Level Drops in Colder Temps

[Damian Kimmins]

I was going to post this on the Avon Board but thought putting it out to wider discussion might find the answer.
As everyone knows, the past 12 months have been incredibly dry and this has reduced water tables to record low levels.
In monitoring the water levels on the Avon during the cold weather, I noticed the rate at which the river was dropping was greatly decreased, for it to speed up again once the colder weather had passed.
Now I work outside every day, occasionally breaking ground with heavy plant and have realised this year just how dry the ground was. I doubt that the water tables have been restored to what they were 12 months ago, but other than that I don't know what might explain the reduction in the levels drop, even if it won't explain the increased rate of dropping consequently.
Would anyone be interested in hazarding a guess or perhaps even know?

 

[John Care]

Zero abstraction in winter?

 

[Joe Winstanley]

The hydrological conductivity of soil is influenced by temperature. It increases with an increase in temperature due to increased viscosity and vice-versa. I suspect this explains the trend you have observed.

The Avon has nearly 1,800 km2 of land in the catchment, so even a very small change in hydraulic conductivity is likely to register in the river levels towards the lower end of the catchment.

 

[Joe Winstanley]

And obviously less evaporation when the air is cooler and winds speeds much reduced.

 

[Jim Ufton]

A really obvious one, water freezing in top soil?????