Quote from TfL e-mail:
PLANNED CLOSURES ON GOSPEL OAK - BARKING LINE:
To enable the running of more frequent and reliable services across London, on time for the Olympics in 2012, there will be temporary closures on various lines of the Overground network. TfL will provide alternative travel arrangements to keep passengers connected to the public transport network. The first set of improvements, to enable the running of 4 trains per hour will take place at weekends on the Gospel Oak to Barking line from 7 February until 25 October 2009 during which time there will be a reduced service each weekend.
Works will take place as follows
Saturday 7 and Sunday 8 February, line closed Gospel Oak - Barking
Saturday 14 and Sunday 15 February, line closed Gospel Oak - Barking
Sunday 22 February, line closed Gospel Oak - Barking
Saturday 28 February and Sunday 1 March, normal service
Saturday 7 and Sunday 8 March, normal service
Saturday 14 March, line closed South Tottenham - Barking
Saturday 21 March, line closed South Tottenham - Barking
Saturday 28 and Sunday 29 March, line closed Gospel Oak - Barking
Saturday 4 and Sunday 5 April, line closed Gospel Oak - Barking
Saturday 11 (from 10pm) until Tuesday 14 April, line closed Gospel Oak - Barking
ALL Saturdays between 18 April and 1 August (inclusive), line closed South Tottenham - Barking
Saturday 8 and Sunday 9 August, line closed Gospel Oak - Barking
Saturday 15 and Sunday 16 August, line closed Gospel Oak - Barking
Saturday 22 August, line closed South Tottenham - Barking
Saturday 29 August, line closed South Tottenham - Barking
Saturday 5 and Sunday 6 September, line closed Gospel Oak - Barking
Saturday 12 and Sunday 13 September, line closed Gospel Oak - Barking
Saturday 19 and Sunday 20 September, line closed Gospel Oak - Barking
Saturday 26 and Sunday 27 September, line closed Gospel Oak - Barking
Sundays 4 11 18 and 25 October, line closed Gospel Oak - Barking