October 12 2006. The previously cited qualitative records of rain during this dry year on the London Clay illustrated (September 29 2006) can be compared to rain gauge records in decimal inches made by John Bird in his garden 0.35 km east of the photograph of Eastwood. Combined with my observations of when it rained during the day these diurnal totals can be put in order as a guide to likely flash floods in 2006:
Overnight April 9/10 0.78 (April total 1.54)
Rains until evening October 6 0.6 inch
Evening thunderstorm Sept 13 0.5 (Sept. total 1.04)
Overnight May 6/7 0.48 (May total 3.00)
Overnight Aug. 23/24 0.38 (Aug. tot. 2.10)
Continues daylight Aug. 23 0.38
Afternoon x later March 7 0.30 (March total 1.15)
Around 1hrs. G.M.T. August 17 0.23
Around 4 hrs. G.M.T. August 28 0.22
General “some rain” on June 15 0.22 (June total 0.73)
Rain x windy night Feb. 15 0.22 (Feb total 0.84)
It will be seen that much of the monthly rainfall took place on single days or nights, and often with most of it falling within an hour or so, in sudden bursts on a time-scale of a few minutes. This water then runs off the modern gardens converted into parking lots, decking and sheds, as well as roof areas, which were originally designed to similarly flood the street and sewers, not wet the subsoil. consequently most of the water forms a torrent down the street and a flash flood in the river despite improvements made to stop it overflooding the road seen in the photograph (which used to flood, but not now the river is in a deeper concrete channel). A more sustained gentle rain would have been better for reducing subsidence claims even in tradition gardens.
Looking now at the monthly rainfall totals from the same local source one needs to also consider when the hawthorn and other more substantial local trees developed leaves able to extract water from their tiny roots below dwellings (although the conifers, often more popular in gardens obviously operate all the year). The leaves have recently been falling in November and appear again in the middle of April (my diary notes April 14 2006 for a hawthorn, which I had fully removed because it was causing damage by September 10). It did not help that the first third of the year was also unusually dry (Jan. 0.68, Feb. 0.84, March 1.15), but there was some improvement in the spring (April 1.54, May 3.00) causing a large development of leaves, which partly became yellow and fell-off during the summer drought (June 0.73, July 0.29). Rain did return on August 12/13 but not in substantial amounts until the end of the month when it came in the potential flash floods recorded above (Aug. tot. 2.10, Sept. 1.04). These records are only up to October 11 but the present month is clearly relatively wet and the cracks in buildings are closing up. It is unavoidable that some trees have to be removed due to this type of dry weather and their proximity to dwellings with concrete foundations resting in the London Clay. However removal of all the trees from Essex, now increasingly covered in this way by dwellings and concrete, will contribute to climate change globally and to flash flooding locally.
In the longer-term the sea level and tidal range at Rochford will influence the ability of the river shown on the left of the photograph to discharge any rain which happens to fall when the tide is in. Before the late 18th Century there was no road there and it was termed a mead.
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