The publication of this Handbook was supported by the Russian Federation

Drainage network quality including assessments of  the following:
 
– hydrogeological conditions, validity of  calculations, types and parameters of  drainage 
systems;
 
– the volume, salinity and chemical composition of  drainage water and its disposal techniques 
(repeated use in irrigation, discharge into natural reservoirs, etc.);
 
– salinity of  irrigated drained lands. It would be incorrect to assess the soil desalinization effect 
by the total sum of  salts removed with drainage water. Instead, the amount of  salts removed 
from the assessment layer of  soil should be used: ΔG = Go – αД, where: ΔG – change in salt 
content within the assessment layer, t/ha; Go – amount of  salts brought with irrigation water, 
t/ha; Д -the total amount of  salts removed with drainage water, t/ha; α – the share of  salts 
removed from the assessment layer, which is calculated from drainage system parameters. 
The deeper the drains and the greater the distance between drains, the lower the α value (that 
varies within a range from 0.4 to 0.8). A horizontal drainage system can remove 20-60% of  
salts from the assessment layer [1].