AELTC GRASS COURTS NEIL STUBLEY HEAD OF COURTS AND HORTICULTURE, AELTC 1 CONTENTS 1. Cross section of a court 2. Construction of a grass tennis court 3. Court preparation - diary guide 4. Annual maintenance of grass courts 5. The Championships 6. Grass cultivars 2 SECTION 1 CROSS SECTION OF CHAMPIONSHIP GRASS TENNIS COURT Grass 275mm Rootzone (23% clay content) 50mm Blinding Layer (7– 10mm washed pea gravel) 150mm Stone (20 – 40mm washed angular Aggregate) 100mm main drain 75mm Lateral drains Rootzone mix Stone Nil Coarse gravel Nil Fine gravel 1% Very coarse sand 2% Coarse sand 5% Medium sand 15% Fine sand 20% Very fine sand 9% Coarse silt 10% Silt 15% Clay 23% 3 SECTION 2 CONSTRUCTION OF GRASS TENNIS COURTS Before discussing the all important annual maintenance, the preparation to The Championships and The Championships itself, it is important to look at the construction of the tennis courts and the method used when relaying. All construction is designed to help achieve the aforementioned performance criteria. It is important to note that to achieve a top quality playing surface, a newly constructed grass court will need a minimum of 15 months between construction and professional play as the court will need time to settle and structure. Before any construction takes place there are a number of factors to consider. Orientation Ideally this would be in the line of north and south. The reason for this is to minimise the effect of the sun on the players’ eyes. If it is not possible to achieve the ideal for social and club play, it may not be a deciding factor. Size While the playing surface measures 23.774m x 10.973m, the area required, when including the run-off, will vary depending on the type of play catered for. Championship play requires a minimum area of 36.57m x 20.12m. Wherever possible this dimension should be considered for club play, but if not possible the area can be reduced to 33.53m x 16.45m. If a smaller area has to be settled upon, it has to be appreciated that play can be affected as there is an increasing risk of players colliding with surrounding fences. Levels The Lawn Tennis Association states that falls should not exceed 1:120 for Championship play and 1:100 for club and social play. The gradient should, ideally, be across the line of play, but if this is not possible then the fall can be in the line of play. Whether in line or across the line of play, falls must always be in a single plane. Other arrangement, e.g. a camber throughout the middle has the effect of altering the effective height of the net and is not acceptable. Access When choosing the site for a new tennis court, access must be considered for construction purposes. There is a real need to be able to deliver new materials as close as possible to the site. This is also essential for the removal of materials from any excavation which may be required. If access is limited then construction costs will rise by the very fact that labour would be required to move materials over a greater length. Drainage Outlet This can be a major factor for consideration and will have an effect on the final costings. If it is into a stream or another drainage system, permission will need to be sought from the Local and Water Authorities. Services If irrigation or electricity is required then it is important to know where they have to be linked from local supplies. Also decide where the control points are to be housed in relation to the courts. Irrigation A detailed assessment and recommendations should be carried out by a reputable engineer for your irrigation requirements. For simplicity, the building of a Championship court will be discussed. 4 THE CONSTRUCTION OF A CHAMPIONSHIP GRASS COURT THE CONSTRUCTION OF THE RING BEAM SURROUNDS WILL DEPEND ON WHAT SERVICES WILL NEED TO RUN THROUGH THEM. An average ring beam will measure 600mm x 600mm. This will allow for covers to be installed if needed and give enough stability for the support around the court. There is no one set construction profile of a grass court. The profile used at Wimbledon is one that has proved successful over the years. All the Championship courts are constructed to this one design. This requires the area used to be excavated to a depth of 475mm below the final level of the court and then backfilled with: • 150mm of 20-40mm washed angular aggregate • 50mm of 7-10mm pea gravel aggregate • 275mm of root zone Stages of Construction Mark out the exact area that is to be excavated and decide upon the exact depth of the excavation. The final levels should allow for the surface of the court to be in the region of 25-75mm proud of all surrounds. Any less and there is a considerable risk of damaging machinery when maintaining the court. It may also be dangerous for players. Excavate trenches for the drain pipes. These should be positioned across the line of play at 9m intervals to a minimum of 1:200. These drain runs are known of laterals. The lateral leads to a main drain located along the edge of one side of the construction. The main drain will continue out of the court area to a point where drainage water is discharged. Wherever possible it is advisable to have a silt trap located within the main drain not far from the court itself. The purpose of this is to allow the main drain within the court construction to be cleaned if it becomes blocked in the future as any material, such as silt, that enters into the pipe will be collected at this point rather than running the risk of blocking the pipe as it runs to the outfall. The silt trap should have a removable cover to allow for easy and regular inspection. The trap consists of a manhole type, brick construction, with the outlet pipe from the drain being placed at a higher level than the outlet pipe that runs to the discharge area. This outlet pipe should be positioned at least 150mm above the floor of the trap. The principle is that any material washed through the drainage system will sink to the bottom of the trap from where it can be periodically removed, so avoiding unwanted material passing through the system. When the drainage excavation is complete, place a thin layer of pea gravel or sand on the bed of the trenches, ensuring that the falls are correct. A suitable land drain pipe can now be placed in the trenches to a minimum depth of 230mm (invent level, bottom of the pipe) below the excavated level. The pipe sizes are 75mm for the laterals and 100mm for the main drain. When laying the pipes it is essential they are positioned at the correct levels to allow a satisfactory passage of the water without any risk of it becoming static. It is advisable to test that the pipes are working before carefully filling the trench back in with stone, avoiding any disturbance to the pipes. Once all the land drain work has been completed then construction can commence. 5 The next procedure is to lay the stone and pea gravel to the correct depth throughout the court. To ensure that the materials are laid at the correct level one of two methods can be used: 1. If a laser level is available, constant checks can be made very quickly. 2. By placing pegs at 3m centres and making a line at 150mm to show the level of the angular stone and a further marker at 50mm above the line of the stone to indicate the final level of the pea gravel. When installing the materials care must be taken not to damage any work that has been completed or to the firm soil base upon which the stone is to be laid. During wet weather it can be an advantage to lay a geo-textile on the soil so avoiding the stone being pushed into the soil during construction. Whatever product is used, care must be taken to avoid placing it over the drain ditches if there is a risk of impeding water movement in the future. To avoid the pea gravel layer becoming mixed with the stone layer, divide the area into quarters and start at the furthest section from the access to the court. Lay the stone and then the pea gravel, consolidating both to the correct levels before commencing the next quarter. Any movement of the stone caused by the wheels of the machinery should be constantly raked back to level. When the operation is completed, remove any pegs used and fill the holes with the appropriate stone. The completion of the stone installation should result in an even bed on which to introduce the root zone. The most important element when introducing the root zone is to ensure that the materials are compacted evenly so avoiding the creation of any air pockets or soft non compacted areas which will be prone to sinkage at some time in the future. The method used at Wimbledon is to introduce the soil in 50mm layers, consolidating each layer with a 3-5 tonne track digger, raking level before the next 50mm layer is introduced. The levels can be checked using the same procedure as with the stone. During the process of introducing the soil it is vital that the area is kept dry.