Model of a Fluid-Level System for the Design and Analysis of Detention Basins Considering Recent Weather Extreme Events and Historic Precipitation Data

Abstract

Abstract Engineering systems such as flood control dams and storm drain systems are designed to adhere to specific requirements outlined in engineering design codes. These codes heavily rely on local historic climate and precipitation data, which are updated every few years. However, the revision cycles of engineering codes and climate data are not necessarily synchronized. Consequently, it can take a decade or more for a shift in historic climate data to be reflected in the engineering codes. Meanwhile, climate change has increased the frequency and severity of extreme weather conditions. To address the impact of climate change until federal and state governments and regulatory agencies adopt new approaches, design engineers and firms may need to employ mathematical models to assess the resilience of their designs against recent changes in the local climate. The purpose of these models is not to replace the code requirements but to provide an additional layer of confidence that infrastructure can withstand future extreme weather conditions based on the most up-to-date data available. This paper utilizes a model of a fluid-level system comprising three interconnected tanks to simulate a runoff rainwater detention basin in Northern California. Each tank represents a pond within the detention basin and is modeled as a truncated cone, exhibiting nonlinear capacitance. The pipes connecting the tanks are modeled as resistances. Additionally, a bi-linear model is employed to represent a two-level pumping station that discharges water from the last pond into a man-made flood control channel. Sub-hourly rainfall intensity records from the National Weather Service (NWS) were obtained for the few days leading to the most recent historic highs. By integrating these data numerically, the inlet flow rate to each tank was determined as a function of time, enabling the calculation of rainfall water levels. The primary objective of this modeling exercise is to answer the question of whether the detention basin would overflow under specific rainfall intensity conditions. The significance of this question lies in the fact that overflow from one or more ponds can result in flooding events affecting adjacent buildings and infrastructure. Our model demonstrates that, despite meeting the construction code, the detention basin may experience overflows and cause damage to the serviced area under certain conditions. Consequently, future resilience may require a redesign of the basin.