© Bishops Stortford Town Council Moat Task & Finish Group 12 th April 2011 Options Summary Health warning – This pack is all the personal work of the Chief Executive who is not: a water engineer a water engineer a pump technologist a pump technologist a specialist in renewable energy a specialist in renewable energy Just a humble physicist!

© Bishops Stortford Town Council Current Status To proceed we need Environment agency permissions Environment agency permissions Impoundment licence (we have this) Impoundment licence (we have this) Flood defence licence Flood defence licence Landowner permissions Landowner permissions A technical solution A technical solution Funding Funding EA have indicated EA have indicated that they will not renew the flood defence licence if it requires the construction of a weir in the river that they will not renew the flood defence licence if it requires the construction of a weir in the river That they would be amenable to a sustainable pumped solution That they would be amenable to a sustainable pumped solution Next step Next step Challenge the EA – fruitless? Challenge the EA – fruitless? Explore: is an un-pumped solution feasible without creating a weir in the river – probably not (with the existing inlet/outlet configuration) Explore: is an un-pumped solution feasible without creating a weir in the river – probably not (with the existing inlet/outlet configuration) Investigate a viable pumped solution Investigate a viable pumped solution

© Bishops Stortford Town Council Unpumped solution without weir? Depends on levels Depends 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

© Bishops Stortford Town Council (Sustainable) Pumped solution the energy equation? FlowVolume Pump and power Energy consumption Annual electricity cost Solar option Full width, rapid flow 25-50l/s4000W96kWh/day (1kWh = 1 unit of electricity) £3600 Solar not viable 1change/day; 50cm depth* 2.8l/s 158W 240W (240v) (12V) 5kWh/day£170 Large Solar 3m*3m 1change/day; 20cm depth* 1l/s 35W 36W (240V) (12V) 1kWh/day£36 Medium Solar: 1mx1m *Assumes no leakage! The numbers for wind power are fairly similar, but less reliable, particularly in summer

© Bishops Stortford Town Council Where to put the pump and weir? A pumped solution requires two weirs in the moat, and a pump at the upstream weir. A pumped solution requires two weirs in the moat, and a pump at the upstream weir. The downstream weir will be at P7 in all cases; Options for upstream weir are: The downstream weir will be at P7 in all cases; Options for upstream weir are: P6 (inlet): On EHDC Land; possible high(er) water loss than other options, power feed from? P6 (inlet): On EHDC Land; possible high(er) water loss than other options, power feed from? Between P4 and P3: BSTC Land; existing channel would provide feed stream, may need to be cleared. Sump to be dug; power feed from? Between P4 and P3: BSTC Land; existing channel would provide feed stream, may need to be cleared. Sump to be dug; power feed from? P2 (existing weir): BSTC Land; existing channel would be extended to provide feed stream; sump to be dug; power feed from pump house? P2 (existing weir): BSTC Land; existing channel would be extended to provide feed stream; sump to be dug; power feed from pump house?

© Bishops Stortford Town Council Unpumped solution without weir – part 2 We know for certain We know for certain The river does flow from P10 to P7 The river does flow from P10 to P7 The water does enter the moat at p6 with the river at current levels The water does enter the moat at p6 with the river at current levels Therefore: Therefore: The right gradient on the moat must create a flow in the moat The right gradient on the moat must create a flow in the moat So… our problem is the outlet not the inlet. The outlet is too high! So… our problem is the outlet not the inlet. The outlet is too high! Unpumped option Unpumped 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 trench possibly we could mole rather than trench Job done – but its quite a big job! Job done – but its quite a big job!

© Bishops Stortford Town Council Next 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 opex In 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 levels will also establish levels Experimental digging to establish depth of moat Experimental digging to establish depth of moat Excavate vs pump: excavate considerations Excavate vs pump: excavate considerations Difficulty of creating outlet Difficulty of creating outlet Difficulty of excavation Difficulty of excavation Is the moat deep enough? Is the moat deep enough? Excavate vs pump: pump considerations Excavate vs pump: pump considerations Difficulty of running electrical feed Difficulty of running electrical feed Weir construction Weir construction Establish Establish Excavate vs pump Excavate vs pump Estimated cost Estimated cost Landowner consent from EHDC Landowner consent from EHDC Or just do it – probably not for excavate solution Or just do it – probably not for excavate solution The good news The good news There is £2000 in the budget for a feasibility study and we have a 4 (=high capacity) pump. There is £2000 in the budget for a feasibility study and we have a 4 (=high capacity) pump.