WATER MANAGEMENT FAQ’S Part 1: Issued 17/02/2012 http://www.waterscape.com/features-and-articles/features/water-management-faqs Managing the water in a 200-year-old canal system throws up lots of challenges, particularly in a dry year. British Waterways’ water management team are often asked questions about their work by boaters or members of the public. Here, they’ve collected some of the most common questions and explained the answers. If you have any further questions on water management or drought mitigation, please feel free to post them in the comments. The water management team will either respond to them directly, or include them in future FAQs. How much water is there in a lock? The volume of water used in the operation of a broad lock is roughly 0.24 megalitres (240,000 litres, or more nearly 53,000 gallons). In a narrow lock this figure is about 0.14 megalitres (140,000 litres or 31,000 gallons). How many lock operations are there in a year, week or day? This varies across the network and some locks are obviously busier than others. Braunston, at the heart of the network, sees around 6,000 lock operations each year. The average figure for locks across the South East is in the region of 4,000 lock operations. In comparison, locks in the Kennet & Avon region average around 2,300 lock operations per year. BW produces an Annual Lockage Report every January/February, detailing lockage for the previous year, which is available for download on the BW website. At the peak of summer, a popular lock may see in the region of 230 lockages per week (or 33 lock operations a day). A maximum of six lock operations is the most you could feasibly expect in one hour - ten minutes for each passage through a lock. Do pumping stations operate all year round? Pumping stations don’t generally operate outside of the main boating season as demands are low and the canal pounds are mostly fed by surface water inflows. Throughout the boating season, pumps are generally automated – they kick in when sensors detect that water levels need topping up. Page 2 of 7 What rate do the pumps work at? They are all different, but, for example, pumps at Hillmorton on the North Oxford Canal can move 17 megalitres per day (17,300,000 litres or 3,800,000 gallons per day). That’s more than 120 narrow locks of water. On the Kennet & Avon Canal near Bath, the Claverton pumps abstract up to 36 megalitres per day (36,000,000 litres or 8,000,000 gallons per day). A chain of backpumps recirculate lockage water, and transfer water from the River Avon up to the Summit pound to meet canal demands. Why don’t pumping stations operate all the time? There are a few reasons why pumping stations cannot operate all the time. Before we go through them it may help to explain that pumps have a number of roles – to take water from neighbouring rivers and groundwater sources; to recirculate water displaced during lock operations; and, in some cases, to transfer water from one pound to another. In the case of taking water from rivers, it is important to bear in mind that, under Environment Agency regulations, we are only able to do so when the rivers have enough water in them. For example, the three pumps at the River Tove (that feeds into the Grand Union Canal north of Milton Keynes) have a total capacity of 19 megalitres per day, but we are restricted in periods of low river flows to only 4 megalitres per day. Similarly Hillmorton pumps water from the River Swift up to the Braunston Pound where it can then be pumped up to the South Oxford Summit by the Napton pumps. However, in drought conditions the volume of water abstracted from the River Swift reduces and therefore the frequency with which the pumps operate reduces. Pumping stations can’t instantly recirculate water displaced through lock operations as, at peak times, they simply can’t keep up. Therefore the water level in upstream pounds may gradually fall and downstream pounds may rise during the course of a busy day. We’re continually monitoring the operational settings of our pumping stations to make sure they work as efficiently as possible. In the long term, we are planning to introduce more ‘intelligent’ pumping controls that dynamically control pound levels by concentrating pumping outside of times of peak demand, rather than reactively responding to lockage demands. How do you deal with broken pumping stations? Where possible we plan pump maintenance and downtime outside the main boating season. However, if a pumping station has a fault during the boating season we will try to get it back up and running as quickly as possible. In an ideal world we would have a spare pump for each site but, as each is so different, it just isn’t practical for us to do that. Some pump stations have a standby pump which can be used if the main pump has a problem. Sadly this doesn’t mean that we can run both pumps together, as the connecting pipework will only be big enough to take the flow from one of the pumps. Page 3 of 7 Why don’t you add more pumping stations or increase pump capacities when there is a drought? Pumping stations exist at locations where it strategically makes sense to have them for recirculating or transferring water. Many pumping stations in the South East were introduced at key locations during the mid-1990s, following regular droughts and water shortages. Initially these were temporary pumps designed to deal with an immediate drought problem, but they have since been converted into permanent installations. At some locations it wouldn’t make sense to have pumps. For example it isn’t worth having a backpump at Foxton, as this would deplete water to the GU North, or recirculate water south from the South Oxford Summit which isn’t a feasible option. The Hatton Flight has no backpumping and therefore water always flows to waste in Leamington. Why are you not transferring this water up the Radford to Calcutt Flight? Our aim is to operate the canal as efficiently as possible to minimise water demands. However, there will always be residual terminal flows in certain trough pounds, such as at Leamington. Pumping trials and data that we have collected from our telemetry system shows that we are successfully recirculating lockage water along Radford to Calcutt. However, for a number of reasons (other than the capacity of the pumps) achieving an actual net transfer of water from Leamington is difficult. The ‘hydraulic’ capacity of the flight to transfer water is restricted by short pounds with limited freeboard. A solution to this issue (involving longer rising mains bypassing multiple locks) has been investigated but, at the moment, it is disproportionately expensive for the water resources gain. Why don’t you fix all your leaking lock gates? The majority of water lost from the canal is through seepage and evaporation. The canal network is more than 200 years old and largely features a clay-lined canal bed which is not 100% watertight. While we have more water travelling through some locks than we would like, most of it remains within the canal system to feed demand lower down. In these cases, the lock leakage simply allows water to pass downstream, which is water that we would otherwise have had to feed via sluices and bypass weirs. This winter we are spending over £20m across the network on a wide range of maintenance works, with an additional £10m of construction works coming from third party funding. As part of this maintenance over 200 lock gates are being replaced. What did the restrictions during the summer of 2011 actually achieve? The weather last year was extremely dry. As the main boating season progressed, it became clear that the drought would have a significant impact on canal water resources. We have estimated that had the restrictions not been implemented a full closure of navigation would have occurred across much of the Grand Union Mainline, GU North and the Oxford Canal by the end of August. Therefore restrictions were introduced which had the following aims: They reduced demands by discouraging boat usage from areas most at risk (i.e. the Leicester Line and GU North, served by Naseby, Welford, Sulby and Saddington Reservoirs). Limited operating hours enabled more effective recirculation of lockage and efficient supply of water around the ‘hydrological unit’ via backpumping Page 4 of 7 By concentrating lockage to peak times, boaters were encouraged to share locks and make the most efficient use of water. Do restrictions simply concentrate the same lock usage (and hence water use) into a shorter period? No, our experience and monitoring of lock usage shows that the restrictions led to decreases in lock usage. The decrease depended on the location and the nature of the restriction. Areas seeing lockage restricted to 10am-2pm typically saw a reduction in daily lockage of 20%. The Foxton Flight, where essential movements only were allowed 10am-2pm saw a reduction in daily lockage of up to 40%. Given that reservoirs are so low, what are you doing to prepare for next season? In addition to the annual winter stoppage programme, £700,000 is being spent on vital drought mitigation works in the Midlands and South East to try and conserve as much water as possible. The schemes include clearing canal feeders, pumping and transferring additional water into our reservoirs, installing additional monitoring equipment to allow existing backpumps to be used more effectively, accelerating existing major works projects to deliver in time for the main boating season and relining a number of leaking lock gates in the worst affected areas to reduce demands for water.