Current water level management issues.
At this time, we are holding levels at –150mm below normal datum level of Zero in the Hampshire pound above Ash Lock. This is due to the on-going leak issue at Crookham Deeps embankment. Simple repairs on this leak over proceeding years have already been tried and not been found to be successful for any length of time. Hence a much bigger scheme was required that also covered a wider area, as there is evidence of leaks of varying levels in several spots. The leak has also clearly got much worse in recent times. A repair was commenced this winter however the contractor left site without completing the work.
The figure we are holding water at of –150mm is based on the rate of flow that we are experiencing of the leak in its worst area. It goes from several minutes to fill a litre tub of water at –150mm to increasing to only a few seconds to fill a tub of water when raised. We measure this rate daily. It should be noted that maintaining levels over 16 miles to within a few millimetres is very difficult to be exact with, when influenced by so many different factors. People will have noticed the water level fluctuating during this time. This is for one or more of the following reasons;
- Rainfall
- Lack of rainfall
- Opening/closing of sluices
- Sending of water down the Canal to feed the lock flights
- Building up of water ready to send down the lock flights
- Opening of a paddle at Ash lock to help feed water
- Resetting of boards on weirs to help build up or reduce levels
Some of these actions can take several days to affect the Canal. At all times we are monitoring and managing the water on a daily basis to achieve management of the Canal for navigation and its Site of Special Scientific Interest status. While at the same time trying to maintain levels as close to –150mm as possible to reduce risk. Fluctuations in levels are an entirely normal part of the water management as we put water where we need it, however this is simply more noticeable in the Hampshire pound at the moment with lower levels.
Can I assure everyone that even when senior staff members are away there are staff allocated to water management on a daily basis and this is of primary importance.
With the repair to Crookham embankment not completed, we have been left in a difficult situation which we do realise is already affecting particularly deeper drafted boats in a negative way. However, with the leak as it is and the known consequences of a potential breach, we have to prioritise on-going public safety.
We have been trying to accommodate boat movements as best as we can up to now, however we are reaching the time when hot weather will beat us, and water will stop coming into the Canal from the feeder streams, the Greywell aquifer water will reduce, and the evaporation (from hot summer days) and transpiration (from all those thousands of thirsty trees) will out way any input from the aquifer. This is not unfortunately unusual for the Canal with no other summer summit feed of water, however this year with 150mm less water in the Hampshire pound to start with, we are inevitably going to reduce to this point sooner.
Contrary to some beliefs, enabling the Boat Rally and passage of so many boats up and down the Canal did not affect the longer-term levels for the Canal. At the time of the rally, we still had plenty of water coming into the Canal and were having to artificially hold the levels low. Allowing lots of lock use would only have been an issue if there was no water coming into the Canal, or not enough to outweigh the volume going out through evaporation, transpiration, or lock use.
Effects of summer weather
At the moment both Broad Oak feeder and the aquifer are still feeding the Canal water, however this level has noticeably reduced. With the hot weather forecast for this coming week and no significant rainfall predicted we will introduce restrictions on the locks to maintain levels as long as possible in the Hampshire and Mytchett pounds. Thus, from Monday 20th June, Ash Lock will be reduced to 9am-5pm opening only and will be locked and caulked at 5pm each day.
We are anticipating that inflow will continue to drop off, and that we will therefore need to start lock closures soon after this. To ensure that boaters have adequate notice we plan that Mon 27th June will be our last day of opening on Deepcut and Brookwood lock flights. Please can any visiting boats or boats wishing to leave the Canal onto the Wey, or boats wishing to return to their home mooring above Deepcut need to have navigated the Deepcut and Brookwood flights by the end of Monday 27 June at the very latest.
We will continue to monitor the situation daily and be back in contact if the situation changes in any way.
James Taylor – Strategic Manager Basingstoke Canal
Fiona Shipp – Canal Manager