Oxford & Grand Union Hydrological Unit water resource position statement: 31 July 2020

We approach the water management of the canal system using a concept of hydrological units. We define a “hydrological unit” as a canal or group of canals that are supplied from the same water sources.

The Oxford & Grand Union Hydrological Unit

The Oxford & Grand Union Hydrological Unit (Ox&GU) is a complex hydrological unit that is made up of several connecting canals, with three groups of reservoirs. It is connected via a system of pumps that can recirculate and transfer water around the system.

The Ox&GU consists of: the Oxford Canals (North and South); the Grand Union Canal from the Leamington Trough Pound, over the Braunston Summit then down to the Milton Keynes Trough Pound; the Coventry and Ashby Canals; and the Grand Union Leicester Line. There are three reservoirs on the Leicester Summit (Naseby, Sulby and Welford) and a further reservoir (Saddington). There are two reservoirs on the Braunston Summit (Daventry and Drayton), and three reservoirs on the Oxford Summit (Boddington, Clattercote and Wormleighton). There is also a small balancing reservoir at Napton.

During the unprecedented period of lockdown in the spring the canal network was largely absent of boat movement. Since the relaxation of constraints to our everyday lives, particularly the allowance for people to stay away from home, parts of the canal network have been exceptionally busy. For example, in recent weeks the Napton and Claydon lock-flights have been busier than normal at this time of year. The nearby Braunston Summit has remained slightly less busy than usual for the time of year.

The weather in April and May was notably dry resulting in flows receding in the rivers and streams that feed into the canal. A return to normal weather patterns in June and July has not resulted in a sustained improvement to river inflows. As such, the backpumps at Napton are working at capacity. Boddington Reservoir, the largest reservoir on the South Oxford Summit has been feeding at a significant rate, however excessive weed growth in the feeder channel is limiting the channel conveyance. Typically, this feeder channel has not previously had a problem with weed growth. It may be likely that the channel became overgrown as a result of the climate conditions in combination with the fact that there was no flow in the channel during the lockdown period.

As such the South Oxford Summit is currently operating at a lower level than we’d hope for and Boddington Reservoir level is lower than we’d usually expect for this time of year.

Reservoirs

As of 27 July 2020, the total Ox&GU reservoir holding was 76%. Reservoir levels and holdings are shown below in Table 1.

Table 1 Ox&GU reservoir levels and holdings 27/07/2020 Table 1 Ox&GU reservoir levels and holdings 27/07/2020

All reservoir holdings are normal for the time of year except for Boddington which is currently at 64% of its total capacity.

Figure 1 below shows the total group holding for the reservoirs in the South Oxford (comprising Boddington, Clattercote and Wormleighton), against 2019 holdings and the long-term average.

Figure 1 South Oxford Reservoirs (Boddington, Wormleighton & Clattercote) Figure 1 South Oxford Reservoirs (Boddington, Wormleighton & Clattercote)

What are we doing about it?

Our Regional teams are identifying and clearing vegetation where possible along the Boddington feeder channel. A combination of Napton backpumps with feeds balanced from Boddington and Clattercote reservoirs are meeting canal demands. To maximise water resources, the Trust is taking the sensible precaution of locking targeted locks up overnight. This measure is intended to reduce the potential for water losses overnight and allow backpumps more time to transfer water around the hydrological unit. At locks where opening hours have been further revised the aim is to reduce lockage demands on this part of the canal network.

In summary, the following actions will be taken from 14th August 2020:

  • Gates locked overnight at Marston Doles Lock’s 15 and 16 10am to 5pm last entry on the flight 4pm
  • Gates locked overnight at Claydon Lock’s 17 to 21
    9.30am to 4pm last entry on the flight 3pm

Depending on rainfall, drought measures may increase in severity and location before the on-set of the winter stoppage season. This is not something we undertake lightly, and we will avoid it where possible. Conversely, as we move through the boating season, if we receive sufficient rainfall we will review measures to minimise disruption.

Currently there are no plans to introduce restrictions elsewhere in the hydrological unit.

For the latest information regarding how we are managing drought, please visit https://canalrivertrust.org.uk/specialist-teams/managing-our-water/drought

What can I do to help?

Boaters also have a really important role to play and we ask that they help us to save water by making sure that all gates and paddles are closed after use, sharing a lock if possible and waiting for oncoming boats where appropriate.

Last date edited: 31 July 2020