Environmental Engineering Reference
In-Depth Information
movements between the thirteenth and fifteenth centuries, corresponding with the period of climatic de-
terioration. In addition, studies of tidal levels show that the general level of the tide was steadily increas-
ing during the twelfth and thirteenth centuries, with a peak around 1433, and that it remained very high
during the two following centuries before diminishing. This combination of increasingly stormy weath-
er and higher tides played a significant part in determining the fate of many coastal settlements in South
Wales.
Incursions of sand are thought to be responsible for settlements at Rhossili, Penmaen and Pennard be-
ing abandoned during the thirteenth and fourteenth centuries, although it appears that their abandonment
was more the result of a loss of interest in maintaining them, rather than a result of the settlements being
rapidly submerged beneath deep sand. Sand movement is usually sufficiently gradual for land to remain
inuseifnecessary.AtRhossili,forexample,thereseemstobeevidencefortheabandonmentofthelower
village on economic grounds alone, land on the plateau being about twice as productive as that on the
solifluctionbenchwherethedesertedsettlement waslocated.Thepresenceofastripfieldinthemedieval
fieldcomplexadjacenttothemedievalvillagecalled'Sandylands'suggeststhatwindblownsandaffected
both parts of the manor and not just the area below Rhossili Down. The besanding of settlements such as
these, on cliff tops situated well above sea level, is not a common phenomenon, but studies have shown
that winds of sufficient speed to carry sand up to the top of cliffs can be expected to occur about eighty
times a year, even in today's climate. Once sand is airborne it remains so until it is caught by a suitable
surface, or the local wind speed falls below a critical velocity, which is dependent on particle size. In this
situation it is the local topography that determines where the deposition of sand takes place (Table 5).
TABLE
5.
Besanded sites in Gower. (Adapted and simplified from Toft, 1988)
There are two documents relating to sand at Pennard (Fig. 21), one from the fourteenth century and
another 200 years later. The first, from 1317, has been generally accepted as marking the beginning of
the advance of the sand. In the document William de Breos III granted hunting rights on the 'sandy waste
at Pennard'. Excavations at a medieval house site close to Pennard Castle, however, revealed that sand
