Hydraulics of tile drains in peat and muck soils

Abstract

Agricultural drainage is the removal of excess water, known as free water or gravitational water, from the surface or below the surface of farm land so as to create a favourable soil conditions for crop growth. The process of removing the excess water from land surface is called surface drainage. The excess water saturates the pore space of the soil, the process of its removal by downward flow through the soil is known as subsurface drainage or internal drainage. In the case of kari land of Kuttanad the field level is below the surrounding waterbodies, there is always an upward movement of water from the subsoil to the surface. The upward movement of water from the subsoil brings along with it harmful byproducts of decomposition of organic matter which when come into contact with roots of plant adversely affect the gorwth and yield. With regard to the experiment on finding the suitable envelope material for subsurface drainage system in peat and muck soils revealed that the river sand (big size) was adequate in terms of filtration quality and hydraulic conductivity. Thus river sand (big size) could be considered as a suitable envelope material for subsurface drainage experiments. In the second experiment the performance of tile drains viz. PVC and baked clay pipe were assessed. From the comparison of head loss fraction and entrance resistance between PVC and baked clay pipe showed that the performance of baked clay pipe was good compared to PVC pipe. Considering the performance and economical reasons related to cost of baked clay pipe and its local availability, the use of the same as tile drains in peat and muck soils was confirmed. A close study of weekly values of EC of irrigation and subsurface drainage water revealed that a quantity of 124.80 kg of salts/ha/cm drop of drained water, could be washed off from the experimental area. From the observations on the growth and yield attributing characters it could be concluded that subsurface drainage was effective upto 30 m spacing. However, further studies are to be carried out for finding out a higher spacing. Economic analysis related to subsurface drainage using tile drains and envelop material (river sand) for a 100 ha area revealed that this project is economically and financially viable.