Runway Runoff

Living in the Heathrow flight path I will obviously be effected by any expansion of the airport but at the same time am suspicious of the nimbyism that motivates a good deal of the anti-expansion protest. Regarding the environmental issues, it seems to me that it is pretty pointless talking about airport expansion outside of a general discussion about what kind of economy and society we would like to see in the future. Unless of course you think that we have somehow arrived at a situation where we have a number and frequency of flights that is "just right"; any more would lead to environmental disaster but any less would be economically and socially unsustainable. 

Having said this there is one very good reason for being wary of building new runways at Heathrow that seems to have had very little publicity, the increase in flood risk. I'm not going to get into the complex subject of hydrology in any depth, fascinating though it is, but will just point out that every road, roof, car park etc. increases what hydrologists call urban runoff. Rainwater, rather than soaking slowly into the ground, runs into the nearest watercourse at a rapid rate with the resultant increase in flood risk. A huge area such as a runway provides for massive runoff that in the case of Heathrow runs into the River Crane and in the case of Gatwick, the Mole. Both these rivers discharge into the Thames in West London. One of the many disturbing climate change predictions is an increase in the frequency of severe weather events, i.e. storms, very heavy rainfall. All in all more runways would seem to be a less than clever idea.