The Clay Research Group The Clay Research The Clay ... 91.pdfclay soils, and within influencing...
Transcript of The Clay Research Group The Clay Research The Clay ... 91.pdfclay soils, and within influencing...
The Clay Research Group Issue 91 – December 2012 – Pag
The Clay Research Group
Monthly Bulletin
TheClay Research
Group
December 2012
RESEARCH AREAS
Climate Change Data Analysis Electrical Resistivity Tomography
Time Domain Reflectometry BioSciences Ground Movement
Soil Testing Techniques Telemetry Numerical Modelling
Ground Remediation Techniques Risk Analysis
Mapping Software Analysis Tools
The Clay Research Group Issue 91 – December 2012 – Page 1
CONTENTSIssue 91, December, 2012
It’s all about Sutton
Page 1Claims, sector and terrain maps.
Page 2GeologyPage 3
Trees by HeightPage 4
SM1 3 – Risk MetricsPage 5
SM1 3 – Sector RiskPage 6
SM1 3HG – Unit RiskPage 7
Building the Model
NEXT MONTH
Evidence of the adage “Time isMoney”. Policy life and risk. Do the
odds stack up? How manyvalid/repudiated claims by season,
and then by peril.
Climate Update
The Met Office (as reported in The Times by JonathanLeake, their Environment Editor) have recorded that theworlds climate has cooled over the last two years. PeterStott of the Met Office says “it is a short period that isscientifically meaningless. Climate Change can only berecorded over decades – and records show that theworld has warmed by 0.75 degrees over the pastcentury.”
The first 10 months of 2010 were 0.110C warmer thanthe same period in 2012, which was attributable tonatural variations associated with El Nino – not ClimateChange, said Stott.
Apparently, global temperatures have hardly risen forthe past 15 years.
London Borough of SuttonStudy Area
The London Borough of Sutton is situated to the southof London (see map below). Our study includes plots ofclaims, the risk at sector level, topography, geology andtree metrics. All are combined to demonstrate how ourrisk model is constructed.Weather Watch – data courtesy of Met Office
SMD at end of November, 2012
The Clay Research Group Issue 91 – December 2012 – Page 2
The terrain map (below) reveals the gradualslope down towards the Thames (to the north ofthe map), with the chalk outcropping to thesouth and south east and clay deposits in thebasin to the north. It is interesting to note thecorrelation between height and surface geology.
The London Borough of Sutton
The South London Borough of Sutton has anarea of 43 sq.km and a population of around190,000.
The publication, ‘Chainsaw Massacre’ lists thetotal number of street trees removed over afive year term = 1,205, of which 33 wereremoved due to subsidence. This loss amountsto 2.74% compared with the London Boroughaverage of 5%.
Claims (red dots) occur predominantly to theNW of the Borough on the clay series – seefollowing page.
Next is a map showing claim distribution bysector, and expressed as frequency. The modelsuggests that postcode sectors SM1 3 and SM39 have the highest claims frequency.
The Clay Research Group Issue 91 – December 2012 – Page 3
THE GEOLOGY of SUTTON
The geology of Sutton as revealed using ourunique tiled grid, (top) and an extract fromthe 1:625,000 scale extract from the BGSmap, below. The BGS do of course havemuch larger scale maps.
The CRG map is useful because in each 250mcell there is a value reflecting the indexproperty (in the case of clay soils) of the soilat a depth relevant to tree root activity.
The values have been derived from actualinvestigations over a twenty year period, andthe shrink/swell potential has been extractedfrom a depth of around 2mtrs.
The settled cost of claims has a relationshipto the geology, both in terms of the presenceor absence of shrinkable soil, but also theirplasticity index. Setting the cost at 1 for aclaim on a non‐cohesive soil and then using amultiplier based on the index propertiesprovides indemnity values representingindustry averages.
The BGS map reveals the presence of Londonclay to the North of the Borough, and chalkto the south.
In this instance, both deliver a similar pictureand explain the distribution of claims on theprevious page.
The Clay Research Group Issue 91 – December 2012 – Page 4
SUTTON ‐ TREES by HEIGHT
Public trees, top, and private trees below,thematically plotted by height.
Public trees are predominantly in the heightrange 7–10mtrs with the taller running northsouth just to the left of the Borough.
Private trees tend are slightly smaller,averaging 7‐8mtrs in height.
If we restrict our analysis to trees situated onclay soils, and within influencing distance ofhouses, and exclude trees on chalk, wellaway from buildings, we find the following.
There are around 27,000 trees in privateownership on clay soil, within influencingdistance of buildings. The average height is7mtrs, and the tallest private tree in theBorough is 30mtrs.
Public trees on clay soils, and withininfluencing distance of buildings total inexcess of 5,000. They have an average heightof 7.5mtrs – maximum height, around24mtrs. This compares with the total numberof street trees estimated by the Borough toamount to 22,000.
The location of the tallest trees, both publicand private, are shown very approximatelyby the arrows on the maps.
tallest tree.
tallest tree.
Public Trees by Height
Private Trees by Height
The Clay Research Group Issue 91 – December 2012 – Page 5
SM1 3 ‐ Metrics
SM1 3 is one of the higher risk postcodesectors in Sutton. In the adjoining column wegraph the number of properties with rootswithin influencing distance, and theirestimated overlap.
The 5,106 properties form the ‘x’ axis of thegraphs in the adjoining column.
All are situated on clay – PI in range max68%, average 52%, and some very low values– less than 10%.
The maximum tree height is 25mtrs, and theaverage = 6.7mtrs.
The maximum root overlap beneathbuildings is 1,535 sq mtrs and the average =26 sq mtrs.
The estimated % overlap is maximum 100%:the average is 22%.
There are 2,232 properties with no treeinfluence out of a total of 5,106 buildings.
To improve our understanding of risk, thevarious parameters have been plotted in thesame rank order to combine the risk of rootoverlap, tree height and soil shrink/swellpotential.
On the following page the spatial distributionof the above elements are mapped tovisualise these relationship. Where are the‘hot spots’? When do they combine and doesthis reflect claims experience?
% Olap
0
10
20
30
40
50
60
70
80
90
100
1 189 377 565 753 941 1129 1317 1505 1693 1881 2069 2257 2445 2633 2821 3009 3197 3385 3573 3761 3949 4137 4325 4513 4701 4889 5077
Max H
0
5
10
15
20
25
30
Soil PI
0
0.1
0.2
0.3
0.4
0.5
0.6
Top (orange), the count of properties in modelledinfluencing distance of trees, by estimated rootoverlap. The model suggests that 43% of the
buildings in Sutton postcode SM1 3 are outside theinfluencing distance of trees. The green line plots thetrees by height, in the rank order of the graph above,and the red dots are the soil PI – again, plotted in the
same rank order.
Modelled Root Overlap
Tree Height by Property
Soil PI by Property
The Clay Research Group Issue 91 – December 2012 – Page 6
SECTOR RISK ‐ SM1 3
By combining the risk posed by the heightof the tree in terms of D/H with the soilshrink/swell potential the spatial modelsallow us to visualise the interactionbetween trees, possible root zones andgeology (following page).
Top left, a map plotting trees by height.Centre, possible root zones and bottomleft, the distribution of clay soil in termsof their plasticity index.
By laying one on top of the other thecontribution from each can deliver a sumthat defines the risk.
Red zones are the riskiest, greenintermediate and blue, relatively low risk.
Where red zones from each elementcoincide, then the risk is greater. Talltrees, near to buildings on highlyshrinkable clay soils are easily identified.
The fact that each layer is built from adata grid (see following page) makes thecalculation much easier.
The Clay Research Group Issue 91 – December 2012 – Page 7
Unit Postcode – SM1 3HGOr “13 Acacia Avenue”
The same technique allows us to drill downstill further and make house‐by‐houseassessments by adding the OS MasterMapseries, and superimposing the LiDAR data toderive the most advanced assessment of riskavailable.
The Clay Research Group Issue 91 – December 2012 – Page 8
Deriving Risk
By layering datasets, each with a value onthe pre‐defined grid, the risk can bederived.
If at one location each of the maps has ared coding and a high risk value – that is,a highly shrinkable clay, high claimsexperience and within influencingdistance of a tree – then the cumulativescore will be high.
Each of the layers is weighted. A clay soilis far riskier if there is a tree nearby thanit would be without. The weighting has tobe reduced if the dataset is incomplete toavoid blighting areas.
Add in age of property, style etc., torefine the model even further.
To Conclude
So, where does Sutton stand in the schemeof things, in relation to the risk ofsubsidence? What is its position in the UK,and compared with other LondonBoroughs? It’s individual sectors are ratedin the graph, right. Scores of between 0.22and 0.28, across the Borough suggest itranks 66th out of 413 Districts across theUK in terms of subsidence risk, and 15thout of the 33 London Boroughs.
The Clay Research Group Issue 91 – December 2012 – Page 9
Melting Ice Raises Sea Levels“The Ice Sheet Mass Balance Inter‐Comparison
Exercise”Prof A Sheppard et al
Journal Science
In a paper published in the Science journal lastweek, scientists suggest that melting ice from theAntarctica and Greenland have caused the oceansto rise by 11.1mm over the last two decades.
The lead author, Prof Sheppard from LeedsUniversity says that past satellite measurementseither were limited in scope or suffered frommethodological inconsistencies. Current readingshave been compared with those taken in 1992.
The study suggests that melting of the iceaccounted for 10% of the rise in sea level in the1990’s, but now accounts for around 30%.
Other contributory causes include warmingresulting in an increase in volume and run‐offfrom glaciers.
Prof. Sheppard concludes “there is no immediatethreat from rising sea levels” but goes on tosuggest that there are instabilities that need to beinvestigated.
The graph, left, is reproduced from an article inThe Wall Street Journal.
Measuring 11mm rise in sea levels is quiteremarkable using satellite data from oceansand we imagine the estimates are based onalgorithms that derive averages.
Global DroughtEstimates use a Flawed Index
In an unrelated article, Justin Sheffield fromPrinceton University suggests that the weatheris likely to get wetter, and that prediction ofmore droughts could be wrong.
He bases this on what he considers to be theincorrect use of what is known as PalmerDrought Severity Index (PDSI) used in climatemodels.
The index looks at the difference betweenprecipitation and evaporation to deliver a‘drought index’. Because evaporation isdifficult to measure, temperature is used as aproxy, which is where the method falls down.
Instead, the Penman‐Monteith method shouldbe used which takes account of wind speed,hours of sunshine and humidity etc., to delivera more accurate estimate.
Based on this revised estimate, Sheffield found“little change in global drought over the past60 years”.
We are a little embarrassed to mention ourarticle in Newsletter 70, March 2011 when wecame up with the same flawed method. Ourmodel used precipitation and temperature tomodel tension in the xylem.