Letter from EA Dated 15Th December 2016 Thank You for Sending Further

Letter from EA dated 15th December 2016 Thank you for sending further information relating to the above proposals. We offer the following comments. WBCT response in red. Water Resources and Hydrology While it has been very useful to see the water balance spreadsheet and the other documents recently submitted, unfortunately they have raised further questions about the canal operation particularly when the water balance spreadsheet is considered with the ‘Movement of Boats and Water through Melksham Link Waterway’ document. The latter document suggests water flows from Semington Pound into Berryfields pound each time the lock is operated whereas the spreadsheets suggest no lockage water is lost from Semington pound and consequently that there is no lockage inflow to Berryfiields pound. This means that the volume back-pumped from Berryfields pound is relatively small, which seems to contradict the document. It would be helpful to understand which is correct and if the spreadsheet is correct how the movement of boats through Berryfield lock will work, although we do appreciate it will not have an impact on the water demand on the River Avon. There is no contradiction here. It must be borne in mind that Berryfield Lock is of unconventional design in that it is filled by pumping water up from Berryfield pound, rather than by gravity through lock gear from Semington pound. So, when the lock is discharged, it is Berryfield pound water returning to Berryfield pound. There will, of course be some mixing of water between the two pounds when the upper lock gates are open, but apart from that, the two bodies of water will in effect, be segregated. This is also apart from the small flow of water required to replace Semington pound water lost through evaporation, seepage and leakage, which will be provided by a small pump independent of the large lock-filling pumps, and would run at agreed times and rate to feed Semington pound from Berryfield pound. Looking at the River Avon end of the canal it is now much clearer how it will operate with an intermittent abstraction and discharge regime, with water being discharged as boats move through the lock system and then Berryfields pound being refilled independently from the river. What we need to assess now is what impact this intermittent abstraction and discharge regime will have on the river. At times of low flow the 287m3 discharge and 302m3 abstraction could be significant when compared to flow in the river. We wish to see some hydrograph analysis of the potential impacts of the instantaneous abstraction and discharge on flow and level in the river. We suggest that the applicant presents what the impact on flows would be over a 24 hour period when flows are at Q95, i.e. show how the flows would go up and down over this time at the sub-daily time-step, using 15-min flow data. This is because the reported abstraction and discharge volumes are a significant proportion (i.e. reported ~ 33%) of the River Avon Q95 flow and have the potential to cause environmentally significant 'pulsing' of flow and level in the River Avon downstream. It would also be useful to see the impacts over a month at the daily mean level - we suggest an August when flows are low. This should be presented as several scenarios of potential operation, i.e. a worst case (i.e. no back pumping), as well as several scenarios around more likely typical operation under low flows. These should all take into account likely peaks of lockage within the week such as may presumably occur at the weekend or August Bank Holiday. We also wish to understand what impact the operation will have on levels in the river. We understand it is proposed to construct a new weir in the river to raise levels. How will the intermittent abstraction and discharge regime impact flows over the weir and on downstream? Will there be the potential for cessation of spilling flow over the new weir structure when flows are being abstracted from the River Avon? We have considered your request for some hydrograph analysis of the effect of lock discharge and abstraction for back pumping, on river levels in low flow conditions, and concluded that any attempt to predict river response with the data we currently have, would be unreliable. The reason for this conclusion can be appreciated if we consider the variables in the system which are: 1. The river flow data which is questionable. We are working on Q95 being 1 m3/sec but Mike Lee, the Project Team Engineer worked for the Bristol Avon River Authority in the 1970’s and recalls that even when the Melksham gauging station was working, the data it provided was unreliable. The Black & Veatch 2007 report included in Appendix 4.1 of the new ES gives flow estimates but comments that they “may underestimate flows appreciably”. River flows could also change in the future. Cooper Tires abstract a significant volume but they have publicly stated they are looking to relocate their plant. Longer term, climate change could have a significant effect on river flows. 2. The river bed profile we are working on is based on the survey done in the 1990’s. We acknowledge that before a detail dredging plan is finalised, we will need to commission a new survey but as the river bed is continuously changing, we see no point in commissioning this until we have a clearer idea of the project timescale. 3. The design of the fish/canoe passes has yet to be finalised. The minimum flow over these will be important in establishing when the river is closed to navigation due to insufficient flow. 4. Lock gear design, sizing of back pumps and pump timing regimes have yet to be established so the rates of discharge and abstraction are currently ‘ball-park’ estimates. These rates can be optimised once the above variables are tied down more clearly. Our proposal is that rather than attempt an analysis based on too many unknowns, we accept that there will be states of the river, as yet unquantified, where it will be closed to navigation. When the flows are high, the determining factor will be safe navigation, and when flows are low, environmental protection. We accept that the numbers will need be agreed with yourselves, and would suggest that your support of our Planning Application could be conditional upon such an agreement. The applicant is reminded that an abstraction licence will be required to transfer water into the canal from the Bristol Avon and an impoundment licence will be required for the new weir. Understood. Yours sincerely Ms Ellie Challans Sustainable Places - Planning Advisor Paul Lenaerts Project Manager, Wilts & berks Canal Trust .

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