Post script from the 27th

This is the lowest point in our garden and it is always pretty much a swamp throughout the winter.  We are on clay and not exactly free-draining.  We excavated channels and filled them with grit but it didn't make a scrap of difference; so now we just live with the black lagoon.  Sometimes the water backs up and lies on the surface of the lawn for a while.  This is the worst we have ever seen. This last week It filled up to the top of the edging strip of wood and overflowed down the back.