Date of Award

Spring 1-1-2015

Document Type


Degree Name

Master of Science (MS)

First Advisor

James Guo

Second Advisor

Balaji Rajagopalan

Third Advisor

Joseph Kasprzyk


Urban sprawl resulting from unplanned or sub-optimal development is increasing at an alarming rate of two million acres per year in the US (Davis & McCuen, 2005). As urban sprawl increases so does the amount of impervious surfaces and vehicular traffic required to get from point A to point B. The pollutants from urbanization adhere to the impervious surfaces and are then dislodged and transported by a precipitation event, flowing into receiving waters or treatment plants. The polluted stormwater flow jeopardizes the water quality of the watersheds or strains the treatment facilities. To combat the issues that come with development and urban sprawl, municipalities are moving toward low impact development (LID). LID uses systems based on natural processes to reduce stormwater peak flows and runoff volume while increasing water quality to pre-development levels. States have developed best management practices (BMP) for the implementation of LID processes appropriate to their areas. BMPs that are used for pollutant removal such as a bioretention BMP, or rain garden, are designed to capture a volume of stormwater, which is then infiltrated or be absorbed by vegetation. While hydrologists and engineers use various methods to calculate rain garden volume, a key component to each method is capturing the first flush. The first flush contains the high pollutant content, which is dislodged at the inception of a precipitation event. Since LID mimics natural processes, it follows that the volume to capture for water quality is related to an aspect of the hydrological cycle. This thesis shows the relationship of the volume necessary to capture for water quality to the depression storage lost due the increase in impervious area. The study is based on historical precipitation data in Denver, Colorado, and the depression storage design values for pre- and post-development for the area. The study shows that the lost depression storage is a reasonable estimate of the derived water quality capture volume (WQCV) used for the design of bioretention BMPs in Colorado. This finding is significant for the future design of water quality BMPs by providing a simple, robust, cost-effective and transferrable method to size water quality basins.