A Guide to Drainage
It is worth stating that as the name says slits and bands are ‘ secondary ’ drainage – they overlay and link to a primary piped drainage system . This needs emphasising because sand slits and gravel bands are often thought to be stand alone drainage schemes . By themselves they will temporarily alleviate a surface water problem for a short while but if there is nowhere for the water to go they will soon cease to function .
Sand slits and gravel bands are installed at right angles to the pipe and intercept the permeable backfill above the pipe to provide a connection to the piped system . Their purpose is to provide a more speedy short cut for surface water to reach the piped drainage system rather than going through the soil . This is why they are sometimes referred to as ‘ by-pass ’ systems because they bypass the soil , transporting surface water direct to the drainage system and thus to an outfall .
DRAINAGE LAYOUT
Traditional layout for drainage schemes was the ‘ herringbone ’ with a centre main drain and laterals running off it an angle like the backbone of a fish which is why it got its name .
Though it is still used , a grid system is now more common especially in sportsturf drainage . In any drainage scheme wherever there is a junction between a lateral and a main drain there is more concentration of pipe at that point and more permeable backfill over the pipe and around the junction . Hence there is a higher rate of drainage at that point which results in uneven plant growth . In some situations this doesn ’ t matter but in sportsturf if you use a herringbone layout with the main drain running down the centre of a pitch , or fairway , this uneven grass growth will be clearly visible in certain conditions . So aesthetically it is not pleasing , also it is more expensive in time and materials because there are more junctions and shorter runs of laterals for a given area .
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