Module 4c: Stormwater Treatment using Grass Swales

.........................................................................................................................................................................1 Roadside Drainage Design for Channel Stability ..........................................................................................................2 Allowable Velocity and Shear Stress........................................................................................................................2 Allowable Velocity Approach to Channel Design ...............................................................................................2 Allowable Shear Stress Calculations....................................................................................................................4 Shear Stress in Channels having Bends ...............................................................................................................7 Design Steps for Maximum Permissible Velocity/Allowable Shear Stress Method.................................................9 Design of Grass-Lined Channels ............................................................................................................................15 Plant Species Selection for Vegetative-Lined Channels ....................................................................................15 Site Considerations ............................................................................................................................................16 Seasonal Considerations.....................................................................................................................................16 Selecting the Right Grasses for Channel Lining ................................................................................................17 Determination of Channel Design Parameters ...................................................................................................18 Selection of Roughness Factor for Grass Lined Channels .................................................................................24 Example Problem for the Selection of Roughness for Grass-Lined Channels ...................................................24 Drainage Design using Turf-Reinforcing Mats.......................................................................................................25 Historical Use of Grass Swales for Stormwater Quality Control ................................................................................34 Introduction.............................................................................................................................................................34 Terminology ...........................................................................................................................................................35 Reported Pollutant Removal Efficiencies for Grass Swales ...................................................................................36 Modeling.................................................................................................................................................................37 Kentucky Model.................................................................................................................................................37 Deletic Model.....................................................................................................................................................39 Sediment Trapping Model for Grass Swales and Grass Filters ...................................................................................4