Hello. Could I get some advice from professionals on here who install patios please. My friend had a new patio installed around a year ago. There was originally a concrete area that had a small drain located on the line with the grass and there was never any problems with surface water. The contractor installed a retaining wall using sleepers. raised the level of the lawn, increased the size of the concreate area and and laid paving slabs. He covered the original drain and put a long gully grill along the sleepers which appears to just run the water away to the far corner. As soon as it rains, the whole area floods as can be seen in the pictures. They asked the contractor if he could do something to put the original drain back in but he has said that he needs to install a french drainage system under the lawn and he will need to dig down 2 metres. My friends cannot understand what this would be for. It looks like the problem is rain falling on the patio area rather than rain falling on the grassed area. It looks like the water simply runs in the gully along to the side of the garden. They are thinking that they maybe need to get another contractor to lift the patio slabs and re-instate the original drain somehow? We would really appreciate any advice you could offer please. Thanks