Depression depth impact on the stormwater hydrographs from impervious catchment

Method of numerical analysis of the influence of initial depression depth coupled with absolute surface roughness and with Manning's roughness coefficient onto the key hydraulic parameters of the stormwater runoff is proposed. Small highly urbanized catchment with 100% impervious cover was used in stormwater management model numerical simulations for climatic conditions of the Lviv City (Ukraine) at the return period of 1 year. An increase in depression depth from 1 to 5 mm causes reduction in the specific maximum peak runoff from 5.13∙10−3 L/(s∙m2) to 3.29∙10−3 L/(s∙m2), while the critical duration of rainfall increase from 17 min to 56 min. The dimensionless maximum peak flow rate is expressed as a two-parameter exponent function of the initial depression depth, allowing the estimation of the lower limit of this discharge for the practically significant range of the depression depth.