Introduction to DDMS Surveying
- Steve Peregrine
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Introduction to DDMS Surveying
DDMS is National Highways’ technical information about the location and condition of all drainage infrastructure on their network.
It includes data on all drainage assets, not just below-ground pipes. These include surface items like ditches, kerbs and ponds as well as below ground pipes and manholes. HADDMS drainage investigations can be:
Full inspections – a full and detailed analysis of all the drainage assets with the scope of work.
Connectivity surveys – a more simplified investigation that does not necessarily include any condition data, but still includes all the connectivity and GIS elements.
Common mistake that are made by CCTV contractors in this area include assuming that this type of inspection is only about drains and pipes, where as in truth the scope is much bigger than this and involves a lot of GIS supporting data collection and validation.
The work is usually tendered by the HE Areas, also sometimes known as the Managing Agents and information for the current managing agent for any area can be found online. There are 13 Areas across England split into 6 Regions, areas numbered from 1 to 14 (there is no Area 11) and the areas are now grouped into regions under National Highways.
Map of the old Highways England Areas and new National Highways Regions.
Herein, we will refer to ‘The Area’ or similar as any of these operational areas.
Given that HADDMS inspection work is usually carried out at night due to the high risks associated with working on busy roads, common phrases that are often used by the Areas in tender negotiations with contractors refer to how the contractor should behave when they discover that an asset cannot be inspected dues to its current operational condition (i.e. a pipe is full of silt, so how do we inspect it, but it’s the middle of the night so there is nobody I can call at the Area to ask the question regarding what to do next).
The following is a guide only and must not be taken for granted. The details of these kinds of terminology must always be negotiated and agreed between the client (The Area) and the contractor, or between the contractor and the sub-contractor.
Do Nothing – in very simple terms, these means that the contractor will not make any reasonable attempt to clean the pipe. They will just record in the data that an inspection has been attempted and the current condition of the asset.
Do Something – the contractor will agree with the client that they will make a considered attempt to clear the asset and to get a good CCTV inspection. Maybe they will give the pipe 3 passes with an appropriately sized jetting machine (this should also be clearly specified for different pipe sizes).
Do Everything – the contractor will agree to keep on cleaning the pipe until it is at an agreed cleanliness level (this is usually specified as something like ‘less than 10% debris’), and then complete the CCTV inspection.
Clearly, the requirements of the tender can have a significant effect on the price that the contractor submits to complete the work.
Whatever the scope of work or the scheme extents, the process of delivering HADDMS inspection data to the client using the specified standard always begins with the existing known data of the drainage network within the scheme. This is the beginning of the round-tripping process (described later in this document), and the contractor (or sub-contractor) MUST receive these shapefiles in plenty of time before they start work on site.
Other questions that the contractor should always fully understand before entering into HADDMS works include:
Scheme Extents – on motorways, this is usually described by the road description (i.e. M25, Junction 3 to 4), or by Marker Post IDs which are the small black, red and white posts every 100 metres along the side of all motorways. On non-motorways and all projects, this should always be accompanied by drawings supplied by the client outlining the extent of the scheme of work by an outline on a plan.
Then, the contractor should understand which parts of the road are included in the requested inspection data. Terms like ‘verges only’, ‘central reservation only’, ‘inner ring of the roundabout’ etc are common when understanding these needs.
A crude example of a scheme extents drawing may look something like.
Traffic Management – all work on the highways network always requires traffic management, and in most cases, this is provided by sub-contractors. The key here is to understand who is going to organise and fund this resource. It is often the contractor’s (or the sub-contractor’s) responsibility, but sometimes maybe the Area is already doing some other work on the carriageway and so they already have TM (Traffic Management) in place which the contractor can also utilise.
Hours of Work – these describe the start and end times of the permit to work on the road and caries across different areas. Area 5 (the M25 around London) has the shortest road space times because of the sheer volume of traffic on that road. An example of the hours might be 8pm to 6am, but this does not mean that the contractor will be able to start work at 8pm and go straight through to 6am. This means that the TM crews will start putting their management precautions (signs and cones etc) out from 8pm, and they may have to be all off the road by 6am, so the result to the CCTV contractor is that they are only likely to actually get on site from 9:30pm until 4:30am, because their access to the site is controlled and monitored by the TM.
Waste Disposal and Water – where jetting and suction machines are used to clean pipes (usually this is the case), there may be requirements like; ‘The jetting machine is not allowed to leave site to fill up with water’. So, the contractor must consider how they are going to keep the machine working for the whole shift, maybe with bowsers on site. Additionally, it is common for highways drains to have significant quantities of silt inside, and large combination jetting machine can comfortably suck up 10 tonnes of silt in a shift. This silt must be disposed of safely to a registered facility and this of course costs money, and the truck operators need reasonable time in their shift to complete this task before returning home so that the truck is ready for the next shift.
Welfare – the operators on site always need welfare facilities because there are no toilets dotted along the sides of the motorway, and they should always be provided with a safe-haven for breaks etc.
Deliverables – the standard deliverables required for HADDMS are not particularly complicated although they do require a high level of validation and post-processing, but it is most often the case that the Area requires a significant amount of additional data on top of the standard deliverables, usually because they are using the data collected for design and modelling. The contractor should understand exactly what these requirements are. Not all Areas have the same needs here.
Delivery Date – when does the client expect to receive their data? HADDMS data processing is tough work and takes a long time after all works have completed on site, and the client’s needs here may dictate how many vans and/or trucks are needed on site at any one time to complete the works.
Training – it is usual for Areas to specify levels of training that is required by operators on site. These will follow national standards and codes of practice and are likely to be higher than those required for non-HADDMS inspections.