Date of Award

Spring 2013

Project Type

Dissertation

Program or Major

Civil Engineering

Degree Name

Doctor of Philosophy

First Advisor

Thomas Ballestero

Abstract

Low Impact Development - Stormwater Management (LID-SWM) systems are relatively new technologies that were developed in order to meet the water quality criteria imposed by the Clean Water Act. LID-SWM is also used to replicate the natural hydrology of developed sites. However, the hydrological benefits of LID systems cannot be accurately predicted with the existing simulation models. Currently used software packages represent LID systems as storage units and do not specifically represent water routing through the systems' hydraulically restrictive sublayers. Since the LID's functionality at system level is not fully understood, the relationships of design variables and the systems' hydrological outcome were not yet empirically related.

In this dissertation, the appropriate equations for representing different flow components of LID systems are investigated. Special attention was given to modeling water routing through the filter media layers of LID systems. The water movement through a permeable pavement system was monitored for over a year and it was found that the system functions under unsaturated conditions. Saturation was never observed at any levels in the system over the period of study. Solving Richards' Equation, which is typically used to represent flow in unsaturated soils, requires knowledge of the moisture characteristic curves, theta (psi) and relative hydraulic conductivity, Kr(theta) functions. These functions are unique for each soil and have not been analyzed for coarse engineered soils used in stormwater treatment systems. A framework for computing the theta (psi) and Kr(theta) functions for soils used as filter media for four LID systems (permeable pavement, sand filter, gravel wetland, and bioretention system) was developed and tested against laboratory measurements. This framework requires information on soils that is easily accessible to stormwater engineers (porosity and particle size distribution), and allows a detailed representation of filter media soils containing gravel and wood chips.

The theta (psi) and Kr(theta) development framework used in conjunction with Richards' Equation performed well when tested against real time moisture profile in the sublayers of a permeable pavement system under natural precipitation. This framework for modeling flow through the filter media was integrated in a full permeable pavement system model.

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