Holderness Coast Erosion and the Significance of Ords

EARTH SURFACE PROCESSES AND LANDFORMS, VOL. 10, 107-124 (1985)

HOLDERNESS COAST EROSION AND THE SIGNIFICANCE OF ORDS

ADA W. PRINGLE (nee PHILLIPS) Department of Geography, University of Laneaster. Laneaster LA1 4YR. U.K.

Received 13 October 1983 Revised 30 June 1984

ABSTRACT A sample ord, a low section of beach characteristic of the Holderness coast, is examined as it moved southwards between 1977 and 1983 and its significant role in coast erosion is demonstrated. The reduction in beach level at the cliff foot by up to 3.9m enabled most HWN tides to reach it, as compared with only some HWS tides along the inter-ord beach, and the volume of till eroded from the cliffs increased by eight times to an annual mean of 72m3m-’. The Holderness tills are shown to be composed of 31 per cent sand and coarser sediment which is the sediment range of the beaches. Where an ord is sited the massive injection of beach sediment goes to form the ord’s most prominent constructional feature, the lower beach ridge which extends southwards from the centre of the ord. Analysis of 12 months’ observer wave data collected at Withernsea in 1969/70indicates that a net southward sand movement of l44000m~occurred. Comparison of this rate with beach sediment input rates along the whole coast backed by till cliffs suggests a sediment deficit at the northern end and a surplus towards the southern end. This conclusion is supported by an overall increase in beach sediment volume southwards from Barmston. Within this longshore sediment transport system, the ords migrate southwards from their point of origin in the Barmston-Skipsea area, without losing their identity until reaching the tip of Spurn Head.

KEY WORDS Rhythmic beach feature Till cliff erosion Beach sediment input Wave analysis Longshore sediment movement

INTRODUCTION The 60 km long Holderness coast, lying between the chalk promontory of Flamborough Head in the north and the sand and shingle spit of Spurn Head in the south takes the form of a zeta-cume (see Figure 1). The coast is backed by Pleistocene glacial till cliffs, which are renowned for their very rapid rate of erosion, calculated by Valentin (1954) as 1.2myr-’. This provides sand and coarser sediment for the beach, whilst silt and clay is carried away in suspension by waves and currents. The form of the beach and its response to varying wind, wave and tidal conditions was considered in an earlier paper (Pringle, 1981). It was observed that the most rapid rate of erosion occurred at the positions of low sections of beach, which form irregularly-spa& rhythmic features along the coast between Barmston in the north, and Spurn Head in the south. These features known locally as ‘ords’ migrate southwards along this coast, moving their associated zones of maximum cliff erosion with them. The characteristics of an ord are shown in Figure 2. The relationship of ords to previously described rhythmic coastal features found on a variety of coasts throughout the world (Komar, 1976) was examined earlier (Pringle, 1981) and it was concluded that the only similar feature was the low sections between ‘beach pads’ identified on St. Joseph Peninsula, Florida, U.S.A. (Entsminger, 1977). The absence of sand bars below Low Water Mark along the Holderness coast and the general absence of rip currents do not suggest the presence of cellular flows with which many other rhythmic features are associated; nor does it seem likely that ords are related to edge wave formation because of their wide, irregular spacing.

0 1 97-933 7/85/020 1 07- 1 8$0 1.80 0 1985 by John Wiley & Sons, Ltd. 108 A. W.PRINGLE

Figure 1. Location map

This paper reports on the study of a selected, sample ord as it migrated along the southern part of the Holderness coast between 1977 and 1983. Its movement has been monitored since 1969, when it was centred 250m south of Withernsea and Scott (1976) studied its development as it migrated from Hollym to Holmpton between 1973 and 1976. It has subsequently continued its southerly movement to lie south of Dimlington ORDS AND COASTAL EROSION 109

1 Steep, rapidly eroding till cliff 2 Lower angled, more stable cliff 3 Upper beach of coarse sand and pebbles 4 Till shore platform with armoured mud balls 5 Water-filled channel 6 Lower beach sand ridge 7 Lower beach, sand with surface water

Figure 2. The characteristic features of a Holderness ord

Highland in April 1983. This represents an overall movement of 7 km, or on average 0.5 kmyr- between 1969 and 1983.

MONITORING THE SAMPLE ORD Field surveys were carried out in April and October each year from 1977 to 1983 to measure winter and summer changes respectively, and during the first three years, two additional surveys were made during the summer. The position of the ord was surveyed relative to a datum point at Old Hive, and within the ord five cross-profiles and one linking longitudinal profile were surveyed by automatic level and related to Ordnance Datum. The most northerly and southerly cross-profiles demarcated the limits of the ord along the coast and the remaining three cross-profiles were positioned within its central part. Height variations were thus recorded throughout the ord together with the extent and form of the main elements: the upper beach towards both ends, and the till platform and lower beach sand bar which characterize the central section. A plan of the ord was constructed from the survey data and further observations, which enabled area measurement to be made (see Figure 3). Cliff top erosion measurements were taken in April 1978 and 1979 and at six-month intervals thereafter. The datum points established for these were spaced at closer intervals than those of the Holderness Borough Council from which additional data was obtained annually each autumn. From these cliff top measurements volumes of till eroded from the cliffs were calculated, and, taking the composition of the till into account, volumes of sand and coarser sediment supplied to the beach could be estimated. As it was not possible to install a wave recorder for this project, wave measurements could be taken only at survey times from the coast although this data can be compared with daily observer wave measurements taken for 12 months in 1969/70. Three-hourly wind data was obtained throughout the whole period 1977 to 1983 from the Meteorological Office for Spurn Head.

MOVEMENT OF THE ORD ALONG THE COAST The average rate of movement of 0.5 km southwards per year masks considerable variation as shown in Table I. The figures were calculated from the mid-point position of the exposure of till shore platform at or 11.4.8

NWI I SE IIIII 11111111I,,IIII I11111 11 (1111 111[1111,#, 750 1ooo 1250 1500 1750 2000 2250 2500 2750 3OoO A Upper beach sand and shingle Lower beach sand ridge Lower beach sand with surface water ? 1 Till shore platform Till shore platform wlth patches 1.4.8 of upper beach sedment Upper beach sediment wlth surface water m Water A to E Cross profiles NW SE Ill 1111111111111,1,111,,~~~~~1 20oo 2250 2500 2750 3ooo 3250 3500

B metres southeast of OM Hive Datum

Figure 3. Ord plans. A: Under high wave energy, northerly storm conditions, with a tidal surge on 11.04.82. B Under low wave energy conditions on 01.04.83 ORDS AND COASTAL EROSION 111

Table I. Rate of movement of Ord

Per 05yr Per year Date (m) (m) 4.4.77 - 29.10.77 668 S 7.4.78 68 S 736 S 21.10.78 245 S 14.4.79 175 S 420 S 2 1.10.79 360 S 16.4.80 355 N 5s 25.10.80 197 S 18.4.8 1 368 S 565 S 30.10.8 1 287 S 1 1.4.82 190 S 417 S 23.10.82 395 s 1.4.83 380 S 715 S Total 1977-1983 2978 S Annual mean 496 S

close to the cliff foot. The half-yearly rates of movement varied between 668 m southwards and 355 m northwards. The latter was the only northward movement recorded and it was produced when the ord lengthened in both directions. The annual rates varied between 5 m southwards (this including the northward six-monthly record) and 775m southwards. It is noteworthy that the mean annual movement of 496m southwards for the six years 1977 to 1983 is almost the same as that already noted for the period 1969 to 1983.

CHANGING FEATURES WITHIN THE ORD Height variations The height of the beach or exposed till shore-platform controls the degree of exposure of the cliff foot to direct wave attack and is therefore very important when considering varying rates of cliff erosion. Table 11 shows variations in cliff-foot height between the ord’s northern and southern ends, where cross-profile A and E respectively were surveyed, and its lower central section surveyed by cross-profiles B, C,and D. The 19 surveys carried out between 1977 and 1983 show that the mean heights of the northern and southern ends were 3.91 m and 3.37 m OD respectively (ranging between extremes of 2.61 m and 5.37 m at the north end, and 0.97 m and 5.25 m at the south end). Within the ord the mean height was 2.56 m OD (ranging between extremes of 0.90m and 4.18m). The height range within individual surveys varied between 1.06m and 3.87m, with a mean of 2.20 m. Much of the height variation takes place within the upper beach sediment composed of coarse sand (1-1.5 mm) and shingle up to about 20cm, although this may be completely stripped away from the central section of the ord near the cliff foot to reveal the till shore-platform, the surface of which ranged between 0.90m and 33mOD during the six years. It is difficult to relate these heights to published predicted tide heights. The nearest Standard Ports to Holderness where tidal records are kept and for which tidal predictions are available in the Admiralty Tide Tables (e.g. 1982)are River Tees Entrance and Immingham. From predictions for the former, predictions for the Secondary Port of Bridlington at the northern end of the Holderness coast can be calculated but none are available for the southern end of this coast where the sample ord is currently positioned. The nearest predictions to the south are for Bull Sand Fort in the middle of the entrance to the Humber Estuary, which are calculated from Immingham figures. Neither Bridlington nor Bull Sand Fort data provide accurate tide height 112 A. W. PRINGLE

Table 11. Variations in cliff-foot height through Holmpton-Dimlington ord Cliff-foot heights Ht. range mOD at cliff- (Nl Cross-mofiles 61 foot Date 'A' B 6 D E

4.4.77 2.6 1 2.99 4.10 3.19 - 1.49 7.5.77 3.40 3.22 3.11 3.91 4.32 1.21 17.9.77 2.67 4.18 1.15 0.90 097 3.28 29.10.77 3.32 3.55 2.38 2.65 2.12 1.43 7.4.78 3.53 2.3 2.23 2.17 - 1.36 3.6.78 4.33 3.36 3.15 2.06 3.49 2.27 2.9.78 5.37 2.52 2.80 1.86 3.67 3.5 1 21.10.78 3.95 2.96 3.06 2.01 3.12 1.94 14.4.79 4.03 2.55 3.41 3.64 3.83 1.48 14.7.79 4.03 3.1 1 -2.62 2.32 3.49 1.71 22.9.79 3.80 3.47 3.55 2.74 3.00 1.06 21.10.79 5.12 __1.52 1.25 1.99 3.33 3.87 16.4.80 3.73 2.65 2.28 2.41 3.73 1.45 25.10.80 4.38 2.89 -2.90 1.70 2.54 2.68 18.4.81 3.92 -2.98 1.53 2.33 2.82 2.39 30.10.81 4.60 2.78 235 2.32 5.25 2.93 1 1.4.82 4.38 -2.6 1 1.46 1.38 2.59 300 23.10.82 3.44 __2.1 5 2.59 2.14 5.11 2.97 1.4.83 3.69 -2.1 5 2.04 2.53 3-85 1.81 Mean 1977-83 3.9 1 2.84 2-52 2-33 3.37 2.20 -2.56 Surveys above MHWST 6 1 0 0 0 Surveys above MHWNT 17 11 8 4 13

~~ Figures underlined indicate till platform exposed at cliff-foot.

predictions for the south Holderness coast and therefore the heights of sample tides under calm conditions were surveyed to Ordnance Datum at Dimlington to obtain the following data:

Tide heights Dimlington-Easington

Max. HWST 4.5m OD Mean HWST 4-1 m OD Mean HWNT 2.7m OD Min. HWNT 2.4m OD

By relating these tide heights to the cliff foot heights, it can be seen that a MHWS tide would have been able to reach the southern end and central part of the ord at the time of all the surveys. At the northern end such a tide would have failed to reach the foot on six surveys, and on one survey it would not have reached the cliff foot at the northern end of the central section. The majority of MHWN tides were below the cliff-foot heights on the surveys at either end of the ord (on 17 surveys at the north end and 13 surveys at the south end), but would have reached the cliff foot in the central section on over half the surveys. ORDS AND COASTAL EROSION 113

The height variation through an ord in a north-south direction occurs not only at the cliff foot but also further seaward in the intertidal zone. Table Ill summarizes these variations in beach and shore-platform height. The mean figures reveal a slight increase in range from 2.2 m at the cliff-foot to 2.4 m at 20 m seaward and then a gradual overall reduction in variation to 08m at 130m seaward. This confirms that an ord is essentially an intertidal feature which dwindles seawards, as suggested by Scott (1976) after echo-sounding seaward of both this ord and one further north at Atwick revealed a gentle, even slope seaward of LWM, and showed no evidence of sandbank or bar development in the near-shore zone. Variations in ord length and sediment volume The central section of the ord, where the till platform is exposed at or near the cliff-foot, varied markedly in length between 265 m in April 1977 when the ord was in a relatively small and ill-defined form, to 1930m in October 1981 when it was a major, distinctive feature (see Table IV). The average length during the six years was 1187 m. From the length and height measurements taken each time the ord was surveyed the loss of beach sediment within the ord has been calculated. The cross-profile at A was taken as typifying the height of the inter-ord beach north of the sample ord and it was compared with profiles B, C, D, and E. Taking into account distance between profiles, the total amount of sediment absent within the ord was calculated for the zone between the cliff-foot and 80m seawards (see Table IV). The volume missing varied between the extremes of 10,400m3and 435,300m3, with a mean loss of 157,600m3.

Variations in lower beach sand-bar development and exposure of till shore-platform The central section of the ord contains two main features: to seaward, a sand bar composed of medium to fine sand and to landward, the till shore-platform which may be patchily covered in coarse sand and shingle, and which forms a wedge-shaped feature in plan at the southern end of the ord, tapering southwards.

Table 111. Variation in beach height through Holmpton-Dimlington ord Maximum range between cross-profiles A(N) and E(S) from cliff-foot seawards (m) Cliff- Date foot 10 20 30 40 50 60 70 80 90 100 110 120 130

4.4.77 1.5 1.6 1.6 1.9 2.0 2.2 2.0 1.6 1.7 1.6 1.5 1.3 1.4 1.5 7.5.77 1.2 1.6 1.5 1.6 1.1 0.4 0.6 0.7 0.8 1.0 0.7 0.3 0.3 0.5 17.9.77 3.3 3.2 3.2 3.1 3.2 2.9 2.7 2.5 1.9 1.9 1.9 1.9 29.10.77 1.4 1.9 1.8 1.2 1.1 1.3 1.1 1.2 1.4 1.5 7.4.78 1.4 1.5 1.5 1.3 0.3 0.4 0.5 0.4 0.5 0.5 0.5 0.5 0.6 3.6.78 2.3 1.7 1.9 2.1 1.8 1.8 1.5 0.8 0.8 0.5 0.5 2.9.78 3.5 3.6 3.5 3.4 2.9 2.0 0.7 1.3 21.10.78 1.9 2.2 2.2 2.2 1.5 1.3 1.5 1.0 0.9 14.4.79 1.5 1.7 1.7 1.8 0.9 0.9 1.2 1.5 1.2 14.7.79 1.7 2.1 2.5 2.5 2.1 1.5 1.7 1.9 1.9 1.0 22.9.79 1.1 1.1 1.2 0.8 1.2 1.4 1.6 1.5 1.2 21.10.79 3.9 3.4 3.7 3.5 3.6 3.7 3.6 3.5 3.4 2.9 0.9 0.8 0.5 0.3 16.4.80 1.5 2.3 2.3 2.1 1.4 0.6 0.4 0.7 1.1 1.1 1.3 0.5 25.10.80 2.7 2.3 2.3 2.1 1.6 1.0 1.0 1.4 1.8 2.1 2.1 2.0 1.8 18.4.8 1 2.4 2.5 2.5 2.1 2.1 2.1 2.0 2.1 1.9 1.4 1.4 30.10.8 1 2.9 2.9 3.0 2.9 2.7 2.8 2.8 2.8 1.7 1.7 11.4.82 3.0 3.6 4.3 4.2 3.8 2.7 1.7 23.10.82 3.0 2.4 3.2 3.0 2.4 1.6 0.4 1.4.83 1.8 2.5 3.1 2.9 2.7 2.2 1.5 1.1 0.7 0.8 Mean 1977-83 2.2 2.3 2.4 2.3 2.0 1.7 1.5 1.6 1.5 1.4 1.2 1.0 0.9 0.8

Note: Range includes all five cross-profiles, in upper and middle beach. At seaward end it includes at least A or E and two of B, C and D. 114 A. W.PRINGLE

Table IV. Length, width, and volumetric changes within Holmpton-Dimlington ord Max till platform width from cliff-foot. Length of Sediment Max intertidal Area of exposed central section volume loss width in brackets till platform Date (m) (m3 x lo2) (m) (m2) 4.4.77 265 360 78 (163) 9,375 7.5.77 970 145 78 (166) 38,750 17.9.77 795 922 55 (156) 11,875 29.10.77 690 104 50 (161) 10,Ooo 7.4.78 735 438 70(156) 14,065 3.6.78 lo00 1371 78 (135) 20,940 2.9.78 915 2601 80 (133) 25,625 21.10.78 955 1378 68 (115) 26,565 14.4.79 1435 965 150 (166) 36,875 14.7.79 1155 1610 168 (174) 36,250 22.9.79 1290 700 75 (148) 29,690 2 1.10.79 1135 3872 115(164) 1,565 16.4.80 1605 1190 50(196) 9,690 25.10.80 1840 2158 1 1 8 ( 1 83) 85,315 18.4.81 1695 2139 83 (130) 38,750 30.10.81 1930 3618 93 (166) 48,125 11.4.82 1650 4353 65 (100) 62,500 23.10.82 1260 838 63 (104) 23,750 1.4.83 1230 1175 79 (1 52) 3 1,775 Mean 1977-1983 1187 1576 85 29,550

The sand bar develops opposite the northern end of the centre of the ord and there lies in its closest position to the cliff-foot. It extends southwards at a low angle seawards past the remainder of the ord's centre and disappears below LWM towards the southern end of the ord. Characteristically this bar is asymmetrical in cross-section, with a short, steeper landward slope and a longer seaward slope of more gentle gradient. The maximum width of till platform exposure seaward of the cliff foot is shown in Table IV to vary between 50 m and 168 m with a mean of 85 m. The area of exposed till platform was calculated from the plans of the ord and reveals variations between 1,565m2 and 85,315m2 (mean 29,550m'). When exposed the till platform is actively eroded and the features produced are partly controlled by structures within the till. Closely spaced gullying approximately at right angles to the coast and to a depth of 0.5 m is commonly found in the middle of the intertidal zone. Where gullies are absent the till surface may be smooth or irregularly undulating. On occasions the generally smooth surface form is covered in small ripples with some coarse sand and small pebbles embedded in the till surface. During the summer months dessication cracking may affect parts of the till platform surface which then breaks up into small flakes of till, which themselves form into short-lived till 'pebbles'. All the cross-profiles of the till platform surveyed between 1977 and 1983, from between 400m north and 3250 m south of the Old Hive datum are shown in Figure 4. The position of the cliff foot varied slightly from profile to profile depending on whether it was taken from a cliff promontory or embayment and whether or not it was affected by a major cliff fall. Two main slope elements make up the shore platform, a steeper slope between 9" and 5" extending from the cliff foot to about 40 m seawards and a gentler slope between 1.5" and 1" extending from there to about 90 m seaward, where the till platform disappears beneath the sand bar. In only one survey, on 15 April 1979, was till platform exposed throughout the length of the ord in the middle of the intertidal zone. A detailed survey along this, approximately parallel to the cliff foot, and on the seaward ORDS AND COASTAL EROSION 115

metres N% 2; 2; 4; 6: 8p 1qO 1;Om 400 ,

Vertical scale '"1 \ 01 cross profiles Old Hive (Datum) 1 division = 1 metre

Out Newton

C m E Dimlington Highland

,Oooi ' 3200 ------

British Gas 34000 - Terminal (N. side)

Figure 4. Till shore-platform cross-profiles 1977-1983. All surveyed sections across exposed till platform have been included. They show the steeper slope of 9"-5" between the cliff-foot and about 40m seaward and the gentler slope of 1.5"-1" further seaward edge of an almost continuous cover of coarse sand and shingle, revealed a variation in height of the till surface of only 1 m in a total length of 1790m. 'Armoured mud balls' often lie on the exposed till shore-platform and a concentration of them clearly indicates the location of especially rapid erosion at a particular time. They originate as angular blocks of till 116 A. W. PRINGLE derived mainly from cliff falls but sometimes from the eroding shore platform itself. Small pebbles become embedded in their surfaces as they are rapidly rounded by wave action and usually they are destroyed in less than a week.

CLIFF EROSION The effect of the reduction in cliff-foot height within an ord on tidal and therefore wave exposure of the cliff has been discussed above. The undermining of the cliff by wave attack above the cliff-foot rapidly produces instability in the unconsolidated glacial till, and the partially vegetated cliff which had formed under ‘non-ord’ conditions is steepened commonly to almost vertical. The steepening is produced by a number of processes, including rotational slumping, mud flows and mass falls, which vary in importance between winter when the water content of the tills is high and the drier summer conditions. Two sets of cliff-top erosion measurements are the source for Figure 5; firstly those taken between Holmpton and Easington as part of this project, and secondly those taken by Holderness Borough Council between Withernsea and Easington as part of their coastal erosion monitoring programme. The longitudinal profile of the cliff along this part of the Holderness coast is shown at the top of Figure 5 and the marked increase in height to about 40 m at Dimlington is clearly seen. Below this cliff profile the annual cliff-top erosion is plotted using September/October measurements from Holderness Borough Council and April measurements from the present study, and the ord position for each measurement date is indicated. The increase in erosion with the presence of the ord is clearly shown together with the continued high erosion rate for some time after the ord has moved away southwards but before a lower angled, more stable cliff form is reestablished. The cliff erosion measurements and cliff height data have been used to calculate volumetric loss from the cliff face (see Table V). The coast was divided into the section under the influence of the ord (both by its direct presence and its continued but dwindling effect to the north) and the ‘inter-ord’coast to the north and south of the ord. Within the ord’s influence the total volume of till eroded from the cliffs varied between 97,039 m3 and 532,043 m3yr- ’ (mean 233,916 m3 for the October data and 273,893 m3 for the April data) and the mean volume per metre length of cliff ranged between 34.7 m3 and 247.5 m3 (mean 72.1 m3 for the October data and 1233 m3 for the April data). Along the inter-ord sections of this coast the total volume eroded from the cliffs varied between 19,562 m3and 117,057 m3yr- ’ (mean 55,634m3)and the mean volume per metre length of cliff was between 4.7 m3 and 15.1 m3 (mean 8.9 m3). In total over four times the volume of sediment was eroded from the cliffs affected by the ord, as compared with the inter-ord cliffs, between 1974 and 1982 (using October data). However, the overall length of the inter-ord cliffs was nearly three times as great as those affected by the ord. In order to investigate possible variations in the rate of erosion between winter and summer, cliff top measurements were taken at six-month intervals between April 1979 and April 1983. The average loss during the four summer periods, between April and October was 0.7 m per datum point, whereas the average loss during the winter periods between October and April was 3.4 m. This indicates that during this relatively short period, about 80 per cent of the volume of till eroded from these cliffs was removed during the winter and only about 20 per cent during the summer. Erosion of the till cliffs provides the main source of sediment input to the Holderness beaches and as particle size analysis carried out by Scott (1976)on a large number of beach samples has demonstrated, the full range of sand size and coarser particles are present (> 44 or > 0-063 mm) but the finer silt and clay particles are removed in suspension by wave action. In order to understand the beach sediment budget it is important to know the size of the sand and coarser sediment fraction in the tills. Table VIA (after Madgett, 1974) shows the results of particle size analysis of 62 till samples, taken from both coastal and inland sites, but covering only the sand, silt, and clay fraction. The Hessle, Drab, and Purple Tills had a total mean of 29.6 per cent sand and the Basement Till 29.2 per cent (mean for all samples, 29.6 per cent). Table VIB shows the results of particle size analysis of the whole of 44 out of the 62 samples, that is including the coarsest fraction as well as the sand, silt, and clay. The total percentage of sand size and coarser sediment in the renamed tills was: Withernsea Till 27.2 per cent, Skipsea Till 35.4 per cent (mean 31.3 per cent); and ORDS AND COASTAL EROSION 117 4 5 $

Cliff Profile 3

SE NW

1tl 1974 - 1976 5

0 22.5.74tl '1.74 ' ' 7.1.76

1976 - 1977 l:L --A 0 -17.9.77

10- 1978 - 1979 5-

m 10- 1979 - 1980 5-

0- 2,

10- 1981 - 1982 5- -

- - - - - Project Data. April measurements

~ Holderness Borough Council Data, Sept/Oct measurements Ord position on given date ' 8.lo.74 '

Figure 5. Cliff-top erosion between Withernsea and Easington 19741982

Basement Till 31.2 per cent, giving an overall mean of 31.3 per cent. Table VIC shows till analysis data provided by E. Derbyshire for the RAF Cowden site in Skipsea Till where the total percentage of sand and coarser sediment was 30.7 per cent. All three tables show a marked increase in quantity from coarse sand to fine sand within the tills. 118 A. W. PRINGLE

Table V. Cliff erosion, Withernsea-Easington 1974-1983 Holmpton-Dimlington ord Inter-ord Mean vol/ Mean vol/ m length Total volume m length Total volume Date (m3) (m3) (m3) (m 3,

1974-76* 79.0 256,854 14.3 59,537 197677 57.0 256,599 10.8 49,772 1977-78 102.1 520,823 4.7 19,562 1978-79 April 91.4 192,032 Oct. 106.0 264,980 10.3 74,9 18 1979-80 April 53.9 110,526 Oct. 63.5 158,819 15.1 117,057 198C-81 April 154.5 370,889 Oct. 34.7 97,039 4.7 34,888 1981-82 April 247.5 532,043 Oct. 134.6 3 16,216 11.3 89,341 1982-83 April 70.0 163,973 1974-82 (Oct. data) 1,871,330 445,075 Annual Mean 1974-82 72.1 233,916 8.9 55,634 (October data) Annual Mean 1978-83 123.5 273,893 (April data)

*Two years.

The cliffs between Holmpton and Easington show the complete succession with Basement Till at the cliff- foot in most places, overlain by Skipsea Till, overlain by Withernsea Till. Between Holmpton and Withernsea the Basement Till is absent. It can now be demonstrated that about 31 per cent of the ti11 eroded from the cliffs each year between 1974 and 1983 (see Table V) was sand and coarser sediment. Thus, within the ord's influence the total volume of sand and coarser sediment derived from cliff erosion ranged between 30,082m3 and 164,933m3yr- (mean 72,514m3 for the October data and 84,907 m3 for the April data); equivalent to between 10.8m3 and 76.7m3m-' of cliff length (mean 22.4m3 for the October data and 38-3m3 for the April data). Along the inter-ord sections of coast between Withernsea and Easington and total volume of sand and coarser sediment derived from cliff erosion varied between 6,064 m3 and 36,288 m3yr- (mean 17,247m3) equivalent to between 1.5 m3 and 4.7 m3m-' of cliff length (mean 2.8 m3).

WAVE CONDITIONS AND LONGSHORE SEDIMENT TRANSPORT The limited amount of wave data collected at Withernsea at the time of each ord survey (see Table VII) shows wave periods varying between 4.6 sand 12.0 s, wave height at breakpoint ranging from 025 m to 2.50 m and the angle of approach being predominantly southwards with a maximum of 42"s and only one northward angle, of 3"N being recorded. As no wave recorder records were available for comparison it was not possible to test the accuracy of this observer data and Cambers (1975) and Vincent and Ratcliffe (undated, about 1978) have shown that similar observer wave data for the East Anglian coast contained overestimations of wave height. Care was taken especially over this parameter at Withernsea and all height observations were taken against a groyne. As the data are limited, calculations of wave energy and longshore sediment transport rates were kept as simple as possible and the method adopted was that proposed by Caldwell (1956) and used by Cambers (1975) and Vincent and Ratcliffe (see TableIX). The incident wave energy, the total energy transmitted ORDS AND COASTAL EROSION 119

Table VI. Sand and coarser sediment in Holderness tills A. Coastal and inland sites. Particle size analysis as percentages, from samples covering fraction < 2 mm (- 14) (after Madgett, 1974, Table 6) Mean percentage Total % - 110 0/1 112 213 314 >44 Number Till 2/1 1/05 05/0.25 0.25/0125 0.125/0.063 > 0.063mm of samples

~ ~~ Hessle 1.4 1.9 4.4 10.7 11.5 299 35 Purple 1.3 1.4 2.4 6.1 9.1 20.3 6 Drab 1.9 2.4 5.5 12.1 11.1 3 3.0 14 Mean of Hessle/ PurpleJDrab 1.5 2.0 4.5 10.6 11.1 29.6 55 Basement 0.9 1-4 4.3 11.7 109 29.2 I Mean of all tills 1-4 1.9 4.5 10.7 11.1 29.6 62

B. Coastal and inland sites. Particle size analysis as percentages from total samples (after Madgett, 1974) Mean percentage Total % > -1 -110 011 112 213 314 >44 Number >2 211 1/05 05/0-25 025/0.125 0.125/0063 >0.063mm of samples Withernsea 4.0 1.4 1.6 3.0 7.4 9.8 27.2 19 Skipsea 4.7 1.3 1.9 4.7 11.4 11.4 35.4 18 Mean of Wit hernsea/Skipsea 4.4 1.4 1.8 3.9 9.4 10.6 31.3 37 Basement 2.3 0.9 1.4 4.2 11.3 11.1 31.2 7 Mean of all tills 3.1 1.2 1.6 4.0 10.0 10.8 31.3 44 C. RAF Cowden site. Particle size analysis as percentages from total samples (after E. Derbyshire) Mean percentage Total % > -4 -41-3 -31-2 -21-1 -110 011 112 213 314 >44 Number >16 1618 814 412 211 1/05 05/0.25 0.25/0.125 0.125/0063 >0.063mm of samples Skipsea 1.5 1.6 2.5 2.7 2.4 2.2 3.5 6.2 8.1 307 20

NB: The 'Purple Till' was renamed as 'Withernsea Till'and 'Drab Till'as 'Skipsea Till'by Madgett and Catt (1978).The 'Hessle Till' is now recognized as the weathered upper surface of either 'Withernsea' or 'Skipsea Till'.

forwards without the incorporation of the alongshore component, varied on the dates of the ord surveys between 11 MJm- ' and 3635 MJm- ' of beach per day. The alongshore sediment movement ranged between 773 m3day-' northwards and 51,428 m3day-' southwards. The latter figure is especially noteworthy as it shows sediment movement during northerly storm conditions which also produced a tidal surge. This wave data can help to explain conditions within an ord on a given date and it can give an indication of the range of energy conditions experienced along this coast. As noted previously (Pringle, 1981)and borne out by these long-term observations from 1977 to 1983, an ord becomes a relatively subdued feature under off- shore wind conditions and relatively low energy waves. Even on-shore easterly winds and northerly winds below about 10 ms- ' and their associated waves produce only small changes. It is however northerly onshore winds over 1Oms-' and their associated waves developed in the maximum fetch available to the Holderness coast and therefore of high energy content which deepen an ord and move it most rapidly. The prime example relates to the survey of 11 April 1982 carried out during such a northerly storm, then in its fourth day, with waves containing 2104 MJm- ' of incident wave energy and which were producing 30,000m3 of alongshore sediment transport southwards (see Figure 3). When compared with all 19 surveys, this revealed maximum variation in beach height across the beach and maximum sediment volume loss. It also showed a high beach 120 A. W. PRINGLE

Table VII. Withernsea wave and sediment movement data 1977-1983

Alongshore Wave Angle of Incident sediment period approach wave energy transport Date (s) ("1 (MJm - ') (m3) 1977 April 4 7.5 1.80 22 s 1552 21,952 S May 7 5.5 0.25 0 11 0 Sept. 17 8.5 1.50 27 S 997 16,424 S Oct. 29 6.6 0.40 36 S 37 717 S 1978 April 7 4.6 0.60 22 s 106 1,494 S Sept. 2 7.5 0.75 38 S 188 3,723 S 1979 April 14 12.0 1.20 42 S 583 11,800 S July 14 6.0 0.30 22 s 19 272 S Sept. 22 8.5 0.90 22 s 298 4,219 S Oct. 21 7.5 0.30 32 S 19 355 s 1980 April 16 7.5 0.25 2s 11 16 S Oct. 25 10.0 2.00 23 S 2104 30,822 S 1981 April 18 6.0 0.50 0 62 0 Oct. 29 8.5 0.50 0 63 0 1982 April 8 11.0 2.50 22 s 3635 51,428 S April 9 10.0 2.00 12 s 2104 17,428 S April 11 10.0 2.00 22 s 2104 29,765 S Oct. 23 8.5 0.25 0 11 0 1983 April 1 5.5 1.00 3N 363 773 N

Table VIII. Withernsea wave and sediment movement data, October 196P-September 1970

Wave Wave Angle of Incident period height (Hb) approach wave energy Alongshore sediment transport (mean) (mean) (mean) (total) (m3) Date (4 (m) (") (MJm-') Total S Total N Net

1969 October 6.9 0.64 3N 5,506 49,699 16,527 33,172 S November 8.3 0.73 10 s 6,201 55,283 8,902 46,381 S December 6.5 0.6 1 5N 4,158 14,229 20,014 5,785 N 1970 January 7.0 0.64 1N 4,254 8,111 10,355 2,244 N February 7.4 0.49 6s 2,097 13,961 739 13,222 S March 8.6 0.58 9s 3,613 26,510 1,432 25,078 S April 7.3 0.49 8s 2,593 23,79 1 390 23,401 S May 6.4 0.40 6s 1,526 6,138 3,522 2,616 S June 5.9 0.34 IS 1,003 2,155 3,382 1,227 N July 7.0 0.30 10 s 853 8,139 60 8,079 S August 6.1 0.30 4s 912 2,558 172 2,386 S September 6.8 0.27 1N 577 2,510 3,247 737 N Winter (0ct.-March) 7.4 0.62 3s 25,829 167,793 57,969 109,824 S Summer (April-Sept.) 6.6 0.35 5s 7,464 45,291 10,773 34,518 S Year 7.0 0.48 4s 33,293 2 13,084 68,742 144,342 S

height variation along the cliff foot, a long ord length and a large area of exposed till shore-platform. During the following six months the maximum rate of cliff erosion was experienced. It is important to set the isolated daily wave records taken on the survey dates against a more complete set of wave observer data collected daily from the same position at Withernsea for 12 months from October 1969 to ORDS AND COASTAL EROSION 121

Table IX. Wave energy and sediment transport formulae

The following formulae from Caldwell (1956) were used to calculate wave energy and sediment transport:

where E, = total energy in wave in ft Ibs W = density of water T = wave period in seconds d, = depth of water at observation point in feet h, = wave height in feet at depth d, L, = wave length in feet at depth d,

E,, = (E,n/T 1t where Etf = total energy in ft Ibs transmitted forward over time interval t (converted to joules/m) 1 4nd,/L, n=- I+ (3) 2 sinh 4nd,/L, E,, = E,, sin 4 cos 4 (4) where E, = total alongshore energy in ft Ibs Etf = total incident wave energy in ft Ibs 4 = angle of wave crest with beach where E, = intensity of net alongshore wave energy in millions of ft Ibs per foot of beach per day Q, = intensity of net alongshore sand movement in cubic yards per day (converted to metres) k = factor of proportionality. Value 237 taken from US. Army CERC manual (1973) and Cambers (1975)

September 1970. Table VIII summarizes this to show mean monthly wave period, height at break point and angle of wave approach. It shows also monthly totals of incident wave energy and alongshore sediment transport. The data is then grouped to reveal differences between winter and summer and finally the year's data is shown. The greater winter mean wave period of 7.4 s and height of 0.62 m produced 25,829 MJm- ' of total incident wave energy as compared with the summer mean period of 6.6s and height of 0-35m yielding 7,464 MJm- ' of total incident wave energy. Whereas the monthly alongshore sediment transport data reveals a net southward movement for eight months and a net northward movement for four months, the winter months together show a net southward movement of 109,825m3 and the summer months a net southward movement of 34,518 m3. During the whole year therefore there was a marked net movement of 144,342 m3 southwards. The fact that the maximum daily incident wave energy reached only 1056MJm-' and the maximum daily alongshore sediment transport was only 14,940m3 southwards reveals that no major northerly storms occurred during this year, as occurred between 8 and 11 April 1982.

THE ORDS ROLE IN THE SEDIMENT BUDGET OF THE HOLDERNESS COAST The reduction of the beach level within an ord was important at the cliff foot where a lowering of up to 3.9 m enabled most HWN tides to reach it, as compared with only some HWS tides along the inter-ord beach (see Figure 6). The lowering of the beach seaward of the cliff foot within an ord exposed till shore platform to erosion. The volume of till cliff eroded therefore increased to an annual mean of 72 m'm- ' with an ord present as compared with only 9 m3rn-' along the inter-ord coast. The Holderness tills are composed of about 31 per cent of sand and coarser sediment and this is the range of sediment particle sizes of which the beach is formed. Where an ord is present therefore a massive injection of beach sediment occurs and the high 122 A. W.PRINGLE

Figure 6. The ord viewed northwards from Dimlington Highland on 5 April 1982. Waves approach the cliff foot in the centre of the ord (in the foreground) whereas the higher beach at the northern end protects the cliff from wave attack at high water on this nap tide. (Photograph by J. L. Davies)

Figure 7. The ord viewed southwards from Dimlington Highland on 2 April 1983. Beyond the northern end of the ord (in the foreground), a 'plume' of sand forming the lower beach sand ridge can be seen extending southwards from the centre of the ord, where cliff erosion and the injection of beach sediment is especially rapid ORDS AND COASTAL EROSION 123

proportion of medium to fine sand goes to form the prominent constructional feature of the ord, the lower beach ridge. The fact that this ridge forms closest to the cliffs at the centre of an ord and from there extends southwards at a low angle seaward suggests a net southward sediment movement (see Figure 7). 3. The dominance of a net southward sediment movement is suggested also by the analysis of wave data collected during the surveys of the sample ord and it is confirmed by the year’s wave data collected in 1969-70, during which a net transport of lM,000m3 southwards occurred. A pronounced seasonal variation in the net transport rate from 1 10,Wm3southwards during the winter to 35,000m3 southwards during the summer reflects lower wave energy conditions and lower cliff erosion rates, during the summer. 4. Figure 8B shows the total input of sand and coarser sediment from till cliff erosion between Withernsea and Easington and the considerable range which exists about the annual mean. Similar data is shown for approximately equal length sections of the Holderness coast as far north as Barmston at the northern limit of the till cliffs. (As cliff erosion data was not available at the extreme northern end, extrapolation has taken place from data north of Hornsea.) The low level of input in the north contrasts with the highest levels immediately south of Hornsea. Although this data spans the eight years from 1974 to 1982 it is strongly influenced by the irregular distribution of ords and is likely to change with their southward movement. Also shown on Figure 8B is the net rate of longshore sediment movement southwards, calculated from the Withernsea wave observer data for 1969/70. Along this only slightly curving coast it is probable that the m3x105 A 4-

3- Mean Annual Input of sand and coarser sediment from Cliff Erosion 1974/82

2- maximum Withernsea Wave Data 196917% - 1sn178 Input of sand and coarser t44.000m7TnelngshoT sediment from cliff erosmn 1- sand movement southwards annual mean Withernsea-Eaaington

minimum 1980/81

-/-- # 0 I V/A I NW SE 1 kilometres 0 5 10 15 20

1173x105 B 2- Max. 1977178 ---- -.- Annual- Mean Withernsea Wave Data 1969/70 ------144M)Om3 net bngshore sand movement southwards Annual Mean 1- Max. - - - - 1979180 I . L - - -A_?. Mean Min. 1980181 Min. 1979180 -1 Min. 1980/81 I----- Min. I 1977178 0-172- 7 NW Barmston Hornsea Withernsea Easington SE

Figure 8. Annual input of sand and coarser sediment to the beach from till cliff erosion 1974-1982. A Data plotted as a cumulative curve from near Barmston southwards. The net longshore sand movement southwards calculated from Withernsea wave observer data October 1969-September 1970 is indicated also. B: Data plotted as a histogram 124 A. W. PRINGLE

wave energy levels are similar from near Barmston southwards at least to Dimlington. Only immediately south of Hornsea was the annual mean sediment input above this rate of southward sediment movement, although the maximum annual input levels south of Hornsea were all above it. The cumulative sediment input curve (see Figure 8A), drawn from Barmston south in the light of this pronounced net southward longshore sediment movement, emphasizes the sediment deficit from Barmston to south of Hornsea and the excess of sediment further south. As this curve was drawn from mean annual data it must be remembered that it will vary considerably from year to year as input levels vary, sometimes in opposite directions along adjacent sections of coast. Probably little sediment input occurs alongshore from Bridlington Bay, which because of the shelter afforded by Flamborough Head especially from northerly storms, experiences lower levels of wave energy than the more exposed Holderness coast further south. The beaches especially between Barmston and Hornsea are relatively low and narrow and in addition to ords are characterized by containing bare patches of till shore-platform. They contrast markedly with the beaches south of Withernsea which are higher, broader and except within ords rarely show any bare shore-platform. This contrast in beach sediment volume certainly suggests a sediment deficit in the north and a surplus in the south. This study gives no support to the suggestion of Winkelmolen (1978) that beach sediment derived from the Holderness till cliffs is primarily carried off-shore with only a fraction returning to the beach as prograding bars. The southward alongshore energy levels, together with the general increase in beach volume from north to south and the detailed form and direction of movement of the ords, all suggest a dominant southward sediment movement along the Holderness beaches.

ACKNOWLEDGEMENTS I am pleased to acknowledge the help of the following: Prof. E. Derbyshire and Dr. P. A. Madgett for making available unpublished data on particle size analysis of Holderness till samples; Holderness Borough Council for providing annual cliff top erosion measurements; my parents for assistance in collecting the 1969-1970 wave data; Dr. R. T. N. Flowerdew for writing a computer program for analysis of the wave data; my husband George for considerable assistance and encouragement with the field work and for drawing Figure 2; and Mrs. Anne Jackson for drawing the remainder of the figures in the Geography Department at Lancaster University. The project was supported by a University of Lancaster Research Grant during 1978 and 1979.

REFERENCES

Admiralty Tide Tables 1982. Vol. 1. European Waters Including Mediterranean Sea, Hydrographer of the Navy. Caldwell, J. M. 1956. Wave Action and Sand Mooement Near Anaheim Bay, California, Beach Erosion Board, Technical Memorandum 68, 21 PP. Cambers, G. 1975. Sediment Transport and Coastal Change, East Anglian Coastal Research Programme, Report 3, School of Environmental Sciences, University of East Anglia, 65 pp. Entsminger, L. D. 1977. ‘Migration of beach pads on St. Joseph Peninsula’, in Tanner, W. F. (Ed.), Coastal Sedimentology, Geology Department, Florida State Univ., Tallahassee. Komar, P. D. 1976. Beach Processes und Sedimentation, PrenticeHall, New York, 429 pp. Madgett, P. A. 1974. The Mineralogy and Weathering ofDeoensian Tills in Eastern England, Unpublished Ph.D. thesis, London University. Madgett, P. A. and Catt, J. A. 1978. ‘Petrography, stratigraphy and weathering of Late Pleistocene tills in East Yorkshire, Lincolnshire, and North Norfolk’, Proc. Yorks. Geol. Soc., 42, 55--108. Pringle, A. W. 1981. ‘Beach development and coast erosion in Holderness, North Hurnberside’, in Neale, J. and Flenley, J. (eds), The Quaternary in Britain, Pergamon Press, Oxford, 194-205. Scott, P. A. 1976, Beach Development along the Holderness Coast, North Humberside, with Special Reference to Ords, Unpublished Ph.D. thesis, University of Lancaster. US Army Coastal Engineering Research Center 1973. Shore Protection Manual, Dept. of Army, Corps. of Engineers, 3 vols. Valentin, H. 1954. ‘Der Landverlust in Holderness, Ostengland, von 1852 bis 1952’, Erde, Berl., 6(3-4), 296-315. Vincent, C. E. and Ratcliffe, K. undated, c. 1978. Waoe Climate and Longshore Wave Power, East Anglian Coastal Research Programme, Report 7, School of Environmental Sciences, University of East Anglia, 86 pp. Winkelmolen, A. M. 1978. ‘Size, shape and density sorting of beach material along the Holderness coast, Yorkshire’, Proc. Yorks. Geol. Soc., 42, 109-141.