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Central London Model Scenarios

Central London Model Scenarios. HEAPS – Dolphin Square Wellfield. 10 July 2019 (v10). Introduction.

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Central London Model Scenarios

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  1. Central London Model Scenarios HEAPS – Dolphin Square Wellfield 10 July 2019 (v10)

  2. Introduction • The purpose of the scenarios modelled is to demonstrate the impact of different abstractions scenarios in the HEAPS, KRTST and Battersea area and their possible impact on particularly the Dolphin Square wellfield. • The abstraction rate used is sufficient to lower the lower aquifer piezometric pressure (water level) to those that enable the safe construction of the shaft at HEAPS. There are two pressure requirements: • August to October 2019 at lower than 66 maTD (-34 maOD) • November to December 2019 at lower than 60 maTD (-40 maOD) • The model uses known abstraction data to 4 June 2019, with assumed abstraction rates thereafter. • The abstraction rates at shaft sites are guided by the actual rates required by the ongoing lower aquifer abstractions at BLABF and ALBEF. • Model aquifer properties have been adjusted to better match observed data.

  3. Scenarios Notes: * Battersea abstraction if on is assumed to be operated at 5.3 Ml/d continuously. This is the peak daily rate in May 2019, note that since the simulation was run the actual peak daily abstraction for June 2019 has been 4 Ml/d. See abstraction chart on following sheet.

  4. Abstraction win simulations Model assumes 5.3 Ml/d Battersea PWS data Unknown future abstractions

  5. Impact at Shaft Sites CHEEF KRTST HEAPS ALBEF VCTEF BLABF

  6. CHEEF Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on Dewatering abstraction not needed at CHEEF if the Battersea TWU source is operational Run 138 – HEAPS on / Battersea on

  7. KRTST Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on KRTST dewatering is not required in lower aquifer in the future scenario period Run 138 – HEAPS on / Battersea on Observed data plotted on chart from KRTST-PM2-TSF

  8. HEAPS HEAPS dewatering is adjusted to achieve below the required levels Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on Run 138 – HEAPS on / Battersea on Observed data plotted on chart from SR7103b

  9. ALBEF Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on Run 138 – HEAPS on / Battersea on Observed data plotted on chart from ALBEF-PM1(CK)

  10. VCTEF Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on Run 138 – HEAPS on / Battersea on Observed data plotted on chart from ALBEF-PZ1(CK)

  11. BLABF Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on BLABF water levels in are lower than simulated due to well loss effects that are not simulated. Abstraction rates are in line with actual pumping. Run 138 – HEAPS on / Battersea on Observed data plotted on chart from BLABF-SP1(CK)

  12. Impact at Dolphin Square Wellfield Well 1/2 Well 3 Well 4 Well 5 & SR6908

  13. Dolphin Square Well 1 / 2 Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on Run 138 – HEAPS on / Battersea on Note: 46maTD = Top Thanet 33maTD = Top Chalk 27.1maTD Lowest Possible Level & Critical Level Actual level data to 3 July 2019. Actual abstraction data to 4 June 2019

  14. Setting the Critical Level for Well 3 Yield drawdown curve for borehole from analysis of step test undertaken in 2003 Critical Level: 54maTD, to achieved an output of 2.8 l/s Possible position of yield curve when rest water level declines to 54maTD as a result of external regional gw abstraction Lowest Possible Level: 20.7maTD, determined from pump depth of 83m , but operational data declines to 18maTD. Operational data daily minimum level Aug 2018 to July 2019. Abstraction rate determined from duration of pumping and daily totalizer flowmeter records. Smoothed by running mean function

  15. Dolphin Square Well 3 Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on Run 138 – HEAPS on / Battersea on Note: 46maTD = Top Thanet 33maTD = Top Chalk 20.7maTD Lowest Possible Level Actual level data to 3 July 2019. Actual abstraction data to 4 June 2019 Critical Level 54maTD could achieve 2.8 l/s

  16. Dolphin Square Well 3 (with rwl & pwl) Critical Level 54maTD could achieve 2.8 l/s Note: 46maTD = Top Thanet 33maTD = Top Chalk 20.7maTD Lowest Possible Level Actual level data to 3 July 2019. Actual abstraction data to 4 June 2019

  17. Setting the Critical Level for Well 4 Yield drawdown curve for borehole from analysis of step test undertaken in 2018 Critical Level: 57maTD, to achieved an output of 7.5 l/s Pump curve Possible position of yield curve when rest water level declines to 57maTD as a result of external regional gw abstraction Operational data daily minimum level Aug 2018 to July 2019. Abstraction rate determined from duration of pumping and daily totalizer flowmeter records. Smoothed by running mean function Operational pump curve estimated from operational data reflects the behaviour of impeller driven submersible pumps with change of head. Lowest Possible Level: 30.5maTD, to allow 2m headroom above a pump installed on 75m of BSP rising main

  18. Dolphin Square Well 4 (with rwl & pwl) Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on Run 138 – HEAPS on / Battersea on Note: 46 maTD = Top Thanet 33 maTD = Top Chalk 30.5 maTD Lowest Possible Level Actual level data to 3 July 2019. Actual abstraction data to 4 June 2019 Critical Level 57maTD from possible pump curve to achieve an output of > 7 l/s

  19. Setting the Critical Level for Well 5 Rest water levels Aug 2018-July 2019 Operational rest water levels from monitoring Yield drawdown curve for borehole from analysis of step test undertaken in 2018 Critical Level: 56maTD, to achieved an output of 3 l/s Possible position of yield curve when rest water level declines to 56maTD as a result of external regional gw abstraction Pump curve Operational data daily minimum level Aug 2018 to July 2019. Abstraction rate determined from duration of pumping and daily totalizer flowmeter records. Smoothed by running mean function Operational pump curve estimated from operational data reflects the behaviour of impeller driven submersible pumps with change of head. Lowest Possible Level: 4maTD, to allow 3m headroom above a pump installed on 100m of wellmaster rising main

  20. Dolphin Square Well 5 Run 140 – HEAPS off / Battersea off Run 141 – HEAPS on / Battersea off Run 139 – HEAPS off / Battersea on Run 138 – HEAPS on / Battersea on Note: 46maTD = Top Thanet 33maTD = Top Chalk 4.3maTD Lowest Possible Level Actual level data to 3 July 2019. Actual abstraction data to 4 June 2019 Critical Level 56 maTD

  21. Dolphin Square Well 5 (with rwl & pwl) Critical Level 56 maTD RWL/PWL range at critical level to achieve an output of 3 l/s Lowest Possible Level 4 maTD Note: 46maTD = Top Thanet 33maTD = Top Chalk 4.3maTD Lowest Possible Level Actual level data to 3 July 2019. Actual abstraction data to 4 June 2019

  22. Claverton Street Borehole SR6908 Model achieves a good calibration to mid 2018 Predicted levels are up to 4m lower than observed Predicted levels predicted to be 60 maTD at SR6908 in Dec 2019. But will probably only decline to 64maTD as a minimum.

  23. Key Points • The CLM simulations reduce levels at the shaft sites to below the target levels thus allowing safe construction. • At Dolphin Square the rest water levels are not reduced below the critical level based on lower instantaneous abstraction rates. • At SR6908 the levels are modelled to decline to 60maTD but will probably only decline to 64maTD in the observation location.

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