MRA Response to Affinity Water Options Report - August 2013





Misbourne River Action (MRA) is delighted to have been invited to comment on Affinity Water’s Option Appraisal Report (OAR) and grateful for the interesting and frank briefing held at The White Hills Centre on 01 July and subsequent discussions recently.   We are also extremely encouraged to learn that Affinity Water (AW) and the Environment Agency (EA) have now agreed on target abstraction reductions from the Misbourne catchment of 5 Ml/d (within a total reduction of 73Ml/d of which 28Ml/d from the Chilterns catchment).  We note that this development will supersede some sections of the OAR.

Clearly  various factors that have to be reconciled in creation of the Asset Management Plan are complex and contradictory.  We do not have the facts or expertise to meaningfully comment on Affinity Water’s network options for replacing borehole sourced Deployable Output (DO) – particularly as these will be global in nature rather than specific to the Misbourne as assumed and costed in the OAR 

We note that the OAR and this agreement comes after more than 25 years of investigations and reports produced with differing conclusions by a range of consultants in response to different commissioning bodies.  In our view, if deemed realistic and supported by political will, the final recommendations of this exercise will have a strong chance of being implemented through funding within AMP 6.  It is therefore possibly the most important Misbourne study of our generation and it is essential that this opportunity to address the issue of low flow in the river’s central section is seized and maximised.  There is unlikely to be another in the foreseeable future.

We are very surprised and disappointed that some sections of the OAR suggest that occasional drying of the river should be accepted.  The whole focus of attention for many years has been the elimination of periods of no flow with their attendant set-backs to the fragile ecosystems.  The notion that intermittent flow is a natural or desirable feature of mid catchment chalk-streams, and particularly of the Amersham to Chalfont Park section of the River Misbourne, is not accepted by our environmental advisers, our members or, we believe, the public.  There is a complete difference between the upper winterbourne reaches of a chalk stream and the mature lower reaches.  It should be noted that, after months of good flow following the dry period 2010 – 2012, the invertebrate populations show only modest recovery.  Fish, and indeed herons, have yet to return to the valley between Amersham and Chalfont Park. 

We read with interest the sections of the OAR describing the computer programme “DRIED-UP” but do not consider that it is well suited for this application.  We also note its very limited previous use and lack of calibration.  As commented above, other respected experts using different methodology have completed much work previously recommending substantial improvements.  We are very concerned by indications within the OAR that counter-intuitive suggestions derived by this programme could be adopted in support of a low-cost minimal scheme

To MRA the principle that drying-out is to be avoided is paramount (as it is to The Chilterns Conservation Board, The Chiltern Society, The Chalk Stream Charter and others).  We will campaign and lobby to establish this goal.  (Of course we accept there can never be an absolute guarantee of constant and continuous flow but this should be a design objective under all normal scenarios).

We note that a variety of minimum flows have been mooted over the years and are discussed in the report along with some new, lower, values.  It is extremely disappointing that the very least of these figures is suggested as a target flow.  Over 25 years ago, consultants recognised that a minimum flow of 2.5Ml/d was an appropriate minimum target, that it was unlikely to be achieved through ALF1, and that further work in the form of an ALF2 would be required to deliver a sustainable regime.  We do not accept the suggestions that 1.0Ml/d is a viable target and draw attention to the attached photographs showing a trivial flow of 1.75 Ml/d in a small spring-fed tributary of the river at Chalfont St Peter and, by contrast, a flow of 12.7Ml/d in the river itself.

We are therefore unable to support any Option that does not deliver a very high chance of constant and continuous bed wetting and a target flow of greater than 2.5Ml/d at all locations at all times.

Substantial sections of the OAR are concerned with analysis of groundwater levels and data from the trials undertaken during 2011.  The situation at the time of the trials was unusual and very volatile with the river drying up at a rate in the order of hundreds of linear metres per day and groundwater falling in some locations by 0.5m to 1.0m in a month.  We do not find some of this work convincing and would be happy to debate the accuracy of these sections in the light of our records.   However, we doubt that would lead to any major changes in the overall conclusions as, basically, all parties agree that current abstraction affects flow in the river, particularly in drier periods.

Turning to consideration of the Options presented, the difficulty of objectively and comprehensively analysing and comparing all Options and sub-sets is apparent.  While fully understanding the issues and the commentary, we do not have the operational data, or current information regarding other parameters (such as the long overdue Abingdon Reservoir) to enable a valid detailed critique of the input and output figures and costs tabled.  However, using the headings of the OAR in the order presented, we offer the following:

1.0 Reduction in Abstraction: In principle, reduction in abstraction overall is seen as “desirable”.  We believe that ALF 1 reduced regular abstraction from the Misbourne catchment by some 50% - from approx. 30Ml/D to 15 Ml/d – in 1997.  This reduction produced a noticeable improvement, particularly in the reaches from Great Missenden through to Amersham.  From the OAR we learn that current annual average abstractions by AW total 12.0 Ml/d and assume that the difference (15Ml/d – 12Ml/d = 3Ml/d) represents abstraction by others.  The proposed reduction in abstraction of 5Ml/d for DO agreed with EA therefore represents a useful but only partial improvement of 33% of current totals – (42% of AW’s totals).

Study of groundwater levels vs rainfall vs flows indicates that flows from the source as far as and beyond Great Missenden are dependent upon groundwater levels in the hills.  This upper section is the true winterbourne and, as noted in the OAR (p47), the abstraction at Great Missenden (1Ml/d) has a relatively minimal impact on flow.

On the contrary, abstraction at Amersham and Chalfont St Giles has a noticeable effect on ground water levels.  While a complex issue, involving consideration of differing chalk types and other factors, it is inescapable that the depth of groundwater levels below bed level is greatest around Chalfont St Giles and accentuated during summer/dry periods.

We are therefore particularly keen to see abstraction reduced at the Amersham and Chalfont St Giles Sources.  Setting aside the possibility of augmentation at this stage, and assuming there are no overriding operational imperatives, our expectation is that the agreed 5Ml/d overall reduction would be best realised as 3Ml/d at Amersham and 2Ml/d at Chalfont St Giles.  We would be delighted to assist in measurement and observation of trials with various ratios.

We would welcome confirmation that the above may be considered a minimum assured position.  Nevertheless, we consider that some additional measures will also be required to achieve the modest sustainable minimum conditions we seek.

2.0 Relocation of Abstraction/replace resources:  In the light of the subsequent agreement with EA to reduce abstraction by 5Ml/d from Misbourne sources, we assume that “relocation of abstraction” can only apply to the remaining 7Ml/d.  Full closure of the three existing pumping stations would clearly have additional benefit to the challenged reaches of the Misbourne.  We doubt that new boreholes at Gerrards Cross or Denham would adversely affect flow in the Misbourne.  However, we are uncertain of the wider environmental impact of such a development and are mindful of the high costs associated with reconfiguring and extending the distribution network.  Perhaps conclusively from our point of view is the fact that closure of the existing sources and relocation elsewhere essentially eliminates any opportunity for using part of their output for recharge in the short or longer term

As noted elsewhere, we are not in a position to comment on AW’s alternatives for replacing resources from other assets.

3.0   Water demand management:  In view of the substantial anticipated reduction in abstraction from the Chilterns and the background of pressure on water supplies nationally, management of demand must be part of AW’s proposition to Offwat.  MRA will be pleased to support a variety of measures – e.g. compulsory metering, water saving fittings, education, etc.   In so far as they may facilitate other measures, e.g. reduction in abstraction, these campaigns are helpful to our aims but do not directly affect river flows.

4.0 STW Effluent return to the Misbourne:  In our opinion, due to costs, public opinion, and other factors the Option of a new STW at Amersham may be ignored.   Further, the many years programme for such a development would be extremely unattractive and would remove any trace of certainty of improvement to the current lamentable situation.

 We would expect that return of water from the river Colne, either from above (chalk stream flow?), or below (dilute treated effluent?), to the Misbourne would have higher capital and operating costs than augmentation from boreholes in the Misbourne valley.  However, if expert advice demonstrated advantage, we have no objection in principle.

5.0 River support from new augmentation boreholes:  a minimum 5Ml/d reduction in DO from abstraction prompts two new questions:

       a.      Can the 5Ml/d “saved” continue to be abstracted for use in augmentation to secure the required                                     environmental benefit?

       b.      Similarly, on the basis that it returns to the river and has no net effect on the catchment, can                                       additional abstraction be developed for use in augmentation?

Substantial augmentation involving significant extra targeted abstraction can be postulated – say to an “ideal” of greater than 10Ml/d design flow at all locations.  However, this would undoubtedly and understandably fail to gain support with EA and attract adverse opinion from many quarters, not least on the grounds of “waste of energy/water/money”.  It might also introduce a flooding risk when added to natural storm flows unless carefully and reliably controlled.  In short it would not be considered a sustainable option. 

However, to secure the minimum goals of continually saturated bed and minimum flow, an additional augmentation borehole delivering a modest 1 – 2 Ml/d during periods of low flow in the Chalfont St Peter area would, in our opinion be extremely beneficial.  While the ideal location might be opposite Cherry Acre, practicality and land ownership issues would suggest that adjacent to the Chalfont St Peter tennis courts on council owned land and taking advantage of the existing 415V supply would be a more realistic alternative.  Given the lack of any need for treatment, minimal length of cabling or pipework, minimal suction head and the modest (and occasional) flow required, we envisage costs for this proposition would be relatively minor.  We believe the high level of environmental benefit (this site is immediately adjacent to a wetland nature reserve) and amenity enhancement provide a strong benefit:cost ratio and strongly recommend its inclusion as a secondary item within AW’s overall submission.

6.0 River support from AW boreholes:  In 1) above, we recommend that the given reduction in abstraction for DO is concentrated at Amersham and Chalfont St Giles.   However, we consider that the environmental and amenity benefit of this reduction would be significantly leveraged if current levels of abstraction were maintained during periods of low flow and the 5Ml/d not being used for DO were returned to the river as augmentation. 

MRA is extremely keen to work with AW to study the effects (including costs) of balancing flows into service with flows into augmentation taking account of peak demand times etc. 

A further advantage of retaining the boreholes at Amersham and Chalfont St Giles, rather than re-locating, is the potential for their use for augmentation and we hope that, in the event of any serious low-flow situations, AW will also work with us in the future to provide support to the river from these facilities.

7.0 Bed lining:  The Chiltern Society strongly supports bed lining of two specific short sections.  Given the low cost associated with this work and the value it would bring as full-size trials for other Chiltern rivers, we would be pleased to support this as part of a package of measures.

8.0 Restoration of river channel to its original course:  Noting that it would be almost impossible to decide what “the original course” might have been, and considering the risks of seriously exacerbating losses, the enormous difficulties associated with land issues, the limited river length currently apparently “off course”, and complete lack of any evidence or science to suggest that re-location would lead to any improvement, MRA strongly recommends that no further consideration is given to this Option.

9.0 River re-profiling/habitat enhancement: Over the past 5 years of activity, we have noticed the ability of the river to establish an efficient profile, exposing the all-important gravel from very severely overgrown, flat, shallow sections with only a little assistance provided there is adequate flow.  It should be noted that the mid to lower sections of the river carry large (>15ML/d) flows frequently after heavy rain.  MRA considers that extensive re-profiling is unnecessary downstream of Amersham – with the exception of the reach immediately below Bottom House Farm Lane - and is comfortable that volunteer work can suffice for the time being.

Similarly, habitat enhancement is an area where MRA is comfortable to continue to work at a local level on small tasks and projects under the overall guidance of the Chiltern Conservation Board without call for major funding.  Our view is that the most significant element of habitat enhancement, without which all else fails, is the provision of significant and constant flow.

10.  Creation of a dual flow river profile: See 9 above.

11.  Do nothing:  We are delighted that continuing to “do nothing” is agreed not to be a viable Option. 


·       MRA is delighted to note the agreement between AW and EA to reduce abstraction for DO by 5ML/d and strongly           recommends the relevant parties to adopt this (or a greater reduction) in the AMP6.

·       MRA is happy to endorse proposals for limited bed-lining and notes these have a relatively small cost and significant         value as full-size trials.

·       MRA considers that reductions in abstraction for DO should be targeted on Amersham and Chalfont St Giles                   sources and, further, that these should be retained and used for the provision of modest augmentation during               periods of low flow.

·       MRA recommends the construction of an additional borehole facility at Chalfont St Peter of say 2Ml/d capacity for           augmentation use in periods of low flow.

·       MRA would be very pleased indeed to work closely with AW to develop and study these proposals, including making         observations from further trials.

·       MRA echoes the OAR conclusion that “Do Nothing is not a viable Option.

·      MRA does not consider that Options 2 (Relocation of Abstraction), 4 (STW Effluent return to the Misbourne), 8)              Restoration of river channel to its original course), 9 & 10(Re-profiling, with the exception of very local stretches),          warrant further consideration at this stage.

·      MRA cannot support the proposition that routine drying has to be accepted, nor that a flow of 1.0Ml/d is an                    appropriate goal.  We have been deeply concerned that this unique opportunity for significant improvement to the          river corridor environment is put at risk by these notions. Our minimum goal is a flow of 2.5Ml/d in all reaches                below the perennial head in Little Missenden.