Waterlogging on Construction Sites - 22/11/2012 - Giles Landscapes CMS
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Waterlogging on Construction Sites – 22/11/2012

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This year is the worst I have experienced in all my career of landscaping.

It has,as always been aggravated on sites where Contract Managers, Area Managers and Site Managers see the building of a structure through to it’s high spec finish. Then draw a sigh of relief “job done”. But is ” job done” the ambiance of a magnificent building?  Can it then be destroyed 6 months or a year later by a lack lustre, struggling, waterlogged landscape?

[Too much water kills more plants than too little water]

A 3-prong tyne. 

Bits of light kit to break up pan, as used on our compact tractor and  mini digger.

But of course, we do use heavy gear as needed. Mick George is always quick off the mark and has often been on-site for us within 24 hours with a D8 and multi tyned ripper.




The only trees that had to be replaced, on the whole park, were Jugalans Rega, as you can see, they have been replaced by the water tolerant Alnus near the main building, originally a well drained area, but, a temporary bund had stopped the drainage, the Jugalans Rega (Walnut) started to die, not liking its feet in the waterlogged ground.

All  the  other  planting  on  rest  of  park  was  earth  sculpture  mounds which  of  course  drained.


Gunpowder Park – Before

When I came out of a pre-contractural meeting my heart sank. Damien Debski the Halcrow consultant Chief Engineer said this project will be different to any project you have ever had, then you said one problem after another will occur.

I looked across the potential park we had taken ownership of, it was waterlogged as far as the eye could see.

The extensive earth sculpture mounds, of pure subsoil, were heavily compacted on the famous Gunpowder Park at Enfield, due to wet conditions at the construction phase.

We double dug these areas with a 20 ton 360 digger, to a metre deep, to de-compact them. We then turned Bio Gram (heat treated sewage sludge) in, with a heavy duty land reclamation spading  machine to 400 mm. We then got top results planting trees and shrubs straight into the sub soil by putting fungus mycorrhizings in the soil to assist with the establishment of the soil population.

Gunpowder Park – After:

 The scene behind me shows the development of wildness on the park on the day of opening by HRH Prince Phillip.


Alnus cordata: These were originally Juglans regia but had to be replaced with a more water tolerant tree variety due to a temporary water logging problem. These were the only plants on the whole site that needed to be replaced.

Above is a view of the park to the left of the main gate.

Some areas were left unseeded and ended up like this.

 Above is a seeded wildflower area, much of the park was seeded by a Emorsgate’s Seeds, Lea Valley Park indiginous mix.



I was introduced to HRH the Duke of Edinburgh by my client David Thompson of LDA – the landscape architect for Gunpowder Park (David is standing next to me in the last photo). None of us knew it at the time but David was to go on to be a big player in the design process of the Olympic site just down the road from Gunpowder Park.

If you scroll down, the first thing you will see is the Gun Cotton Grinding Wheels.

Because of the precise procedures required to safely produce armaments, strict health and safety systems were written and this was the beginning of ISO9000.

Continue to scroll down to see the original gates to the site and various stages of seeding and planting throughout the project.

Our very resourceful agricultural team of Ray and Russel were having trouble with equipment being smashed. They worked 24/7, cut up an articulated lorry and used it as a levelling bar to help with final preparation.

Read  on  for  symptoms, cures and  case  studies re Compaction and Water-logging (especially  on  construction  sites  that  is  in  most  cases so  easily  avoided  at  the onset).

The symptoms of anaerobic and waterlogged damage are many. The effects can  be  brought  on  by  waterlogging  caused  mainly  by  no  attention  to  ripping  through  the  site  pan  prior  to  the spreading  of  top  soil.  A  little  bit  of  preparation  before top  soiling  takes  hardily  any  time.  Of  course,  the  normal    checking  for  cables and drains etc.  prior  to  ripping is essential.  What  can  happen   if  these  normal    good  husbandry  techniques  are not  catered  for?

When  it  has  a  nice  open  structure,  preferably  with  some  humus  in    the  soil, it is  then  populated  by  aerobic  bacteria  and  other  microbial  fungus  type  organisms,  often  pertinent to the development  and  well  being  of  certain  plants.  Plus  worms  and  the plethora  of  other  creatures  flourish  working  the  soil,  keeping  it  well  and  truly open  and alive.  When  it  is  waterlogged,  it  is  only  populated  by  anaerobic  souring  bacteria.  It  then becomes  dead  and  inert:  inhospitable  to  most  life  and  plants.  What are the symptoms? Often very much the same as drought.  Some  plants  die,  with others having yellow leaves  and  droop.

Root balled, semi mature trees, struggle when the bottom of the root ball is waterlogged, killing all the lower roots. The few roots near the top of the ground, that are left, struggle to serve the tree in drought. To test anaerobic inert soil, dig out a spit or two. There will be a sour rotten smell and often, a short way down, the profile of the soil will be mottled and lacking any noticeable form of life.

The effect on turfed rear gardens that have to be installed at certain dates to co-incide with clients moving into a property:

These often have to be turfed in less than ideal conditions on building sites. If the subsoil has been scraped out evenly and drainage is good, as well as there being a good depth of topsoil, there will only be slight shrinkage across the whole area and the garden will keep its level as it dries out.

However, if the topsoil has been intermittently spread across undulating, non-ripped, compacted undersoil the chances are, as the top soil settles, the garden will follow the underlying contours and swales and hollows will appear.

2. If the topsoil has been taken up without care and includes chunks of subsoil, it is sometimes up to 2 years later (if there is an exceptional dry period) that undulations may appear, as the different types settle.


3. Cambridge clays, but mainly Milton Keynes type soilers are the landscaper’s original nightmare! When Milton Keynes’ soil is put into a topsoil pile slightly wet, I have seen it come out in lumps; some as big as footballs, that get tipped in rear gardens on sites, blinded over with finer soil that looks great but store up problems because, as the years go by the topsoil migrates into the hollows below. We can all do our best to make it work, but, with the best will in the world, if it suddenly becomes very dry, 6 months later or so, the chances are that Customer Services get a call stating ‘Our garden has hollows, dips and subsidence etc.’

Some case history on how Giles Landscapes started getting main landscaping projects by trouble shooting on waterlogged sites….


I visited the site and met the project manager.

I told him I had local knowledge of the soil conditions, having just planted up the adjacent motorway on the same type of soil.

I was sent away with a flea in my ear. I got the same when I rang the developer. I was told ‘we have a top class landscape architect running the project, your outfit does not have the credentials we need’. I did not agree with him, but left my card with the developer and the project manager. However, we did did not get invited to price for the project.

About a year later, Author Amos, a landscape architect who specialized in pulling problematic sites round, had been retained by the developer for the sole purpose of getting their client to accept a failing planting scheme and to get their project signed off.

The original project was £250,000 for the landscaping scheme. The building project had run over its deadline, the weather was diabolical and wet. Three sides of the building were heavily landscaped with trees, shrubs and ornamentals. This area co-incided with the Tempery Hall Road, so that most of the materials were carted round the building. The deadline for the store to open was fast approaching, the developer pushed the top soil in (probably not paying much attention to the drainage and ripping), the heavens opened; the plants went in badly, as landscapers struggled to meet the dates of opening the store. The very wet site then suffered from a heat wave. The fine black sandy soil set like concrete, the plants started to droop and die. Bark mulch was added, containing a high percentage of fines. The plants appeared to be drying out, but the fines compounded the problem, not letting the soil breath. Auther Amos, the trouble shooting Landscape Architect, had been given our card as a landscape company with local knowledge. Another consultant had been originally called in by the developer to give their opinion, which was “apparently”, that the top soil had been originally stored in larger piles for a period of time, thus becoming inert; losing it’s soil population. Thus the cure was, rip everything! Bring in new topsoil and replant. This new scheme was priced at £250,000 to rip it all out, dispose of the waste, plus bring in new soil, then, possibly another £250,000 making it half a million. Plus, it was bandied about that the store would want compensation for the disruption, bringing the rescue project to about £1 million”.

As  you  can  imagine, the  developer  did  not  like  this  whatsoever,   so  chose Author Amos  to  lead  our  team  into  battle.  First  of  all,  I  went  round  with  Auther, he  stuck  his  little  probe  in  everywhere  and  it  was  all  stinking  rotten!  The plan was devised as follows;

1. A  Terra lift  machine  was brought  in. This  banged a hefty  charge  of  air  into the  ground  about  a  metre  down,  cracking  fissures  in  the  sub  arrears.  If  I  remember,  each  charge  was  inserted  every  15  metres,  filling  the fissures  with  graduals  to  keep them open.

2. The  fine  bark mulch  was  scraped  into  rows,  to  let the ground  breath.

3. A  breaking  bar  was  used  down,  to  about  400 t0 450 mm, to  further  heave the ground. The  rest  of  the gaps  between  the plants  was  heaved  with  heavy  fork  dissipating with a  bit  of  bark  back  into  the  ground.  Well  before  we  had  finished,  the  improvement  became  apparent. The  Store Manager got  a  smile  back  on  his  face and  even  invited  the  lads  to  lunch  in  the  store  canteen.

The  final    operation  was  to  replace the dead  plants  and  trees.  This  was  easy,  as  most  of  them  amazingly  recovered  once  the  ground  was  opened  up  and  aerated.  The  cost  from  us  to  the client    was  £45,000 on top of whatever Author  Amos  charged  them.  The  bonus  to  us  was,  it  gave  our struggling  little  outfit  credibility.  The Store Manager  moved  on,   but  if  we  needed   references  for  new  clients,  he  would  sing  our  praises  when  they  rang.

We were then awarded a couple of similar schemes putting us right on track.

The 2 projects gave us over £400,000 of work.

On one of these projects, we knew exactly what to do, it was so simple. We had noted a  few  acres  of  sloping  sandy  land  had  been  used  by  main  developer,  who  built  a  bypass  by  a  market  town,  to  store  all the heavy   plant  and  machinery.   When  this  was  top soiled  and  planted  by the original  landscapers,   the  under  pan  was  just  as  good  as  a  pond  liner.  Consequently,  every  time  it  rained  a  black  stinking  mess ran  over the pavement  across the road  to  the  horde of  hoteliers  opposite!  Once the soil  pan  was  cracked,  it  drained  easily.  Under  the  pan,  a  metal  spike  could  be  pushed  in by  hand into  well  drained soil. Why  do  only  people  from farming  back grounds understand  how to rectify these so  simple and unnecessary  problems?

Just  as  the  last  recession was  finishing,  we  looked  after  about  15  sites  for  a  NATIONAL BUILDER.  This  builder  had  stored  up  quite  a  few  problems and the NHBC were  on  his  back.  Waterlogging occurs mainly  were  there are  rows  of  houses which  have  attracted  a  bit  of  compaction from  machinery hauling equipment  along  the  back of sites.  Some builders  and  developers when they finish sites, spread topsoil on top of the compaction, then fence the site. Then the landscaper  comes  in who rotavates,  levels  and  turfs  the gardens  in  a  dry times and often it can  look  good.  However, we then  get  the wet  season and every house owner is onto  the  builder’s Customer Services that the garden appear to be waterlogged!

Despite being paid by the builder to  put in   land  drains to all the gardens, it  was  a  miserable  job.  I  became  frustrated and had  a  row  with  a  few  site  agents;  trying  to  convince  them  to  do  somthing  about  compaction and finished  up  meeting  the  main  contracts  manager at  head  office  and after  an  insalubrious  meeting,  we  parted  company.

To  cut  a  long  story  short,   we  were  back  working  for   the  company  again after  a  couple  of  years.

The contracts  manager &  I shook  hands,  both apologised  to  each  other;  agreeing  we  had  been  pointlessly arrogant.

It  tuned  out  that   he  had  engaged  a  couple of  farm  boys  as  site  managers  who undestood  soil, we  then  developed  a  team  with  build  area  managers,   sales  area  managers, public open  space technical  managers  and customer  service  staff. We  put on PowerPoint  presentations  at  site  manager  level on  soil  and  compaction, we  worked  as  a great  team then for 15  years  helping  to  give  the  builder presentations  with  his  show  houses and public  open spaces forging  links  with councils etc.

If  you  scrowl  right  down  on  our  Awards page,  the  sites  run  by  the  farm  boys  won  a  few NHBC awards.

This  year,  we  all  know  there  will  be  complaints  about  waterlogging. Even  when  site  conditions  are  well  drained  and  perfect.


All  this  jargon I have  preached  about is because, I would  hope to encourage developers to  put  in  their  specifications  a  tick  box  for  site  managers  to  check; mot, tempory  base  has  been  removed, site  has  been  leveled and  tyne  riped  prior  to spreading  topsoil.

I now  see  the  original  customer  service man  we  used  to  work  with, he  is  a poacher  turned  game  keeper  inspector  for  NHBC.









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