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Applied Geospatial Sciences Assignment: GIS-based mapping and interpretation at Holton Lee, Dorset.

Introduction:

Holton Lee, is situated on the western edge of Poole Harbour, and has several statutory designations relating to its cultural heritage, ecological significance and natural environment. As part of a long term management plan, a number of non-invasive investigations have been conducted throughout the site, and a large map-based dataset has been collated.

This assignment integrates these data sets into GIS and carries out a series of data analyses to aid in the implementation of the Holton Lee management strategy. Five maps have been completed, each displaying the various datasets. Each map has been appropriately annotated and presented with its own interpretation and discussion in order to quantify what the map shows.

Figures: Figure 1 – Site location plan showing Roman and Iron Age scheduled ancient monuments, overlaying the bedrock geological layer. Figure 2 – Holton Lee Digitised Aerial Photo Land Cover Map. Figure 3 – 0, 1 and 2m lidar-derived contours and High Water Mark, overlaying Holton Lee Digitised Aerial Photo Land Cover Map. Figure 4 – 18th Century waste dump and digitised anomalies, overlaying Ordnance Survey 1:10000 Base map. Figure 5 – Pitfall trap locations and invertebrate community, overlaying superficial geology layer.

Tables: Table 1 - Land Cover Areas. Table 2 - Land Cover and Area Lost following 1m Sea Level Rise. Table 3 - Land Cover and Area Lost Following 2m Sea Level Rise. Table 4 - Anomalies A, B and C Attributes and total area inundated following One and Two Metre Sea Level Rise.

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(Figure 1) Holton Lee site location plan showing Roman and Iron Age scheduled ancient monuments, overlaying the bedrock geological layer.

The above map illustrates the distribution of both Roman and Iron Age Scheduled Ancient Monuments which lie above a bedrock geology mix of Oakdale Clay Member and Poole Formation.

In the wider map there are seven sites in total; four Roman and three Iron Age. Within the Holton Lee study area however, there are three, with two further sites intersecting the boundary on its northern edge. These sites vary in size with the largest; the Iron Age settlement (marked in green), having an area of 21902.2 m². The map also contains two roman roads, one in a north - south direction, the other in an east – west. The east – west Roman road was most likely connected to the north – south road in the past and linked the Roman Dock (dark blue) and the Roman tile kiln (orange). The location of the Roman tile kiln is perhaps the least surprising of all the monuments where it overlays the clay formation. Roman tiles were almost exclusively produced from clay and therefore this could explain the Kiln’s position (Warry 2006).

The Iron Age sites vary in size with the two largest sites being the Iron Age Settlement (green) and the Iron Age Field System (purple). All three including the Iron Age Furnace and Hearths however, overlie the Poole Formation Bedrock Geology layer.

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(Figure 2): Holton Lee Digitised Aerial Photo Land Cover Map.

The minimum map-able unit (MMU) selected for this land cover map was 5m². This map unit was selected in order to simplify the map in order to include land covers only visible to the naked eye. The map has therefore lost a certain level of detail which could have been obtained by using a lower MMU. However, had a lower MMU been applied, many of the land covers would have been difficult to identify.

This map although accurate to a degree will have several uncertainty issues. One of the major issues faced during the production of this map was the complexity and multi-layered nature of the landscape. The aerial photo displays a complex mosaic of land types which was difficult to present and map precisely. Many of the smaller land covers were less than the minimum map-able unit and thus would not have shown in the final exported map.

This is why many of the digitised land covers feature as large blocks. These blocks merely represent the aerial photograph in a more simplified, easy to view format. Therefore, some of these land covers may well be subject to scrutiny. Although best attempts were made to ascertain the correct land cover, there could be some level of discrepancy. Scrub and Shrub land for example were often a mixture of many land covers where it was not easy to see the boundaries between land covers. (Table 1) quantifies the total area of each individual land cover below.

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Land Cover Total Area (m²)Bare Land 1118Beach Cover 5737Car Park 609Commercial 35372Farmed Land 221212Grass Land 572472Heathland 517880Hedgerow 6000In Land Water 9189Railway 19624Residential 1031Road Cover 32746Salt Marsh 114467Salt Water 851200Scrub Land 426483Shrub Land 135421Tree Cover 635790Wet Land 424684Total Area 4011035

Table 1: Land Cover Area (m²)

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#Figure 3: 0, 1 and 2m Lidar-Derived Elevation contours and High Water Mark, overlaying Holton Lee Digitised Aerial Photo Land Cover Map.

As expected, the high water mark lies behind and above the 0m contour especially in salt marsh and wet land areas. At its maximum extent, the high water mark lies 324m behind the 0m contour roughly in line with the 1m contour. The High water mark also extends 462m beyond the 0m contour down the minor estuary located 396,556.893E and 91,840.052N.

This map can also be adapted in order to estimate the areas of specific land covers which could be inundated following a sea level rise event of one and two metres. The ARCGIS intersect tool was used in this case to determine the total area lost as well as the overall percentage loss of each individual land cover. Tables 2 and 3 summarise these estimates below.

These estimates again, like the land cover map have their own limitations. One of the major constraints placed on this exercise were the extent of the contours; which did not spread to the outer edge of the land cover map. This meant that not all land covers potentially affected by one and two metre sea level rise could be recorded. Thus only land cover contained within the contours were recorded.

In spite of this, the data which was gathered from the map showed significant inundation of coastal areas. Worst affected land covers in both scenarios included Salt Marsh, Wet Land and beach cover. This is relatively unsurprising due to their inclusion within the high water mark and the flat relief of the land.

Sea level rise in such areas will have profound consequences, especially for the flora and fauna species which inhabit them. Sea level rise will increase the probabilities of both accretion and erosion with the result being; an overall more dynamic coast line (Boorman 2003).

Moreover, a higher sea level and high water mark could result in salt water intruding further inland and up estuaries and water-ways, thus increasing overall salinity. Organisms such as barnacles and shipworms which require high salinity to survive, could move inland and increase species competition as well as attacking wooden structures in areas they inhabit (Oberrecht 2005).

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Land Cover Area Lost in 1m Sea Level Rise (m²) Percentage Land Cover Lost (%)Beach Cover 975.9 17Grassland 34616.4 6Inland Water 7584.9 82.5Railway 142.7 0.7Salt Marsh 61489.4 53.7Scrub Land 96200.5 22.6Shrub Land 7115.1 5.3Tree Cover 9384.6 1.5Wet Land 256095.1 60.3Total 473604.6 11.8

Land Cover Area Lost in 2m Sea Level Rise (m²) Percentage Land Cover Lost (%)Beach Cover 1333.1 23.2Grassland 67077.9 11.7Heathland 1445.5 0.3Inland Water 7584.8 82.5Railway 3167.1 16.1Salt Marsh 61489.4 53.7Scrub Land 106775.1 25Shrub Land 33172 24.5Tree Cover 29990.3 4.7Wet Land 321348.8 75.7Total 633384.0 15.8

Table 2: Land Cover and Area Lost Following 1m Sea Level Rise.

Table 3: Land Cover and Area Lost Following 2m Sea Level Rise.

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Total Area (m²)

Area Inundated 1m Sea Level Rise (m²)

Area Inundated 2m Sea Level Rise (m²)

Land Cover(s)

Bedrock Geology

Superficial Geology

A 4311.0 1417.7 4311.0 Shrub Land and Wet Land

Poole Formation

Gravel, Sand, Silt and Clay

B 1736.5 451.8 1736.5 Wet Land

Poole Formation

Gravel, Sand, Silt and Clay

C 579.5 0 579.5 Wet Land

Poole Formation

Gravel, Sand, Silt and Clay

Figure 4: 18th Century waste dump and digitised anomalies, overlaying Ordnance Survey 1:10000 Base map.

The Root Mean Square Error of the geo-referencing process was 0.356413. Below is a table which documents the total area of anomalies, the area inundated following one and two metre sea level rise, the land covers and both bedrock and superficial geology.

Table 4: Anomalies A, B and C Attributes and total area inundated following One and Two Metre Sea Level Rise.

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The extent of land inundation following sea level rise is perhaps the most significant data displayed within the table. By applying the intersect tool on ARCGIS, the total area of the anomalies flooded by sea level rise can be calculated. A 2m sea level rise for example, will likely inundate the entire 18th century waste dump as well as the three anomalies.

Any Intruding salt-water would most likely contaminate groundwater and threaten landfill and hazardous-waste sites old and new (Flynn et al 1984). Although the waste dump in question is over 200 year old, much of the underlying land may well continue to be contaminated even in the present day.

The underlying geology consisting of predominantly gravel sand and silt is highly permeable. In general, the permeability of soil underlying waste disposal sites is of great importance. The higher the permeability, the greater risks presented by land pollution.

Many landfill waste sites before the 20th century were generally placed over-land in ‘uncontrolled’ dumps. Such dumps became breeding grounds for rats, rodents and other disease carrying organisms. These sites often produced a highly contaminating liquid known as leachate which is often contained within the soil. Sea level rise could however, extract this liquid and cause it to be distributed into other areas. This in turn could affect localised ground-water reserves and pose a threat to public health and environmental quality (Nathanson 2016).

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Figure 5: Pitfall trap locations and invertebrate community, overlaying superficial geology layer.

Displayed above are the pitfall trap locations together with the underlying superficial geology. This map shows how a large proportion of the pitfall locations overlay the Sand and Gravel geology layer. On the other hand, very few are found to overlay the Gravel, Sand, Silt and Clay layer.

Moreover, the pie charts demonstrate how the Black Clock Beetle ‘pterostichus madidus’ was found in greater concentrations towards the southern-sea-ward side of the map. These species are typically found in grassland habitats but are also known to inhabit areas of tree cover under loose bark (Nature Spot 2015). When comparing their predominant locations with the land cover map, the two major land covers which appear most frequent are ‘Grass Land’ and ‘Tree Cover’

Cinindela Campestris, the Green Tiger Beetle on the other hand is predominantly found in the sandier underlying geology. Lying above the geology is sandy heathland which is ideal for the Green Tiger Beetle and perhaps explains their presence in pitfall traps in this area.

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References:

Boorman, L.A., 2003. Saltmarsh Review. An overview of coastal saltmarshes, their dynamic and sensitivity characteristics for conservation and management. JNCC Report, No. 334.

Flynn, T, J., et al. 1984. Implications of sea level rise for hazardous waste sites in coastal floodplains. Greenhouse Effect and Sea Level Rise: A Challenge for this Generation, p271-294.

Nathanson, J, H., 2016. Britannica Online. Available from: http://www.britannica.com/science/land-pollution, Accessed [25th April 2016].

Nature Spot, 2014. Black Clock Beetle - Pterostichus madidus. Available from: http://www.naturespot.org.uk/species/black-clock-beetle [Accessed 25 April 2016].

Oberrecht, K., 2005. Estuaries Feature Series articles & study guide questions: "The Effects of Rising Sea Levels", South Slough National Estuarine Research Reserve, p153.

Warry, P., 2006. A dated typology for Roman roof-tiles (tegulae). Journal of Roman Archaeology, 19, p246-265.

Total Word Count excluding tables, figures and references - 1296