© Bishop’s Stortford Town Council © Bishop’s Stortford Town Council

Moat Task & Finish Group 12Moat Task & Finish Group 12thth April April 20112011

Options SummaryOptions Summary

Health warning – This pack is all the personal work of the Chief Executive who is not:Health warning – This pack is all the personal work of the Chief Executive who is not:

a water engineera water engineera pump technologista pump technologista specialist in renewable energya specialist in renewable energy

Just a humble physicist!Just a humble physicist!

© Bishop’s Stortford Town Council © Bishop’s Stortford Town Council

Current StatusCurrent Status

To proceed we needTo proceed we need Environment agency permissionsEnvironment agency permissions

Impoundment licence (we have this)Impoundment licence (we have this) Flood defence licence Flood defence licence

Landowner permissionsLandowner permissions A technical solutionA technical solution FundingFunding

EA have indicated EA have indicated that they will not renew the flood defence licence if it requires that they will not renew the flood defence licence if it requires

the construction of a weir in the riverthe construction of a weir in the river That they would be amenable to a ‘sustainable’ pumped That they would be amenable to a ‘sustainable’ pumped

solutionsolution Next stepNext step

Challenge the EA – fruitless?Challenge the EA – fruitless? Explore: is an un-pumped solution feasible without creating a Explore: is an un-pumped solution feasible without creating a

weir in the river – probably not (with the existing inlet/outlet weir in the river – probably not (with the existing inlet/outlet configuration)configuration)

Investigate a viable pumped solutionInvestigate a viable pumped solution

© Bishop’s Stortford Town Council © Bishop’s Stortford Town Council

Unpumped solution without weir?Unpumped solution without weir?

Depends on levelsDepends on levels

Outtake from Stort Inlet from Stort submerged

Weir (covers electric cable?) Outlet to Stort

If bed is approximately level – unpumped solution currently not feasible without a weir in river

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(Sustainable) Pumped solution(Sustainable) Pumped solutionthe energy equation? the energy equation?

FlowFlow VolumeVolume Pump and Pump and powerpower

Energy Energy consumptioconsumptionn

Annual Annual electricity electricity costcost

Solar optionSolar option

Full width, Full width, rapid flowrapid flow

25-50l/s25-50l/s 4000W4000W 96kWh/day96kWh/day

(1kWh = 1 (1kWh = 1 unit of unit of electricity)electricity)

£3600£3600 Solar not Solar not viableviable

1change/1change/day; 50cm day; 50cm depth*depth*

2.8l/s2.8l/s 158W 240W 158W 240W (240v) (12V)(240v) (12V)

5kWh/day5kWh/day £170£170 Large Solar Large Solar 3m*3m3m*3m

1change/1change/day; 20cm day; 20cm depth*depth*

1l/s1l/s 35W 36W35W 36W

(240V) (240V) (12V)(12V)

1kWh/day1kWh/day £36£36 Medium Medium Solar: Solar: 1mx1m1mx1m

*Assumes no leakage!

The numbers for wind power are fairly similar, but less reliable, particularly in summer

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Where to put the pump and weir?Where to put the pump and weir? A pumped solution requires two weirs in the moat, and a pump at the A pumped solution requires two weirs in the moat, and a pump at the

upstream weir. upstream weir. The downstream weir will be at P7 in all cases; Options for upstream weir The downstream weir will be at P7 in all cases; Options for upstream weir

are:are: P6 (inlet): On EHDC Land; possible high(er) water loss than other options, power P6 (inlet): On EHDC Land; possible high(er) water loss than other options, power

feed from? feed from? Between P4 and P3: BSTC Land; existing channel would provide feed stream, Between P4 and P3: BSTC Land; existing channel would provide feed stream,

may need to be cleared. Sump to be dug; power feed from?may need to be cleared. Sump to be dug; power feed from? P2 (existing weir): BSTC Land; existing channel would be extended to provide P2 (existing weir): BSTC Land; existing channel would be extended to provide

feed stream; sump to be dug; power feed from pump house?feed stream; sump to be dug; power feed from pump house?

© Bishop’s Stortford Town Council © Bishop’s Stortford Town Council

Unpumped solution without weir – Unpumped solution without weir – part 2part 2

We know for certainWe know for certain The river The river doesdoes flow from P10 to P7 flow from P10 to P7 The water The water doesdoes enter the moat at p6 with the river at current levels enter the moat at p6 with the river at current levels

Therefore:Therefore: The right gradient on the moat The right gradient on the moat mustmust create a flow in the moat create a flow in the moat

So… our problem is the So… our problem is the outletoutlet not the not the inlet. inlet. The outlet is too high!The outlet is too high! Unpumped optionUnpumped option

Excavate the moat (we believe there is 50cm+ of silt)Excavate the moat (we believe there is 50cm+ of silt) build another outlet (needs only to be drainpipe-sized)build another outlet (needs only to be drainpipe-sized)

possibly we could ‘mole’ rather than trenchpossibly we could ‘mole’ rather than trench Job done – but its quite a big job!Job done – but its quite a big job!

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Next StepsNext Steps

Have I covered all options?Have I covered all options? Consult EA about non-sustainable pumped solution Consult EA about non-sustainable pumped solution

Do they have a say, this is no more extensive than a garden water feature!Do they have a say, this is no more extensive than a garden water feature! ‘‘In principle’ view from (new) Council on capex and opexIn principle’ view from (new) Council on capex and opex Possible experimental pumping to establish rate of loss etc Possible experimental pumping to establish rate of loss etc

will also establish levelswill also establish levels Experimental digging to establish depth of moatExperimental digging to establish depth of moat Excavate vs pump: excavate considerationsExcavate vs pump: excavate considerations

Difficulty of creating outletDifficulty of creating outlet Difficulty of excavationDifficulty of excavation Is the moat deep enough?Is the moat deep enough?

Excavate vs pump: pump considerationsExcavate vs pump: pump considerations Difficulty of running electrical feedDifficulty of running electrical feed Weir constructionWeir construction

Establish Establish Excavate vs pumpExcavate vs pump Estimated costEstimated cost

Landowner consent from EHDCLandowner consent from EHDC Or just do it – probably not for excavate solutionOr just do it – probably not for excavate solution

The good newsThe good news There is £2000 in the 2011-2012 budget for a feasibility study and we have a 4” There is £2000 in the 2011-2012 budget for a feasibility study and we have a 4”

(=high capacity) pump.(=high capacity) pump.