A relative relief map of Suffolk

A RELATIVE RELIEF MAP OF SUFFOLK ROSEMARY H O P P I T T

Various writers (Trist, 1971; Scarfe, 1972; Martin, 1988) have in the recent past divided the County of Suffolk into homogeneous regions, the characteristics of which are based largely on the combined effect of relief, geology, soils, history and land-use. From these our concepts of the Sandlings, the Brecklands, the Fielding and High Suffolk have become well-established in our understanding of the County's character, and it is to these regions that we turn when attempting to account for the distribution of data - economic, botanical, historical or whatever.

However, one aspect of the County's topography not taken into account in the definition of these regions is the Relative Relief. This is a term used by geographers and is defined as a measure of the amplitude of available relief within a given area. Put very simply it describes how flat or sloping the land is over a given area. It is the purpose of this paper to present a Relative Relief map of the County of Suffolk (Fig. 1) which will provide, for those wishing to make use of it, a basic set of data giving Relative Relief measurements for each of the kilometre grid squares of the Ordnance Survey.

The original purpose of constructing the map illustrated here was to provide a measure by which the distribution of certain features of the historical landscape (medieval deer parks, ancient woodland, greens and commons) could be examined in relation to the flatness of the high clayland areas of the County (Hoppitt, forthcoming).

Construction of the Map Two main techniques exist for the measurement of Relative Relief. Firstly that concerned with plotting difference in height over a given area, and secondly that concerned with plotting the average angle of slope over a given area. The calculation of slope angles is extremely time-consuming and this method was shelved in favour of one whereby the difference between the highest and lowest point within the squares of a grid is measured and recorded. The grid used here is that of the Ordnance Survey.

Measurements were recorded from the OS 1:25000 maps. For each grid Square the highest and lowest point was established. These two heights were then recorded. The difference between the two heights was calculated, and the resulting measurements - over 3,500 of them - plotted onto the grid. The readings were then converted according to a key to produce quantised shading.

Measurements ranged from no measurable difference in height within a grid Square, to as much as 54m difference, although readings above 40m difference represent less than 2% of the data.

Description and Interpretation of the Map Thus the map (Fig. 1) illustrates for each kilometre grid-square the differTrans. Suffolk Nat. Soc. 25

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ence in height between the highest and lowest point, otherwise known as the Relative Relief. It does not show this information in relation to the actual height of the land. Therefore the area in the northwest of the County (north of northing 80 and west of easting 70) where the general height of the land is between 2 m - 5 m , has a relative relief of less than 5m, as do areas of the higher parts of the County, for example in Square TM2366 where the maximum height is about 77m.

Analysis of the map shows clearly the nature of the topography of the County, and allows the identification of regions within it. (Refer to Figs. 1 and 2) West of easting 70 and north of northing 70 is an almost continuous area of where the relative relief is less than 5m. This corresponds with the low-lying level Fens. Eastwards of this the land becomes more undulating with minor plateaux dissected by areas with relative relief as high as 30m and over. These mark the rising 'fen-edge' region, and the gentle plateaux of the Breckland sands, cut by minor streams flowing to the Little Ouse and by small dry Valleys.

To the south and west of this, the Newmarket 'peninsula' appears as a level area, with relative relief becoming increasingly high eastwards as far as easting 90, marking firstly the scarp slope of the chalk escarpment which runs South-West to North-East at this point, and secondly and further east, the valley of the River Lark and its tributaries flowing NW through the chalk upland.

South of northing 60 and west of easting 90 are areas of high relative relief interspersed with level areas. These correspond with the deep valley of the upper Stour and the Valleys running south down the dipslope of the sand-, gravel- and clay-covered chalk, into the R. Stour as it flows eastwards from Wixoe towards Long Melford. Between these Valleys are narrow interfluves.

The intensity of the high relative relief is lessened where the tributary Valleys running N E into the Glem and SW into the Stour are more open giving a gentler relief. The interfluve between the Glem and the Lark/Brett headwaters is equally low in relative relief, although cut by a number of small tributary Valleys.

The area east of easting 90 divides into two sections, that north of northing 50, and that to the south. The northern region is characterised by areas of low relative relief, the lowest values occurring in the north, east of the Black Bourn, whose valley can be traced as a group of intermediate readings running N N W from TL9370. South of northing 70 the land is more undulating, with the landscape cut by numerous minor Valleys at the headwaters of the Black Bourn, and the Gipping tributaries.

To the south of northing 50 the high readings correspond with the deep Valleys of the Brett, and then in the far south, the River Box as it runs SE to join the Stour. The high readings at the southern edge mark the steep valley sides of the Stour at Bures, although the valley floor at this point is quite broad and flat. The level interfluve between the Box and the Stour is picked out by the group of lower readings.

East of easting 00 as far as easting 30, and stretching as far south as northing 60 is a large area of relatively level land giving a broad plateau, Trans. Suffolk Nat. Soc. 25

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where t h e relative relief rarely exceeds 24m. T h e Valleys of the northeastward flowing W a v e n e y tributaries a p p e a r as groups of slightly higher readings ( R e d g r a v e Basin and D o v e Valley). T h e level area then extends north-east as plateau and interfluve between the W a v e n e y and the h e a d w a t e r tributaries of the A i d e and Blyth and the o t h e r minor rivers flowing southeastward t o w a r d s the sea. This a r e a continues north-east to easting 40 where relative relief values a r e slightly higher. N o r t h and east of this i n t e r m e d i a t e values indicate very gently undulating land, the higher values coinciding mainly with coastal cliffs at L o w e s t o f t , and with the right bank of the R. W a v e n e y as it runs n o r t h to join t h e R. Y a r e .

East of easting 00 as far as easting 20 and south of northing 60 the t o p o g r a p h y is d o m i n a t e d by the Gipping valley (the Valleys sides giving rise to high relative relief readings), and its tributaries. Further east between eastings 20 and 30 and south of northing 65 the h e a d w a t e r s of the D e b e n and Fyn cut t h r o u g h the landscape, leaving narrow but quite level interfluves in b e t w e e n . High relative relief at TM2649 coincides with minor Valleys meeting with t h e u p p e r tidal reaches of the D e b e n .

T h e coastal a r e a is d o m i n a t e d by gently imdulating land extending a b o u t 10km inland f r o m t h e coast to the point w h e r e t h e south and eastward flowing rivers have cut t h r o u g h t h e clay-covered chalk upland. A l o n g t h e whole of the coastal Stretch, f r o m the Orwell estuary to the n o r t h e r n e x t r e m e of the C o u n t y , the relative relief rarely exceeds 19m, being highest along the D e b e n valley n o r t h of northing 40. E l s e w h e r e the highest readings coincide with the coastal cliffs, for e x a m p l e north of Kessingland (TM5386) and at Dunwich (TM4768).

Summary The relative relief of t h e C o u n t y varies considerably, f r o m areas with little or no Variation over o n e S q u a r e k m , t o as high as 53m. T h e areas of highest Variation lie in t h e south and west of t h e C o u n t y , particularly associated with the d e e p Valleys cut t h r o u g h t h e uplands. North-east of t h e Gipping the relative relief values a r e in general much lower, with the high clay plateau on the north-west divided f r o m the coastal piain by a b a n d of country with m o r e p r o n o u n c e d relief resulting f r o m t h e Valleys cutting down through the dip slope of t h e clay-covered chalk uplands which in this part of the county are lower t h a n in t h e south-west. T h e areas of least Variation are in the northwest associated with t h e Fenland regions.

Conclusion T h e m a p was in its conception Seen as a tool providing basic geographical data to h e l p in the i n t e r p r e t a t i o n of other distributions associated with t h e a u t h o r ' s r e s e a r c h e s into medieval landscape history. It is p r e s e n t e d h e r e simply f o r the p u r p o s e of making t h e data available for o t h e r s to use.

H o w e v e r p e r h a p s a brief c o m m e n t should be m a d e on its contribution to the regional g e o g r a p h y of the C o u n t y , for examination of the m a p d o e s

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reveal some new information which contributes to a new view on the topographical nature of the County.

The first main contribution is the appearance on this map of a region running parallel to the coastal lowlands, between them and the high clayland plateau. This 'new' region (Intermediate Valley Region on Fig. 2) is characterised by the higher relative relief brought about by the valley development of the smaller rivers as they leave their headwaters on the clay and before they reach the more level sandy coastal lowland. This area is not identified on other County regional divisions - the perceived boundary between coastal lowlands and high plateau is generally drawn as a line coinciding with the geological division between the Boulder Clay of the plateau and the Sand of the coastal region.

The second contribution is a region which is brought to light in the south and west of the County ( ' D e e p Valley Region' on Fig. 2). It is a region of very high relative relief values and ought to be considered distinct, at least in topographical terms from the rest of the County's claylands with which it is generally allied as 'High Suffolk' (Martin, 1988).

The appearance of these two distinct regions suggests that there may be a need to re-examine the current regional divisions of the County and perhaps to refine them to take account of the Relative Relief. This may be particularly so in the area of natural history where slope, drainage and aspect have an important influence on habitat development.

References Martin, E . , (1988). T h e Soil regions of Suffolk in An Historical Atlas of Suffolk, eds. D y m o n d , D . , & Martin, E . , pp. 14-15.

Hoppitt, R . , University of East Anglia PhD Thesis (forthcoming). Deer Parks of Suffolk to 1600.

Scarfe, N . , (1972). The Suffolk Landscape, pp. 25-29.

Trist, P. J. O . , (1971). Survey ofthe Agriculture of Suffolk, pp. 68-70,137.

R . A . S . E . , London.

Rosemary Hoppitt, 4 Hilly Fields, Woodbridge, Suffolk, IP12 4 D X

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