A Kinematic Model for Urban Drainage Study

Abstract

<p>This study describes the development and use of a numerical storm model as a pre-processor for a detailed urban runoff model. The storm model simulates the spacial and temporal growth and decay of a system of storm cells as they move across an urban catchment system by generating hyetographs for each subcatchment.</p> <p>Traditionally, design storms are developed from statistical analysis of point rainfall records that include all types of rainstorms. This methodology was considered appropriate for flood predictions based on the so-called rational formula. However, rain distributions resulting from point rainfall analysis are unlike any types of observed rainstorm. This synthetic temporal distribution is typically applied uniformly across the catchment and hydrographs are consequently unlike observed hydrographs.</p> <p>The storm model presented in this study is based on synoptic observations of rain cells reported in whether radar literature. Statistics of the size and distribution of rain cells can be obtained from reported weather radar studies. Large static or slow-moving cells of uniform rainfall intensity are rare even in prolonged frontal events. Convective cells tend to be circular with a circular rainfall intensity pattern. Rain cells in frontal precipitations events tend to be elliptical, aligned sub-parallel to the front and moving sub-parallel to it. Rainfall is typically most intense near the leading edge of the cell. Fast moving storms produce very rapid point-intensity-duration changes.</p> <p>A model with these features is developed. The model is applied to urban catchments of the City of Hamilton in Southern Ontario. The sensitivity of the time-to-peak and rate of rise of hydrographs and pollutographs indicate that storm cell kinematics are significant in peak runoff estimates and water pollutant loading estimates.</p>