Trying to estimate the rainfall

It has been raining hard in Cumbria this weekend. They were predicting up to 250mm. That certainly hasn't happened in Wigton but when we drove down to Keswick today it was very wet. I'd estimate that Derwent Water was about a metre up on normal. Here are some pictures:

The lake is fed from the streams that come in from the hills. Any land that feeds a stream going into Derwent Water is its catchment area. From the map, I'd estimate the catchment area as perhaps 14km x 7km making an area of about 100 square km to 1 significant figure. Estimating the lake as 4km x 2km gives it an area of 8 square km. This puts the catchment area as 12 x the lake area. Water in the lake 1m higher would mean a rainfall of 80mm over the catchment. Some of the water would not yet have fallen; some of the water is still flowing down from the hills and some of the water has flowed out towards Bassenthwaite Lake. Even so, 250mm hasn't happened, which is wonderful news. That's what they are saying on the weather bulletins tonight.