The method of calculating the error that occurs when determining the flow rate in the initial section of the pressure distribution drainage pipeline when it passes transit flow rate is proposed in the paper. It is based on the analysis of differential equations describing the fluid motion with variable flow rate in such pipelines. The analysis is presented in dimensionless form. The impact of transit flow on the main flow is estimated using the values of the drainage pipeline resistance coefficient ζl and the generalized parameter of the perforated drain A, which takes into account its constructive and filtration characteristics. The proposed method allows to perform calculations of drainage pipelines that operate in the presence of transit flow rate, according to the method of these pipes calculation that distribute water without passing transit flow. Herewith, the possible error, which includes in the calculation results, determines. To illustrate the obtained dependences, the corresponding graphs are given in the paper. The results of the analysis allow to determine the limits within which a simplified method of calculating the distribution drainage pipelines can be used and the error, that occurs, can be estimated.

Simple and convenient dependences for calculating basic hydraulic and design characteristics of pressure collecting horizontal drainage pipelines operating in the presence of transit flow, in which the fluid collection along the path occurs in the filtration mode, are presented in the paper. They are based on the analysis of a system of differential equations that describe the fluid motion in such pipes. The solutions are based on the assumption that the member, which takes into account the effect of the flow variation along the pass, is neglected. The concept of a fictitious infinitely long collecting drainage pipeline or a pipeline with an infinitely large amount of the pipe walls permeation is used in the analysis. It is assumed that the actual flow at the end of this pipelines is replaced by a conditional flow, which is collected at the fictitious end section of the pipeline. The flow in the end section of the fictitious pipes is assumed to be zero. The introduced assumptions allow to use formulas for calculation of the mentioned pipelines with a certain approximation which are applied at calculation of pipelines operation without transit. These dependences allow to calculate the effect of transit flow on the hydraulic characteristics of the collecting drainage pipelines.