Results of long-term researches of the maximum sizes of modules of a drain on meliorative system RUP " OfPolessie Experimental Station of Ameliorative Agriculture and Grass Farming" during the periods of winter, spring and aestivo-autumnal high waters are resulted. It is established, that the observable greatest size of the maximum module of a drain of a spring high water makes 0,97 l/s.ga at security of 5 %. The maximum settlement modules of a drain of a spring high water 25 %-s' and 10 %-s' securities are accordingly equal 0,65 and 0,83 l/s.ga. Observable greatest sizes of the maximum modules of a drain of aestivo-autumnal and winter high waters are accordingly equal 0,83 l/s.ga at security of1,9 % and 0,8 l/s.ga at security of 4 %. The maximum settlement module of a drain of an aestivo-autumnal high water 10%-s' securities makes 0,56 l/s.ga. It is recommended to inspect a meliorativenetwork on the admission of the expense of an aestivo-autumnal high water 5-2 %-s' securities for creation of conditions of more operative tap of freshet waters. To this security there will correspond settlement maximum modules of a drain equal 0,66-0,83 l/s.ga.