Climate change is the cause of extreme weather around the world, for example extreme rainfall. Detention-retention systems are an effective way of reducing peak flow and equalising flow rates from stormwater runoffs. The theoretical analysis and the experimental investigation of the regulative volume of the storm water storage tanks, depending from the four generalized parameters, are presented in the paper. There are dimensionless parameters were calculated: initial regulation coefficient α_o, pressure change coefficient b, dimensionless rainfall duration X_rfl and coefficient of the regulating volume K_reg. Numerical experiments were carried out in the range α_o = 0–0.9; X_rfl = 1–10 and b = 0–10. The accuracy of finding the dimensionless regulating volume was 0.1%. The experimental installation was designed and implemented - the model of a runoff basin and rainfall to perform experimental research in order to confirm the theoretical model. The results are in the good accordance with both the theoretical results and numerical calculation results.