Uniform TitleWater quality design storms for stormwater hydrodynamic separators
NameFernandez, Victoria Julia (author), Guo, Qizhong (chair), Medlar, Steven (internal member), Yook-Kong, Yong (internal member), Rutgers University, Graduate School - New Brunswick,
SubjectCivil and Environmental Engineering,
Water quality management,
DescriptionStormwater runoff has become an important source of non-point pollution for surface waters. Management practices such as the installation of hydrodynamic separators are implemented in order to treat the stormwater runoff. In New Jersey, the efficiency of these devices is verified and certified by NJCAT and NJDEP, respectively. When the measure of the device performance is based on laboratory data, NJCAT calculates the average annual removal efficiency using weighting factors. The weighting factors were developed by NJDEP based on the average annual distribution of runoff volumes and the assumed similarity with the distribution of runoff peak flow rates. In this study, 10 years of precipitation records were used to evaluate the frequency distributions of the runoff volumes as well as the runoff peak flow rates. USEPA's SWMM model was used to simulate the runoff events produced by the given precipitation events. From the model results, three sets of weighting factors were determined. The first was based on the runoff volume frequency distribution expressed as percentage of the volume produced by the water quality design storm (uniform or non-uniform). The second was based on the runoff peak flow rates frequency distribution expressed as percentage of the peak flow rate generated by the uniformly distributed water quality design storm. The third was also based on the runoff peak flow rates frequency distribution, but expressed as percentage of the peak flow generated by the non-uniformly distributed water quality design storm. The results indicate that the weighting factors, based on the peak runoff rates generated from the uniform design storm, are the closest to the NJDEP weighting factors.
The impact of two different water quality design storms, uniform vs. non-uniform distribution, on the sizing of a certified hydrodynamic separator was also evaluated. One sets the design flow rate of the device equal to the peak flow rate generated by the uniform design storm. The other sets the design flow rate of the device equal to the peak flow rate generated by the non-uniform design storm. USEPA's SWMM model was used to continuously simulate solids loading to the treatment device. The lab-measured relationship between flow rate and removal efficiency was used to specify the removal rate of solids within the storm event. The results indicate that sizing with the uniform design storm would achieve a removal efficiency close to the one verified but that sizing with the non-uniform storm would achieve a removal efficiency significantly higher than the one verified.
It is concluded that setting design flow rate equal to the peak flow rate generated by the uniform water quality design storm is more consistent with use of the existing weight factors in calculating the average annual solids removal efficiency. Use of the non-uniform water quality design storm is too conservative.
NoteIncludes bibliographical references (p. 79-80).
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.