Drainage system layout
Although there may be many possible layout for a given field specific drainage objectives should be evaluated to find the best layout (Figure 10). System layout and drainage needs should be based anticipating future needs where possible. Additions to a system will be much easier to make if the established mains are already large enough and located appropriately.
Spacing between drains
When there is a linear flow of ground water, spacing between drains is given by the relationship,
where S = Spacing between drains K = hydraulic conductivity Q=rate of discharge,
H=Maximum height of water table above bottom of drains and H = height of water in the drain. d = depth of impervious layer below the drain.
Measurement of in situ hydraulic conductivity
Measurement of hydraulic conductivity on disturbed soil samples is not a very reliable approach. Similarly, determining these values on undisturbed samples drawn with a core sampler is also not a flawless method. Considerable errors are caused due to presence of root holes. Methods have, therefore, been developed to measure hydraulic conductivity in situ. Three simple methods in this respect are those of hooghoudt, Ernst and Childs. These are described below.