This problem with chestnut trees is due to the Horse Chestnut Leaf Miner Moth. (Cameraria ohridella) The larvae overwinter in the fallen leaves, and will hatch to start the cycle over again in late spring, when you will start to see brown spots appearing on the leaves. The advice to sweep up and burn all the leaves is therefore sound advice. I have noticed that where this occurs regularly the trees looked a lot healthier and kept their leaves until autumn, whereas the badly affected trees started losing their leaves in August. In some cases, they will grow new leaves and even start to blossom again in the autumn. I understand that this attack should not cause the trees to die, as the damage occurs late in the season. Therefore there is no reason to fell the trees. More information at http://www.forestry.gov.uk/fr/INFD-68JJRC or http://en.wikipedia.org/wiki/Cameraria_ohridella