Introduction
‘Water – an inorganic, colourless, transparent, odourless liquid that forms the seas, lakes, rivers and rain and is the basis of the fluids of living organisms’. As defined by a dictionary, water is also known by its’ chemical formula as H20. Each molecule of water contains two atoms of hydrogen (H) joined to a single atom of oxygen (0). It has an Imperial weight usually defined at ten pounds per gallon.
It is unique, in being the only substance that can be a gas, liquid or solid, dependent on its state at that moment. It can evaporate and disappear or expand when frozen. When referring to the amount of moisture in the atmosphere, we are actually talking about the amount of water vapour. This is all basic science. Water is essential and wonderful, except when it becomes invasive, excessive, or contaminated, when it can cause many problems for landscape contractors and builders.
Invasive, when flooding the site or laying above ground when we are trying to work on projects. Invasive, when it decides to enter neighbouring properties whilst we are on site – even if the movement has nothing to do with us, we still get the blame simply by being on site! Excessive, when ground water levels rise above the soil level and turn previously solid soil into mush and slurry, ruining foundations and undermining existing completed works. And contaminated if surface water runs into the site from beyond, occasionally bringing unpleasant odours, silt and sewage into the site.
During torrential downpours, we can add ‘airborne’ water to ground water, causing even more havoc. Of course, we are used to coping with all sorts of site conditions, and normally manage to handle even quite difficult levels of problems involving water. There are however, many steps we can take to mitigate water issues – some by careful research, and others by looking at a list of solutions before undertaking a project. Some of these may need to be included in a tender so that our terms and conditions are clearly set out in the quotation and highlighted as necessary and not simply ‘lost’ in the plethora of words forming the legal element of a quotation.
In plain English – any special precautions that you deem necessary, should be included in the main body at the quotation stage, and not buried in the small print. These should be referenced and costed as part of the tender, as Preliminaries, priced to be used if the occasion arises. (Ensure that any such costs are time related i.e. weekly hire, to be included only if essential)
Because so many houses – new builds and refurbishments – are being constructed at breakneck speed, it is a fact that some are being erected on sites that would have been considered too much at risk of water problems – flood plains in effect – in previous years. Thanks to the regulations regarding Sustainable Drainage Systems (SuDS), Local Authorities are placing great reliance on a series of grand plans, many of which are theoretical and unproven, before giving planning permission to erect dozens or even hundreds of new homes of what may be considered unsuitable sites due to potential problems with high water tables.
Any landscaper with experience of working on new-build sites will know the danger signs – indeed, almost anticipate the problems they are likely to encounter. As a dispute expert witness, I am involved in dozens of claims cases each year, many involving ‘water’ as a major factor in a Court case. I will be looking at some of these cases in detail, using them as examples of genuine litigation claims, highlighting details of the background of the cases, and outcome/resolution (if any) in a min-series written for The Landscape Library.
There are already two relevant articles featured in the Landscape Library – Soakaways and Riparian Rights and Responsibilities which will be of interest and germane to this group of articles, and I will try to avoid repeating some of the information unless it is necessary to describe a situation.
One term that is widely applied to ground water is Field Capacity. This term refers to the volume of water that any given body of soil can accommodate before the water rises above ground level. The volume of the capacity will depend on the nature of the soil in question. Therefore, there can be no hard and fast rules concerning the likely volume of water that an area of soil can cope with before ground water becomes a problem for those working on or near the surface.
I am a very strong advocate of conducting site research before tendering for a project. Many decades of working across Britain have caused me to be careful when pricing, and not simply working off a set price menu. I use a site survey and logistics template (see Landscape Library) when carrying out surveys, taking into account many factors and features that may appear well beyond the immediate boundaries of the site I am measuring. This survey includes areas surrounding the immediate garden, paying special attention to the heights and levels of neighbouring properties, the amount of hard landscaping, plus assessing the nature of the soil in the garden with regard to compaction and type.
Evaluating existing sites.
Whether new-build or existing properties, I am keen to evaluate potential issues with ground water, as this is the only matter that I have no control over in the short term. If the soil is clay, expect ground heave, whereby the ground mass can swell when saturated or at field capacity, or shrink during hot, dry weather, causing issues with subsidence and movement.
Using Google Earth maps as a general guide, and aerial photographs in particular, it is possible to conduct an historical survey of a site. Photos are generally available taken at two-year intervals, and a series of images will clearly show how, and if, the area has changed. Of particular interest is the variation of tree cover. Woods and large trees (especially oaks) may be identified, and if a sufficient number of specimens have been lost, I am immediately aware of potential issues with groundwater. Mature trees can take up hundreds of gallons of water per week, and this water will be likely to remain in the ground once the tree has been removed.
Going further, the use of LiDAR (Light Detection and Ranging) surveys can show how the terrain has altered over the years. There is also a system available to trace water movement by use of a hydrological scan, indicating the likely movement of water across the ground. Any alterations to the terrain caused by developments could be the signal for a potential ground water problem on a site. As a consultant, I use these tools on a regular basis, as invaluable evidence to back up my reports.
On new-build sites, a copy of the overall site layout plan will show the datum levels of the floors of each unit, including the garages. Each one has a number showing plus or minus the datum point, and will show the lay of the land across the whole site. Using this as a guide, and looking at the amount of hard landscaping (driveways/car ports etc) you will gain a good idea of the volume of water that could be moving around the site. Simply check and evaluate your site position within the whole development.
Although this research may sound time consuming, once you have the information, you are in a very strong position to use that knowledge when it comes to quoting for other houses in the immediate area. Whether on a single site or multiple development, the information you have gathered will require interpreting into a meaningful document. By tracking and tracing potential water movement across a site, assessing the potential volume of water likely to be moving from the high ground to low ground, and combining your findings regarding soil type and any loss of tree cover, you will quickly possess a valuable document.
Matching information with the project.
As the scale and complexity of any project will be bespoke to a given site, the temptation to use previous examples of such field work may be great, but should be resisted. In the event of a future claim, the only information that will be of benefit to you is that specifically applicable to the named site. If you have done your homework properly, conducted with due diligence, you do need to hold a degree in science to prove that you have taken care to ensure that you were aware of potential issues and have addressed them thoroughly and professionally.
As previously mentioned, the use of a standard site survey and logistics template is highly recommended, as it is not only an aide memoire to ensure that you have covered all issues on a site, but it Is seen as a positive and professional way to conduct business with clients. By raising issues such as flooding and ground water levels with the customer, actively involving them in the research, you are far less likely to be on the wrong end of a future claim for works that fail due to water issues.
Summary
As with all projects, care taken at the outset can save a lot of problems in the future. If a site has the potential to be affected by significant water issues, either ground water pressures or flooding, recognising this fact, and drawing the client’s attention to the possibilities and danger signs, you will be able to integrate any costs or solutions into the project proposals, even if they are ultimately found to be unwarranted and unutilised.