scheme was only possible because the eastern half of the site was to be quarried creating a void of sufficient proportions. Today there is no plan to quarry this area: DCC states "site appraisal found that there is likely to be a significant impact on the water environment (and consequently on biodiversity) if mineral extraction occurred in the eastern half of the S7 site", and it did not therefore form part of the Consultation. To create an area now to hold the amount of water planned in 1968 would require the extraction of approximately 1.2 million tonnes of material. We wonder how much area Aggregate Industries are now proposing to set aside to capture storm run-off to protect the residents at Thorne Farm, Cadhay, Salston and Coombelake from flooding? 

It was also clear from the Public Inquiry report that the Devon River Authority did not believe that ECC's proposals to recharge the aquifer would work. "336) As to the recharge proposals; the company seek to effect flood-control, maintain river flows, and recharge the aquifer sufficiently to compensate the losses as a result of the proposals, all by means of lakes formed from silt ponds. 337) These are incompatible objectives, and in particular such experience as exists on the artificial recharge of aquifers indicates the impracticability of the proposals in that respect. 338) This is apparent when the recharge proposals are considered in more detail. The shallow - sloping faces of the Pebble Beds intended to effect the recharge would experience silting on the lower and weed and algae growth on the upper sections, thus achieving the opposite effect. Furthermore the lakes would range in level from about their full 10 feet depth to perhaps 6 feet depth in extreme conditions. Therefore accurate control of the rate of recharge would be impossible with such wide variations, and the wide band of expected Pebble Beds when lake levels were low would encourage weed growth still further."

Something to bear in mind if Aggregate Industries think they can maintain the wetland habitats of Cadhay Bog and Cadhay Wood through recharge ponds; the ponds that would of course be contrary to the advice of Exeter Airport.

Cross section of 1967 restoration scheme