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Kent Archaeological Review extract
 

Below the Water Table Cooling '69.
by Alec Miles and Mike Syddell.

Is it possible to excavate a site below the average water table? Much controversy has raged over this problem and many an excavator has adopted the plea that the watertable has stopped him from reaching the lower levels. But as Sir Mortimer Wheeler has written, "no site should be dug unless it is sectioned and diagnosed to the lowest levels ... water should not normally be accepted as a bar."

Especially in the North Kent Marshes, many archaeologists have been deterred by the waterlogged conditions. However, in the past three years at the Cooling marsh Romano-British industrial site much experience has been gained in excavating to minus 3 feet OD some 8 feet below the water table, in still alluvial clay. It must be pointed out that not all the site is below the water table. Much excavation is done above the water table using conventional techniques. And in mid-summer the water table drops considerably -- by 3 feet during 1969's exceptionally dry summer.

Although normal recording methods can be used, special excavation techniques are often, although not always, required because, while the water can be easily pumped away, there is a constant seepage of water from all sides of the squares or trenches which makes the working surface very soft. In such conditions, the inexperienced digger would be quickly up to his knees in a quagmire. One way to overcome this problem is to dig a small sump in one corner and slightly slope the working surface towards it while the digger stands on duckboards. The surface being worked can actually be trowelled perfectly easily, even 6-8 feet below the water table. It should be borne in mind that excavation will take somewhat longer than usual to complete.

The one essential piece of equipment is a pump. Recently the Council for Kentish Archaeology purchased a second-hand Pegson Marlow pump, which is now available on loan to constituent groups. This is a centrifugal type pump with a 2 inches delivery, powered by a 50 cc J.A.P. petrol engine, complete with 30 feet of hose. The pump has certain advantages for excavation work, such as a high output and the ability to deal with high concentrations of vegetable matter. Usually a filter can be dispensed with, if precautions are taken to avoid stones being sucked into the impellor, which could have disasterous results. The only disadvantage of the pump is that the casing is made of aluminium and therefore it is not suitable for use with sea water.

The exceptionally dry summer in 1969 enabled the Cooling RB industrial site excavations to continue much later than in previous years. Close down was finally made in the last few days of November.

As in previous years, it is not the temperature which halts work for winter, but the rainfall. As the winter rains close in, the water table starts to rise quickly and by early winter reaches the surface of the site -- and even the CKA pump cannot cope with such quantities of water. In mid-summer in previous years the lowest the water table has reached is 31 feet below the surface -- this year it went down to 5 feet and stayed there. This, coupled with the use of the new CKA pump, enabled a great amount of work to be done at the lower levels.

In 1969, the west side of the Romano-British mound was reached (see the interim report in REVIEW Number 17, page 16). The west, east and possibly the north sides have now been located. Indications are that the mound is not circular but probably wedge-shaped or rectangular-bounded on the west by a creek and on the east by a dyke which may be artificial. The west creek was undoubtedly tidal at some period, evidence being provided by marine life remains and a "beach." The size of this creek makes it likely that there was direct access to the sea by boat from the site.

The original marsh level in the immediately pre-Roman period was again established and an interesting series of 1st century AD pottery sherds discovered. During the 2nd century, the mound was extended in size and height and on part of the extensions, a hearth structure was discovered. The full extent of this hearth has now been found and sections made. The exact firing method cannot at the moment be established but further work next season in an adjacent area should settle this point. Around the kiln was a chalk floor and arranged in a square about it, four chalk piers which may have carried a structure associated with the kiln.

 
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