Particle-size distribution from urban land use and source areas

Science Center Objects

Many control options for sediments and associated contaminants in storm-water runoff from urban areas rely on settling of solids. This study characterizes particle-size distributions in urban storm-water runoff from specific source areas and land-use categories, with the hopes of assisting watershed managers and engineers design better control devices for reducing sediment in urban runoff.

Figure comparing median particle size distribution from five source areas and one land use.
Comparison of median particle size distribution from five source areas and one land use.

Problem

Sediments in storm-water runoff from urban areas and contaminants associated with these sediments are a substantial source of contamination to receiving waters and associated toxic effects to aquatic organisms.

Treatment options for urban storm water should include specific plans to target sediment as the primary source of contamination to receiving streams. Watershed managers in urban areas need information to help choose the most effective means to reduce sediment-associated contaminants in urban runoff.

Numerous structural best-management practices (BMPs) provide some level of sediment control and are readily available. However, since many of these devices rely on settling of solids, their effectiveness is largely dependent on the range of particle sizes in storm-water runoff. In order to select the most appropriate BMP for sediment control, characterization of particles found in storm-water runoff becomes increasingly important.

 

Objectives

The primary objective of this study is to address the first step in providing watershed managers with the information needed to make decisions on treatment options: to characterize particle-size distributions in urban storm-water runoff from specific source areas and land-use categories. This information will be used to assist watershed managers and engineers in designing the most appropriate control device for reduction of sediment in urban storm- water runoff. Additionally, data collected from this study will be used to improve understanding on the uncertainty of measuring sediment in stormwater through the collection, preparation, and analytical reporting process. Furthermore, data will be used to improve the Source Loading and Management Model for Windows (WinSLAMM) data tables with particle-size distribution curves for specific source areas and land uses.

 

Photo of the depth-integrated sample arm (DISA)
A new depth-integrated sample arm (DISA) was developed to improve the representation of solids in stormwater, both organic and inorganic, by collecting a water quality sample from multiple points in the water column.Public domain

Approach

This study will characterize particle-size distribution in stormwater runoff for several urban land use and source area categories. Flow-weighted water quality samples will be collected by use of autosamplers  at locations representing urban source areas (e.g. roof tops, streets, and parking lots) and land uses (e.g. shopping center and strip mall). Sites are chosen based on dominance in the urban landscape and the lack of data available to characterize particle-size distribution.