The sprinkler irrigation (spray heads, rotary mini-sprinklers or sprinklers) of the tramway platforms and their approaches has several objectives with a number of significant constraints. We are now going to elaborate on these issues that have arisen or may arise in connection with a number of current and future projects. We will then take the example of an on-going project, which is near the completion of its first stage in the south-east of France: the tramway of the urban community (Communauté d’Agglomération) of Avignon.
• Create a green belt area within an urban environment that basically consists of concrete and tarmac in order to blend in with and hide the scars of the earthwork and civil engineering works undertaken for the massive infrastructure required for an environmentally-friendly public transport system.
• Improve the aesthetic aspect and comfort of the people who travel in the City: pedestrians, cyclists, drivers and, of course, users of the public transport systems.
• Take advantage of the installation of a tramway to ‘revitalise’ and modernise the avenues. Lighting, street furniture, street patterns and green spaces will be renovated.
• Create a green oasis in the city, which will bring about a drop in the maximum temperature during the summer period and in particular during heat waves.
• Improve the cleanliness and hygiene of the area concerned by mowing the grass regularly in the city centres where passers-by are not always clean and tidy or civic-minded.
The specific constraints
of this type of installation
• The space available for installing the sprinkler systems is small and confined, particularly on slabs, where the soil depth is very shallow. In this case, they are buried at around 20/23 cm.
• The irrigation programme must be short because of the operating constraints. For example, it is only possible to irrigate from 1 am to 6 am when the trams are not running. This means that the total duration of the irrigation programme will only be 5 hours. As a general rule, for a ‘traditional’ landscape irrigation system, only 8 to 10 hours per night are available for sprinkling.
• To avoid the problem of vandalism or breakage of equipment, the irrigation devices have to be discreetly hidden. In fact, these installations are often found in ‘open’ spaces and in the hyper-centre, which is very busy, even at night.
• Given the constraints to construction (particularly on slabs), the depth of the soil/irrigation equipment is very shallow. The water reserve is, therefore, minimal and daily irrigation is required during dry periods. Sometimes, the irrigations have to be divided up into short periods so as to optimise water use and avoid any wastage through ponding or runoff. Furthermore, the environment (concrete, slabs, hard core…) leads to a ‘storage’ of the heat during the day, releasing it at night, which increases the evaporation even more.
• Maintenance is difficult and inconvenient because of the difficulties of gaining access (basically, only possible at night) to the manholes, distribution chambers or main boxes and the equipment (solenoid valves, sprinklers…).
• It is almost indispensable to be equipped with a remote-controlled management system to facilitate maintenance and be able to react quickly to any alerts (problems with the flow rate or water leakage in particular).
• The use of spray heads with a short pop-up (Hunter Industries’ Pro Spray 03, at a height of 7.5 cm, for example) is often the only solution for being able to bury the spray head and its connection in the soil depth available (around 20/23 cm).
• Depending on the radius required, the use of long-throw rotary nozzles (MP Rotator 3000 or 3500, for example) is the only solution for spacings of 8 or 10 m. This spacing corresponds to the average width of the green strips to be irrigated alongside the tramway.
• Bearing in mind the long sections of the irrigation system, the controllers with decoders represent an ideal solution for being able to control the solenoid valves, sometimes at a distance of several kms. This makes it easier for the company to implement the system and it allows for the costs of ever more expensive copper cables to be kept down,
• The use of real time water meters providing feedback allows for two essential functions: Firstly, checking the flow rate in real time, which triggers an automatic reaction from the system and notifies the person in charge in real time when there is a leakage.
Secondly, this option provides very precise information about the accumulated volumes of water used, allowing for an efficient management of the water resource for the entire duration of the operation.
• The implementation of pressure regulation systems at the solenoid valves and/or at the sprinklers and spray heads allows for a good uniformity of pressure, and consequently uniformity between the devices placed in the large sectors. The flow rates and sprinkler ranges are exactly the same, whatever the position of the sprinkler device in the city centre.
• The installation of a computerised central control system for managing the irrigation enables the sprinkler programmes to be optimised as well as significant time-saving for any operation. Most of the on-site interventions can, therefore, be replaced by a remote management system resulting in a considerable saving in time and labour.
An example of a project
in progress in the Greater Avignon area and the City of Avignon
To replace the original tramway lines (closed in 1932) and thus provide the population with a more reliable means of transport, the Agglomeration Community of Greater Avignon has decided to install rapid transit tramway and bus services. After a number of years of studies and preliminary work, the project is now advancing quite significantly. In fact, the opening of the first line of around 8.4 km is planned for mid-2019. It may even happen before the Avignon Festival, which takes place, as everyone knows, during the first three weeks of July each year.
Client: The Agglomeration Community of Greater Avignon, TECELYS of Greater Avignon
Project Manager: ILEX Paysages et Urbanismes
Contractors: Pépinières Environnement Commercialisation Pernes/ Avignon and its subcontractor Provence Languedoc Environnement Pernes
The main features of the irrigation system being constructed are described below. The irrigation installations (water supply, networks, solenoid valves, control systems and devices) have had to be separated and treated individually according to the future operator of each zone:
• Platform section (client, agglomeration community of Greater Avignon):
- 4 boreholes sunk into the aquifer of the Rhône/ Durance, each delivering 30 m3/h.
- 4 self-cleaning filters of equivalent flow-rates
- 4 ACC99D controllers with decoder and remote control
- 40 1½-inch PGV solenoid valves
- 1500 ProSpray 03 or 04 spray heads
- 1500 MP Rotators of different sprinkler distances
- 30 PGP sprinklers for the largest zones, in particular the area near the Maintenance Centre.
• Approaches section, particularly at the bottom of the ramparts (client: the agglomeration community of Greater Avignon and the future manager the City of Avignon):
- 8 1½-inch PGV solenoid valves
- 8 NODE battery-operated controllers
- 300 ProSpray spray heads
- 300 MP Rotator
Site visit of 26th October 2018. The contractors began laying the turf at the end of September. The main networks of the primary and secondary pipes, as well as the solenoid valves, were already in place. The spray heads and MP Rotators were positioned in advance of the laying of the turf. The very high water requirements during this period (in September, the temperatures in the region regularly exceed 30°) could only be met by applying 4 irrigations per day, of varying durations, depending on the zones and the stage of the growing season.
The contractor’s choice was to ‘flood’ the zones to ensure that the laid turf would recover, bearing in mind the high temperatures.
When we visited the site, two-thirds of the project was already in place. There was positive feedback from all parties: the general public, client, project manager… the green area below the historical medieval ramparts of the city visually enhances this world heritage site.
The contractor’s technicians, in particular, appreciated the ease of use and hardiness of the installed equipment. The very efficient irrigation system enabled the turf to recover in spite of the very hot temperatures experienced in September and early October. The grass has already been mowed in some zones.
This winter, a central control system (Hunter IMMS) will be installed for the irrigation, which will make it even easier to manage and obtain feedback from the site. Water meters have been installed at each borehole and they will be connected to the computerised management system.